Use bytes:// schema for included bytes loader

crates/egui/src/context.rs

@@ -1912,6 +1912,9 @@ impl Context {
     /// Associate some static bytes with a `uri`.
     ///
     /// The same `uri` may be passed to [`Ui::image`] later to load the bytes as an image.
+    ///
+    /// By convention, the `uri` should start wtih `bytes://`.
+    /// Following that convention will lead to better error messages.
     pub fn include_bytes(&self, uri: impl Into<Cow<'static, str>>, bytes: impl Into<Bytes>) {
         self.loaders().include.insert(uri, bytes);
     }

crates/egui/src/lib.rs

@@ -437,13 +437,16 @@ pub fn warn_if_debug_build(ui: &mut crate::Ui) {
 ///     egui::Image::new(egui::include_image!("../assets/ferris.png"))
 ///         .rounding(egui::Rounding::same(6.0))
 /// );
+///
+/// let image_source: egui::ImageSource = egui::include_image!("../assets/ferris.png");
+/// assert_eq!(image_source.uri(), Some("bytes://../assets/ferris.png"));
 /// # });
 /// ```
 #[macro_export]
 macro_rules! include_image {
     ($path: literal) => {
         $crate::ImageSource::Bytes(
-            ::std::borrow::Cow::Borrowed($path),
+            ::std::borrow::Cow::Borrowed(concat!("bytes://", $path)), // uri
             $crate::load::Bytes::Static(include_bytes!($path)),
         )
     };

crates/egui/src/load/bytes_loader.rs

@@ -1,5 +1,8 @@
 use super::*;
 
+/// Maps URI:s to [`Bytes`], e.g. found with `include_bytes!`.
+///
+/// By convention, the URI:s should be prefixed with `bytes://`.
 #[derive(Default)]
 pub struct DefaultBytesLoader {
     cache: Mutex<HashMap<Cow<'static, str>, Bytes>>,
@@ -27,13 +30,22 @@ impl BytesLoader for DefaultBytesLoader {
     }
 
     fn load(&self, _: &Context, uri: &str) -> BytesLoadResult {
+        // We accept uri:s that don't start with `bytes://` too… for now.
         match self.cache.lock().get(uri).cloned() {
             Some(bytes) => Ok(BytesPoll::Ready {
                 size: None,
                 bytes,
                 mime: None,
             }),
-            None => Err(LoadError::NotSupported),
+            None => {
+                if uri.starts_with("bytes://") {
+                    Err(LoadError::Loading(
+                        "Bytes not found. Did you forget to call Context::include_bytes?".into(),
+                    ))
+                } else {
+                    Err(LoadError::NotSupported)
+                }
+            }
         }
     }
 

crates/egui/src/widgets/image.rs

@@ -74,6 +74,8 @@ impl<'a> Image<'a> {
 
     /// Load the image from some raw bytes.
     ///
+    /// For better error messages, use the `bytes://` prefix for the URI.
+    ///
     /// See [`ImageSource::Bytes`].
     pub fn from_bytes(uri: impl Into<Cow<'static, str>>, bytes: impl Into<Bytes>) -> Self {
         Self::new(ImageSource::Bytes(uri.into(), bytes.into()))
@@ -472,6 +474,8 @@ pub enum ImageSource<'a> {
 
     /// Load the image from some raw bytes.
     ///
+    /// For better error messages, use the `bytes://` prefix for the URI.
+    ///
     /// The [`Bytes`] may be:
     /// - `'static`, obtained from `include_bytes!` or similar
     /// - Anything that can be converted to `Arc<[u8]>`

examples/images/src/main.rs

@@ -1,12 +1,11 @@
 #![cfg_attr(not(debug_assertions), windows_subsystem = "windows")] // hide console window on Windows in release
 
 use eframe::egui;
-use eframe::epaint::vec2;
 
 fn main() -> Result<(), eframe::Error> {
     env_logger::init(); // Log to stderr (if you run with `RUST_LOG=debug`).
     let options = eframe::NativeOptions {
-        drag_and_drop_support: true,
+        initial_window_size: Some(egui::vec2(600.0, 800.0)),
         ..Default::default()
     };
     eframe::run_native(
@@ -27,10 +26,7 @@ impl eframe::App for MyApp {
     fn update(&mut self, ctx: &egui::Context, _frame: &mut eframe::Frame) {
         egui::CentralPanel::default().show(ctx, |ui| {
             egui::ScrollArea::new([true, true]).show(ui, |ui| {
-                ui.add(
-                    egui::Image::new(egui::include_image!("ferris.svg"))
-                        .fit_to_fraction(vec2(1.0, 0.5)),
-                );
+                ui.image(egui::include_image!("ferris.svg"));
                 ui.add(
                     egui::Image::new("https://picsum.photos/seed/1.759706314/1024")
                         .rounding(egui::Rounding::same(10.0)),