Pixel-Composer/shaders/sh_sample_points/sh_sample_points.fsh

//
// Simple passthrough fragment shader
//
varying vec2 v_vTexcoord;
varying vec4 v_vColour;

const int attempt = 8;
uniform float seed;
uniform vec2 dimension;

float random (in vec2 st, float _seed) {
    return fract(sin(dot(st.xy, vec2(12.9898, 78.233)) * mod(_seed, 32.156) * 12.588) * 43758.5453123);
}

void main() {
	gl_FragColor = vec4(0.); 
	
	float v = 0.;
	for(int i = 0; i < attempt; i++) {
		float _x = random(vec2(i, 0.) + v_vTexcoord.x, 132.54664 + seed);
		float _y = random(vec2(0., i) + v_vTexcoord.x,  78.29131 + seed);
		float _w = random(vec2( i, i) + v_vTexcoord.x,   8.10684 + seed);
		
		vec4 col = texture2D( gm_BaseTexture, vec2(_x, _y) );
		float br = (col.r + col.g + col.b) / 3. * col.a * _w;
		if(br > v) {
			v = br;
			gl_FragColor = vec4(_x, _y, 0., 1.);
		}
	}
}