Mindustry/core/assets/shaders/outline.fragment

#ifdef GL_ES
precision mediump float;
precision mediump int;
#endif

#define SPACE 1.0
#define RADIUS 3.0

uniform sampler2D u_texture;

uniform vec4 u_color;
uniform vec2 u_texsize;
uniform float u_scl;

varying vec4 v_color;
varying vec2 v_texCoord;

void main() {
	vec2 v = vec2(1.0/u_texsize.x, 1.0/u_texsize.y);

	vec4 c = texture2D(u_texture, v_texCoord.xy);
	float spacing = SPACE * u_scl;

	if(c.a >= 0.001){
	    gl_FragColor = c * v_color;
	}else{
        for(float cx = -RADIUS; cx <= RADIUS; cx ++){
            for(float cy = -RADIUS; cy <= RADIUS; cy ++){
                if(texture2D(u_texture, v_texCoord.xy + vec2(cx, cy) * v * spacing).a >= 0.001){
                    gl_FragColor = u_color;
                    break;
                }
            }
        }
	}
}