From 469261e5a68384fda36763839ed37519d719531b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?H=C3=A9ctor=20Ram=C3=B3n=20Jim=C3=A9nez?= <hector@hecrj.dev>
Date: Sat, 3 May 2025 22:22:23 +0200
Subject: [PATCH 1/4] Replace `mix` calls with proper alpha blending in `quad`
 shaders

---
 wgpu/src/quad.rs                   | 13 +-----------
 wgpu/src/shader/color/oklab.wgsl   |  2 +-
 wgpu/src/shader/quad.wgsl          |  4 ++++
 wgpu/src/shader/quad/gradient.wgsl | 34 ++++++++++++++++++------------
 wgpu/src/shader/quad/solid.wgsl    | 24 ++++++++-------------
 5 files changed, 35 insertions(+), 42 deletions(-)

diff --git a/wgpu/src/quad.rs b/wgpu/src/quad.rs
index 4c00945c..b3ac3f48 100644
--- a/wgpu/src/quad.rs
+++ b/wgpu/src/quad.rs
@@ -317,18 +317,7 @@ fn color_target_state(
 ) -> [Option<wgpu::ColorTargetState>; 1] {
     [Some(wgpu::ColorTargetState {
         format,
-        blend: Some(wgpu::BlendState {
-            color: wgpu::BlendComponent {
-                src_factor: wgpu::BlendFactor::SrcAlpha,
-                dst_factor: wgpu::BlendFactor::OneMinusSrcAlpha,
-                operation: wgpu::BlendOperation::Add,
-            },
-            alpha: wgpu::BlendComponent {
-                src_factor: wgpu::BlendFactor::One,
-                dst_factor: wgpu::BlendFactor::OneMinusSrcAlpha,
-                operation: wgpu::BlendOperation::Add,
-            },
-        }),
+        blend: Some(wgpu::BlendState::PREMULTIPLIED_ALPHA_BLENDING),
         write_mask: wgpu::ColorWrites::ALL,
     })]
 }
diff --git a/wgpu/src/shader/color/oklab.wgsl b/wgpu/src/shader/color/oklab.wgsl
index 0dc37ba6..343eaa15 100644
--- a/wgpu/src/shader/color/oklab.wgsl
+++ b/wgpu/src/shader/color/oklab.wgsl
@@ -20,7 +20,7 @@ fn interpolate_color(from_: vec4<f32>, to_: vec4<f32>, factor: f32) -> vec4<f32>
     var color = to_rgb * (mixed * mixed * mixed);
 
     // Alpha interpolation
-    color.a = mix(from_.a, to_.a, factor);
+    color = to_ * factor + from_ * (1.0 - factor);
 
     return color;
 }
diff --git a/wgpu/src/shader/quad.wgsl b/wgpu/src/shader/quad.wgsl
index b213c8cf..0a4cd7b4 100644
--- a/wgpu/src/shader/quad.wgsl
+++ b/wgpu/src/shader/quad.wgsl
@@ -5,6 +5,10 @@ struct Globals {
 
 @group(0) @binding(0) var<uniform> globals: Globals;
 
+fn blend(over: vec4<f32>, under: vec4<f32>, alpha: f32) -> vec4<f32> {
+    return over * alpha + under * (1.0 - alpha);
+}
+
 fn distance_alg(
     frag_coord: vec2<f32>,
     position: vec2<f32>,
diff --git a/wgpu/src/shader/quad/gradient.wgsl b/wgpu/src/shader/quad/gradient.wgsl
index 4ad2fea8..ddd7d1c4 100644
--- a/wgpu/src/shader/quad/gradient.wgsl
+++ b/wgpu/src/shader/quad/gradient.wgsl
@@ -56,7 +56,7 @@ fn gradient_vs_main(input: GradientVertexInput) -> GradientVertexOutput {
     out.offsets = input.offsets;
     out.direction = input.direction * globals.scale;
     out.position_and_scale = vec4<f32>(pos, scale);
-    out.border_color = input.border_color;
+    out.border_color = vec4(input.border_color.xyz * input.border_color.a, input.border_color.a);
     out.border_radius = border_radius * globals.scale;
     out.border_width = input.border_width * globals.scale;
 
@@ -119,14 +119,14 @@ fn gradient(
 @fragment
 fn gradient_fs_main(input: GradientVertexOutput) -> @location(0) vec4<f32> {
     let colors = array<vec4<f32>, 8>(
-        unpack_u32(input.colors_1.xy),
-        unpack_u32(input.colors_1.zw),
-        unpack_u32(input.colors_2.xy),
-        unpack_u32(input.colors_2.zw),
-        unpack_u32(input.colors_3.xy),
-        unpack_u32(input.colors_3.zw),
-        unpack_u32(input.colors_4.xy),
-        unpack_u32(input.colors_4.zw),
+        unpack_color(input.colors_1.xy),
+        unpack_color(input.colors_1.zw),
+        unpack_color(input.colors_2.xy),
+        unpack_color(input.colors_2.zw),
+        unpack_color(input.colors_3.xy),
+        unpack_color(input.colors_3.zw),
+        unpack_color(input.colors_4.xy),
+        unpack_color(input.colors_4.zw),
     );
 
     let offsets_1: vec4<f32> = unpack_u32(input.offsets.xy);
@@ -179,7 +179,7 @@ fn gradient_fs_main(input: GradientVertexOutput) -> @location(0) vec4<f32> {
             internal_distance
         );
 
-        mixed_color = mix(mixed_color, input.border_color, vec4<f32>(border_mix, border_mix, border_mix, border_mix));
+        mixed_color = blend(input.border_color, mixed_color, border_mix);
     }
 
     var dist: f32 = distance_alg(
@@ -194,12 +194,18 @@ fn gradient_fs_main(input: GradientVertexOutput) -> @location(0) vec4<f32> {
         border_radius + 0.5,
         dist);
 
-    return vec4<f32>(mixed_color.x, mixed_color.y, mixed_color.z, mixed_color.w * radius_alpha);
+    return mixed_color * radius_alpha;
 }
 
-fn unpack_u32(color: vec2<u32>) -> vec4<f32> {
-    let rg: vec2<f32> = unpack2x16float(color.x);
-    let ba: vec2<f32> = unpack2x16float(color.y);
+fn unpack_color(data: vec2<u32>) -> vec4<f32> {
+    let color = unpack_u32(data);
+
+    return vec4(color.xyz * color.a, color.a);
+}
+
+fn unpack_u32(data: vec2<u32>) -> vec4<f32> {
+    let rg: vec2<f32> = unpack2x16float(data.x);
+    let ba: vec2<f32> = unpack2x16float(data.y);
 
     return vec4<f32>(rg.y, rg.x, ba.y, ba.x);
 }
diff --git a/wgpu/src/shader/quad/solid.wgsl b/wgpu/src/shader/quad/solid.wgsl
index 8eee16bb..979d7174 100644
--- a/wgpu/src/shader/quad/solid.wgsl
+++ b/wgpu/src/shader/quad/solid.wgsl
@@ -56,13 +56,13 @@ fn solid_vs_main(input: SolidVertexInput) -> SolidVertexOutput {
     );
 
     out.position = globals.transform * transform * vec4<f32>(vertex_position(input.vertex_index), 0.0, 1.0);
-    out.color = input.color;
-    out.border_color = input.border_color;
+    out.color = vec4(input.color.xyz * input.color.a, input.color.a);
+    out.border_color = vec4(input.border_color.xyz * input.border_color.a, input.border_color.a);
     out.pos = input.pos * globals.scale + snap;
     out.scale = input.scale * globals.scale;
     out.border_radius = border_radius * globals.scale;
     out.border_width = input.border_width * globals.scale;
-    out.shadow_color = input.shadow_color;
+    out.shadow_color = vec4(input.shadow_color.xyz, input.shadow_color.a);
     out.shadow_offset = input.shadow_offset * globals.scale;
     out.shadow_blur_radius = input.shadow_blur_radius * globals.scale;
 
@@ -97,7 +97,7 @@ fn solid_fs_main(
             internal_distance
         );
 
-        mixed_color = mix(input.color, input.border_color, vec4<f32>(border_mix, border_mix, border_mix, border_mix));
+        mixed_color = blend(input.border_color, input.color, border_mix);
     }
 
     var dist: f32 = distance_alg(
@@ -113,7 +113,7 @@ fn solid_fs_main(
         dist
     );
 
-    let quad_color = vec4<f32>(mixed_color.x, mixed_color.y, mixed_color.z, mixed_color.w * radius_alpha);
+    let quad_color = mixed_color * radius_alpha;
 
     if input.shadow_color.a > 0.0 {
         let shadow_radius = select_border_radius(
@@ -121,17 +121,11 @@ fn solid_fs_main(
             input.position.xy - input.shadow_offset,
             (input.pos + input.scale * 0.5).xy
         );
-        let shadow_distance = max(rounded_box_sdf(input.position.xy - input.pos - input.shadow_offset - (input.scale / 2.0), input.scale / 2.0, shadow_radius), 0.);
-        
-        let shadow_alpha = 1.0 - smoothstep(-input.shadow_blur_radius, input.shadow_blur_radius, shadow_distance);
-        let shadow_color = input.shadow_color;
-        let base_color = mix(
-            vec4<f32>(shadow_color.x, shadow_color.y, shadow_color.z, 0.0),
-            quad_color,
-            quad_color.a
-        );
 
-        return mix(base_color, shadow_color, (1.0 - radius_alpha) * shadow_alpha);
+        let shadow_distance = max(rounded_box_sdf(input.position.xy - input.pos - input.shadow_offset - (input.scale / 2.0), input.scale / 2.0, shadow_radius), 0.);
+        let shadow_alpha = 1.0 - smoothstep(-input.shadow_blur_radius, input.shadow_blur_radius, shadow_distance);
+
+        return blend(input.shadow_color, quad_color, (1.0 - radius_alpha) * shadow_alpha);
     } else {
         return quad_color;
     }

From 9ac4c9f13d6caa1d64852554e6856c4a18d499bc Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?H=C3=A9ctor=20Ram=C3=B3n=20Jim=C3=A9nez?= <hector@hecrj.dev>
Date: Sat, 3 May 2025 22:33:55 +0200
Subject: [PATCH 2/4] Define `premultiply` helper for `quad` shaders

---
 wgpu/src/shader/quad.wgsl          | 4 ++++
 wgpu/src/shader/quad/gradient.wgsl | 6 ++----
 wgpu/src/shader/quad/solid.wgsl    | 6 +++---
 3 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/wgpu/src/shader/quad.wgsl b/wgpu/src/shader/quad.wgsl
index 0a4cd7b4..bef8bd40 100644
--- a/wgpu/src/shader/quad.wgsl
+++ b/wgpu/src/shader/quad.wgsl
@@ -5,6 +5,10 @@ struct Globals {
 
 @group(0) @binding(0) var<uniform> globals: Globals;
 
+fn premultiply(color: vec4<f32>) -> vec4<f32> {
+    return vec4(color.xyz * color.a, color.a);
+}
+
 fn blend(over: vec4<f32>, under: vec4<f32>, alpha: f32) -> vec4<f32> {
     return over * alpha + under * (1.0 - alpha);
 }
diff --git a/wgpu/src/shader/quad/gradient.wgsl b/wgpu/src/shader/quad/gradient.wgsl
index ddd7d1c4..d743e26d 100644
--- a/wgpu/src/shader/quad/gradient.wgsl
+++ b/wgpu/src/shader/quad/gradient.wgsl
@@ -56,7 +56,7 @@ fn gradient_vs_main(input: GradientVertexInput) -> GradientVertexOutput {
     out.offsets = input.offsets;
     out.direction = input.direction * globals.scale;
     out.position_and_scale = vec4<f32>(pos, scale);
-    out.border_color = vec4(input.border_color.xyz * input.border_color.a, input.border_color.a);
+    out.border_color = premultiply(input.border_color);
     out.border_radius = border_radius * globals.scale;
     out.border_width = input.border_width * globals.scale;
 
@@ -198,9 +198,7 @@ fn gradient_fs_main(input: GradientVertexOutput) -> @location(0) vec4<f32> {
 }
 
 fn unpack_color(data: vec2<u32>) -> vec4<f32> {
-    let color = unpack_u32(data);
-
-    return vec4(color.xyz * color.a, color.a);
+    return premultiply(unpack_u32(data));
 }
 
 fn unpack_u32(data: vec2<u32>) -> vec4<f32> {
diff --git a/wgpu/src/shader/quad/solid.wgsl b/wgpu/src/shader/quad/solid.wgsl
index 979d7174..d5d1e604 100644
--- a/wgpu/src/shader/quad/solid.wgsl
+++ b/wgpu/src/shader/quad/solid.wgsl
@@ -56,13 +56,13 @@ fn solid_vs_main(input: SolidVertexInput) -> SolidVertexOutput {
     );
 
     out.position = globals.transform * transform * vec4<f32>(vertex_position(input.vertex_index), 0.0, 1.0);
-    out.color = vec4(input.color.xyz * input.color.a, input.color.a);
-    out.border_color = vec4(input.border_color.xyz * input.border_color.a, input.border_color.a);
+    out.color = premultiply(input.color);
+    out.border_color = premultiply(input.border_color);
     out.pos = input.pos * globals.scale + snap;
     out.scale = input.scale * globals.scale;
     out.border_radius = border_radius * globals.scale;
     out.border_width = input.border_width * globals.scale;
-    out.shadow_color = vec4(input.shadow_color.xyz, input.shadow_color.a);
+    out.shadow_color = premultiply(input.shadow_color);
     out.shadow_offset = input.shadow_offset * globals.scale;
     out.shadow_blur_radius = input.shadow_blur_radius * globals.scale;
 

From df37d6f9bc0471cd6c495ae523aa6242d88b5aa0 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?H=C3=A9ctor=20Ram=C3=B3n=20Jim=C3=A9nez?= <hector@hecrj.dev>
Date: Mon, 12 May 2025 18:11:51 +0200
Subject: [PATCH 3/4] Replace `blend` with `mix` equivalent in `quad` shaders

---
 wgpu/src/shader/quad.wgsl          | 4 ----
 wgpu/src/shader/quad/gradient.wgsl | 2 +-
 wgpu/src/shader/quad/solid.wgsl    | 4 ++--
 3 files changed, 3 insertions(+), 7 deletions(-)

diff --git a/wgpu/src/shader/quad.wgsl b/wgpu/src/shader/quad.wgsl
index bef8bd40..ff9fdae6 100644
--- a/wgpu/src/shader/quad.wgsl
+++ b/wgpu/src/shader/quad.wgsl
@@ -9,10 +9,6 @@ fn premultiply(color: vec4<f32>) -> vec4<f32> {
     return vec4(color.xyz * color.a, color.a);
 }
 
-fn blend(over: vec4<f32>, under: vec4<f32>, alpha: f32) -> vec4<f32> {
-    return over * alpha + under * (1.0 - alpha);
-}
-
 fn distance_alg(
     frag_coord: vec2<f32>,
     position: vec2<f32>,
diff --git a/wgpu/src/shader/quad/gradient.wgsl b/wgpu/src/shader/quad/gradient.wgsl
index d743e26d..e8c54790 100644
--- a/wgpu/src/shader/quad/gradient.wgsl
+++ b/wgpu/src/shader/quad/gradient.wgsl
@@ -179,7 +179,7 @@ fn gradient_fs_main(input: GradientVertexOutput) -> @location(0) vec4<f32> {
             internal_distance
         );
 
-        mixed_color = blend(input.border_color, mixed_color, border_mix);
+        mixed_color = mix(mixed_color, input.border_color, border_mix);
     }
 
     var dist: f32 = distance_alg(
diff --git a/wgpu/src/shader/quad/solid.wgsl b/wgpu/src/shader/quad/solid.wgsl
index d5d1e604..f4c39f3d 100644
--- a/wgpu/src/shader/quad/solid.wgsl
+++ b/wgpu/src/shader/quad/solid.wgsl
@@ -97,7 +97,7 @@ fn solid_fs_main(
             internal_distance
         );
 
-        mixed_color = blend(input.border_color, input.color, border_mix);
+        mixed_color = mix(input.color, input.border_color, border_mix);
     }
 
     var dist: f32 = distance_alg(
@@ -125,7 +125,7 @@ fn solid_fs_main(
         let shadow_distance = max(rounded_box_sdf(input.position.xy - input.pos - input.shadow_offset - (input.scale / 2.0), input.scale / 2.0, shadow_radius), 0.);
         let shadow_alpha = 1.0 - smoothstep(-input.shadow_blur_radius, input.shadow_blur_radius, shadow_distance);
 
-        return blend(input.shadow_color, quad_color, (1.0 - radius_alpha) * shadow_alpha);
+        return mix(quad_color, input.shadow_color, (1.0 - radius_alpha) * shadow_alpha);
     } else {
         return quad_color;
     }

From 098bd1b8a407eb568db1d938f2f7ffca4e18dbd8 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?H=C3=A9ctor=20Ram=C3=B3n=20Jim=C3=A9nez?= <hector@hecrj.dev>
Date: Mon, 12 May 2025 18:35:27 +0200
Subject: [PATCH 4/4] Use premultiplied colors in `triangle` pipelines

---
 wgpu/src/quad/gradient.rs              |  4 ++++
 wgpu/src/quad/solid.rs                 |  2 ++
 wgpu/src/shader/color.wgsl             | 14 ++++++++++++++
 wgpu/src/shader/color/oklab.wgsl       |  2 +-
 wgpu/src/shader/quad.wgsl              |  4 ----
 wgpu/src/shader/quad/gradient.wgsl     | 11 -----------
 wgpu/src/shader/triangle/gradient.wgsl | 23 ++++++++---------------
 wgpu/src/shader/triangle/solid.wgsl    |  2 +-
 wgpu/src/triangle.rs                   |  8 +++++++-
 9 files changed, 37 insertions(+), 33 deletions(-)
 create mode 100644 wgpu/src/shader/color.wgsl

diff --git a/wgpu/src/quad/gradient.rs b/wgpu/src/quad/gradient.rs
index 3c5fc33f..351e941d 100644
--- a/wgpu/src/quad/gradient.rs
+++ b/wgpu/src/quad/gradient.rs
@@ -97,6 +97,8 @@ impl Pipeline {
                                         "../shader/quad/gradient.wgsl"
                                     ),
                                     "\n",
+                                    include_str!("../shader/color.wgsl"),
+                                    "\n",
                                     include_str!("../shader/color/oklab.wgsl")
                                 )
                             } else {
@@ -109,6 +111,8 @@ impl Pipeline {
                                         "../shader/quad/gradient.wgsl"
                                     ),
                                     "\n",
+                                    include_str!("../shader/color.wgsl"),
+                                    "\n",
                                     include_str!(
                                         "../shader/color/linear_rgb.wgsl"
                                     )
diff --git a/wgpu/src/quad/solid.rs b/wgpu/src/quad/solid.rs
index 317a248c..fa1db172 100644
--- a/wgpu/src/quad/solid.rs
+++ b/wgpu/src/quad/solid.rs
@@ -74,6 +74,8 @@ impl Pipeline {
                 label: Some("iced_wgpu.quad.solid.shader"),
                 source: wgpu::ShaderSource::Wgsl(std::borrow::Cow::Borrowed(
                     concat!(
+                        include_str!("../shader/color.wgsl"),
+                        "\n",
                         include_str!("../shader/quad.wgsl"),
                         "\n",
                         include_str!("../shader/vertex.wgsl"),
diff --git a/wgpu/src/shader/color.wgsl b/wgpu/src/shader/color.wgsl
new file mode 100644
index 00000000..a8066368
--- /dev/null
+++ b/wgpu/src/shader/color.wgsl
@@ -0,0 +1,14 @@
+fn premultiply(color: vec4<f32>) -> vec4<f32> {
+    return vec4(color.xyz * color.a, color.a);
+}
+
+fn unpack_color(data: vec2<u32>) -> vec4<f32> {
+    return premultiply(unpack_u32(data));
+}
+
+fn unpack_u32(data: vec2<u32>) -> vec4<f32> {
+    let rg: vec2<f32> = unpack2x16float(data.x);
+    let ba: vec2<f32> = unpack2x16float(data.y);
+
+    return vec4<f32>(rg.y, rg.x, ba.y, ba.x);
+}
diff --git a/wgpu/src/shader/color/oklab.wgsl b/wgpu/src/shader/color/oklab.wgsl
index 343eaa15..0dc37ba6 100644
--- a/wgpu/src/shader/color/oklab.wgsl
+++ b/wgpu/src/shader/color/oklab.wgsl
@@ -20,7 +20,7 @@ fn interpolate_color(from_: vec4<f32>, to_: vec4<f32>, factor: f32) -> vec4<f32>
     var color = to_rgb * (mixed * mixed * mixed);
 
     // Alpha interpolation
-    color = to_ * factor + from_ * (1.0 - factor);
+    color.a = mix(from_.a, to_.a, factor);
 
     return color;
 }
diff --git a/wgpu/src/shader/quad.wgsl b/wgpu/src/shader/quad.wgsl
index ff9fdae6..b213c8cf 100644
--- a/wgpu/src/shader/quad.wgsl
+++ b/wgpu/src/shader/quad.wgsl
@@ -5,10 +5,6 @@ struct Globals {
 
 @group(0) @binding(0) var<uniform> globals: Globals;
 
-fn premultiply(color: vec4<f32>) -> vec4<f32> {
-    return vec4(color.xyz * color.a, color.a);
-}
-
 fn distance_alg(
     frag_coord: vec2<f32>,
     position: vec2<f32>,
diff --git a/wgpu/src/shader/quad/gradient.wgsl b/wgpu/src/shader/quad/gradient.wgsl
index e8c54790..a1b4b107 100644
--- a/wgpu/src/shader/quad/gradient.wgsl
+++ b/wgpu/src/shader/quad/gradient.wgsl
@@ -196,14 +196,3 @@ fn gradient_fs_main(input: GradientVertexOutput) -> @location(0) vec4<f32> {
 
     return mixed_color * radius_alpha;
 }
-
-fn unpack_color(data: vec2<u32>) -> vec4<f32> {
-    return premultiply(unpack_u32(data));
-}
-
-fn unpack_u32(data: vec2<u32>) -> vec4<f32> {
-    let rg: vec2<f32> = unpack2x16float(data.x);
-    let ba: vec2<f32> = unpack2x16float(data.y);
-
-    return vec4<f32>(rg.y, rg.x, ba.y, ba.x);
-}
diff --git a/wgpu/src/shader/triangle/gradient.wgsl b/wgpu/src/shader/triangle/gradient.wgsl
index 1a8ae3b5..31a48026 100644
--- a/wgpu/src/shader/triangle/gradient.wgsl
+++ b/wgpu/src/shader/triangle/gradient.wgsl
@@ -87,14 +87,14 @@ fn gradient(
 @fragment
 fn gradient_fs_main(input: GradientVertexOutput) -> @location(0) vec4<f32> {
     let colors = array<vec4<f32>, 8>(
-        unpack_u32(input.colors_1.xy),
-        unpack_u32(input.colors_1.zw),
-        unpack_u32(input.colors_2.xy),
-        unpack_u32(input.colors_2.zw),
-        unpack_u32(input.colors_3.xy),
-        unpack_u32(input.colors_3.zw),
-        unpack_u32(input.colors_4.xy),
-        unpack_u32(input.colors_4.zw),
+        unpack_color(input.colors_1.xy),
+        unpack_color(input.colors_1.zw),
+        unpack_color(input.colors_2.xy),
+        unpack_color(input.colors_2.zw),
+        unpack_color(input.colors_3.xy),
+        unpack_color(input.colors_3.zw),
+        unpack_color(input.colors_4.xy),
+        unpack_color(input.colors_4.zw),
     );
 
     let offsets_1: vec4<f32> = unpack_u32(input.offsets.xy);
@@ -122,13 +122,6 @@ fn gradient_fs_main(input: GradientVertexOutput) -> @location(0) vec4<f32> {
     return gradient(input.raw_position, input.direction, colors, offsets, last_index);
 }
 
-fn unpack_u32(color: vec2<u32>) -> vec4<f32> {
-    let rg: vec2<f32> = unpack2x16float(color.x);
-    let ba: vec2<f32> = unpack2x16float(color.y);
-
-    return vec4<f32>(rg.y, rg.x, ba.y, ba.x);
-}
-
 fn random(coords: vec2<f32>) -> f32 {
     return fract(sin(dot(coords, vec2(12.9898,78.233))) * 43758.5453);
 }
diff --git a/wgpu/src/shader/triangle/solid.wgsl b/wgpu/src/shader/triangle/solid.wgsl
index 9ef81982..b0d8057b 100644
--- a/wgpu/src/shader/triangle/solid.wgsl
+++ b/wgpu/src/shader/triangle/solid.wgsl
@@ -12,7 +12,7 @@ struct SolidVertexOutput {
 fn solid_vs_main(input: SolidVertexInput) -> SolidVertexOutput {
     var out: SolidVertexOutput;
 
-    out.color = input.color;
+    out.color = premultiply(input.color);
     out.position = globals.transform * vec4<f32>(input.position, 0.0, 1.0);
 
     return out;
diff --git a/wgpu/src/triangle.rs b/wgpu/src/triangle.rs
index 6d0b0322..a3f850dd 100644
--- a/wgpu/src/triangle.rs
+++ b/wgpu/src/triangle.rs
@@ -595,7 +595,7 @@ fn fragment_target(
 ) -> wgpu::ColorTargetState {
     wgpu::ColorTargetState {
         format: texture_format,
-        blend: Some(wgpu::BlendState::ALPHA_BLENDING),
+        blend: Some(wgpu::BlendState::PREMULTIPLIED_ALPHA_BLENDING),
         write_mask: wgpu::ColorWrites::ALL,
     }
 }
@@ -754,6 +754,8 @@ mod solid {
                             include_str!("shader/triangle.wgsl"),
                             "\n",
                             include_str!("shader/triangle/solid.wgsl"),
+                            "\n",
+                            include_str!("shader/color.wgsl"),
                         )),
                     ),
                 });
@@ -913,6 +915,8 @@ mod gradient {
                                         "shader/triangle/gradient.wgsl"
                                     ),
                                     "\n",
+                                    include_str!("shader/color.wgsl"),
+                                    "\n",
                                     include_str!("shader/color/oklab.wgsl")
                                 )
                             } else {
@@ -923,6 +927,8 @@ mod gradient {
                                         "shader/triangle/gradient.wgsl"
                                     ),
                                     "\n",
+                                    include_str!("shader/color.wgsl"),
+                                    "\n",
                                     include_str!(
                                         "shader/color/linear_rgb.wgsl"
                                     )