AnyToXYTransform.java

package org.poly2tri.transform.coordinate;

/**
 * A transform that aligns given source normal with the XY plane normal [0,0,1]
 * 
 * @author thahlen@gmail.com
 */

public class AnyToXYTransform extends Matrix3Transform {
	/**
	 * Assumes source normal is normalized
	 */
	public AnyToXYTransform(double nx, double ny, double nz) {
		setSourceNormal(nx, ny, nz);
	}

	/**
	 * Assumes source normal is normalized
	 * 
	 * @param nx
	 * @param ny
	 * @param nz
	 */
	public void setSourceNormal(double nx, double ny, double nz) {
		double h, f, c, vx, vy, hvx;

		vx = -ny;
		vy = nx;
		c = nz;

		h = (1 - c) / (1 - c * c);
		hvx = h * vx;
		f = (c < 0) ? -c : c;

		if (f < 1.0 - 1.0E-4) {
			m00 = c + hvx * vx;
			m01 = hvx * vy;
			m02 = -vy;
			m10 = hvx * vy;
			m11 = c + h * vy * vy;
			m12 = vx;
			m20 = vy;
			m21 = -vx;
			m22 = c;
		} else {
			// if "from" and "to" vectors are nearly parallel
			m00 = 1;
			m01 = 0;
			m02 = 0;
			m10 = 0;
			m11 = 1;
			m12 = 0;
			m20 = 0;
			m21 = 0;
			if (c > 0) {
				m22 = 1;
			} else {
				m22 = -1;
			}
		}
	}
}