Godot sky shader that displays the moon based on light direction

moon_sky.gdshader

shader_type sky;

uniform sampler2D moon_texture:source_color, repeat_disable;

// updirection of moon texture will try to align with this
uniform vec3 north = vec3(0, 0, -1);

void sky() {
	vec3 light_dir = normalize(-LIGHT0_DIRECTION);
	vec3 side_dir = normalize(cross(light_dir, north));
	vec3 up_dir = normalize(cross(light_dir, side_dir));

	vec3 diff = normalize(EYEDIR) + light_dir; //difference between view dir and moon dir

	vec2 moon_uv = (vec2(dot(side_dir, diff), dot(up_dir, diff)) * 5.0) + 0.5;
	vec4 moon = texture(moon_texture, moon_uv);
	moon.rgb = moon.rgb * clamp(dot(normalize(EYEDIR), light_dir) * -2.0, 0.0, 1.0); // make sure only one moon

	COLOR = vec3(0, 0, 0) + moon.rgb;
}