Add documentation to fragment shader

Signed-off-by: Hans Kokx <hans.d.kokx@gmail.com>

packages/wolf_3d_renderer/shaders/wolf_world.frag

@@ -1,24 +1,32 @@
 #include <flutter/runtime_effect.glsl>
 
+// Output surface size in pixels.
 uniform vec2 uResolution;
+// One source-texel step in UV space: (1/width, 1/height).
 uniform vec2 uTexel;
+// Source frame produced by the software renderer.
 uniform sampler2D uTexture;
 
 out vec4 fragColor;
 
+// Perceptual brightness approximation used for edge detection.
 float luma(vec3 color) {
   return dot(color, vec3(0.299, 0.587, 0.114));
 }
 
 void main() {
+  // Convert fragment coordinates to normalized UV coordinates.
   vec2 uv = FlutterFragCoord().xy / uResolution;
+  // Read the base color from the source frame.
   vec4 centerSample = texture(uTexture, uv);
 
+  // Sample 4-neighborhood (N/S/E/W) around the current pixel.
   vec3 sampleN = texture(uTexture, uv + vec2(0.0, -uTexel.y)).rgb;
   vec3 sampleS = texture(uTexture, uv + vec2(0.0, uTexel.y)).rgb;
   vec3 sampleE = texture(uTexture, uv + vec2(uTexel.x, 0.0)).rgb;
   vec3 sampleW = texture(uTexture, uv + vec2(-uTexel.x, 0.0)).rgb;
 
+  // Compute local luma range; wider range means a stronger edge.
   float lumaCenter = luma(centerSample.rgb);
   float lumaMin = min(
     lumaCenter,
@@ -30,9 +38,14 @@ void main() {
   );
 
   float edgeSpan = max(lumaMax - lumaMin, 0.0001);
+  // Convert raw edge strength into a smooth 0..1 blending amount.
   float edgeAmount = smoothstep(0.03, 0.18, edgeSpan);
+
+  // Average neighbors and blend toward that average only near edges.
+  // This acts like a lightweight edge-aware anti-aliasing pass.
   vec3 neighborhoodAvg = (sampleN + sampleS + sampleE + sampleW) * 0.25;
   vec3 aaColor = mix(centerSample.rgb, neighborhoodAvg, edgeAmount * 0.45);
 
+  // Preserve source alpha and output the anti-aliased color.
   fragColor = vec4(aaColor, centerSample.a);
 }