🔧 Convert window texture alpha from premultiplied to straight

src/TVEffect.js

@@ -162,7 +162,7 @@ if (utils.isInShellProcess()) {
       freeShaders.push(this);
     }
 
-    // This is called by the constructor. This is means it's only called when the effect
+    // This is called by the constructor. This means, it's only called when the effect
     // is used for the first time.
     vfunc_build_pipeline() {
       const declarations = `
@@ -207,6 +207,12 @@ if (utils.isInShellProcess()) {
         float mask = tbMask * lrMask * ffMask;
 
         cogl_color_out = texture2D(uTexture, cogl_tex_coord_in[0].st);
+        
+        // Shell.GLSLEffect uses straight alpha. So we have to convert from premultiplied.
+        if (cogl_color_out.a > 0) {
+          cogl_color_out.rgb /= cogl_color_out.a;
+        }
+
         cogl_color_out.rgb = mix(cogl_color_out.rgb, uColor * cogl_color_out.a, smoothstep(0, 1, progress));
         cogl_color_out.a *= mask;