minetest/client/shaders/the_darkness_of_light/opengl_fragment.glsl

uniform sampler2D myTexture;

void main (void)
{
    vec4 col = texture2D(myTexture, vec2(gl_TexCoord[0]));
    col *= gl_Color;
    gl_FragColor = vec4(1.0-col.r, 1.0-col.g, 1.0-col.b, 1.0);
}