{
  "id": "reaction_diffusion",
  "name": "Reaction Diffusion",
  "description": "A Gray-Scott reaction-diffusion simulation running entirely on the GPU in a GLSL TOP, with the previous state fed back each frame.",
  "tags": ["generative", "glsl", "simulation", "reaction-diffusion", "organic"],
  "difficulty": "advanced",
  "td_version_min": "2022",
  "nodes": [
    {
      "name": "seed1",
      "type": "glslTOP",
      "comment": "Generates the Gray-Scott initial state: A=1 everywhere with sparse organic blobs of B"
    },
    {
      "name": "feedback1",
      "type": "feedbackTOP",
      "comment": "Holds the previous simulation state"
    },
    {
      "name": "glsl1",
      "type": "glslTOP",
      "comment": "Gray-Scott update step (reads feedback as input 0)"
    },
    { "name": "out1", "type": "nullTOP", "comment": "Output of the simulation" }
  ],
  "connections": [
    { "from": "seed1", "to": "feedback1", "to_input": 0 },
    { "from": "feedback1", "to": "glsl1", "to_input": 0 },
    { "from": "glsl1", "to": "out1" }
  ],
  "parameters": [
    {
      "name": "feedback_target",
      "node": "feedback1",
      "param": "top",
      "value": "glsl1",
      "description": "feedbackTOP samples glsl1 (the simulation output)."
    },
    {
      "name": "seed_resmode",
      "node": "seed1",
      "param": "outputresolution",
      "value": "custom",
      "description": "The seed GLSL TOP has no input, so it needs an explicit resolution; it propagates through the feedback loop to size the whole simulation."
    },
    { "name": "seed_resmult", "node": "seed1", "param": "resmult", "value": 0 },
    {
      "name": "seed_resw",
      "node": "seed1",
      "param": "resolutionw",
      "value": 256,
      "label": "Resolution",
      "description": "Simulation grid width."
    },
    {
      "name": "seed_resh",
      "node": "seed1",
      "param": "resolutionh",
      "value": 256,
      "description": "Simulation grid height."
    }
  ],
  "glsl_uniforms": [
    {
      "node": "glsl1",
      "name": "uFeed",
      "kind": "float",
      "value": 0.055,
      "label": "Feed Rate",
      "min": 0.0,
      "max": 0.1,
      "description": "Gray-Scott feed rate — how fast chemical A is replenished. Lower values give sparser patterns."
    },
    {
      "node": "glsl1",
      "name": "uKill",
      "kind": "float",
      "value": 0.062,
      "label": "Kill Rate",
      "min": 0.0,
      "max": 0.1,
      "description": "Gray-Scott kill rate — how fast chemical B is removed. Tune alongside Feed Rate to shift between spots, stripes and mazes."
    }
  ],
  "glsl_code": {
    "seed1": "out vec4 fragColor;\nfloat hash(vec2 p){ return fract(sin(dot(p, vec2(127.1, 311.7))) * 43758.5453); }\nfloat vnoise(vec2 p){\n    vec2 i = floor(p); vec2 f = fract(p);\n    f = f*f*(3.0-2.0*f);\n    float a = hash(i);\n    float b = hash(i+vec2(1.0,0.0));\n    float c = hash(i+vec2(0.0,1.0));\n    float d = hash(i+vec2(1.0,1.0));\n    return mix(mix(a,b,f.x), mix(c,d,f.x), f.y);\n}\nvoid main(){\n    vec2 uv = vUV.st;\n    float n = vnoise(uv * 14.0);\n    float b = smoothstep(0.62, 0.70, n);\n    fragColor = TDOutputSwizzle(vec4(1.0, b, 0.0, 1.0));\n}\n",
    "glsl1": "out vec4 fragColor;\n\nuniform float uFeed;\nuniform float uKill;\n\nvec2 sampleAB(vec2 uv) { return texture(sTD2DInputs[0], uv).rg; }\n\nvoid main()\n{\n    vec2 uv = vUV.st;\n    vec2 texel = uTD2DInfos[0].res.xy;\n    vec2 c = sampleAB(uv);\n    float a = c.r;\n    float b = c.g;\n\n    vec2 lap = vec2(0.0);\n    lap += sampleAB(uv + texel * vec2(-1.0, 0.0)) * 0.2;\n    lap += sampleAB(uv + texel * vec2( 1.0, 0.0)) * 0.2;\n    lap += sampleAB(uv + texel * vec2( 0.0,-1.0)) * 0.2;\n    lap += sampleAB(uv + texel * vec2( 0.0, 1.0)) * 0.2;\n    lap += sampleAB(uv + texel * vec2(-1.0,-1.0)) * 0.05;\n    lap += sampleAB(uv + texel * vec2( 1.0,-1.0)) * 0.05;\n    lap += sampleAB(uv + texel * vec2(-1.0, 1.0)) * 0.05;\n    lap += sampleAB(uv + texel * vec2( 1.0, 1.0)) * 0.05;\n    lap -= c;\n\n    float reaction = a * b * b;\n    float da = 1.0 * lap.r - reaction + uFeed * (1.0 - a);\n    float db = 0.5 * lap.g + reaction - (uKill + uFeed) * b;\n\n    float a2 = clamp(a + da, 0.0, 1.0);\n    float b2 = clamp(b + db, 0.0, 1.0);\n    fragColor = TDOutputSwizzle(vec4(a2, b2, 0.0, 1.0));\n}\n"
  },
  "preview_description": "Evolving coral / fingerprint-like organic patterns growing and dividing across the frame."
}