shader3/res/shader/fullscreenquad_erosion.fs

varying vec2 V_Texcoord;

uniform sampler2D U_MainTexture;

void main()
{
	vec4 minValue = vec4(1.0);
	int coreSize = 6;
	int halfCoreSize = coreSize / 2;
	float texelOffset = 1/100.0;

	for(int y=0; y<coreSize; y++){
		for(int x=0; x<coreSize; x++){
			vec4 color = texture2D(U_MainTexture, V_Texcoord+vec2((-halfCoreSize+x)*texelOffset, (-halfCoreSize+y)*texelOffset));
			minValue = min(minValue,color);
		}
	}

	gl_FragColor=minValue;
}