grey-scott reaction-diffusion http://www.karlsims.com/rd.html

reaction-diffusion.frag

#version 150

uniform float time;
uniform vec2 resolution;
uniform vec2 mouse;
uniform vec3 spectrum;

uniform sampler2D texture0;
uniform sampler2D texture1;
uniform sampler2D texture2;
uniform sampler2D texture3;
uniform sampler2D prevFrame;
uniform sampler2D prevPass;
uniform float d_a;
uniform float d_b;
uniform float dt;
uniform float feed;
uniform float kill;

in VertexData
{
    vec4 v_position;
    vec3 v_normal;
    vec2 v_texcoord;
} inData;

out vec4 fragColor;

void main(void)
{
    vec2 uv = vec2(inData.v_texcoord.x, inData.v_texcoord.y);
 
    vec4 old = texture2D(prevFrame, uv);
    float old_a = old.r;
    float old_b = old.b;

    vec4 left = texture2D(prevFrame, uv - vec2(1/resolution.x, 0));
    vec4 right = texture2D(prevFrame, uv + vec2(1/resolution.x, 0));
    vec4 up = texture2D(prevFrame, uv - vec2(0, 1/resolution.y));
    vec4 down = texture2D(prevFrame, uv + vec2(0, 1/resolution.y));

    vec4 left_up = texture2D(prevFrame, uv + vec2(-1/resolution.x, -1/resolution.y));
    vec4 right_up = texture2D(prevFrame, uv + vec2(1/resolution.x, -1/resolution.y));
    vec4 right_down = texture2D(prevFrame, uv + vec2(1/resolution.x, 1/resolution.y));
    vec4 left_down = texture2D(prevFrame, uv + vec2(-1/resolution.x, 1/resolution.y));
    
    vec4 laplace1 = left/4.0 + right/4.0 + up/4.0 + down/4.0;
    
    vec4 laplace = left/5.0 + right/5.0 + up/5.0 + down/5.0 + left_up/20.0 + right_up/20.0 + right_down/20.0 + left_down/20.0 ;

    float laplace_a = laplace.r - old_a;
    float laplace_b = laplace.b - old_b;
    
 
    float dt_ = dt * 1;
    float a = old_a + (d_a * laplace_a - old_a * old_b * old_b + feed * (1 - old_a)) * dt_;

    float b = old_b + (d_b * laplace_b + old_a * old_b * old_b - ((kill + feed) * old_b)) * dt_;

    if (abs(uv.x - mouse.x) < 0.005 && abs(1 - uv.y - mouse.y) < 0.01) {
        fragColor = vec4(1,0,1,0);
    } else {
        fragColor = vec4(a, 0, b, 0);
    }
    
}