Geom.java

package husacct.graphics.domain.util;

import java.awt.geom.Point2D;

public class Geom {
	
	/**
	 * http://stackoverflow.com/questions/2676719/calculating-the-angle-between-
	 * the-line-defined-by-two-points
	 */
	public static double getAngle(Point2D.Double point1, Point2D.Double point2) {
		double dx = point1.x - point2.x;
		// Minus to correct for coord re-mapping
		double dy = -(point1.y - point2.y);
		
		double inRads = Math.atan2(dy, dx);
		
		// We need to map to coord system when 0 degree is at 3 O'clock, 270 at
		// 12 O'clock
		if (inRads < 0) inRads = Math.abs(inRads);
		else
			inRads = 2 * Math.PI - inRads;
		
		return Math.toDegrees(inRads);
	}
	
	public static Point2D.Double getPointMovementFromLineAngle(
			Point2D.Double pointStart, Point2D.Double pointEnd, double movement) {
		double width;
		if (pointStart.x > pointEnd.x) width = pointStart.x - pointEnd.x;
		else
			width = pointEnd.x - pointStart.x;
		
		double height;
		if (pointStart.y > pointEnd.y) height = pointStart.y - pointEnd.y;
		else
			height = pointEnd.y - pointStart.y;
		
		double diffX = width / (width + height);
		double diffY = height / (width + height);
		
		double movementX = 0;
		double movementY = 0;
		
		double angle = getAngle(pointStart, pointEnd);
		if (angle < 90 || angle > 180 && angle < 270) {
			movementX += diffY * movement;
			movementY -= diffX * movement;
		} else {
			movementX += diffY * movement;
			movementY += diffX * movement;
		}
		
		return new Point2D.Double(movementX, movementY);
	}
}