Reproduce issue

Author: rukai

wgpu/examples/msaa-line/shader.wgsl

@@ -1,5 +1,6 @@
 struct VertexOutput {
     [[location(0)]] color: vec4<f32>;
+    [[location(1), interpolate(flat)]] a: u32;
     [[builtin(position)]] position: vec4<f32>;
 };
 
@@ -11,10 +12,16 @@ fn vs_main(
     var out: VertexOutput;
     out.position = vec4<f32>(position, 0.0, 1.0);
     out.color = color;
+    out.a = 5u32;
     return out;
 }
 
 [[stage(fragment)]]
 fn fs_main(in: VertexOutput) -> [[location(0)]] vec4<f32> {
-    return in.color;
+    if (in.a == 0u32) {
+        return vec4<f32>(1.0, 0.0, 0.0, 1.0);
+    }
+    else {
+        return vec4<f32>(0.0, 0.0, 1.0, 1.0);
+    }
 }