mirror of
https://github.com/patriciogonzalezvivo/thebookofshaders
synced 2024-11-09 19:10:24 +00:00
58 lines
1.4 KiB
GLSL
Executable File
58 lines
1.4 KiB
GLSL
Executable File
// Author @patriciogv - 2015
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#ifdef GL_ES
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precision mediump float;
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#endif
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uniform sampler2D u_tex0;
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uniform vec2 u_resolution;
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uniform float u_time;
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// Permutation polynomial: (34x^2 + x) mod 289
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vec4 permute(vec4 x) {
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return mod((34.0 * x + 1.0) * x, 289.0);
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}
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vec2 cellular2x2(vec2 P) {
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#define K 0.142857142857 // 1/7
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#define K2 0.0714285714285 // K/2
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#define jitter 0.8 // jitter 1.0 makes F1 wrong more often
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vec2 Pi = mod(floor(P), 289.0);
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vec2 Pf = fract(P);
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vec4 Pfx = Pf.x + vec4(-0.5, -1.5, -0.5, -1.5);
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vec4 Pfy = Pf.y + vec4(-0.5, -0.5, -1.5, -1.5);
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vec4 p = permute(Pi.x + vec4(0.0, 1.0, 0.0, 1.0));
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p = permute(p + Pi.y + vec4(0.0, 0.0, 1.0, 1.0));
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vec4 ox = mod(p, 7.0)*K+K2;
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vec4 oy = mod(floor(p*K),7.0)*K+K2;
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vec4 dx = Pfx + jitter*ox;
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vec4 dy = Pfy + jitter*oy;
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vec4 d = dx * dx + dy * dy; // d11, d12, d21 and d22, squared
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// Sort out the two smallest distances
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#if 0
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// Cheat and pick only F1
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d.xy = min(d.xy, d.zw);
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d.x = min(d.x, d.y);
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return d.xx; // F1 duplicated, F2 not computed
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#else
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// Do it right and find both F1 and F2
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d.xy = (d.x < d.y) ? d.xy : d.yx; // Swap if smaller
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d.xz = (d.x < d.z) ? d.xz : d.zx;
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d.xw = (d.x < d.w) ? d.xw : d.wx;
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d.y = min(d.y, d.z);
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d.y = min(d.y, d.w);
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return sqrt(d.xy);
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#endif
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}
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void main(void) {
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vec2 st = gl_FragCoord.xy/u_resolution.xy;
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vec2 F = cellular2x2(st*100.);
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float pct = texture2D(u_tex0,st).r;
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pct = step(1.-pct,F.x);
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gl_FragColor = vec4(vec3(pct), 1.0);
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}
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