Rotation Library – 2D, 3D, Quaternion

This is a shader include file that contains a ton of functions for rotation. It also has a quaternion multiplication function, since it’s needed for axis-angle rotation.

It is recommended that you put this code into a gdshaderinc file (Such as “rotate.gdshaderinc”). You can then include it at the top of any shader with “#include ‘”res://path_to_shader.gdshaderinc”.

Shader code

vec3 rotate_x(vec3 vert, float angle) {
	float s = sin(angle);
	float c = cos(angle);

	// [cos - sin, sin + cos]
	return vec3(vert.x, vert.y * c - vert.z * s, vert.y * s + vert.z * c );
}

vec3 rotate_y(vec3 vert, float angle) {
	float s = sin(angle);
	float c = cos(angle);

	// [cos - sin, sin + cos]
	return vec3(vert.x * c - vert.z * s, vert.y, vert.x * s + vert.z * c );
}

vec3 rotate_z(vec3 vert, float angle) {
	float s = sin(angle);
	float c = cos(angle);

	// [cos - sin, sin + cos]
	return vec3(vert.x * c - vert.y * s, vert.x * s + vert.y * c, vert.z);
}

vec4 quat_multiply(vec4 q, vec4 p) {
	float a = q.w, b = q.x, c = q.y, d = q.z;
	float w = p.w, x = p.x, y = p.y, z = p.z;

	return vec4(
		a * x + b * w + c * z - d * y, // i
		a * y - b * z + c * w + d * x, // j
		a * z + b * y - c * x + d * w, // k
	 	a * w - b * x - c * y - d * z // w
	);
}

vec3 rotate(vec3 vert, vec3 axis, float angle) {
	vec4 q;
	
	q.x = axis.x * sin(angle/2.0);
	q.y = axis.y * sin(angle/2.0);
	q.z = axis.z * sin(angle/2.0);
	q.w = cos(angle / 2.0);

	vec4 p = vec4(vert, 0.0);
	
	vec4 q_conj = vec4(-q.xyz, q.w);
	//q /= sqrt(q.x * q.x + q.y * q.y + q.z * q.z + q.w * q.w);
	return quat_multiply(quat_multiply(q, p), q_conj).xyz;
}

vec2 rotate(vec2 vector, float angle) {
	if (angle == 0.0) {
		return vector;
	}
	float sine = sin(angle);
	float cosine = cos(angle);

	return vec2(vector.x * cosine - vector.y * sine, vector.x * sine + vector.y * cosine);
}

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