From dfcc679d5afaba3130356a2c6c922f7105f5a302 Mon Sep 17 00:00:00 2001
From: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>
Date: Thu, 26 Dec 2024 20:54:24 +0100
Subject: [PATCH 1/2] Round widget coordinates to even multiple of 1/32 (#5517)

* Closes https://github.com/emilk/egui/pull/5197
* Closes https://github.com/emilk/egui/issues/5163

This should help prevent rounding errors in layout code.

@lucasmerlin you may wanna test this with `egui_flex`
---
 crates/egui/src/containers/area.rs            |  10 +-
 crates/egui/src/containers/panel.rs           |   9 +-
 crates/egui/src/containers/resize.rs          |   7 +-
 crates/egui/src/containers/window.rs          |  18 +-
 crates/egui/src/context.rs                    |  15 +-
 crates/egui/src/grid.rs                       |   8 +-
 crates/egui/src/layout.rs                     |   6 +-
 crates/egui/src/style.rs                      |   8 +-
 crates/egui/src/ui.rs                         |  18 +-
 crates/egui/src/widget_text.rs                |   9 +-
 crates/egui_demo_lib/src/rendering_test.rs    |   9 +-
 .../tests/snapshots/demos/Code Example.png    |   4 +-
 .../tests/snapshots/demos/Context Menus.png   |   4 +-
 .../tests/snapshots/demos/Dancing Strings.png |   4 +-
 .../tests/snapshots/demos/Drag and Drop.png   |   4 +-
 .../tests/snapshots/demos/Extra Viewport.png  |   4 +-
 .../tests/snapshots/demos/Font Book.png       |   4 +-
 .../tests/snapshots/demos/Frame.png           |   4 +-
 .../tests/snapshots/demos/Highlighting.png    |   4 +-
 .../tests/snapshots/demos/Misc Demos.png      |   4 +-
 .../tests/snapshots/demos/Multi Touch.png     |   4 +-
 .../tests/snapshots/demos/Painting.png        |   4 +-
 .../tests/snapshots/demos/Pan Zoom.png        |   4 +-
 .../tests/snapshots/demos/Scrolling.png       |   4 +-
 .../tests/snapshots/demos/Strip.png           |   4 +-
 .../tests/snapshots/demos/Table.png           |   4 +-
 .../tests/snapshots/demos/Text Layout.png     |   4 +-
 .../tests/snapshots/demos/TextEdit.png        |   4 +-
 .../tests/snapshots/demos/Undo Redo.png       |   4 +-
 .../tests/snapshots/demos/Window Options.png  |   4 +-
 .../tests/snapshots/modals_1.png              |   4 +-
 .../tests/snapshots/modals_2.png              |   4 +-
 .../tests/snapshots/modals_3.png              |   4 +-
 ...rop_should_prevent_focusing_lower_area.png |   4 +-
 .../snapshots/rendering_test/dpi_1.00.png     |   4 +-
 .../snapshots/rendering_test/dpi_1.25.png     |   4 +-
 .../snapshots/rendering_test/dpi_1.50.png     |   4 +-
 .../snapshots/rendering_test/dpi_1.67.png     |   4 +-
 .../snapshots/rendering_test/dpi_1.75.png     |   4 +-
 .../snapshots/rendering_test/dpi_2.00.png     |   4 +-
 .../tests/snapshots/widget_gallery.png        |   4 +-
 crates/egui_extras/src/layout.rs              |   4 +-
 crates/emath/src/gui_rounding.rs              | 201 ++++++++++++++++++
 crates/emath/src/lib.rs                       |   2 +
 crates/epaint/src/text/font.rs                |  26 +--
 crates/epaint/src/text/fonts.rs               |   6 +-
 crates/epaint/src/text/text_layout.rs         |  22 +-
 crates/epaint/src/text/text_layout_types.rs   |  15 +-
 48 files changed, 377 insertions(+), 136 deletions(-)
 create mode 100644 crates/emath/src/gui_rounding.rs

diff --git a/crates/egui/src/containers/area.rs b/crates/egui/src/containers/area.rs
index a2bfbe1905f..6af762561fc 100644
--- a/crates/egui/src/containers/area.rs
+++ b/crates/egui/src/containers/area.rs
@@ -2,6 +2,8 @@
 //! It has no frame or own size. It is potentially movable.
 //! It is the foundation for windows and popups.
 
+use emath::GuiRounding as _;
+
 use crate::{
     emath, pos2, Align2, Context, Id, InnerResponse, LayerId, NumExt, Order, Pos2, Rect, Response,
     Sense, Ui, UiBuilder, UiKind, UiStackInfo, Vec2, WidgetRect, WidgetWithState,
@@ -66,6 +68,7 @@ impl AreaState {
             pivot_pos.x - self.pivot.x().to_factor() * size.x,
             pivot_pos.y - self.pivot.y().to_factor() * size.y,
         )
+        .round_ui()
     }
 
     /// Move the left top positions of the area.
@@ -80,7 +83,7 @@ impl AreaState {
     /// Where the area is on screen.
     pub fn rect(&self) -> Rect {
         let size = self.size.unwrap_or_default();
-        Rect::from_min_size(self.left_top_pos(), size)
+        Rect::from_min_size(self.left_top_pos(), size).round_ui()
     }
 }
 
@@ -493,12 +496,11 @@ impl Area {
 
         if constrain {
             state.set_left_top_pos(
-                ctx.constrain_window_rect_to_area(state.rect(), constrain_rect)
-                    .min,
+                Context::constrain_window_rect_to_area(state.rect(), constrain_rect).min,
             );
         }
 
-        state.set_left_top_pos(ctx.round_pos_to_pixels(state.left_top_pos()));
+        state.set_left_top_pos(state.left_top_pos());
 
         // Update response with possibly moved/constrained rect:
         move_response.rect = state.rect();
diff --git a/crates/egui/src/containers/panel.rs b/crates/egui/src/containers/panel.rs
index 7cf22a693db..f659a8c4efa 100644
--- a/crates/egui/src/containers/panel.rs
+++ b/crates/egui/src/containers/panel.rs
@@ -15,6 +15,8 @@
 //!
 //! Add your [`crate::Window`]:s after any top-level panels.
 
+use emath::GuiRounding as _;
+
 use crate::{
     lerp, vec2, Align, Context, CursorIcon, Frame, Id, InnerResponse, LayerId, Layout, NumExt,
     Rangef, Rect, Sense, Stroke, Ui, UiBuilder, UiKind, UiStackInfo, Vec2,
@@ -264,6 +266,8 @@ impl SidePanel {
             }
         }
 
+        panel_rect = panel_rect.round_ui();
+
         let mut panel_ui = ui.new_child(
             UiBuilder::new()
                 .id_salt(id)
@@ -756,6 +760,8 @@ impl TopBottomPanel {
             }
         }
 
+        panel_rect = panel_rect.round_ui();
+
         let mut panel_ui = ui.new_child(
             UiBuilder::new()
                 .id_salt(id)
@@ -1130,7 +1136,6 @@ impl CentralPanel {
         ctx: &Context,
         add_contents: Box<dyn FnOnce(&mut Ui) -> R + 'c>,
     ) -> InnerResponse<R> {
-        let available_rect = ctx.available_rect();
         let id = Id::new((ctx.viewport_id(), "central_panel"));
 
         let mut panel_ui = Ui::new(
@@ -1138,7 +1143,7 @@ impl CentralPanel {
             id,
             UiBuilder::new()
                 .layer_id(LayerId::background())
-                .max_rect(available_rect),
+                .max_rect(ctx.available_rect().round_ui()),
         );
         panel_ui.set_clip_rect(ctx.screen_rect());
 
diff --git a/crates/egui/src/containers/resize.rs b/crates/egui/src/containers/resize.rs
index 84f687783aa..0165eba996a 100644
--- a/crates/egui/src/containers/resize.rs
+++ b/crates/egui/src/containers/resize.rs
@@ -221,7 +221,8 @@ impl Resize {
                 .at_most(self.max_size)
                 .at_most(
                     ui.ctx().screen_rect().size() - ui.spacing().window_margin.sum(), // hack for windows
-                );
+                )
+                .round_ui();
 
             State {
                 desired_size: default_size,
@@ -233,7 +234,8 @@ impl Resize {
         state.desired_size = state
             .desired_size
             .at_least(self.min_size)
-            .at_most(self.max_size);
+            .at_most(self.max_size)
+            .round_ui();
 
         let mut user_requested_size = state.requested_size.take();
 
@@ -383,6 +385,7 @@ impl Resize {
     }
 }
 
+use emath::GuiRounding as _;
 use epaint::Stroke;
 
 pub fn paint_resize_corner(ui: &Ui, response: &Response) {
diff --git a/crates/egui/src/containers/window.rs b/crates/egui/src/containers/window.rs
index e2d133f39ad..44c3dda58c1 100644
--- a/crates/egui/src/containers/window.rs
+++ b/crates/egui/src/containers/window.rs
@@ -7,6 +7,7 @@ use crate::{
     Align, Align2, Context, CursorIcon, Id, InnerResponse, LayerId, NumExt, Order, Response, Sense,
     TextStyle, Ui, UiKind, Vec2b, WidgetInfo, WidgetRect, WidgetText, WidgetType,
 };
+use emath::GuiRounding as _;
 use epaint::{emath, pos2, vec2, Galley, Pos2, Rect, RectShape, Rounding, Shape, Stroke, Vec2};
 
 use super::scroll_area::ScrollBarVisibility;
@@ -788,13 +789,12 @@ fn resize_response(
     area: &mut area::Prepared,
     resize_id: Id,
 ) {
-    let Some(new_rect) = move_and_resize_window(ctx, &resize_interaction) else {
+    let Some(mut new_rect) = move_and_resize_window(ctx, &resize_interaction) else {
         return;
     };
-    let mut new_rect = ctx.round_rect_to_pixels(new_rect);
 
     if area.constrain() {
-        new_rect = ctx.constrain_window_rect_to_area(new_rect, area.constrain_rect());
+        new_rect = Context::constrain_window_rect_to_area(new_rect, area.constrain_rect());
     }
 
     // TODO(emilk): add this to a Window state instead as a command "move here next frame"
@@ -819,18 +819,18 @@ fn move_and_resize_window(ctx: &Context, interaction: &ResizeInteraction) -> Opt
     let mut rect = interaction.start_rect; // prevent drift
 
     if interaction.left.drag {
-        rect.min.x = ctx.round_to_pixel(pointer_pos.x);
+        rect.min.x = pointer_pos.x;
     } else if interaction.right.drag {
-        rect.max.x = ctx.round_to_pixel(pointer_pos.x);
+        rect.max.x = pointer_pos.x;
     }
 
     if interaction.top.drag {
-        rect.min.y = ctx.round_to_pixel(pointer_pos.y);
+        rect.min.y = pointer_pos.y;
     } else if interaction.bottom.drag {
-        rect.max.y = ctx.round_to_pixel(pointer_pos.y);
+        rect.max.y = pointer_pos.y;
     }
 
-    Some(rect)
+    Some(rect.round_ui())
 }
 
 fn resize_interaction(
@@ -1070,7 +1070,7 @@ impl TitleBar {
             let item_spacing = ui.spacing().item_spacing;
             let button_size = Vec2::splat(ui.spacing().icon_width);
 
-            let pad = (height - button_size.y) / 2.0; // calculated so that the icon is on the diagonal (if window padding is symmetrical)
+            let pad = ((height - button_size.y) / 2.0).round_ui(); // calculated so that the icon is on the diagonal (if window padding is symmetrical)
 
             if collapsible {
                 ui.add_space(pad);
diff --git a/crates/egui/src/context.rs b/crates/egui/src/context.rs
index 322007113ba..eaca8d36f52 100644
--- a/crates/egui/src/context.rs
+++ b/crates/egui/src/context.rs
@@ -3,6 +3,7 @@
 use std::{borrow::Cow, cell::RefCell, panic::Location, sync::Arc, time::Duration};
 
 use containers::area::AreaState;
+use emath::GuiRounding as _;
 use epaint::{
     emath::{self, TSTransform},
     mutex::RwLock,
@@ -2121,7 +2122,7 @@ impl Context {
     // ---------------------------------------------------------------------
 
     /// Constrain the position of a window/area so it fits within the provided boundary.
-    pub(crate) fn constrain_window_rect_to_area(&self, window: Rect, area: Rect) -> Rect {
+    pub(crate) fn constrain_window_rect_to_area(window: Rect, area: Rect) -> Rect {
         let mut pos = window.min;
 
         // Constrain to screen, unless window is too large to fit:
@@ -2133,9 +2134,7 @@ impl Context {
         pos.y = pos.y.at_most(area.bottom() + margin_y - window.height()); // move right if needed
         pos.y = pos.y.at_least(area.top() - margin_y); // move down if needed
 
-        pos = self.round_pos_to_pixels(pos);
-
-        Rect::from_min_size(pos, window.size())
+        Rect::from_min_size(pos, window.size()).round_ui()
     }
 }
 
@@ -2568,7 +2567,7 @@ impl Context {
 
     /// Position and size of the egui area.
     pub fn screen_rect(&self) -> Rect {
-        self.input(|i| i.screen_rect())
+        self.input(|i| i.screen_rect()).round_ui()
     }
 
     /// How much space is still available after panels has been added.
@@ -2576,7 +2575,7 @@ impl Context {
     /// This is the "background" area, what egui doesn't cover with panels (but may cover with windows).
     /// This is also the area to which windows are constrained.
     pub fn available_rect(&self) -> Rect {
-        self.pass_state(|s| s.available_rect())
+        self.pass_state(|s| s.available_rect()).round_ui()
     }
 
     /// How much space is used by panels and windows.
@@ -2586,7 +2585,7 @@ impl Context {
             for (_id, window) in ctx.memory.areas().visible_windows() {
                 used = used.union(window.rect());
             }
-            used
+            used.round_ui()
         })
     }
 
@@ -2594,7 +2593,7 @@ impl Context {
     ///
     /// You can shrink your egui area to this size and still fit all egui components.
     pub fn used_size(&self) -> Vec2 {
-        self.used_rect().max - Pos2::ZERO
+        (self.used_rect().max - Pos2::ZERO).round_ui()
     }
 
     // ---------------------------------------------------------------------
diff --git a/crates/egui/src/grid.rs b/crates/egui/src/grid.rs
index 0342f6f5227..102027dd8e4 100644
--- a/crates/egui/src/grid.rs
+++ b/crates/egui/src/grid.rs
@@ -1,3 +1,5 @@
+use emath::GuiRounding as _;
+
 use crate::{
     vec2, Align2, Color32, Context, Id, InnerResponse, NumExt, Painter, Rect, Region, Style, Ui,
     UiBuilder, Vec2,
@@ -179,13 +181,15 @@ impl GridLayout {
         let width = self.prev_state.col_width(self.col).unwrap_or(0.0);
         let height = self.prev_row_height(self.row);
         let size = child_size.max(vec2(width, height));
-        Rect::from_min_size(cursor.min, size)
+        Rect::from_min_size(cursor.min, size).round_ui()
     }
 
     #[allow(clippy::unused_self)]
     pub(crate) fn align_size_within_rect(&self, size: Vec2, frame: Rect) -> Rect {
         // TODO(emilk): allow this alignment to be customized
-        Align2::LEFT_CENTER.align_size_within_rect(size, frame)
+        Align2::LEFT_CENTER
+            .align_size_within_rect(size, frame)
+            .round_ui()
     }
 
     pub(crate) fn justify_and_align(&self, frame: Rect, size: Vec2) -> Rect {
diff --git a/crates/egui/src/layout.rs b/crates/egui/src/layout.rs
index 0c9bb494133..e967aaa6d57 100644
--- a/crates/egui/src/layout.rs
+++ b/crates/egui/src/layout.rs
@@ -1,3 +1,5 @@
+use emath::GuiRounding as _;
+
 use crate::{
     emath::{pos2, vec2, Align2, NumExt, Pos2, Rect, Vec2},
     Align,
@@ -394,7 +396,7 @@ impl Layout {
     pub fn align_size_within_rect(&self, size: Vec2, outer: Rect) -> Rect {
         debug_assert!(size.x >= 0.0 && size.y >= 0.0);
         debug_assert!(!outer.is_negative());
-        self.align2().align_size_within_rect(size, outer)
+        self.align2().align_size_within_rect(size, outer).round_ui()
     }
 
     fn initial_cursor(&self, max_rect: Rect) -> Rect {
@@ -634,7 +636,7 @@ impl Layout {
         debug_assert!(!frame_rect.any_nan());
         debug_assert!(!frame_rect.is_negative());
 
-        frame_rect
+        frame_rect.round_ui()
     }
 
     /// Apply justify (fill width/height) and/or alignment after calling `next_space`.
diff --git a/crates/egui/src/style.rs b/crates/egui/src/style.rs
index 14b5aecd6ee..91c0e09dbfa 100644
--- a/crates/egui/src/style.rs
+++ b/crates/egui/src/style.rs
@@ -1168,11 +1168,9 @@ pub struct DebugOptions {
     /// Show interesting widgets under the mouse cursor.
     pub show_widget_hits: bool,
 
-    /// If true, highlight widgets that are not aligned to integer point coordinates.
+    /// If true, highlight widgets that are not aligned to [`emath::GUI_ROUNDING`].
     ///
-    /// It's usually a good idea to keep to integer coordinates to avoid rounding issues.
-    ///
-    /// See <https://github.com/emilk/egui/issues/5163> for more.
+    /// See [`emath::GuiRounding`] for more.
     pub show_unaligned: bool,
 }
 
@@ -1189,7 +1187,7 @@ impl Default for DebugOptions {
             show_resize: false,
             show_interactive_widgets: false,
             show_widget_hits: false,
-            show_unaligned: false,
+            show_unaligned: cfg!(debug_assertions),
         }
     }
 }
diff --git a/crates/egui/src/ui.rs b/crates/egui/src/ui.rs
index 6cc474e141b..9cf2d4b5427 100644
--- a/crates/egui/src/ui.rs
+++ b/crates/egui/src/ui.rs
@@ -3,6 +3,7 @@
 
 use std::{any::Any, hash::Hash, sync::Arc};
 
+use emath::GuiRounding as _;
 use epaint::mutex::RwLock;
 
 use crate::{
@@ -716,7 +717,9 @@ impl Ui {
         self.painter().layer_id()
     }
 
-    /// The height of text of this text style
+    /// The height of text of this text style.
+    ///
+    /// Returns a value rounded to [`emath::GUI_ROUNDING`].
     pub fn text_style_height(&self, style: &TextStyle) -> f32 {
         self.fonts(|f| f.row_height(&style.resolve(self.style())))
     }
@@ -1295,6 +1298,7 @@ impl Ui {
     /// Ignore the layout of the [`Ui`]: just put my widget here!
     /// The layout cursor will advance to past this `rect`.
     pub fn allocate_rect(&mut self, rect: Rect, sense: Sense) -> Response {
+        let rect = rect.round_ui();
         let id = self.advance_cursor_after_rect(rect);
         self.interact(rect, id, sense)
     }
@@ -1302,6 +1306,8 @@ impl Ui {
     /// Allocate a rect without interacting with it.
     pub fn advance_cursor_after_rect(&mut self, rect: Rect) -> Id {
         debug_assert!(!rect.any_nan());
+        let rect = rect.round_ui();
+
         let item_spacing = self.spacing().item_spacing;
         self.placer.advance_after_rects(rect, rect, item_spacing);
         register_rect(self, rect);
@@ -3018,7 +3024,7 @@ impl Drop for Ui {
 /// Show this rectangle to the user if certain debug options are set.
 #[cfg(debug_assertions)]
 fn register_rect(ui: &Ui, rect: Rect) {
-    use emath::Align2;
+    use emath::{Align2, GuiRounding};
 
     let debug = ui.style().debug;
 
@@ -3031,16 +3037,16 @@ fn register_rect(ui: &Ui, rect: Rect) {
                 .text(p0, Align2::LEFT_TOP, "Unaligned", font_id, color);
         };
 
-        if rect.left().fract() != 0.0 {
+        if rect.left() != rect.left().round_ui() {
             unaligned_line(rect.left_top(), rect.left_bottom());
         }
-        if rect.right().fract() != 0.0 {
+        if rect.right() != rect.right().round_ui() {
             unaligned_line(rect.right_top(), rect.right_bottom());
         }
-        if rect.top().fract() != 0.0 {
+        if rect.top() != rect.top().round_ui() {
             unaligned_line(rect.left_top(), rect.right_top());
         }
-        if rect.bottom().fract() != 0.0 {
+        if rect.bottom() != rect.bottom().round_ui() {
             unaligned_line(rect.left_bottom(), rect.right_bottom());
         }
     }
diff --git a/crates/egui/src/widget_text.rs b/crates/egui/src/widget_text.rs
index 011a4adcbb0..d5cd16f09fd 100644
--- a/crates/egui/src/widget_text.rs
+++ b/crates/egui/src/widget_text.rs
@@ -1,5 +1,7 @@
 use std::{borrow::Cow, sync::Arc};
 
+use emath::GuiRounding as _;
+
 use crate::{
     text::{LayoutJob, TextWrapping},
     Align, Color32, FontFamily, FontSelection, Galley, Style, TextStyle, TextWrapMode, Ui, Visuals,
@@ -278,6 +280,8 @@ impl RichText {
     }
 
     /// Read the font height of the selected text style.
+    ///
+    /// Returns a value rounded to [`emath::GUI_ROUNDING`].
     pub fn font_height(&self, fonts: &epaint::Fonts, style: &Style) -> f32 {
         let mut font_id = self.text_style.as_ref().map_or_else(
             || FontSelection::Default.resolve(style),
@@ -635,15 +639,16 @@ impl WidgetText {
         }
     }
 
+    /// Returns a value rounded to [`emath::GUI_ROUNDING`].
     pub(crate) fn font_height(&self, fonts: &epaint::Fonts, style: &Style) -> f32 {
         match self {
             Self::RichText(text) => text.font_height(fonts, style),
             Self::LayoutJob(job) => job.font_height(fonts),
             Self::Galley(galley) => {
                 if let Some(row) = galley.rows.first() {
-                    row.height()
+                    row.height().round_ui()
                 } else {
-                    galley.size().y
+                    galley.size().y.round_ui()
                 }
             }
         }
diff --git a/crates/egui_demo_lib/src/rendering_test.rs b/crates/egui_demo_lib/src/rendering_test.rs
index f9ead5c584c..df3add3776e 100644
--- a/crates/egui_demo_lib/src/rendering_test.rs
+++ b/crates/egui_demo_lib/src/rendering_test.rs
@@ -681,7 +681,7 @@ fn mul_color_gamma(left: Color32, right: Color32) -> Color32 {
 #[cfg(test)]
 mod tests {
     use crate::ColorTest;
-    use egui::vec2;
+    use egui_kittest::kittest::Queryable as _;
 
     #[test]
     pub fn rendering_test() {
@@ -689,13 +689,16 @@ mod tests {
         for dpi in [1.0, 1.25, 1.5, 1.75, 1.6666667, 2.0] {
             let mut color_test = ColorTest::default();
             let mut harness = egui_kittest::Harness::builder()
-                .with_size(vec2(2000.0, 2000.0))
                 .with_pixels_per_point(dpi)
                 .build_ui(|ui| {
                     color_test.ui(ui);
                 });
 
-            //harness.set_size(harness.ctx.used_size());
+            {
+                // Expand color-test collapsing header
+                harness.get_by_label("Color test").click();
+                harness.run();
+            }
 
             harness.fit_contents();
 
diff --git a/crates/egui_demo_lib/tests/snapshots/demos/Code Example.png b/crates/egui_demo_lib/tests/snapshots/demos/Code Example.png
index 162fc51a1df..33121fe85fa 100644
--- a/crates/egui_demo_lib/tests/snapshots/demos/Code Example.png	
+++ b/crates/egui_demo_lib/tests/snapshots/demos/Code Example.png	
@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:01aaa4ef1a167a94fa1e5163550aabe4fa5e9f3a012b26170fe3088a6ca32d94
-size 81064
+oid sha256:f93cbf4968e69e2b51256631ab8703d1af2274147924f8d802d9da0f9767aa1b
+size 81162
diff --git a/crates/egui_demo_lib/tests/snapshots/demos/Context Menus.png b/crates/egui_demo_lib/tests/snapshots/demos/Context Menus.png
index c29267377b7..9191ade8504 100644
--- a/crates/egui_demo_lib/tests/snapshots/demos/Context Menus.png	
+++ b/crates/egui_demo_lib/tests/snapshots/demos/Context Menus.png	
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+++ b/crates/egui_demo_lib/tests/snapshots/demos/Misc Demos.png	
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--- a/crates/egui_demo_lib/tests/snapshots/demos/Multi Touch.png	
+++ b/crates/egui_demo_lib/tests/snapshots/demos/Multi Touch.png	
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index 384840b7101..6a1b79e3d78 100644
--- a/crates/egui_demo_lib/tests/snapshots/demos/Pan Zoom.png	
+++ b/crates/egui_demo_lib/tests/snapshots/demos/Pan Zoom.png	
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index ff972ae484c..dfef3f17542 100644
--- a/crates/egui_demo_lib/tests/snapshots/demos/Text Layout.png	
+++ b/crates/egui_demo_lib/tests/snapshots/demos/Text Layout.png	
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--- a/crates/egui_demo_lib/tests/snapshots/demos/Undo Redo.png	
+++ b/crates/egui_demo_lib/tests/snapshots/demos/Undo Redo.png	
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index ae442978324..b4c96d8397d 100644
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+++ b/crates/egui_demo_lib/tests/snapshots/rendering_test/dpi_1.00.png
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index 428160c867d..82426652255 100644
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index 003a08bd6e3..29514c4e7ff 100644
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diff --git a/crates/egui_demo_lib/tests/snapshots/widget_gallery.png b/crates/egui_demo_lib/tests/snapshots/widget_gallery.png
index 914b3da9ead..a2adca3db43 100644
--- a/crates/egui_demo_lib/tests/snapshots/widget_gallery.png
+++ b/crates/egui_demo_lib/tests/snapshots/widget_gallery.png
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diff --git a/crates/egui_extras/src/layout.rs b/crates/egui_extras/src/layout.rs
index 239e7b1d29b..0121f83e0f2 100644
--- a/crates/egui_extras/src/layout.rs
+++ b/crates/egui_extras/src/layout.rs
@@ -1,4 +1,4 @@
-use egui::{Id, Pos2, Rect, Response, Sense, Ui, UiBuilder};
+use egui::{emath::GuiRounding, Id, Pos2, Rect, Response, Sense, Ui, UiBuilder};
 
 #[derive(Clone, Copy)]
 pub(crate) enum CellSize {
@@ -123,7 +123,7 @@ impl<'l> StripLayout<'l> {
 
         // Make sure we don't have a gap in the stripe/frame/selection background:
         let item_spacing = self.ui.spacing().item_spacing;
-        let gapless_rect = max_rect.expand2(0.5 * item_spacing);
+        let gapless_rect = max_rect.expand2(0.5 * item_spacing).round_ui();
 
         if flags.striped {
             self.ui.painter().rect_filled(
diff --git a/crates/emath/src/gui_rounding.rs b/crates/emath/src/gui_rounding.rs
new file mode 100644
index 00000000000..3c2cf92411b
--- /dev/null
+++ b/crates/emath/src/gui_rounding.rs
@@ -0,0 +1,201 @@
+/// We (sometimes) round sizes and coordinates to an even multiple of this value.
+///
+/// This is only used for rounding _logical UI points_, used for widget coordinates and sizes.
+/// When rendering, you may want to round to an integer multiple of the physical _pixels_ instead,
+/// using [`GuiRounding::round_to_pixels`].
+///
+/// See [`GuiRounding::round_ui`] for more information.
+///
+/// This constant has to be a (negative) power of two so that it can be represented exactly
+/// by a floating point number.
+///
+/// If we pick too large a value (e.g. 1 or 1/2), then we get judder during scrolling and animations.
+/// If we pick too small a value (e.g. 1/4096), we run the risk of rounding errors again.
+///
+/// `f32` has 23 bits of mantissa, so if we use e.g. 1/8 as the rounding factor,
+/// we can represent all numbers up to 2^20 exactly, which is plenty
+/// (to my knowledge there are no displays that are a million pixels wide).
+pub const GUI_ROUNDING: f32 = 1.0 / 32.0;
+
+/// Trait for rounding coordinates and sizes to align with either .
+///
+/// See [`GuiRounding::round_ui`] for more information.
+pub trait GuiRounding {
+    /// Rounds floating point numbers to an even multiple of the GUI rounding factor, [`crate::GUI_ROUNDING`].
+    ///
+    /// Use this for widget coordinates and sizes.
+    ///
+    /// Rounding sizes and positions prevent rounding errors when doing sizing calculations.
+    /// We don't round to integers, because that would be too coarse (causing visible juddering when scrolling, for instance).
+    /// Instead we round to an even multiple of [`GUI_ROUNDING`].
+    fn round_ui(self) -> Self;
+
+    /// Like [`Self::round_ui`], but always rounds towards negative infinity.
+    fn floor_ui(self) -> Self;
+
+    /// Round a size or position to an even multiple of the physical pixel size.
+    ///
+    /// This can be useful for crisp rendering.
+    ///
+    /// The `self` should be in coordinates of _logical UI points_.
+    /// The argument `pixels_per_point` is the number of _physical pixels_ per logical UI point.
+    /// For instance, on a high-DPI screen, `pixels_per_point` could be `2.0`.
+    fn round_to_pixels(self, pixels_per_point: f32) -> Self;
+
+    /// Will round the position to be in the center of a pixel.
+    ///
+    /// The pixel size is `1.0 / pixels_per_point`.
+    ///
+    /// So if `pixels_per_point = 2` (i.e. `pixel size = 0.5`),
+    /// then the position will be rounded to the closest of `…, 0.25, 0.75, 1.25, …`.
+    ///
+    /// This is useful, for instance, when picking the center of a line that is one pixel wide.
+    fn round_to_pixel_center(self, pixels_per_point: f32) -> Self;
+}
+
+impl GuiRounding for f32 {
+    #[inline]
+    fn round_ui(self) -> Self {
+        (self / GUI_ROUNDING).round() * GUI_ROUNDING
+    }
+
+    #[inline]
+    fn floor_ui(self) -> Self {
+        (self / GUI_ROUNDING).floor() * GUI_ROUNDING
+    }
+
+    #[inline]
+    fn round_to_pixels(self, pixels_per_point: f32) -> Self {
+        (self * pixels_per_point).round() / pixels_per_point
+    }
+
+    #[inline]
+    fn round_to_pixel_center(self, pixels_per_point: f32) -> Self {
+        ((self * pixels_per_point - 0.5).round() + 0.5) / pixels_per_point
+    }
+}
+
+impl GuiRounding for f64 {
+    #[inline]
+    fn round_ui(self) -> Self {
+        (self / GUI_ROUNDING as Self).round() * GUI_ROUNDING as Self
+    }
+
+    #[inline]
+    fn floor_ui(self) -> Self {
+        (self / GUI_ROUNDING as Self).floor() * GUI_ROUNDING as Self
+    }
+
+    #[inline]
+    fn round_to_pixels(self, pixels_per_point: f32) -> Self {
+        (self * pixels_per_point as Self).round() / pixels_per_point as Self
+    }
+
+    #[inline]
+    fn round_to_pixel_center(self, pixels_per_point: f32) -> Self {
+        ((self * pixels_per_point as Self - 0.5).round() + 0.5) / pixels_per_point as Self
+    }
+}
+
+impl GuiRounding for crate::Vec2 {
+    #[inline]
+    fn round_ui(self) -> Self {
+        Self::new(self.x.round_ui(), self.y.round_ui())
+    }
+
+    #[inline]
+    fn floor_ui(self) -> Self {
+        Self::new(self.x.floor_ui(), self.y.floor_ui())
+    }
+
+    #[inline]
+    fn round_to_pixels(self, pixels_per_point: f32) -> Self {
+        Self::new(
+            self.x.round_to_pixels(pixels_per_point),
+            self.y.round_to_pixels(pixels_per_point),
+        )
+    }
+
+    #[inline]
+    fn round_to_pixel_center(self, pixels_per_point: f32) -> Self {
+        Self::new(
+            self.x.round_to_pixel_center(pixels_per_point),
+            self.y.round_to_pixel_center(pixels_per_point),
+        )
+    }
+}
+
+impl GuiRounding for crate::Pos2 {
+    #[inline]
+    fn round_ui(self) -> Self {
+        Self::new(self.x.round_ui(), self.y.round_ui())
+    }
+
+    #[inline]
+    fn floor_ui(self) -> Self {
+        Self::new(self.x.floor_ui(), self.y.floor_ui())
+    }
+
+    #[inline]
+    fn round_to_pixels(self, pixels_per_point: f32) -> Self {
+        Self::new(
+            self.x.round_to_pixels(pixels_per_point),
+            self.y.round_to_pixels(pixels_per_point),
+        )
+    }
+
+    #[inline]
+    fn round_to_pixel_center(self, pixels_per_point: f32) -> Self {
+        Self::new(
+            self.x.round_to_pixel_center(pixels_per_point),
+            self.y.round_to_pixel_center(pixels_per_point),
+        )
+    }
+}
+
+impl GuiRounding for crate::Rect {
+    /// Rounded so that two adjacent rects that tile perfectly
+    /// will continue to tile perfectly.
+    #[inline]
+    fn round_ui(self) -> Self {
+        Self::from_min_max(self.min.round_ui(), self.max.round_ui())
+    }
+
+    /// Rounded so that two adjacent rects that tile perfectly
+    /// will continue to tile perfectly.
+    #[inline]
+    fn floor_ui(self) -> Self {
+        Self::from_min_max(self.min.floor_ui(), self.max.floor_ui())
+    }
+
+    /// Rounded so that two adjacent rects that tile perfectly
+    /// will continue to tile perfectly.
+    #[inline]
+    fn round_to_pixels(self, pixels_per_point: f32) -> Self {
+        Self::from_min_max(
+            self.min.round_to_pixels(pixels_per_point),
+            self.max.round_to_pixels(pixels_per_point),
+        )
+    }
+
+    /// Rounded so that two adjacent rects that tile perfectly
+    /// will continue to tile perfectly.
+    #[inline]
+    fn round_to_pixel_center(self, pixels_per_point: f32) -> Self {
+        Self::from_min_max(
+            self.min.round_to_pixel_center(pixels_per_point),
+            self.max.round_to_pixel_center(pixels_per_point),
+        )
+    }
+}
+
+#[test]
+fn test_gui_rounding() {
+    assert_eq!(0.0_f32.round_ui(), 0.0);
+    assert_eq!((GUI_ROUNDING * 1.11).round_ui(), GUI_ROUNDING);
+    assert_eq!((-GUI_ROUNDING * 1.11).round_ui(), -GUI_ROUNDING);
+    assert_eq!(f32::NEG_INFINITY.round_ui(), f32::NEG_INFINITY);
+    assert_eq!(f32::INFINITY.round_ui(), f32::INFINITY);
+
+    assert_eq!(0.17_f32.round_to_pixel_center(2.0), 0.25);
+}
diff --git a/crates/emath/src/lib.rs b/crates/emath/src/lib.rs
index 2f30a55ca98..05210fbb298 100644
--- a/crates/emath/src/lib.rs
+++ b/crates/emath/src/lib.rs
@@ -27,6 +27,7 @@ use std::ops::{Add, Div, Mul, RangeInclusive, Sub};
 
 pub mod align;
 pub mod easing;
+mod gui_rounding;
 mod history;
 mod numeric;
 mod ordered_float;
@@ -42,6 +43,7 @@ mod vec2b;
 
 pub use self::{
     align::{Align, Align2},
+    gui_rounding::{GuiRounding, GUI_ROUNDING},
     history::History,
     numeric::*,
     ordered_float::*,
diff --git a/crates/epaint/src/text/font.rs b/crates/epaint/src/text/font.rs
index d717c3e7355..a3994ca4c3b 100644
--- a/crates/epaint/src/text/font.rs
+++ b/crates/epaint/src/text/font.rs
@@ -1,7 +1,7 @@
 use std::collections::BTreeMap;
 use std::sync::Arc;
 
-use emath::{vec2, Vec2};
+use emath::{vec2, GuiRounding, Vec2};
 
 use crate::{
     mutex::{Mutex, RwLock},
@@ -96,22 +96,18 @@ impl FontImpl {
 
         use ab_glyph::{Font, ScaleFont};
         let scaled = ab_glyph_font.as_scaled(scale_in_pixels);
-        let ascent = scaled.ascent() / pixels_per_point;
-        let descent = scaled.descent() / pixels_per_point;
-        let line_gap = scaled.line_gap() / pixels_per_point;
+        let ascent = (scaled.ascent() / pixels_per_point).round_ui();
+        let descent = (scaled.descent() / pixels_per_point).round_ui();
+        let line_gap = (scaled.line_gap() / pixels_per_point).round_ui();
 
         // Tweak the scale as the user desired
         let scale_in_pixels = scale_in_pixels * tweak.scale;
+        let scale_in_points = scale_in_pixels / pixels_per_point;
 
-        let baseline_offset = {
-            let scale_in_points = scale_in_pixels / pixels_per_point;
-            scale_in_points * tweak.baseline_offset_factor
-        };
+        let baseline_offset = (scale_in_points * tweak.baseline_offset_factor).round_ui();
 
-        let y_offset_points = {
-            let scale_in_points = scale_in_pixels / pixels_per_point;
-            scale_in_points * tweak.y_offset_factor
-        } + tweak.y_offset;
+        let y_offset_points =
+            ((scale_in_points * tweak.y_offset_factor) + tweak.y_offset).round_ui();
 
         // Center scaled glyphs properly:
         let height = ascent + descent;
@@ -247,6 +243,8 @@ impl FontImpl {
     }
 
     /// Height of one row of text in points.
+    ///
+    /// Returns a value rounded to [`emath::GUI_ROUNDING`].
     #[inline(always)]
     pub fn row_height(&self) -> f32 {
         self.height_in_points
@@ -418,7 +416,9 @@ impl Font {
         (point * self.pixels_per_point).round() / self.pixels_per_point
     }
 
-    /// Height of one row of text. In points
+    /// Height of one row of text. In points.
+    ///
+    /// Returns a value rounded to [`emath::GUI_ROUNDING`].
     #[inline(always)]
     pub fn row_height(&self) -> f32 {
         self.row_height
diff --git a/crates/epaint/src/text/fonts.rs b/crates/epaint/src/text/fonts.rs
index 4be2fdfe8d0..b952b2817d1 100644
--- a/crates/epaint/src/text/fonts.rs
+++ b/crates/epaint/src/text/fonts.rs
@@ -519,7 +519,9 @@ impl Fonts {
         self.lock().fonts.has_glyphs(font_id, s)
     }
 
-    /// Height of one row of text in points
+    /// Height of one row of text in points.
+    ///
+    /// Returns a value rounded to [`emath::GUI_ROUNDING`].
     #[inline]
     pub fn row_height(&self, font_id: &FontId) -> f32 {
         self.lock().fonts.row_height(font_id)
@@ -706,6 +708,8 @@ impl FontsImpl {
     }
 
     /// Height of one row of text in points.
+    ///
+    /// Returns a value rounded to [`emath::GUI_ROUNDING`].
     fn row_height(&mut self, font_id: &FontId) -> f32 {
         self.font(font_id).row_height()
     }
diff --git a/crates/epaint/src/text/text_layout.rs b/crates/epaint/src/text/text_layout.rs
index 9db77f888af..2f19e538f60 100644
--- a/crates/epaint/src/text/text_layout.rs
+++ b/crates/epaint/src/text/text_layout.rs
@@ -1,7 +1,7 @@
 use std::ops::RangeInclusive;
 use std::sync::Arc;
 
-use emath::{pos2, vec2, Align, NumExt, Pos2, Rect, Vec2};
+use emath::{pos2, vec2, Align, GuiRounding as _, NumExt, Pos2, Rect, Vec2};
 
 use crate::{stroke::PathStroke, text::font::Font, Color32, Mesh, Stroke, Vertex};
 
@@ -630,7 +630,7 @@ fn galley_from_rows(
         min_x = min_x.min(row.rect.min.x);
         max_x = max_x.max(row.rect.max.x);
         cursor_y += max_row_height;
-        cursor_y = point_scale.round_to_pixel(cursor_y);
+        cursor_y = point_scale.round_to_pixel(cursor_y); // TODO(emilk): it would be better to do the calculations in pixels instead.
     }
 
     let format_summary = format_summary(&job);
@@ -648,20 +648,25 @@ fn galley_from_rows(
 
     let mut rect = Rect::from_min_max(pos2(min_x, 0.0), pos2(max_x, cursor_y));
 
-    if job.round_output_size_to_nearest_ui_point {
+    if job.round_output_to_gui {
+        for row in &mut rows {
+            row.rect = row.rect.round_ui();
+        }
+
         let did_exceed_wrap_width_by_a_lot = rect.width() > job.wrap.max_width + 1.0;
 
-        // We round the size to whole ui points here (not pixels!) so that the egui layout code
-        // can have the advantage of working in integer units, avoiding rounding errors.
-        rect.min = rect.min.round();
-        rect.max = rect.max.round();
+        rect = rect.round_ui();
 
         if did_exceed_wrap_width_by_a_lot {
             // If the user picked a too aggressive wrap width (e.g. more narrow than any individual glyph),
             // we should let the user know by reporting that our width is wider than the wrap width.
         } else {
             // Make sure we don't report being wider than the wrap width the user picked:
-            rect.max.x = rect.max.x.at_most(rect.min.x + job.wrap.max_width).floor();
+            rect.max.x = rect
+                .max
+                .x
+                .at_most(rect.min.x + job.wrap.max_width)
+                .floor_ui();
         }
     }
 
@@ -1133,6 +1138,7 @@ mod tests {
             LayoutJob::single_section("# DNA\nMore text".into(), TextFormat::default());
         layout_job.wrap.max_width = f32::INFINITY;
         layout_job.wrap.max_rows = 1;
+        layout_job.round_output_to_gui = false;
         let galley = layout(&mut fonts, layout_job.into());
         assert!(galley.elided);
         assert_eq!(
diff --git a/crates/epaint/src/text/text_layout_types.rs b/crates/epaint/src/text/text_layout_types.rs
index 64dd827148c..b228d023e66 100644
--- a/crates/epaint/src/text/text_layout_types.rs
+++ b/crates/epaint/src/text/text_layout_types.rs
@@ -78,9 +78,8 @@ pub struct LayoutJob {
     /// Justify text so that word-wrapped rows fill the whole [`TextWrapping::max_width`].
     pub justify: bool,
 
-    /// Rounding to the closest ui point (not pixel!) allows the rest of the
-    /// layout code to run on perfect integers, avoiding rounding errors.
-    pub round_output_size_to_nearest_ui_point: bool,
+    /// Round output sizes using [`emath::GuiRounding`], to avoid rounding errors in layout code.
+    pub round_output_to_gui: bool,
 }
 
 impl Default for LayoutJob {
@@ -94,7 +93,7 @@ impl Default for LayoutJob {
             break_on_newline: true,
             halign: Align::LEFT,
             justify: false,
-            round_output_size_to_nearest_ui_point: true,
+            round_output_to_gui: true,
         }
     }
 }
@@ -168,6 +167,8 @@ impl LayoutJob {
     }
 
     /// The height of the tallest font used in the job.
+    ///
+    /// Returns a value rounded to [`emath::GUI_ROUNDING`].
     pub fn font_height(&self, fonts: &crate::Fonts) -> f32 {
         let mut max_height = 0.0_f32;
         for section in &self.sections {
@@ -178,7 +179,7 @@ impl LayoutJob {
 
     /// The wrap with, with a small margin in some cases.
     pub fn effective_wrap_width(&self) -> f32 {
-        if self.round_output_size_to_nearest_ui_point {
+        if self.round_output_to_gui {
             // On a previous pass we may have rounded down by at most 0.5 and reported that as a width.
             // egui may then set that width as the max width for subsequent frames, and it is important
             // that we then don't wrap earlier.
@@ -200,7 +201,7 @@ impl std::hash::Hash for LayoutJob {
             break_on_newline,
             halign,
             justify,
-            round_output_size_to_nearest_ui_point,
+            round_output_to_gui,
         } = self;
 
         text.hash(state);
@@ -210,7 +211,7 @@ impl std::hash::Hash for LayoutJob {
         break_on_newline.hash(state);
         halign.hash(state);
         justify.hash(state);
-        round_output_size_to_nearest_ui_point.hash(state);
+        round_output_to_gui.hash(state);
     }
 }
 

From d20f93e9bf1e2fe52c1b11aff8cf741d10b2cb85 Mon Sep 17 00:00:00 2001
From: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>
Date: Thu, 26 Dec 2024 21:02:27 +0100
Subject: [PATCH 2/2] Make all lines and rectangles crisp (#5518)

* Merge this first: https://github.com/emilk/egui/pull/5517

This aligns all rectangles and (horizontal or vertical) line segments to
the physical pixel grid in the `epaint::Tessellator`, making these
shapes appear crisp everywhere.

* Closes https://github.com/emilk/egui/issues/5164
* Closes https://github.com/emilk/egui/issues/3667

This undoes a lot of the explicit, egui-side aligning added in:
* https://github.com/emilk/egui/pull/4943

The new approach has several benefits over the old one:

* It is done automatically by epaint, so it is applied to everything (no
longer opt-in)
* It is applied after any layer transforms (so it always works)
* It makes line segments crisper on high-DPI screens
* All filled rectangles now has sides that end on pixel boundaries
---
 crates/egui/src/containers/panel.rs           |  30 ++--
 crates/egui/src/containers/resize.rs          |   4 +-
 crates/egui/src/containers/window.rs          |   2 +-
 crates/egui/src/context.rs                    |  45 -----
 crates/egui/src/introspection.rs              |  15 +-
 crates/egui/src/painter.rs                    |  83 ++++++----
 crates/egui/src/style.rs                      |   8 +-
 crates/egui/src/text_selection/visuals.rs     |  15 +-
 crates/egui/src/ui.rs                         |   8 +-
 crates/egui/src/widgets/separator.rs          |   4 +-
 crates/egui_demo_lib/src/rendering_test.rs    |   7 +-
 .../snapshots/demos/B\303\251zier Curve.png"  |   4 +-
 .../tests/snapshots/demos/Code Editor.png     |   4 +-
 .../tests/snapshots/demos/Code Example.png    |   4 +-
 .../tests/snapshots/demos/Context Menus.png   |   4 +-
 .../tests/snapshots/demos/Dancing Strings.png |   4 +-
 .../tests/snapshots/demos/Drag and Drop.png   |   4 +-
 .../tests/snapshots/demos/Extra Viewport.png  |   4 +-
 .../tests/snapshots/demos/Font Book.png       |   4 +-
 .../tests/snapshots/demos/Frame.png           |   4 +-
 .../tests/snapshots/demos/Highlighting.png    |   4 +-
 .../snapshots/demos/Interactive Container.png |   4 +-
 .../tests/snapshots/demos/Misc Demos.png      |   4 +-
 .../tests/snapshots/demos/Modals.png          |   4 +-
 .../tests/snapshots/demos/Multi Touch.png     |   4 +-
 .../tests/snapshots/demos/Painting.png        |   4 +-
 .../tests/snapshots/demos/Pan Zoom.png        |   4 +-
 .../tests/snapshots/demos/Panels.png          |   4 +-
 .../tests/snapshots/demos/Screenshot.png      |   4 +-
 .../tests/snapshots/demos/Scrolling.png       |   4 +-
 .../tests/snapshots/demos/Sliders.png         |   4 +-
 .../tests/snapshots/demos/Strip.png           |   4 +-
 .../tests/snapshots/demos/Table.png           |   4 +-
 .../tests/snapshots/demos/Text Layout.png     |   4 +-
 .../tests/snapshots/demos/TextEdit.png        |   4 +-
 .../tests/snapshots/demos/Tooltips.png        |   4 +-
 .../tests/snapshots/demos/Undo Redo.png       |   4 +-
 .../tests/snapshots/demos/Window Options.png  |   4 +-
 .../tests/snapshots/modals_1.png              |   4 +-
 .../tests/snapshots/modals_2.png              |   4 +-
 .../tests/snapshots/modals_3.png              |   4 +-
 ...rop_should_prevent_focusing_lower_area.png |   4 +-
 .../snapshots/rendering_test/dpi_1.00.png     |   4 +-
 .../snapshots/rendering_test/dpi_1.25.png     |   4 +-
 .../snapshots/rendering_test/dpi_1.50.png     |   4 +-
 .../snapshots/rendering_test/dpi_1.67.png     |   4 +-
 .../snapshots/rendering_test/dpi_1.75.png     |   4 +-
 .../snapshots/rendering_test/dpi_2.00.png     |   4 +-
 .../tests/snapshots/widget_gallery.png        |   4 +-
 crates/emath/src/gui_rounding.rs              |   1 +
 crates/epaint/src/lib.rs                      |   2 +-
 crates/epaint/src/shape.rs                    |  23 ++-
 crates/epaint/src/shape_transform.rs          |   2 +-
 crates/epaint/src/tessellator.rs              | 155 ++++++++++++++----
 examples/hello_android/Cargo.toml             |   9 +-
 55 files changed, 314 insertions(+), 251 deletions(-)

diff --git a/crates/egui/src/containers/panel.rs b/crates/egui/src/containers/panel.rs
index f659a8c4efa..6fd19e18688 100644
--- a/crates/egui/src/containers/panel.rs
+++ b/crates/egui/src/containers/panel.rs
@@ -78,6 +78,13 @@ impl Side {
             Self::Right => rect.right(),
         }
     }
+
+    fn sign(self) -> f32 {
+        match self {
+            Self::Left => -1.0,
+            Self::Right => 1.0,
+        }
+    }
 }
 
 /// A panel that covers the entire left or right side of a [`Ui`] or screen.
@@ -349,12 +356,8 @@ impl SidePanel {
             // TODO(emilk): draw line on top of all panels in this ui when https://github.com/emilk/egui/issues/1516 is done
             let resize_x = side.opposite().side_x(rect);
 
-            // This makes it pixel-perfect for odd-sized strokes (width=1.0, width=3.0, etc)
-            let resize_x = ui.painter().round_to_pixel_center(resize_x);
-
-            // We want the line exactly on the last pixel but rust rounds away from zero so we bring it back a bit for
-            // left-side panels
-            let resize_x = resize_x - if side == Side::Left { 1.0 } else { 0.0 };
+            // Make sure the line is on the inside of the panel:
+            let resize_x = resize_x + 0.5 * side.sign() * stroke.width;
             ui.painter().vline(resize_x, panel_rect.y_range(), stroke);
         }
 
@@ -562,6 +565,13 @@ impl TopBottomSide {
             Self::Bottom => rect.bottom(),
         }
     }
+
+    fn sign(self) -> f32 {
+        match self {
+            Self::Top => -1.0,
+            Self::Bottom => 1.0,
+        }
+    }
 }
 
 /// A panel that covers the entire top or bottom of a [`Ui`] or screen.
@@ -843,12 +853,8 @@ impl TopBottomPanel {
             // TODO(emilk): draw line on top of all panels in this ui when https://github.com/emilk/egui/issues/1516 is done
             let resize_y = side.opposite().side_y(rect);
 
-            // This makes it pixel-perfect for odd-sized strokes (width=1.0, width=3.0, etc)
-            let resize_y = ui.painter().round_to_pixel_center(resize_y);
-
-            // We want the line exactly on the last pixel but rust rounds away from zero so we bring it back a bit for
-            // top-side panels
-            let resize_y = resize_y - if side == TopBottomSide::Top { 1.0 } else { 0.0 };
+            // Make sure the line is on the inside of the panel:
+            let resize_y = resize_y + 0.5 * side.sign() * stroke.width;
             ui.painter().hline(panel_rect.x_range(), resize_y, stroke);
         }
 
diff --git a/crates/egui/src/containers/resize.rs b/crates/egui/src/containers/resize.rs
index 0165eba996a..bbb86dfbf36 100644
--- a/crates/egui/src/containers/resize.rs
+++ b/crates/egui/src/containers/resize.rs
@@ -400,7 +400,9 @@ pub fn paint_resize_corner_with_style(
     corner: Align2,
 ) {
     let painter = ui.painter();
-    let cp = painter.round_pos_to_pixels(corner.pos_in_rect(rect));
+    let cp = corner
+        .pos_in_rect(rect)
+        .round_to_pixels(ui.pixels_per_point());
     let mut w = 2.0;
     let stroke = Stroke {
         width: 1.0, // Set width to 1.0 to prevent overlapping
diff --git a/crates/egui/src/containers/window.rs b/crates/egui/src/containers/window.rs
index 44c3dda58c1..414c58cfae7 100644
--- a/crates/egui/src/containers/window.rs
+++ b/crates/egui/src/containers/window.rs
@@ -596,7 +596,7 @@ impl<'open> Window<'open> {
                         },
                     );
 
-                    title_rect = area_content_ui.painter().round_rect_to_pixels(title_rect);
+                    title_rect = title_rect.round_to_pixels(area_content_ui.pixels_per_point());
 
                     if on_top && area_content_ui.visuals().window_highlight_topmost {
                         let mut round = window_frame.rounding;
diff --git a/crates/egui/src/context.rs b/crates/egui/src/context.rs
index eaca8d36f52..118cddb31fa 100644
--- a/crates/egui/src/context.rs
+++ b/crates/egui/src/context.rs
@@ -7,7 +7,6 @@ use emath::GuiRounding as _;
 use epaint::{
     emath::{self, TSTransform},
     mutex::RwLock,
-    pos2,
     stats::PaintStats,
     tessellator,
     text::{FontInsert, FontPriority, Fonts},
@@ -2004,50 +2003,6 @@ impl Context {
         });
     }
 
-    /// Useful for pixel-perfect rendering of lines that are one pixel wide (or any odd number of pixels).
-    #[inline]
-    pub(crate) fn round_to_pixel_center(&self, point: f32) -> f32 {
-        let pixels_per_point = self.pixels_per_point();
-        ((point * pixels_per_point - 0.5).round() + 0.5) / pixels_per_point
-    }
-
-    /// Useful for pixel-perfect rendering of lines that are one pixel wide (or any odd number of pixels).
-    #[inline]
-    pub(crate) fn round_pos_to_pixel_center(&self, point: Pos2) -> Pos2 {
-        pos2(
-            self.round_to_pixel_center(point.x),
-            self.round_to_pixel_center(point.y),
-        )
-    }
-
-    /// Useful for pixel-perfect rendering of filled shapes
-    #[inline]
-    pub(crate) fn round_to_pixel(&self, point: f32) -> f32 {
-        let pixels_per_point = self.pixels_per_point();
-        (point * pixels_per_point).round() / pixels_per_point
-    }
-
-    /// Useful for pixel-perfect rendering of filled shapes
-    #[inline]
-    pub(crate) fn round_pos_to_pixels(&self, pos: Pos2) -> Pos2 {
-        pos2(self.round_to_pixel(pos.x), self.round_to_pixel(pos.y))
-    }
-
-    /// Useful for pixel-perfect rendering of filled shapes
-    #[inline]
-    pub(crate) fn round_vec_to_pixels(&self, vec: Vec2) -> Vec2 {
-        vec2(self.round_to_pixel(vec.x), self.round_to_pixel(vec.y))
-    }
-
-    /// Useful for pixel-perfect rendering of filled shapes
-    #[inline]
-    pub(crate) fn round_rect_to_pixels(&self, rect: Rect) -> Rect {
-        Rect {
-            min: self.round_pos_to_pixels(rect.min),
-            max: self.round_pos_to_pixels(rect.max),
-        }
-    }
-
     /// Allocate a texture.
     ///
     /// This is for advanced users.
diff --git a/crates/egui/src/introspection.rs b/crates/egui/src/introspection.rs
index 7f0ced6ba93..85e1ee6c62f 100644
--- a/crates/egui/src/introspection.rs
+++ b/crates/egui/src/introspection.rs
@@ -144,6 +144,8 @@ impl Widget for &mut epaint::TessellationOptions {
                 coarse_tessellation_culling,
                 prerasterized_discs,
                 round_text_to_pixels,
+                round_line_segments_to_pixels,
+                round_rects_to_pixels,
                 debug_paint_clip_rects,
                 debug_paint_text_rects,
                 debug_ignore_clip_rects,
@@ -179,13 +181,22 @@ impl Widget for &mut epaint::TessellationOptions {
 
             ui.checkbox(validate_meshes, "Validate meshes").on_hover_text("Check that incoming meshes are valid, i.e. that all indices are in range, etc.");
 
+            ui.collapsing("Align to pixel grid", |ui| {
+                ui.checkbox(round_text_to_pixels, "Text")
+                    .on_hover_text("Most text already is, so don't expect to see a large change.");
+
+                ui.checkbox(round_line_segments_to_pixels, "Line segments")
+                    .on_hover_text("Makes line segments appear crisp on any display.");
+
+                ui.checkbox(round_rects_to_pixels, "Rectangles")
+                    .on_hover_text("Makes line segments appear crisp on any display.");
+            });
+
             ui.collapsing("Debug", |ui| {
                 ui.checkbox(
                     coarse_tessellation_culling,
                     "Do coarse culling in the tessellator",
                 );
-                ui.checkbox(round_text_to_pixels, "Align text positions to pixel grid")
-                    .on_hover_text("Most text already is, so don't expect to see a large change.");
 
                 ui.checkbox(debug_ignore_clip_rects, "Ignore clip rectangles");
                 ui.checkbox(debug_paint_clip_rects, "Paint clip rectangles");
diff --git a/crates/egui/src/painter.rs b/crates/egui/src/painter.rs
index 232450e3862..e30a148d979 100644
--- a/crates/egui/src/painter.rs
+++ b/crates/egui/src/painter.rs
@@ -1,23 +1,30 @@
 use std::sync::Arc;
 
+use emath::GuiRounding as _;
+use epaint::{
+    text::{Fonts, Galley, LayoutJob},
+    CircleShape, ClippedShape, PathStroke, RectShape, Rounding, Shape, Stroke,
+};
+
 use crate::{
     emath::{Align2, Pos2, Rangef, Rect, Vec2},
     layers::{LayerId, PaintList, ShapeIdx},
     Color32, Context, FontId,
 };
-use epaint::{
-    text::{Fonts, Galley, LayoutJob},
-    CircleShape, ClippedShape, PathStroke, RectShape, Rounding, Shape, Stroke,
-};
 
 /// Helper to paint shapes and text to a specific region on a specific layer.
 ///
 /// All coordinates are screen coordinates in the unit points (one point can consist of many physical pixels).
+///
+/// A [`Painter`] never outlive a single frame/pass.
 #[derive(Clone)]
 pub struct Painter {
     /// Source of fonts and destination of shapes
     ctx: Context,
 
+    /// For quick access, without having to go via [`Context`].
+    pixels_per_point: f32,
+
     /// Where we paint
     layer_id: LayerId,
 
@@ -38,8 +45,10 @@ pub struct Painter {
 impl Painter {
     /// Create a painter to a specific layer within a certain clip rectangle.
     pub fn new(ctx: Context, layer_id: LayerId, clip_rect: Rect) -> Self {
+        let pixels_per_point = ctx.pixels_per_point();
         Self {
             ctx,
+            pixels_per_point,
             layer_id,
             clip_rect,
             fade_to_color: None,
@@ -49,14 +58,10 @@ impl Painter {
 
     /// Redirect where you are painting.
     #[must_use]
-    pub fn with_layer_id(self, layer_id: LayerId) -> Self {
-        Self {
-            ctx: self.ctx,
-            layer_id,
-            clip_rect: self.clip_rect,
-            fade_to_color: None,
-            opacity_factor: 1.0,
-        }
+    #[inline]
+    pub fn with_layer_id(mut self, layer_id: LayerId) -> Self {
+        self.layer_id = layer_id;
+        self
     }
 
     /// Create a painter for a sub-region of this [`Painter`].
@@ -64,13 +69,9 @@ impl Painter {
     /// The clip-rect of the returned [`Painter`] will be the intersection
     /// of the given rectangle and the `clip_rect()` of the parent [`Painter`].
     pub fn with_clip_rect(&self, rect: Rect) -> Self {
-        Self {
-            ctx: self.ctx.clone(),
-            layer_id: self.layer_id,
-            clip_rect: rect.intersect(self.clip_rect),
-            fade_to_color: self.fade_to_color,
-            opacity_factor: self.opacity_factor,
-        }
+        let mut new_self = self.clone();
+        new_self.clip_rect = rect.intersect(self.clip_rect);
+        new_self
     }
 
     /// Redirect where you are painting.
@@ -82,7 +83,7 @@ impl Painter {
     }
 
     /// If set, colors will be modified to look like this
-    pub(crate) fn set_fade_to_color(&mut self, fade_to_color: Option<Color32>) {
+    pub fn set_fade_to_color(&mut self, fade_to_color: Option<Color32>) {
         self.fade_to_color = fade_to_color;
     }
 
@@ -118,24 +119,27 @@ impl Painter {
     /// If `false`, nothing you paint will show up.
     ///
     /// Also checks [`Context::will_discard`].
-    pub(crate) fn is_visible(&self) -> bool {
+    pub fn is_visible(&self) -> bool {
         self.fade_to_color != Some(Color32::TRANSPARENT) && !self.ctx.will_discard()
     }
 
     /// If `false`, nothing added to the painter will be visible
-    pub(crate) fn set_invisible(&mut self) {
+    pub fn set_invisible(&mut self) {
         self.fade_to_color = Some(Color32::TRANSPARENT);
     }
-}
 
-/// ## Accessors etc
-impl Painter {
     /// Get a reference to the parent [`Context`].
     #[inline]
     pub fn ctx(&self) -> &Context {
         &self.ctx
     }
 
+    /// Number of physical pixels for each logical UI point.
+    #[inline]
+    pub fn pixels_per_point(&self) -> f32 {
+        self.pixels_per_point
+    }
+
     /// Read-only access to the shared [`Fonts`].
     ///
     /// See [`Context`] documentation for how locks work.
@@ -180,37 +184,42 @@ impl Painter {
     /// Useful for pixel-perfect rendering of lines that are one pixel wide (or any odd number of pixels).
     #[inline]
     pub fn round_to_pixel_center(&self, point: f32) -> f32 {
-        self.ctx().round_to_pixel_center(point)
+        point.round_to_pixel_center(self.pixels_per_point())
     }
 
     /// Useful for pixel-perfect rendering of lines that are one pixel wide (or any odd number of pixels).
+    #[deprecated = "Use `emath::GuiRounding` with `painter.pixels_per_point()` instead"]
     #[inline]
     pub fn round_pos_to_pixel_center(&self, pos: Pos2) -> Pos2 {
-        self.ctx().round_pos_to_pixel_center(pos)
+        pos.round_to_pixel_center(self.pixels_per_point())
     }
 
     /// Useful for pixel-perfect rendering of filled shapes.
+    #[deprecated = "Use `emath::GuiRounding` with `painter.pixels_per_point()` instead"]
     #[inline]
     pub fn round_to_pixel(&self, point: f32) -> f32 {
-        self.ctx().round_to_pixel(point)
+        point.round_to_pixels(self.pixels_per_point())
     }
 
     /// Useful for pixel-perfect rendering.
+    #[deprecated = "Use `emath::GuiRounding` with `painter.pixels_per_point()` instead"]
     #[inline]
     pub fn round_vec_to_pixels(&self, vec: Vec2) -> Vec2 {
-        self.ctx().round_vec_to_pixels(vec)
+        vec.round_to_pixels(self.pixels_per_point())
     }
 
     /// Useful for pixel-perfect rendering.
+    #[deprecated = "Use `emath::GuiRounding` with `painter.pixels_per_point()` instead"]
     #[inline]
     pub fn round_pos_to_pixels(&self, pos: Pos2) -> Pos2 {
-        self.ctx().round_pos_to_pixels(pos)
+        pos.round_to_pixels(self.pixels_per_point())
     }
 
     /// Useful for pixel-perfect rendering.
+    #[deprecated = "Use `emath::GuiRounding` with `painter.pixels_per_point()` instead"]
     #[inline]
     pub fn round_rect_to_pixels(&self, rect: Rect) -> Rect {
-        self.ctx().round_rect_to_pixels(rect)
+        rect.round_to_pixels(self.pixels_per_point())
     }
 }
 
@@ -337,7 +346,7 @@ impl Painter {
 /// # Paint different primitives
 impl Painter {
     /// Paints a line from the first point to the second.
-    pub fn line_segment(&self, points: [Pos2; 2], stroke: impl Into<PathStroke>) -> ShapeIdx {
+    pub fn line_segment(&self, points: [Pos2; 2], stroke: impl Into<Stroke>) -> ShapeIdx {
         self.add(Shape::LineSegment {
             points,
             stroke: stroke.into(),
@@ -351,13 +360,13 @@ impl Painter {
     }
 
     /// Paints a horizontal line.
-    pub fn hline(&self, x: impl Into<Rangef>, y: f32, stroke: impl Into<PathStroke>) -> ShapeIdx {
-        self.add(Shape::hline(x, y, stroke.into()))
+    pub fn hline(&self, x: impl Into<Rangef>, y: f32, stroke: impl Into<Stroke>) -> ShapeIdx {
+        self.add(Shape::hline(x, y, stroke))
     }
 
     /// Paints a vertical line.
-    pub fn vline(&self, x: f32, y: impl Into<Rangef>, stroke: impl Into<PathStroke>) -> ShapeIdx {
-        self.add(Shape::vline(x, y, stroke.into()))
+    pub fn vline(&self, x: f32, y: impl Into<Rangef>, stroke: impl Into<Stroke>) -> ShapeIdx {
+        self.add(Shape::vline(x, y, stroke))
     }
 
     pub fn circle(
@@ -398,6 +407,7 @@ impl Painter {
         })
     }
 
+    /// The stroke extends _outside_ the [`Rect`].
     pub fn rect(
         &self,
         rect: Rect,
@@ -417,6 +427,7 @@ impl Painter {
         self.add(RectShape::filled(rect, rounding, fill_color))
     }
 
+    /// The stroke extends _outside_ the [`Rect`].
     pub fn rect_stroke(
         &self,
         rect: Rect,
diff --git a/crates/egui/src/style.rs b/crates/egui/src/style.rs
index 91c0e09dbfa..33ab21a6837 100644
--- a/crates/egui/src/style.rs
+++ b/crates/egui/src/style.rs
@@ -2485,12 +2485,8 @@ impl Widget for &mut Stroke {
 
             // stroke preview:
             let (_id, stroke_rect) = ui.allocate_space(ui.spacing().interact_size);
-            let left = ui
-                .painter()
-                .round_pos_to_pixel_center(stroke_rect.left_center());
-            let right = ui
-                .painter()
-                .round_pos_to_pixel_center(stroke_rect.right_center());
+            let left = stroke_rect.left_center();
+            let right = stroke_rect.right_center();
             ui.painter().line_segment([left, right], (*width, *color));
         })
         .response
diff --git a/crates/egui/src/text_selection/visuals.rs b/crates/egui/src/text_selection/visuals.rs
index 2a31d1e1270..dd7c867a222 100644
--- a/crates/egui/src/text_selection/visuals.rs
+++ b/crates/egui/src/text_selection/visuals.rs
@@ -96,19 +96,8 @@ pub fn paint_text_selection(
 pub fn paint_cursor_end(painter: &Painter, visuals: &Visuals, cursor_rect: Rect) {
     let stroke = visuals.text_cursor.stroke;
 
-    // Ensure the cursor is aligned to the pixel grid for whole number widths.
-    // See https://github.com/emilk/egui/issues/5164
-    let (top, bottom) = if (stroke.width as usize) % 2 == 0 {
-        (
-            painter.round_pos_to_pixels(cursor_rect.center_top()),
-            painter.round_pos_to_pixels(cursor_rect.center_bottom()),
-        )
-    } else {
-        (
-            painter.round_pos_to_pixel_center(cursor_rect.center_top()),
-            painter.round_pos_to_pixel_center(cursor_rect.center_bottom()),
-        )
-    };
+    let top = cursor_rect.center_top();
+    let bottom = cursor_rect.center_bottom();
 
     painter.line_segment([top, bottom], (stroke.width, stroke.color));
 
diff --git a/crates/egui/src/ui.rs b/crates/egui/src/ui.rs
index 9cf2d4b5427..19fda5d0fee 100644
--- a/crates/egui/src/ui.rs
+++ b/crates/egui/src/ui.rs
@@ -483,6 +483,12 @@ impl Ui {
         &self.painter
     }
 
+    /// Number of physical pixels for each logical UI point.
+    #[inline]
+    pub fn pixels_per_point(&self) -> f32 {
+        self.painter.pixels_per_point()
+    }
+
     /// If `false`, the [`Ui`] does not allow any interaction and
     /// the widgets in it will draw with a gray look.
     #[inline]
@@ -2385,9 +2391,7 @@ impl Ui {
 
             let stroke = self.visuals().widgets.noninteractive.bg_stroke;
             let left_top = child_rect.min - 0.5 * indent * Vec2::X;
-            let left_top = self.painter().round_pos_to_pixel_center(left_top);
             let left_bottom = pos2(left_top.x, child_ui.min_rect().bottom() - 2.0);
-            let left_bottom = self.painter().round_pos_to_pixel_center(left_bottom);
 
             if left_vline {
                 // draw a faint line on the left to mark the indented section
diff --git a/crates/egui/src/widgets/separator.rs b/crates/egui/src/widgets/separator.rs
index 2cc3a857ce6..d018cfa4d0d 100644
--- a/crates/egui/src/widgets/separator.rs
+++ b/crates/egui/src/widgets/separator.rs
@@ -116,12 +116,12 @@ impl Widget for Separator {
             if is_horizontal_line {
                 painter.hline(
                     (rect.left() - grow)..=(rect.right() + grow),
-                    painter.round_to_pixel_center(rect.center().y),
+                    rect.center().y,
                     stroke,
                 );
             } else {
                 painter.vline(
-                    painter.round_to_pixel_center(rect.center().x),
+                    rect.center().x,
                     (rect.top() - grow)..=(rect.bottom() + grow),
                     stroke,
                 );
diff --git a/crates/egui_demo_lib/src/rendering_test.rs b/crates/egui_demo_lib/src/rendering_test.rs
index df3add3776e..bd454267e7a 100644
--- a/crates/egui_demo_lib/src/rendering_test.rs
+++ b/crates/egui_demo_lib/src/rendering_test.rs
@@ -1,9 +1,9 @@
 use std::collections::HashMap;
 
 use egui::{
-    epaint, lerp, pos2, vec2, widgets::color_picker::show_color, Align2, Color32, FontId, Image,
-    Mesh, Pos2, Rect, Response, Rgba, RichText, Sense, Shape, Stroke, TextureHandle,
-    TextureOptions, Ui, Vec2,
+    emath::GuiRounding, epaint, lerp, pos2, vec2, widgets::color_picker::show_color, Align2,
+    Color32, FontId, Image, Mesh, Pos2, Rect, Response, Rgba, RichText, Sense, Shape, Stroke,
+    TextureHandle, TextureOptions, Ui, Vec2,
 };
 
 const GRADIENT_SIZE: Vec2 = vec2(256.0, 18.0);
@@ -270,6 +270,7 @@ impl ColorTest {
 
 fn vertex_gradient(ui: &mut Ui, bg_fill: Color32, gradient: &Gradient) -> Response {
     let (rect, response) = ui.allocate_at_least(GRADIENT_SIZE, Sense::hover());
+    let rect = rect.round_to_pixels(ui.pixels_per_point());
     if bg_fill != Default::default() {
         let mut mesh = Mesh::default();
         mesh.add_colored_rect(rect, bg_fill);
diff --git "a/crates/egui_demo_lib/tests/snapshots/demos/B\303\251zier Curve.png" "b/crates/egui_demo_lib/tests/snapshots/demos/B\303\251zier Curve.png"
index ad7d9becfaa..c4cd0bd1099 100644
--- "a/crates/egui_demo_lib/tests/snapshots/demos/B\303\251zier Curve.png"	
+++ "b/crates/egui_demo_lib/tests/snapshots/demos/B\303\251zier Curve.png"	
@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:4a725aa81433f301fda4ff8a28be869366332964995d1ae4ed996591596eb7e2
-size 31461
+oid sha256:cf83bead834ec8f88d74b32ae6331715e8c6df183e007e2a16004c019534a30f
+size 31810
diff --git a/crates/egui_demo_lib/tests/snapshots/demos/Code Editor.png b/crates/egui_demo_lib/tests/snapshots/demos/Code Editor.png
index 252c7c8f205..77ebb00947f 100644
--- a/crates/egui_demo_lib/tests/snapshots/demos/Code Editor.png	
+++ b/crates/egui_demo_lib/tests/snapshots/demos/Code Editor.png	
@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:36028d85f49ee77562250214237def2b676ecc9ed413d2fd8afc473d61289ca1
-size 32761
+oid sha256:b8ca5a27491c0589a97e43a70bc10dc52778d25ca3f7e7c895dbbbb784adfcfa
+size 33245
diff --git a/crates/egui_demo_lib/tests/snapshots/demos/Code Example.png b/crates/egui_demo_lib/tests/snapshots/demos/Code Example.png
index 33121fe85fa..04fa9ba3c55 100644
--- a/crates/egui_demo_lib/tests/snapshots/demos/Code Example.png	
+++ b/crates/egui_demo_lib/tests/snapshots/demos/Code Example.png	
@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:f93cbf4968e69e2b51256631ab8703d1af2274147924f8d802d9da0f9767aa1b
-size 81162
+oid sha256:e640606207265b4f040f793b0ffb989504b6a98b89e95e77a9a9d3e3abc9327a
+size 80933
diff --git a/crates/egui_demo_lib/tests/snapshots/demos/Context Menus.png b/crates/egui_demo_lib/tests/snapshots/demos/Context Menus.png
index 9191ade8504..caa3c3a5d96 100644
--- a/crates/egui_demo_lib/tests/snapshots/demos/Context Menus.png	
+++ b/crates/egui_demo_lib/tests/snapshots/demos/Context Menus.png	
@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:b7157cc3a1c87b63a1af41e9c3493beb426f9a2c7e3ce1adf228a8d1aee23818
-size 11549
+oid sha256:332c2af36873d8ccccb36c08fd2e475dc1f18454a3090a851c0889395d4f364f
+size 11518
diff --git a/crates/egui_demo_lib/tests/snapshots/demos/Dancing Strings.png b/crates/egui_demo_lib/tests/snapshots/demos/Dancing Strings.png
index ac28a61122d..e86d10772ef 100644
--- a/crates/egui_demo_lib/tests/snapshots/demos/Dancing Strings.png	
+++ b/crates/egui_demo_lib/tests/snapshots/demos/Dancing Strings.png	
@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:7fcc5ac195fdf455836cce7503c530d56a5c9e053cf743f8165c2b33212bfaae
-size 20645
+oid sha256:d0d0b1b4d2c4b624904250bc8d6870559f0179e3f7f2d6dc4a4ff256df356237
+size 20626
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 version https://git-lfs.github.com/spec/v1
-oid sha256:bef9f6dde686733e04a447be280fd50704db163d330fd8c663357b057cd50e27
-size 1080661
+oid sha256:4d1c99867202e16500146b7146a32fd83d70d60f5ac94aae4ca405a6377e4625
+size 1066559
diff --git a/crates/egui_demo_lib/tests/snapshots/rendering_test/dpi_2.00.png b/crates/egui_demo_lib/tests/snapshots/rendering_test/dpi_2.00.png
index 6890b9d4611..4d76639461c 100644
--- a/crates/egui_demo_lib/tests/snapshots/rendering_test/dpi_2.00.png
+++ b/crates/egui_demo_lib/tests/snapshots/rendering_test/dpi_2.00.png
@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:136c60283286df17e6751220e0c849028bc1379910995cf9e4930c5d63d0a90f
-size 1235057
+oid sha256:08fc1c89fd2d04aa12c75a1829dacfff090e322c65ad969648799833e1b072eb
+size 1235574
diff --git a/crates/egui_demo_lib/tests/snapshots/widget_gallery.png b/crates/egui_demo_lib/tests/snapshots/widget_gallery.png
index a2adca3db43..51596247499 100644
--- a/crates/egui_demo_lib/tests/snapshots/widget_gallery.png
+++ b/crates/egui_demo_lib/tests/snapshots/widget_gallery.png
@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:9da93a7c27e17d370a3df73930d71694d436c300656b054722646ea57db45810
-size 160803
+oid sha256:d122b1a995e691b5049c57d65c9f222a5f1639b1e4f6f96f91823444339693cc
+size 160540
diff --git a/crates/emath/src/gui_rounding.rs b/crates/emath/src/gui_rounding.rs
index 3c2cf92411b..ac624792a27 100644
--- a/crates/emath/src/gui_rounding.rs
+++ b/crates/emath/src/gui_rounding.rs
@@ -116,6 +116,7 @@ impl GuiRounding for crate::Vec2 {
         )
     }
 
+    // This doesn't really make sense for a Vec2, but 🤷‍♂️
     #[inline]
     fn round_to_pixel_center(self, pixels_per_point: f32) -> Self {
         Self::new(
diff --git a/crates/epaint/src/lib.rs b/crates/epaint/src/lib.rs
index 89664cdb844..b769275cc2d 100644
--- a/crates/epaint/src/lib.rs
+++ b/crates/epaint/src/lib.rs
@@ -53,7 +53,7 @@ pub use self::{
         Rounding, Shape, TextShape,
     },
     stats::PaintStats,
-    stroke::{PathStroke, Stroke},
+    stroke::{PathStroke, Stroke, StrokeKind},
     tessellator::{TessellationOptions, Tessellator},
     text::{FontFamily, FontId, Fonts, Galley},
     texture_atlas::TextureAtlas,
diff --git a/crates/epaint/src/shape.rs b/crates/epaint/src/shape.rs
index 6f67a2bc6a6..56af703b669 100644
--- a/crates/epaint/src/shape.rs
+++ b/crates/epaint/src/shape.rs
@@ -35,10 +35,7 @@ pub enum Shape {
     Ellipse(EllipseShape),
 
     /// A line between two points.
-    LineSegment {
-        points: [Pos2; 2],
-        stroke: PathStroke,
-    },
+    LineSegment { points: [Pos2; 2], stroke: Stroke },
 
     /// A series of lines between points.
     /// The path can have a stroke and/or fill (if closed).
@@ -92,7 +89,7 @@ impl Shape {
     /// A line between two points.
     /// More efficient than calling [`Self::line`].
     #[inline]
-    pub fn line_segment(points: [Pos2; 2], stroke: impl Into<PathStroke>) -> Self {
+    pub fn line_segment(points: [Pos2; 2], stroke: impl Into<Stroke>) -> Self {
         Self::LineSegment {
             points,
             stroke: stroke.into(),
@@ -100,7 +97,7 @@ impl Shape {
     }
 
     /// A horizontal line.
-    pub fn hline(x: impl Into<Rangef>, y: f32, stroke: impl Into<PathStroke>) -> Self {
+    pub fn hline(x: impl Into<Rangef>, y: f32, stroke: impl Into<Stroke>) -> Self {
         let x = x.into();
         Self::LineSegment {
             points: [pos2(x.min, y), pos2(x.max, y)],
@@ -109,7 +106,7 @@ impl Shape {
     }
 
     /// A vertical line.
-    pub fn vline(x: f32, y: impl Into<Rangef>, stroke: impl Into<PathStroke>) -> Self {
+    pub fn vline(x: f32, y: impl Into<Rangef>, stroke: impl Into<Stroke>) -> Self {
         let y = y.into();
         Self::LineSegment {
             points: [pos2(x, y.min), pos2(x, y.max)],
@@ -262,6 +259,7 @@ impl Shape {
         Self::Rect(RectShape::filled(rect, rounding, fill_color))
     }
 
+    /// The stroke extends _outside_ the [`Rect`].
     #[inline]
     pub fn rect_stroke(
         rect: Rect,
@@ -670,6 +668,11 @@ pub struct RectShape {
     pub fill: Color32,
 
     /// The thickness and color of the outline.
+    ///
+    /// The stroke extends _outside_ the edge of [`Self::rect`],
+    /// i.e. using [`crate::StrokeKind::Outside`].
+    ///
+    /// This means the [`Self::visual_bounding_rect`] is `rect.size() + 2.0 * stroke.width`.
     pub stroke: Stroke,
 
     /// If larger than zero, the edges of the rectangle
@@ -695,6 +698,7 @@ pub struct RectShape {
 }
 
 impl RectShape {
+    /// The stroke extends _outside_ the [`Rect`].
     #[inline]
     pub fn new(
         rect: Rect,
@@ -730,6 +734,7 @@ impl RectShape {
         }
     }
 
+    /// The stroke extends _outside_ the [`Rect`].
     #[inline]
     pub fn stroke(rect: Rect, rounding: impl Into<Rounding>, stroke: impl Into<Stroke>) -> Self {
         Self {
@@ -761,8 +766,8 @@ impl RectShape {
         if self.fill == Color32::TRANSPARENT && self.stroke.is_empty() {
             Rect::NOTHING
         } else {
-            self.rect
-                .expand((self.stroke.width + self.blur_width) / 2.0)
+            let Stroke { width, .. } = self.stroke; // Make sure we remember to update this if we change `stroke` to `PathStroke`
+            self.rect.expand(width + self.blur_width / 2.0)
         }
     }
 }
diff --git a/crates/epaint/src/shape_transform.rs b/crates/epaint/src/shape_transform.rs
index f072393f557..263f9cf07a6 100644
--- a/crates/epaint/src/shape_transform.rs
+++ b/crates/epaint/src/shape_transform.rs
@@ -21,7 +21,7 @@ pub fn adjust_colors(
         }
 
         Shape::LineSegment { stroke, points: _ } => {
-            adjust_color_mode(&mut stroke.color, adjust_color);
+            adjust_color(&mut stroke.color);
         }
 
         Shape::Path(PathShape {
diff --git a/crates/epaint/src/tessellator.rs b/crates/epaint/src/tessellator.rs
index ebd22f55303..e04eb03bee8 100644
--- a/crates/epaint/src/tessellator.rs
+++ b/crates/epaint/src/tessellator.rs
@@ -11,7 +11,7 @@ use crate::{
     EllipseShape, Mesh, PathShape, Primitive, QuadraticBezierShape, RectShape, Rounding, Shape,
     Stroke, TextShape, TextureId, Vertex, WHITE_UV,
 };
-use emath::{pos2, remap, vec2, NumExt, Pos2, Rect, Rot2, Vec2};
+use emath::{pos2, remap, vec2, GuiRounding as _, NumExt, Pos2, Rect, Rot2, Vec2};
 
 use self::color::ColorMode;
 use self::stroke::PathStroke;
@@ -671,10 +671,21 @@ pub struct TessellationOptions {
     /// from the font atlas.
     pub prerasterized_discs: bool,
 
-    /// If `true` (default) align text to mesh grid.
+    /// If `true` (default) align text to the physical pixel grid.
     /// This makes the text sharper on most platforms.
     pub round_text_to_pixels: bool,
 
+    /// If `true` (default), align right-angled line segments to the physical pixel grid.
+    ///
+    /// This makes the line segments appear crisp on any display.
+    pub round_line_segments_to_pixels: bool,
+
+    /// If `true` (default), align rectangles to the physical pixel grid.
+    ///
+    /// This makes the rectangle strokes more crisp,
+    /// and makes filled rectangles tile perfectly (without feathering).
+    pub round_rects_to_pixels: bool,
+
     /// Output the clip rectangles to be painted.
     pub debug_paint_clip_rects: bool,
 
@@ -708,6 +719,8 @@ impl Default for TessellationOptions {
             coarse_tessellation_culling: true,
             prerasterized_discs: true,
             round_text_to_pixels: true,
+            round_line_segments_to_pixels: true,
+            round_rects_to_pixels: true,
             debug_paint_text_rects: false,
             debug_paint_clip_rects: false,
             debug_ignore_clip_rects: false,
@@ -754,8 +767,11 @@ fn fill_closed_path(
 
     // TODO(juancampa): This bounding box is computed twice per shape: once here and another when tessellating the
     // stroke, consider hoisting that logic to the tessellator/scratchpad.
-    let bbox = Rect::from_points(&path.iter().map(|p| p.pos).collect::<Vec<Pos2>>())
-        .expand((stroke.width / 2.0) + feathering);
+    let bbox = if matches!(stroke.color, ColorMode::UV(_)) {
+        Rect::from_points(&path.iter().map(|p| p.pos).collect::<Vec<Pos2>>()).expand(feathering)
+    } else {
+        Rect::NAN
+    };
 
     let stroke_color = &stroke.color;
     let get_stroke_color: Box<dyn Fn(Pos2) -> Color32> = match stroke_color {
@@ -900,7 +916,7 @@ fn fill_closed_path_with_uv(
 #[inline(always)]
 fn translate_stroke_point(p: &mut PathPoint, stroke: &PathStroke) {
     match stroke.kind {
-        stroke::StrokeKind::Middle => { /* Nothingn to do */ }
+        stroke::StrokeKind::Middle => { /* Nothing to do */ }
         stroke::StrokeKind::Outside => {
             p.pos += p.normal * stroke.width * 0.5;
         }
@@ -932,9 +948,13 @@ fn stroke_path(
             .for_each(|p| translate_stroke_point(p, stroke));
     }
 
-    // expand the bounding box to include the thickness of the path
-    let bbox = Rect::from_points(&path.iter().map(|p| p.pos).collect::<Vec<Pos2>>())
-        .expand((stroke.width / 2.0) + feathering);
+    // Expand the bounding box to include the thickness of the path
+    let bbox = if matches!(stroke.color, ColorMode::UV(_)) {
+        Rect::from_points(&path.iter().map(|p| p.pos).collect::<Vec<Pos2>>())
+            .expand((stroke.width / 2.0) + feathering)
+    } else {
+        Rect::NAN
+    };
 
     let get_color = |col: &ColorMode, pos: Pos2| match col {
         ColorMode::Solid(col) => *col,
@@ -1386,7 +1406,9 @@ impl Tessellator {
 
                 out.append(mesh);
             }
-            Shape::LineSegment { points, stroke } => self.tessellate_line(points, stroke, out),
+            Shape::LineSegment { points, stroke } => {
+                self.tessellate_line_segment(points, stroke, out);
+            }
             Shape::Path(path_shape) => {
                 self.tessellate_path(&path_shape, out);
             }
@@ -1563,10 +1585,10 @@ impl Tessellator {
     ///
     /// * `shape`: the mesh to tessellate.
     /// * `out`: triangles are appended to this.
-    pub fn tessellate_line(
+    pub fn tessellate_line_segment(
         &mut self,
-        points: [Pos2; 2],
-        stroke: impl Into<PathStroke>,
+        mut points: [Pos2; 2],
+        stroke: impl Into<Stroke>,
         out: &mut Mesh,
     ) {
         let stroke = stroke.into();
@@ -1582,10 +1604,38 @@ impl Tessellator {
             return;
         }
 
+        if self.options.round_line_segments_to_pixels {
+            let [a, b] = &mut points;
+            if a.x == b.x {
+                // Vertical line
+                let mut x = a.x;
+                round_line_segment(&mut x, &stroke, self.pixels_per_point);
+                a.x = x;
+                b.x = x;
+            }
+            if a.y == b.y {
+                // Horizontal line
+                let mut y = a.y;
+                round_line_segment(&mut y, &stroke, self.pixels_per_point);
+                a.y = y;
+                b.y = y;
+            }
+        }
+
         self.scratchpad_path.clear();
         self.scratchpad_path.add_line_segment(points);
         self.scratchpad_path
-            .stroke_open(self.feathering, &stroke, out);
+            .stroke_open(self.feathering, &stroke.into(), out);
+    }
+
+    #[deprecated = "Use `tessellate_line_segment` instead"]
+    pub fn tessellate_line(
+        &mut self,
+        points: [Pos2; 2],
+        stroke: impl Into<Stroke>,
+        out: &mut Mesh,
+    ) {
+        self.tessellate_line_segment(points, stroke, out);
     }
 
     /// Tessellate a single [`PathShape`] into a [`Mesh`].
@@ -1660,6 +1710,14 @@ impl Tessellator {
             return;
         }
 
+        if self.options.round_rects_to_pixels {
+            // Since the stroke extends outside of the rectangle,
+            // we can round the rectangle sides to the physical pixel edges,
+            // and the filled rect will appear crisp, as will the inside of the stroke.
+            let Stroke { .. } = stroke; // Make sure we remember to update this if we change `stroke` to `PathStroke`
+            rect = rect.round_to_pixels(self.pixels_per_point);
+        }
+
         // It is common to (sometimes accidentally) create an infinitely sized rectangle.
         // Make sure we can handle that:
         rect.min = rect.min.at_least(pos2(-1e7, -1e7));
@@ -1688,46 +1746,33 @@ impl Tessellator {
             self.feathering = self.feathering.max(blur_width);
         }
 
-        if rect.width() < self.feathering {
+        if rect.width() < 0.5 * self.feathering {
             // Very thin - approximate by a vertical line-segment:
             let line = [rect.center_top(), rect.center_bottom()];
             if fill != Color32::TRANSPARENT {
-                self.tessellate_line(line, Stroke::new(rect.width(), fill), out);
+                self.tessellate_line_segment(line, Stroke::new(rect.width(), fill), out);
             }
             if !stroke.is_empty() {
-                self.tessellate_line(line, stroke, out); // back…
-                self.tessellate_line(line, stroke, out); // …and forth
+                self.tessellate_line_segment(line, stroke, out); // back…
+                self.tessellate_line_segment(line, stroke, out); // …and forth
             }
-        } else if rect.height() < self.feathering {
+        } else if rect.height() < 0.5 * self.feathering {
             // Very thin - approximate by a horizontal line-segment:
             let line = [rect.left_center(), rect.right_center()];
             if fill != Color32::TRANSPARENT {
-                self.tessellate_line(line, Stroke::new(rect.height(), fill), out);
+                self.tessellate_line_segment(line, Stroke::new(rect.height(), fill), out);
             }
             if !stroke.is_empty() {
-                self.tessellate_line(line, stroke, out); // back…
-                self.tessellate_line(line, stroke, out); // …and forth
+                self.tessellate_line_segment(line, stroke, out); // back…
+                self.tessellate_line_segment(line, stroke, out); // …and forth
             }
         } else {
-            let rect = if !stroke.is_empty() && stroke.width < self.feathering {
-                // Very thin rectangle strokes create extreme aliasing when they move around.
-                // We can fix that by rounding the rectangle corners to pixel centers.
-                // TODO(#5164): maybe do this for all shapes and stroke sizes
-                // TODO(emilk): since we use StrokeKind::Outside, we should probably round the
-                // corners after offsetting them with half the stroke width (see `translate_stroke_point`).
-                Rect {
-                    min: self.round_pos_to_pixel_center(rect.min),
-                    max: self.round_pos_to_pixel_center(rect.max),
-                }
-            } else {
-                rect
-            };
-
             let path = &mut self.scratchpad_path;
             path.clear();
             path::rounded_rectangle(&mut self.scratchpad_points, rect, rounding);
             path.add_line_loop(&self.scratchpad_points);
             let path_stroke = PathStroke::from(stroke).outside();
+
             if uv.is_positive() {
                 // Textured
                 let uv_from_pos = |p: Pos2| {
@@ -1741,6 +1786,7 @@ impl Tessellator {
                 // Untextured
                 path.fill(self.feathering, fill, &path_stroke, out);
             }
+
             path.stroke_closed(self.feathering, &path_stroke, out);
         }
 
@@ -1968,6 +2014,45 @@ impl Tessellator {
     }
 }
 
+fn round_line_segment(coord: &mut f32, stroke: &Stroke, pixels_per_point: f32) {
+    // If the stroke is an odd number of pixels wide,
+    // we want to round the center of it to the center of a pixel.
+    //
+    // If however it is an even number of pixels wide,
+    // we want to round the center to be between two pixels.
+    //
+    // We also want to treat strokes that are _almost_ odd as it it was odd,
+    // to make it symmetric. Same for strokes that are _almost_ even.
+    //
+    // For strokes less than a pixel wide we also round to the center,
+    // because it will rendered as a single row of pixels by the tessellator.
+
+    let pixel_size = 1.0 / pixels_per_point;
+
+    if stroke.width <= pixel_size || is_nearest_integer_odd(pixels_per_point * stroke.width) {
+        *coord = coord.round_to_pixel_center(pixels_per_point);
+    } else {
+        *coord = coord.round_to_pixels(pixels_per_point);
+    }
+}
+
+fn is_nearest_integer_odd(width: f32) -> bool {
+    (width * 0.5 + 0.25).fract() > 0.5
+}
+
+#[test]
+fn test_is_nearest_integer_odd() {
+    assert!(is_nearest_integer_odd(0.6));
+    assert!(is_nearest_integer_odd(1.0));
+    assert!(is_nearest_integer_odd(1.4));
+    assert!(!is_nearest_integer_odd(1.6));
+    assert!(!is_nearest_integer_odd(2.0));
+    assert!(!is_nearest_integer_odd(2.4));
+    assert!(is_nearest_integer_odd(2.6));
+    assert!(is_nearest_integer_odd(3.0));
+    assert!(is_nearest_integer_odd(3.4));
+}
+
 #[deprecated = "Use `Tessellator::new(…).tessellate_shapes(…)` instead"]
 pub fn tessellate_shapes(
     pixels_per_point: f32,
diff --git a/examples/hello_android/Cargo.toml b/examples/hello_android/Cargo.toml
index dcb0a5a5c01..a7d27277359 100644
--- a/examples/hello_android/Cargo.toml
+++ b/examples/hello_android/Cargo.toml
@@ -4,7 +4,7 @@ version = "0.1.0"
 authors = ["Emil Ernerfeldt <emil.ernerfeldt@gmail.com>"]
 license = "MIT OR Apache-2.0"
 edition = "2021"
-rust-version = "1.76"
+rust-version = "1.80"
 publish = false
 
 # `unsafe_code` is required for `#[no_mangle]`, disable workspace lints to workaround lint error.
@@ -16,10 +16,7 @@ crate-type = ["cdylib"]
 
 
 [dependencies]
-eframe = { workspace = true, features = [
-    "default",
-    "android-native-activity",
-] }
+eframe = { workspace = true, features = ["default", "android-native-activity"] }
 
 # For image support:
 egui_extras = { workspace = true, features = ["default", "image"] }
@@ -29,4 +26,4 @@ winit = { workspace = true }
 android_logger = "0.14"
 
 [package.metadata.android]
-build_targets = [ "armv7-linux-androideabi", "aarch64-linux-android" ]
+build_targets = ["armv7-linux-androideabi", "aarch64-linux-android"]