2 files changed, 85 insertions, 0 deletions
diff --git a/apps/web/src/lib/shaders/jfa-init.frag.glsl b/apps/web/src/lib/shaders/jfa-init.frag.glsl
new file mode 100644
index 00000000..d199d234
--- /dev/null
+++ b/apps/web/src/lib/shaders/jfa-init.frag.glsl
@@ -0,0 +1,25 @@
+precision mediump float;
+
+uniform sampler2D u_texture;
+uniform vec2 u_resolution;
+uniform float u_invert;
+
+varying vec2 v_texCoord;
+
+void main() {
+  float mask = texture2D(u_texture, v_texCoord).r;
+  bool isSeed = u_invert > 0.5 ? mask < 0.5 : mask > 0.5;
+
+  if (isSeed) {
+    vec2 pixelCoord = floor(v_texCoord * u_resolution);
+    float x = pixelCoord.x;
+    float y = pixelCoord.y;
+    float xHi = floor(x / 256.0);
+    float xLo = x - xHi * 256.0;
+    float yHi = floor(y / 256.0);
+    float yLo = y - yHi * 256.0;
+    gl_FragColor = vec4(xHi / 255.0, xLo / 255.0, yHi / 255.0, yLo / 255.0);
+  } else {
+    gl_FragColor = vec4(1.0, 1.0, 1.0, 1.0);
+  }
+}
diff --git a/apps/web/src/lib/shaders/jfa-step.frag.glsl b/apps/web/src/lib/shaders/jfa-step.frag.glsl
new file mode 100644
index 00000000..5a95f497
--- /dev/null
+++ b/apps/web/src/lib/shaders/jfa-step.frag.glsl
@@ -0,0 +1,60 @@
+precision mediump float;
+
+uniform sampler2D u_texture;
+uniform vec2 u_resolution;
+uniform float u_step_size;
+
+varying vec2 v_texCoord;
+
+vec2 decodeSeed(vec4 encoded) {
+  float x = floor(encoded.r * 255.0 + 0.5) * 256.0 + floor(encoded.g * 255.0 + 0.5);
+  float y = floor(encoded.b * 255.0 + 0.5) * 256.0 + floor(encoded.a * 255.0 + 0.5);
+  return vec2(x, y);
+}
+
+vec4 encodeSeed(vec2 seed) {
+  float xHi = floor(seed.x / 256.0);
+  float xLo = seed.x - xHi * 256.0;
+  float yHi = floor(seed.y / 256.0);
+  float yLo = seed.y - yHi * 256.0;
+  return vec4(xHi / 255.0, xLo / 255.0, yHi / 255.0, yLo / 255.0);
+}
+
+bool isNoSeed(vec4 encoded) {
+  return encoded.r > 0.99 && encoded.g > 0.99 && encoded.b > 0.99 && encoded.a > 0.99;
+}
+
+void main() {
+  vec2 pixelCoord = floor(v_texCoord * u_resolution);
+  vec2 texelSize = 1.0 / u_resolution;
+
+  float bestDist = 1e10;
+  vec2 bestSeed = vec2(65535.0);
+
+  for (int dy = -1; dy <= 1; dy++) {
+    for (int dx = -1; dx <= 1; dx++) {
+      vec2 offset = vec2(float(dx), float(dy)) * u_step_size;
+      vec2 sampleUV = v_texCoord + offset * texelSize;
+
+      if (sampleUV.x < 0.0 || sampleUV.x > 1.0 || sampleUV.y < 0.0 || sampleUV.y > 1.0)
+        continue;
+
+      vec4 encoded = texture2D(u_texture, sampleUV);
+      if (isNoSeed(encoded))
+        continue;
+
+      vec2 seed = decodeSeed(encoded);
+      float dist = distance(pixelCoord, seed);
+      if (dist < bestDist) {
+        bestDist = dist;
+        bestSeed = seed;
+      }
+    }
+  }
+
+  if (bestDist < 1e9) {
+    gl_FragColor = encodeSeed(bestSeed);
+  } else {
+    gl_FragColor = vec4(1.0, 1.0, 1.0, 1.0);
+  }
+}