// Marco13 for [url]http://www.java-forum.org/allgemeine-java-themen/132049-2d-simulation-individuell-gestalbarer-umgebung.html[/url]
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionListener;
import java.awt.geom.Line2D;
import java.awt.geom.Point2D;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
public class LineReflectionTest
{
public static void main(String[] args)
{
SwingUtilities.invokeLater(new Runnable()
{
public void run()
{
JFrame f = new JFrame();
PaintPanel paintPanel = new PaintPanel();
f.getContentPane().add(paintPanel);
f.setSize(600,600);
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.setVisible(true);
}
});
}
}
class PaintPanel extends JPanel implements MouseMotionListener
{
private Line2D wall;
private Point2D p0;
private Point2D p1;
private Line2D reflected;
public PaintPanel()
{
addMouseMotionListener(this);
wall = new Line2D.Double(50, 50, 300, 500);
p0 = new Point2D.Float(320, 320);
p1 = new Point2D.Float(420, 420);
}
@Override
protected void paintComponent(Graphics gr)
{
super.paintComponent(gr);
Graphics2D g = (Graphics2D)gr;
g.setRenderingHint(
RenderingHints.KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON);
g.setColor(Color.BLACK);
g.draw(wall);
g.setColor(Color.BLUE);
paint(g, p0);
paint(g, p1);
g.draw(new Line2D.Float(p0, p1));
if (reflected != null)
{
g.setColor(Color.RED);
g.draw(reflected);
}
}
private static void paint(Graphics g, Point2D p)
{
int x = (int)p.getX();
int y = (int)p.getY();
g.drawOval(x-2, y-2, 5, 5);
}
@Override
public void mouseDragged(MouseEvent e)
{
}
@Override
public void mouseMoved(MouseEvent e)
{
p1.setLocation(e.getPoint());
reflected = Reflection.computeReflected(new Line2D.Double(p0, p1), wall);
repaint();
}
}
class Reflection
{
public static Line2D computeReflected(Line2D incoming, Line2D wall)
{
Point2D intersection = Intersection.computeIntersectionSegmentSegment(
incoming.getX1(), incoming.getY1(), incoming.getX2(), incoming.getY2(),
wall.getX1(), wall.getY1(), wall.getX2(), wall.getY2());
if (intersection == null)
{
return null;
}
// Wall start- and end point and delta
double wx0 = wall.getX1();
double wy0 = wall.getY1();
double wx1 = wall.getX2();
double wy1 = wall.getY2();
double wdx = wx1 - wx0;
double wdy = wy1 - wy0;
// Incoming start- and end point and delta
double ix0 = incoming.getX1();
double iy0 = incoming.getY1();
double ix1 = incoming.getX2();
double iy1 = incoming.getY2();
double idx = ix1 - ix0;
double idy = iy1 - iy0;
// Compute angle between wall and incoming line
double wLen = Math.sqrt(wdx*wdx+wdy*wdy);
double iLen = Math.sqrt(idx*idx+idy*idy);
double dot = dot(idx/iLen, idy/iLen, wdx/wLen, wdy/wLen);
double angRad = Math.acos(dot);
// Reflected segment
double ix = intersection.getX();
double iy = intersection.getY();
double rdx = incoming.getX2() - ix;
double rdy = incoming.getY2() - iy;
// Compute end point of reflected segment
double ca = Math.cos(-angRad*2);
double sa = Math.sin(-angRad*2);
double rex = ix + ca * rdx - sa * rdy;
double rey = iy + sa * rdx + ca * rdy;
// Return result
Line2D reflectedPart = new Line2D.Double(
ix, iy, rex, rey);
return reflectedPart;
}
private static double dot(double x0, double y0, double x1, double y1)
{
return x0 * x1 + y0 * y1;
}
}
/**
* Utility class for computing intersections between lines and line segments.
*/
class Intersection
{
/**
* Epsilon for floating point computations
*/
private static final double epsilon = 1e-6f;
/**
* Computes the intersection of the specified line segments and returns
* the intersection point, or <code>null</code> if the line segments do
* not intersect.
*
* @param s0x0 x-coordinate of point 0 of line segment 0
* @param s0y0 y-coordinate of point 0 of line segment 0
* @param s0x1 x-coordinate of point 1 of line segment 0
* @param s0y1 y-coordinate of point 1 of line segment 0
* @param s1x0 x-coordinate of point 0 of line segment 1
* @param s1y0 y-coordinate of point 0 of line segment 1
* @param s1x1 x-coordinate of point 1 of line segment 1
* @param s1y1 y-coordinate of point 1 of line segment 1
* @param location Optional location that stores the
* relative location of the intersection point on
* the given line segments
* @return The intersection point, or <code>null</code> if
* there is no intersection.
*/
public static Point2D computeIntersectionSegmentSegment(
double s0x0, double s0y0,
double s0x1, double s0y1,
double s1x0, double s1y0,
double s1x1, double s1y1)
{
Point2D location = new Point2D.Double();
Point2D result = computeIntersectionLineLine(
s0x0, s0y0, s0x1, s0y1, s1x0, s1y0, s1x1, s1y1, location);
if (location.getX() >= 0 && location.getX() <= 1.0 &&
location.getY() >= 0 && location.getY() <= 1.0)
{
return result;
}
return null;
}
/**
* Computes the intersection of the specified lines and returns the
* intersection point, or <code>null</code> if the lines do not
* intersect.
*
* Ported from
* [url]http://www.geometrictools.com/LibMathematics/Intersection/[/url]
* Wm5IntrSegment2Segment2.cpp
*
* @param s0x0 x-coordinate of point 0 of line segment 0
* @param s0y0 y-coordinate of point 0 of line segment 0
* @param s0x1 x-coordinate of point 1 of line segment 0
* @param s0y1 y-coordinate of point 1 of line segment 0
* @param s1x0 x-coordinate of point 0 of line segment 1
* @param s1y0 y-coordinate of point 0 of line segment 1
* @param s1x1 x-coordinate of point 1 of line segment 1
* @param s1y1 y-coordinate of point 1 of line segment 1
* @param location Optional location that stores the
* relative location of the intersection point on
* the given line segments
* @return The intersection point, or <code>null</code> if
* there is no intersection.
*/
public static Point2D computeIntersectionLineLine(
double s0x0, double s0y0,
double s0x1, double s0y1,
double s1x0, double s1y0,
double s1x1, double s1y1,
Point2D location)
{
double dx0 = s0x1 - s0x0;
double dy0 = s0y1 - s0y0;
double dx1 = s1x1 - s1x0;
double dy1 = s1y1 - s1y0;
double len0 = Math.sqrt(dx0*dx0+dy0*dy0);
double len1 = Math.sqrt(dx1*dx1+dy1*dy1);
double dir0x = dx0 / len0;
double dir0y = dy0 / len0;
double dir1x = dx1 / len1;
double dir1y = dy1 / len1;
double c0x = s0x0 + dx0 * 0.5;
double c0y = s0y0 + dy0 * 0.5;
double c1x = s1x0 + dx1 * 0.5;
double c1y = s1y0 + dy1 * 0.5;
double cdx = c1x - c0x;
double cdy = c1y - c0y;
double dot = dotPerp(dir0x, dir0y, dir1x, dir1y);
if (Math.abs(dot) > epsilon)
{
double dot0 = dotPerp(cdx, cdy, dir0x, dir0y);
double dot1 = dotPerp(cdx, cdy, dir1x, dir1y);
double invDot = 1.0/dot;
double s0 = dot1*invDot;
double s1 = dot0*invDot;
if (location != null)
{
double n0 = (s0 / len0) + 0.5;
double n1 = (s1 / len1) + 0.5;
location.setLocation(n0, n1);
}
double x = c0x + s0 * dir0x;
double y = c0y + s0 * dir0y;
return new Point2D.Double(x,y);
}
return null;
}
/**
* Returns the perpendicular dot product, i.e. the length
* of the vector (x0,y0,0)x(x1,y1,0).
*
* @param x0 Coordinate x0
* @param y0 Coordinate y0
* @param x1 Coordinate x1
* @param y1 Coordinate y1
* @return The length of the cross product vector
*/
private static double dotPerp(double x0, double y0, double x1, double y1)
{
return x0*y1 - y0*x1;
}
/**
* Private constructor to prevent instantiation
*/
private Intersection()
{
}
}
Also, dann ist der dort markierte "Einfallswirkel" gesucht. 
