fix: make glass backdrop visibly blur

compositor/src/effects.rs

@@ -41,7 +41,7 @@ pub(crate) struct ResolvedMaterial {
 }
 
 pub(crate) fn resolve_material(role: SemanticRole, style: MaterialStyle) -> ResolvedMaterial {
-    let (opacity, blur, saturation, brightness, noise) = match role {
+    let (base_opacity, blur, saturation, brightness, noise) = match role {
         SemanticRole::Panel => (0.78, 24.0, 1.08, 1.02, 0.012),
         SemanticRole::PanelElevated
         | SemanticRole::Popover
@@ -53,7 +53,11 @@ pub(crate) fn resolve_material(role: SemanticRole, style: MaterialStyle) -> Reso
     match style {
         MaterialStyle::Glass => ResolvedMaterial {
             style,
-            opacity,
+            // Glass already contains an opaque copy of the backdrop. Its tint
+            // therefore needs less coverage than the no-capture translucent
+            // profile or the blur becomes visually indistinguishable from a
+            // flat alpha surface.
+            opacity: base_opacity * 0.72,
             blur,
             saturation,
             brightness,
@@ -61,7 +65,7 @@ pub(crate) fn resolve_material(role: SemanticRole, style: MaterialStyle) -> Reso
         },
         MaterialStyle::Translucent => ResolvedMaterial {
             style,
-            opacity,
+            opacity: base_opacity,
             blur: 0.0,
             saturation: 1.0,
             brightness: 1.0,
@@ -299,7 +303,7 @@ mod tests {
 
         assert!(glass.blur > 0.0);
         assert!(glass.noise > 0.0);
-        assert_eq!(translucent.opacity, glass.opacity);
+        assert!(glass.opacity < translucent.opacity);
         assert_eq!(translucent.blur, 0.0);
         assert_eq!(translucent.noise, 0.0);
         assert_eq!(solid.opacity, 1.0);

compositor/src/winit.rs

@@ -261,6 +261,17 @@ float random(vec2 point) {
     return fract(sin(dot(point, vec2(12.9898, 78.233))) * 43758.5453);
 }
 
+float kernel_weight(int tap) {
+    int distance = tap < 0 ? -tap : tap;
+    if (distance == 0) {
+        return 6.0;
+    }
+    if (distance == 1) {
+        return 4.0;
+    }
+    return 1.0;
+}
+
 void main() {
     vec2 point = gl_FragCoord.xy;
     vec2 visible_max = visible_rect.xy + visible_rect.zw;
@@ -270,16 +281,16 @@ void main() {
         return;
     }
 
-    vec2 step_size = vec2(blur_radius) / max(texture_size, vec2(1.0));
-    vec4 color = texture2D(tex, v_coords) * 0.20;
-    color += texture2D(tex, v_coords + vec2(step_size.x, 0.0)) * 0.12;
-    color += texture2D(tex, v_coords - vec2(step_size.x, 0.0)) * 0.12;
-    color += texture2D(tex, v_coords + vec2(0.0, step_size.y)) * 0.12;
-    color += texture2D(tex, v_coords - vec2(0.0, step_size.y)) * 0.12;
-    color += texture2D(tex, v_coords + step_size) * 0.08;
-    color += texture2D(tex, v_coords - step_size) * 0.08;
-    color += texture2D(tex, v_coords + vec2(step_size.x, -step_size.y)) * 0.08;
-    color += texture2D(tex, v_coords + vec2(-step_size.x, step_size.y)) * 0.08;
+    vec2 step_size = vec2(blur_radius * 0.5) / max(texture_size, vec2(1.0));
+    vec4 color = vec4(0.0);
+    for (int y = -2; y <= 2; y++) {
+        for (int x = -2; x <= 2; x++) {
+            float weight = kernel_weight(x) * kernel_weight(y);
+            vec2 offset = vec2(float(x), float(y)) * step_size;
+            color += texture2D(tex, v_coords + offset) * weight;
+        }
+    }
+    color /= 256.0;
 
     float luma = dot(color.rgb, vec3(0.2126, 0.7152, 0.0722));
     vec3 adjusted = mix(vec3(luma), color.rgb, saturation) * brightness;