Pixel-Composer/shaders/sh_atlas/sh_atlas.fsh

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

uniform vec2  dimension;

#define TAU 6.283185307179586
#define angle_sample 4.
#define distance_sample 64.

void main() {
	vec2 pixelPosition = v_vTexcoord * dimension;
	vec4 col = texture2D( gm_BaseTexture, v_vTexcoord );
	vec2 scale = dimension / distance_sample;
	float min_dist = 1.;
    gl_FragColor = col;
	
	if(col.a == 1.) 
		return;
	
	for(float i = 1.; i <= distance_sample; i++) {
		float base = 1.;
		float top  = 0.;
		for(float j = 0.; j <= 64.; j++) {
			float ang = top / base * TAU;
			top += 2.;
			if(top >= base) {
				top = 1.;
				base *= 2.;
			}
			
			vec2  pxs = (pixelPosition + vec2( cos(ang),  sin(ang)) * scale * i) / dimension;
			vec4  sam = texture2D( gm_BaseTexture, pxs );
				
			if(sam.a < 1.) continue;
			
			gl_FragColor = sam;
			return;
		}
	}
}