Mindustry/core/assets/shaders/blockpreview.fragment

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

uniform sampler2D u_texture;

uniform vec4 u_color;
uniform vec2 u_texsize;
uniform vec2 u_uv;
uniform vec2 u_uv2;

varying vec4 v_color;
varying vec2 v_texCoord;

bool id(vec2 coords, vec4 base){
    vec4 target = texture2D(u_texture, coords);
    return  target.a < 0.1 || (coords.x < u_uv.x || coords.y < u_uv.y || coords.x > u_uv2.x || coords.y > u_uv2.y);
}

bool cont(vec2 T, vec2 v){
    float step = 1.0;
    vec4 base = texture2D(u_texture, T);
    return base.a > 0.1 &&
           		(id(T + vec2(0, step) * v, base) || id(T + vec2(0, -step) * v, base) ||
           		id(T + vec2(step, 0) * v, base) || id(T + vec2(-step, 0) * v, base));
}

void main() {
	vec2 t = v_texCoord.xy;
	vec2 v = vec2(1.0/u_texsize.x, 1.0/u_texsize.y);
	vec2 coord = t / v;
	vec4 c = texture2D(u_texture, t);

	if(cont(t, v) ){
		gl_FragColor = u_color;
	}else{
		gl_FragColor = vec4(0.0);
	}
}