Mindustry/core/assets/shaders/fog.frag

uniform sampler2D u_texture;

varying vec4 v_color;
varying vec2 v_texCoord;

void main(){
	vec4 color = texture2D(u_texture, v_texCoord.xy);
	gl_FragColor = vec4(0.0, 0.0, 0.0, 1.0 - color.r);
}