Open GL ES杂色实现

抄了一个杂色

///  3 out, 3 in...
vec3 hash33(vec3 p3)
{
    p3 = fract(p3 * vec3(.1031, .1030, .0973));
    p3 += dot(p3, p3.yxz+33.33);
    return fract((p3.xxy + p3.yxx)*p3.zyx);

}


#define ITERATIONS 6
//----------------------------------------------------------------------------------------
void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
    vec2 position = fragCoord.xy;
    vec2 uv = fragCoord.xy / iResolution.xy;

    vec3 a = vec3(0.0), b = a;
    for (int t = 0; t < ITERATIONS; t++)
    {
        float v = float(t+1)*.132;
        vec3 pos = vec3(position, .3) +   500. + 50.0;
        a += hash33(pos);
    }
   // vec3 col = vec3(mix(b, a, 1.0));
   
   vec3 xx = vec3(a.r);
    
    fragColor = vec4(xx, 1.0);
}