Pixel-Composer/shaders/sh_texture_atlas/sh_texture_atlas.fsh

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

uniform vec2 dimension;
uniform float size;
#define TAU 6.283185307179586

void main() {
	vec2 pixelPosition = v_vTexcoord * dimension;
	vec4 point = texture2D( gm_BaseTexture, v_vTexcoord );
	float tau_div = TAU / 64.;
	gl_FragColor = point;
	
	if(point.a < 1.) {
		for(float i = 1.; i < size; i++) {
			for(float j = 0.; j < 64.; j++) {
				float ang = j * tau_div;
				vec2 pxs = (pixelPosition + vec2( cos(ang) * i,  sin(ang) * i)) / dimension;
				if(pxs.x < 0. || pxs.x > 1. || pxs.y < 0. || pxs.y > 1.) continue;
				
				vec4 sam = texture2D( gm_BaseTexture, pxs );
				if(sam.a > 0.) {
					gl_FragColor = vec4(sam.rgb, 1.);
					i = size;
					break;
				}
			}
		}
	}
}