Rainbow tail.shader

shader_type canvas_item;
render_mode unshaded, blend_add;

vec3 hsv2rgb(vec3 c) {
	vec4 K = vec4(1.0, 2.0 / 3.0, 1.0 / 3.0, 3.0);
	vec3 p = abs(fract(c.xxx + K.xyz) * 6.0 - K.www);
	return c.z * mix(K.xxx, clamp(p - K.xxx, 0.0, 1.0), c.y);
}

void vertex() {
	float time = fract(TIME / 6.28) * 6.28;
	
	VERTEX.x += UV.x * sin(time * 15.0 + UV.y * 20.0) * 10.0;
	VERTEX.x -= UV.x * cos(time * 20.0 + UV.y * 15.0) * 5.0;
}

void fragment() {
	float tail_center = abs(UV.y - 0.5);
	
	vec3 rainbow = vec3(0.0, 0.5, 2.0); // hsv
	rainbow.x += tail_center - fract(TIME / 2.0) * 2.0;
	rainbow = hsv2rgb(rainbow);
	
	COLOR = vec4(rainbow, 2.0 * (0.5 - tail_center));
}