From 121c2577b467ab5d5031b7afd9c2df2df198f2dd Mon Sep 17 00:00:00 2001
From: Mike Welsh <mwelsh@gmail.com>
Date: Thu, 12 May 2022 11:46:52 -0700
Subject: [PATCH] wgpu: Clamp alpha in shaders (fix #6954)

---
 render/wgpu/shaders/bitmap.wgsl   | 3 ++-
 render/wgpu/shaders/color.wgsl    | 9 +++++----
 render/wgpu/shaders/gradient.wgsl | 3 ++-
 3 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/render/wgpu/shaders/bitmap.wgsl b/render/wgpu/shaders/bitmap.wgsl
index 0992dc1e4..3b2c639ef 100644
--- a/render/wgpu/shaders/bitmap.wgsl
+++ b/render/wgpu/shaders/bitmap.wgsl
@@ -28,7 +28,8 @@ fn main_fragment(in: VertexOutput) -> [[location(0)]] vec4<f32> {
     if( color.a > 0.0 ) {
         color = vec4<f32>(color.rgb / color.a, color.a);
         color = color * transforms.mult_color + transforms.add_color;
-        color = vec4<f32>(color.rgb * color.a, color.a);
+        let alpha = clamp(color.a, 0.0, 1.0);
+        color = vec4<f32>(color.rgb * alpha, alpha);
     }
     return color;
 }
diff --git a/render/wgpu/shaders/color.wgsl b/render/wgpu/shaders/color.wgsl
index b42c80d0b..55d9bc3c6 100644
--- a/render/wgpu/shaders/color.wgsl
+++ b/render/wgpu/shaders/color.wgsl
@@ -7,12 +7,13 @@ struct VertexOutput {
 
 [[stage(vertex)]]
 fn main_vertex(in: VertexInput) -> VertexOutput {
-    let pos: vec4<f32> = globals.view_matrix * transforms.world_matrix * vec4<f32>(in.position.x, in.position.y, 0.0, 1.0);
-    return VertexOutput(pos, in.color);
+    let pos = globals.view_matrix * transforms.world_matrix * vec4<f32>(in.position.x, in.position.y, 0.0, 1.0);
+    let color = in.color * transforms.mult_color + transforms.add_color;
+    let alpha = clamp(color.a, 0.0, 1.0);
+    return VertexOutput(pos, vec4<f32>(color.rgb * alpha, alpha));
 }
 
 [[stage(fragment)]]
 fn main_fragment(in: VertexOutput) -> [[location(0)]] vec4<f32> {
-    let out = in.color * transforms.mult_color + transforms.add_color;
-    return vec4<f32>(out.rgb * out.a, out.a);
+    return in.color;
 }
diff --git a/render/wgpu/shaders/gradient.wgsl b/render/wgpu/shaders/gradient.wgsl
index f037ca28c..a2ae6dd40 100644
--- a/render/wgpu/shaders/gradient.wgsl
+++ b/render/wgpu/shaders/gradient.wgsl
@@ -102,5 +102,6 @@ fn main_fragment(in: VertexOutput) -> [[location(0)]] vec4<f32> {
         color = linear_to_srgb(color);
     }
     let out = color * transforms.mult_color + transforms.add_color;
-    return vec4<f32>(out.rgb * out.a, out.a);
+    let alpha = clamp(out.a, 0.0, 1.0);
+    return vec4<f32>(out.rgb * alpha, alpha);
 }