thebookofshaders/12/2d-fbm.frag

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#ifdef GL_ES
precision mediump float;
#endif
uniform vec2 u_resolution;
uniform vec2 u_mouse;
uniform float u_time;
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float random (in vec2 st) {
return fract(sin(dot(st.xy,
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vec2(12.9898,78.233)))*
43758.5453123);
}
// Based on Morgan McGuire @morgan3d
// https://www.shadertoy.com/view/4dS3Wd
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float noise (in vec2 st) {
vec2 i = floor(st);
vec2 f = fract(st);
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// Four corners in 2D of a tile
float a = random(i);
float b = random(i + vec2(1.0, 0.0));
float c = random(i + vec2(0.0, 1.0));
float d = random(i + vec2(1.0, 1.0));
vec2 u = f * f * (3.0 - 2.0 * f);
return mix(a, b, u.x) +
(c - a)* u.y * (1.0 - u.x) +
(d - b) * u.x * u.y;
}
#define NUM_OCTAVES 5
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float fbm ( in vec2 st) {
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float v = 0.0;
float a = 0.5;
vec2 shift = vec2(100.0);
// Rotate to reduce axial bias
mat2 rot = mat2(cos(0.5), sin(0.5),
-sin(0.5), cos(0.50));
for (int i = 0; i < NUM_OCTAVES; ++i) {
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v += a * noise(st);
st = rot * st * 2.0 + shift;
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a *= 0.5;
}
return v;
}
void main() {
vec2 st = gl_FragCoord.xy/u_resolution.xy;
st.x *= u_resolution.x/u_resolution.y;
vec3 color = vec3(0.0);
float noise = noise(st*3.0);
float fractal = fbm(st*3.0);
color = vec3(mix(noise,fractal,abs(sin(u_time))));
gl_FragColor = vec4(color,1.0);
}