gistfile1.txt

float rand(vec3 co)
{
 return fract(sin( dot(co.xyz ,vec3(12.9898,78.233,45.5432) )) * 43758.5453);
}


void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
    vec2 squares = vec2(80.0,60.0);
	vec2 uv = fragCoord.xy / iResolution.xy;
    float r = mod(iGlobalTime, 3.0) / 3.0;
   	vec2 squareP = floor(uv * squares);
    float b = abs(rand(vec3(squareP,1.0)));
	float dim;
    if (b < r) {
    	dim = 1.0;
    } else { 
    	dim = 0.0;
    }
           
    
    fragColor = texture2D(iChannel0,uv)*dim + texture2D(iChannel1,uv)*(1.0-dim);

}