webgcode

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// expected #define: int gridX, gridY
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highp float encodingFactor = (exp2(24.0) - 1.0) / exp2(24.0);
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const vec2 gridSize = vec2(gridX, gridY);
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uniform sampler2D modelHeight;
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//we will scale the result by that value, it helps for chaining renderers
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uniform float scale;
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highp float DecodeFloatRGB(vec3 rgb) {
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    return dot(rgb, vec3(1.0, 1.0 / 255.0, 1.0 / 255.0 / 255.0)) / encodingFactor;
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}
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highp vec3 EncodeFloatRGB(highp float v) {
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    highp vec3 enc = fract(vec3(1.0, 255.0, 255.0 * 255.0) * encodingFactor * v);
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    enc -= enc.yzz * vec3(1.0 / 255.0, 1.0 / 255.0, 0.0);
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    return enc;
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}
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vec3 FakeEncodeFloatRGB(highp float v) {
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    return vec3(v, 0.0, 0.0);
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}
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highp float FakeDecodeFloatRGB(vec3 rgb) {
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    return rgb.r;
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}
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float readValue(int dx,int dy) {
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    return FakeDecodeFloatRGB(texture2D(modelHeight, vec2(float(dx), float(dy)) / gridSize).rgb);
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}
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void main() {
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    float maxValue = readValue(0, 0);
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    for(int i = 0; i < gridX; i++)
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        for(int j = 0; j < gridY; j++)
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            maxValue = max(maxValue, readValue(i, j));
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    gl_FragColor = vec4(FakeEncodeFloatRGB(maxValue * scale), 1.0);
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}