shader_type canvas_item;

uniform vec4 color = vec4(1.0f, 1.0f, 1.0f, 1.0f);
uniform float thickness = 0.1f;
uniform float rotation_speed = 1.0f;

vec2 rotate(vec2 v, float angle) {
	return vec2(
		v.x * cos(angle) + v.y * sin(angle),
		v.x * sin(angle) - v.y * cos(angle)
	);
}

void fragment() {
	float distance_from_centre = distance(vec2(0.5f, 0.5f), UV.xy) * 2.0f;
	float inner_circle = smoothstep((1.0f - (SCREEN_PIXEL_SIZE.x * 96.0f)) - thickness, 1.0f - thickness, distance_from_centre);
	float outer_circle = 1.0f - smoothstep((1.0f - (SCREEN_PIXEL_SIZE.x * 96.0f)), 1.0f, distance_from_centre);
	float throbber_edge = outer_circle * inner_circle;

	vec2 relative = rotate(UV - vec2(0.5f, 0.5f), TIME * rotation_speed);
	float angle = atan(relative.x, relative.y);

	float t = (angle + PI) / 2.0f / PI;
	COLOR *= throbber_edge * mix(vec4(color.rgb, 0.0f), vec4(color.rgb, 1.0f), t);
}