♻️ Move edge mask to snippets

src/shaderSnippets.js

@@ -33,6 +33,33 @@ function standardUniforms() {
   `;
 }
 
+// This method returns a mask which smoothly transitions towards zero when approaching
+// the window's borders. There is a variant which takes the transition area width in
+// pixels and one which takes this as a percentage.
+function edgeMask() {
+  return `
+  float getEdgeMask(vec2 uv, vec2 maxUV, float fadeWidth) {
+    float mask = 1.0;
+    mask *= smoothstep(0, 1, clamp(uv.x / fadeWidth, 0, 1));
+    mask *= smoothstep(0, 1, clamp(uv.y / fadeWidth, 0, 1));
+    mask *= smoothstep(0, 1, clamp((maxUV.x - uv.x) / fadeWidth, 0, 1));
+    mask *= smoothstep(0, 1, clamp((maxUV.y - uv.y) / fadeWidth, 0, 1));
+
+    return mask;
+  }
+
+  float getAbsoluteEdgeMask(float fadePixels) {
+    vec2 uv = cogl_tex_coord_in[0].st * vec2(uSizeX, uSizeY);
+    return getEdgeMask(uv, vec2(uSizeX, uSizeY), fadePixels);
+  }
+  
+  float getRelativeEdgeMask(float fadeAmount) {
+    vec2 uv = cogl_tex_coord_in[0].st;
+    return getEdgeMask(uv, vec2(1.0), fadeAmount);
+  }
+  `;
+}
+
 // These noise algorithms are based on implementations by various authors from
 // shadertoy.com, which are all available under the MIT License. See the respective links
 // in the comments below.