Fix alpha blending issue

Signed-off-by: Torstein Grindvik <[email protected]>

crates/bevy_core_pipeline/src/picking/picking.wgsl

@@ -1,5 +1,15 @@
 #define_import_path bevy_core_pipeline::picking
 
+fn picking_alpha(a: f32) -> f32 {
+    // If e.g. a sprite has slightly transparent pixels, we make that opaque (by setting alpha to 1.0)
+    // for picking purposes.
+    // If we don't do this, blending will occur on the entity index value, which makes no sense.
+    //
+    // An alternative is to truncate the alpha to 0.0 unless it's 1.0, but that would shrink
+    // which parts of the translucent entity are pickable, which is not desirable.
+    return ceil(a);
+}
+
 // TODO: Describe why/what
 fn entity_index_to_vec3_f32(entity_index: u32) -> vec3<f32> {
     let mask_8 = 0x000000FFu;

crates/bevy_pbr/src/render/pbr.wgsl

@@ -123,7 +123,7 @@ fn fragment(in: FragmentInput) -> FragmentOutput {
 
     out.color = output_color;
 #ifdef PICKING
-    out.picking = vec4(entity_index_to_vec3_f32(mesh.entity_index), output_color.a);
+    out.picking = vec4(entity_index_to_vec3_f32(mesh.entity_index), picking_alpha(output_color.a));
 #endif
 
     return out;

crates/bevy_render/src/picking/mod.rs

@@ -124,7 +124,10 @@ impl Picking {
     /// Panics if the coordinate is out of bounds.
     pub fn get_entity(&self, camera: &Camera, coordinates: UVec2) -> Option<Entity> {
         let guard = self.try_lock().expect("Should have been unlocked");
-        let resources = guard.as_ref().expect("Resources should have been prepared");
+        let Some(resources) = guard.as_ref() else {
+            // Picking resources not yet prepared.
+            return None
+        };
 
         let slice = resources.pick_buffer.slice(..);
 
@@ -347,6 +350,9 @@ where
     let start = (y * padded_width) + (x * pixel_size);
     let end = start + pixel_size;
 
+    // TODO: Sometimes we're able to go out of bounds here:
+    //  "panicked at 'range end index 7381600 out of range for slice of length 7372800'",
+    // we have to figure out when this can happen and why.
     let view_bytes = &buffer_view[start..end];
 
     make_data_from_viewed_bytes(view_bytes)

crates/bevy_sprite/src/mesh2d/color_material.wgsl

@@ -1,6 +1,8 @@
 #import bevy_sprite::mesh2d_types
 #import bevy_sprite::mesh2d_view_bindings
 
+// TODO: Fix this one
+
 struct ColorMaterial {
     color: vec4<f32>,
     // 'flags' is a bit field indicating various options. u32 is 32 bits so we have up to 32 options.

crates/bevy_sprite/src/mesh2d/mesh.rs

@@ -409,7 +409,7 @@ impl SpecializedMeshPipeline for Mesh2dPipeline {
 
             targets.push(Some(ColorTargetState {
                 format: PICKING_TEXTURE_FORMAT,
-                // TODO: Check this works
+                // TODO: Check this works for different situations
                 blend,
                 write_mask: ColorWrites::ALL,
             }));

crates/bevy_sprite/src/render/sprite.wgsl

@@ -81,7 +81,7 @@ fn fragment(in: VertexOutput) -> FragmentOutput {
     out.color = color;
 
 #ifdef PICKING
-    out.picking = vec4(entity_index_to_vec3_f32(entity_indices[in.vertex_index]), color.a);
+    out.picking = vec4(entity_index_to_vec3_f32(entity_indices[in.vertex_index]), picking_alpha(color.a));
 #endif
 
     return out;

crates/bevy_ui/src/render/ui.wgsl

@@ -66,7 +66,7 @@ fn fragment(in: VertexOutput) -> FragmentOutput {
     out.color = color;
 
 #ifdef PICKING
-    out.picking = vec4(entity_index_to_vec3_f32(in.entity_index), color.a);
+    out.picking = vec4(entity_index_to_vec3_f32(in.entity_index), picking_alpha(color.a));
 #endif
 
     return out;

examples/app/picking.rs

@@ -3,6 +3,8 @@
 //!
 //! Combines parts of the 3D shapes example and the UI example.
 
+// TODO: Update to store mouse position across frames like many_sprites.
+
 use std::f32::consts::PI;
 
 use bevy::{