#define SAMPLES 8
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uniform float delta;
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uniform float sigma;
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uniform float direction; // 0.0 for x direction, 1.0 for y direction
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uniform sampler2D colorTexture;
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#ifdef USE_STEP_SIZE
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uniform float stepSize;
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#else
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uniform vec2 step;
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#endif
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varying vec2 v_textureCoordinates;
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// Incremental Computation of the Gaussian:
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// https://developer.nvidia.com/gpugems/GPUGems3/gpugems3_ch40.html
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void main()
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{
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vec2 st = v_textureCoordinates;
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vec2 dir = vec2(1.0 - direction, direction);
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#ifdef USE_STEP_SIZE
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vec2 step = vec2(stepSize * (czm_pixelRatio / czm_viewport.zw));
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#else
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vec2 step = step;
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#endif
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vec3 g;
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g.x = 1.0 / (sqrt(czm_twoPi) * sigma);
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g.y = exp((-0.5 * delta * delta) / (sigma * sigma));
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g.z = g.y * g.y;
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vec4 result = texture2D(colorTexture, st) * g.x;
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for (int i = 1; i < SAMPLES; ++i)
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{
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g.xy *= g.yz;
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vec2 offset = float(i) * dir * step;
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result += texture2D(colorTexture, st - offset) * g.x;
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result += texture2D(colorTexture, st + offset) * g.x;
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}
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gl_FragColor = result;
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}
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