Implement a few more blend modes and switch to premultiplied alpha for layer

compositing

canvas/src/lib.rs

@@ -524,6 +524,11 @@ pub enum LineJoin {
 #[derive(Clone, Copy, Debug, PartialEq)]
 pub enum CompositeOperation {
     SourceOver,
+    DestinationOver,
+    DestinationOut,
+    SourceAtop,
+    Xor,
+    Lighter,
     Lighten,
     Darken,
 }
@@ -531,7 +536,12 @@ pub enum CompositeOperation {
 impl CompositeOperation {
     fn to_blend_mode(self) -> BlendMode {
         match self {
-            CompositeOperation::SourceOver => BlendMode::SourceOver,
+            CompositeOperation::SourceOver => BlendMode::SrcOver,
+            CompositeOperation::DestinationOver => BlendMode::DestOver,
+            CompositeOperation::DestinationOut => BlendMode::DestOut,
+            CompositeOperation::SourceAtop => BlendMode::SrcAtop,
+            CompositeOperation::Xor => BlendMode::Xor,
+            CompositeOperation::Lighter => BlendMode::Lighter,
             CompositeOperation::Lighten => BlendMode::Lighten,
             CompositeOperation::Darken => BlendMode::Darken,
         }

content/src/effects.rs

@@ -58,14 +58,19 @@ pub enum Filter {
 #[derive(Clone, Copy, Debug)]
 pub enum CompositeOp {
     /// The default.
-    SourceOver,
+    SrcOver,
 }
 
 /// Blend modes that can be applied to individual paths without creating layers for them.
 #[derive(Clone, Copy, PartialEq, Debug)]
 pub enum BlendMode {
-    SourceOver,
     Clear,
+    SrcOver,
+    DestOver,
+    DestOut,
+    SrcAtop,
+    Xor,
+    Lighter,
     Lighten,
     Darken,
 }
@@ -76,25 +81,31 @@ pub struct DefringingKernel(pub [f32; 4]);
 impl Default for CompositeOp {
     #[inline]
     fn default() -> CompositeOp {
-        CompositeOp::SourceOver
+        CompositeOp::SrcOver
     }
 }
 
 impl Default for BlendMode {
     #[inline]
     fn default() -> BlendMode {
-        BlendMode::SourceOver
+        BlendMode::SrcOver
     }
 }
 
 impl BlendMode {
     /// Whether the backdrop is irrelevant when applying this blend mode (i.e. destination blend
-    /// factor is zero).
+    /// factor is zero when source alpha is one).
     #[inline]
     pub fn occludes_backdrop(self) -> bool {
         match self {
-            BlendMode::SourceOver | BlendMode::Clear => true,
+            BlendMode::SrcOver | BlendMode::Clear => true,
-            BlendMode::Lighten | BlendMode::Darken => false,
+            BlendMode::DestOver |
+            BlendMode::DestOut |
+            BlendMode::SrcAtop |
+            BlendMode::Xor |
+            BlendMode::Lighter |
+            BlendMode::Lighten |
+            BlendMode::Darken => false,
         }
     }
 }

gl/src/lib.rs

@@ -965,6 +965,8 @@ impl BlendFactorExt for BlendFactor {
             BlendFactor::One => gl::ONE,
             BlendFactor::SrcAlpha => gl::SRC_ALPHA,
             BlendFactor::OneMinusSrcAlpha => gl::ONE_MINUS_SRC_ALPHA,
+            BlendFactor::DestAlpha => gl::DST_ALPHA,
+            BlendFactor::OneMinusDestAlpha => gl::ONE_MINUS_DST_ALPHA,
             BlendFactor::DestColor => gl::DST_COLOR,
         }
     }

gpu/src/lib.rs

@@ -226,6 +226,8 @@ pub enum BlendFactor {
     One,
     SrcAlpha,
     OneMinusSrcAlpha,
+    DestAlpha,
+    OneMinusDestAlpha,
     DestColor,
 }
 

metal/src/lib.rs

@@ -1170,6 +1170,8 @@ impl BlendFactorExt for BlendFactor {
             BlendFactor::One => MTLBlendFactor::One,
             BlendFactor::SrcAlpha => MTLBlendFactor::SourceAlpha,
             BlendFactor::OneMinusSrcAlpha => MTLBlendFactor::OneMinusSourceAlpha,
+            BlendFactor::DestAlpha => MTLBlendFactor::DestinationAlpha,
+            BlendFactor::OneMinusDestAlpha => MTLBlendFactor::OneMinusDestinationAlpha,
             BlendFactor::DestColor => MTLBlendFactor::DestinationColor,
         }
     }

renderer/src/gpu/renderer.rs

@@ -762,7 +762,7 @@ where
             ],
             viewport: self.draw_viewport(),
             options: RenderOptions {
-                blend: Some(BlendMode::SourceOver.to_blend_state()),
+                blend: Some(BlendMode::SrcOver.to_blend_state()),
                 depth: Some(DepthState { func: DepthFunc::Less, write: false, }),
                 clear_ops: ClearOps { color: clear_color, ..ClearOps::default() },
                 ..RenderOptions::default()
@@ -848,7 +848,7 @@ where
         ];
 
         let blend_state = match composite_op {
-            CompositeOp::SourceOver => BlendMode::SourceOver.to_blend_state(),
+            CompositeOp::SrcOver => BlendMode::SrcOver.to_blend_state(),
         };
 
         self.device.draw_elements(6, &RenderState {
@@ -1133,15 +1133,6 @@ trait BlendModeExt {
 impl BlendModeExt for BlendMode {
     fn to_blend_state(self) -> BlendState {
         match self {
-            BlendMode::SourceOver => {
-                BlendState {
-                    src_rgb_factor: BlendFactor::SrcAlpha,
-                    dest_rgb_factor: BlendFactor::OneMinusSrcAlpha,
-                    src_alpha_factor: BlendFactor::One,
-                    dest_alpha_factor: BlendFactor::One,
-                    ..BlendState::default()
-                }
-            }
             BlendMode::Clear => {
                 BlendState {
                     src_rgb_factor: BlendFactor::Zero,
@@ -1151,9 +1142,63 @@ impl BlendModeExt for BlendMode {
                     ..BlendState::default()
                 }
             }
+            BlendMode::SrcOver => {
+                BlendState {
+                    src_rgb_factor: BlendFactor::One,
+                    dest_rgb_factor: BlendFactor::OneMinusSrcAlpha,
+                    src_alpha_factor: BlendFactor::One,
+                    dest_alpha_factor: BlendFactor::OneMinusSrcAlpha,
+                    ..BlendState::default()
+                }
+            }
+            BlendMode::DestOver => {
+                BlendState {
+                    src_rgb_factor: BlendFactor::OneMinusDestAlpha,
+                    dest_rgb_factor: BlendFactor::DestAlpha,
+                    src_alpha_factor: BlendFactor::OneMinusDestAlpha,
+                    dest_alpha_factor: BlendFactor::One,
+                    ..BlendState::default()
+                }
+            }
+            BlendMode::DestOut => {
+                BlendState {
+                    src_rgb_factor: BlendFactor::Zero,
+                    dest_rgb_factor: BlendFactor::OneMinusSrcAlpha,
+                    src_alpha_factor: BlendFactor::Zero,
+                    dest_alpha_factor: BlendFactor::OneMinusSrcAlpha,
+                    ..BlendState::default()
+                }
+            }
+            BlendMode::SrcAtop => {
+                BlendState {
+                    src_rgb_factor: BlendFactor::DestAlpha,
+                    dest_rgb_factor: BlendFactor::OneMinusSrcAlpha,
+                    src_alpha_factor: BlendFactor::DestAlpha,
+                    dest_alpha_factor: BlendFactor::OneMinusSrcAlpha,
+                    ..BlendState::default()
+                }
+            }
+            BlendMode::Xor => {
+                BlendState {
+                    src_rgb_factor: BlendFactor::OneMinusDestAlpha,
+                    dest_rgb_factor: BlendFactor::OneMinusSrcAlpha,
+                    src_alpha_factor: BlendFactor::OneMinusDestAlpha,
+                    dest_alpha_factor: BlendFactor::OneMinusSrcAlpha,
+                    ..BlendState::default()
+                }
+            }
+            BlendMode::Lighter => {
+                BlendState {
+                    src_rgb_factor: BlendFactor::One,
+                    dest_rgb_factor: BlendFactor::One,
+                    src_alpha_factor: BlendFactor::One,
+                    dest_alpha_factor: BlendFactor::One,
+                    ..BlendState::default()
+                }
+            }
             BlendMode::Lighten => {
                 BlendState {
-                    src_rgb_factor: BlendFactor::SrcAlpha,
+                    src_rgb_factor: BlendFactor::One,
                     dest_rgb_factor: BlendFactor::OneMinusSrcAlpha,
                     src_alpha_factor: BlendFactor::One,
                     dest_alpha_factor: BlendFactor::One,
@@ -1162,7 +1207,7 @@ impl BlendModeExt for BlendMode {
             }
             BlendMode::Darken => {
                 BlendState {
-                    src_rgb_factor: BlendFactor::SrcAlpha,
+                    src_rgb_factor: BlendFactor::One,
                     dest_rgb_factor: BlendFactor::OneMinusSrcAlpha,
                     src_alpha_factor: BlendFactor::One,
                     dest_alpha_factor: BlendFactor::One,

resources/shaders/gl3/tile_alpha.fs.glsl

@@ -27,6 +27,8 @@ out vec4 oFragColor;
 void main(){
     float coverage = texture(uStencilTexture, vMaskTexCoord). r;
     vec4 color = texture(uPaintTexture, vColorTexCoord);
-    oFragColor = vec4(color . rgb, color . a * coverage);
+    color . a *= coverage;
+    color . rgb *= color . a;
+    oFragColor = color;
 }
 

resources/shaders/metal/tile_alpha.fs.metal

@@ -28,7 +28,10 @@ fragment main0_out main0(main0_in in [[stage_in]], constant spvDescriptorSetBuff
     main0_out out = {};
     float coverage = spvDescriptorSet0.uStencilTexture.sample(spvDescriptorSet0.uStencilTextureSmplr, in.vMaskTexCoord).x;
     float4 color = spvDescriptorSet0.uPaintTexture.sample(spvDescriptorSet0.uPaintTextureSmplr, in.vColorTexCoord);
-    out.oFragColor = float4(color.xyz, color.w * coverage);
+    color.w *= coverage;
+    float3 _41 = color.xyz * color.w;
+    color = float4(_41.x, _41.y, _41.z, color.w);
+    out.oFragColor = color;
     return out;
 }
 

shaders/tile_alpha.fs.glsl

@@ -25,5 +25,7 @@ out vec4 oFragColor;
 void main() {
     float coverage = texture(uStencilTexture, vMaskTexCoord).r;
     vec4 color = texture(uPaintTexture, vColorTexCoord);
-    oFragColor = vec4(color.rgb, color.a * coverage);
+    color.a *= coverage;
+    color.rgb *= color.a;
+    oFragColor = color;
 }

svg/src/lib.rs

@@ -240,7 +240,7 @@ impl BuiltSVG {
                                            style,
                                            state.clip_path,
                                            fill_rule,
-                                           BlendMode::SourceOver,
+                                           BlendMode::SrcOver,
                                            name));
     }
 }

swf/src/lib.rs

@@ -201,7 +201,7 @@ pub fn draw_paths_into_scene(library: &SymbolLibrary, scene: &mut Scene) {
                     paint_id,
                     None,
                     FillRule::EvenOdd,
-                    BlendMode::SourceOver,
+                    BlendMode::SrcOver,
                     String::new()
                 ));
             }

text/src/lib.rs

@@ -82,7 +82,7 @@ impl SceneExt for Scene {
                                      paint_id,
                                      None,
                                      FillRule::Winding,
-                                     BlendMode::SourceOver,
+                                     BlendMode::SrcOver,
                                      String::new()));
 
         Ok(())