#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,
    min(min(luma(sampleN), luma(sampleS)), min(luma(sampleE), luma(sampleW)))
  );
  float lumaMax = max(
    lumaCenter,
    max(max(luma(sampleN), luma(sampleS)), max(luma(sampleE), luma(sampleW)))
  );

  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);
}