shader_type canvas_item;

uniform vec4 bottom_color: source_color = vec4(1.0);
uniform vec4 top_color: source_color = vec4(vec3(0.0), 1.0);

uniform sampler2D tex;
uniform int layer_count: hint_range(2, 80, 1);
uniform float time_scale: hint_range(0.0, 1.0) = 0.2;
uniform float base_intensity: hint_range(0.0, 1.0) = 0.5;
uniform float size: hint_range(0.00001, 1.0) = 0.1;


vec4 lerp(vec4 a, vec4 b, float w) {
	return a + w * (b - a);
}


float fmod(float x, float y) {
	return x - floor(x / y) * y;
}


float rand(float n){return fract(sin(n) * 43758.5453123);}


bool cloud_layer(float x, float y, float h) {
	return y - sqrt((1.0 - pow(y - h, 2.0))) * base_intensity * texture(tex, vec2(fmod(x / size + rand(h), 1.0), fmod(y / size - TIME * time_scale, 1.0))).r < h;
}


void fragment() {
	float y = 1.0 - UV.y;

	for (int i = 0; i < layer_count; i++) {
		float h = float(i) / float(layer_count - 1);
		if (cloud_layer(UV.x, y, h)) {
			COLOR = lerp(bottom_color, top_color, h);
			break;
		}
	}
}