- Applets : 3D : Tetraeder 2 -

Ein rotierender Tetraeder als Java-Applet.

Tetraeder2.java

import java.awt.*;
import java.applet.*;

public class Tetraeder2 extends Applet {

    // 4 Eckpunkte 1-4
    // mit je 3 Koordinaten 1,2,3
    double p[][] = new double[5][4];

    int x=1, y=2, z=3;

    public void init() {
        setBackground(new Color(255,255,255));

        // Tetraeder-Höhe
        double th = Math.sqrt(2/3.0)*300;

        // Höhe des Tetraeder-Mittelpunkts
        double tm = Math.sqrt(1/24.0)*300;

        // Strecke Ecke-Mittelpunkt eines Dreiecks
        double em = Math.sqrt(1/3.0)*300;

        // Strecke Seite-Mittelpunkt eines Dreiecks
        double sm = Math.sqrt(1/12.0)*300;

        // 4 Eckpunkte im lokalen Tetraeder-Koordinatensystem
        // Nullpunkt = Mittelpunkt
        p[1][x] = -150; p[1][y] = -tm;    p[1][z] = +sm;
        p[2][x] =    0; p[2][y] = -tm;    p[2][z] = -em;
        p[3][x] = +150; p[3][y] = -tm;    p[3][z] = +sm;
        p[4][x] =    0; p[4][y] = +th-tm; p[4][z] =   0;

        //         4
        //       / | \
        //      /  |  \
        //     /   |   \
        //    1 - -|- - 3
        //      `  2  ´

        // y-Werte spiegeln
        for (int i=1;i<5;i++) {
            p[i][y] = -p[i][y];
        }
    }

    // Rotationswinkel in rad
    double angle_x = 0.01;
    double angle_y = 0.007;
    double angle_z = 0.001;

    Image buffer;
    Graphics2D gBuffer;

    int w = 200; // ->  Weltkoordinaten

    public void paint(Graphics g) {

        // Double-Buffering
        if (buffer==null) {
            buffer=createImage(this.getSize().width, this.getSize().height);
            gBuffer=(Graphics2D)buffer.getGraphics();
        }
        gBuffer.clearRect(0,0,this.getSize().width, this.getSize().height);

        // Antialiasing
        gBuffer.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
            RenderingHints.VALUE_ANTIALIAS_ON);

        // Kreuzprodukt der eine Fläche aufspannenden Vektoren bilden
        // Wenn Betrag der z-Koordinate positiv: Fläche anzeigen

        if((p[1][x]-p[2][x])*(p[3][y]-p[2][y])-(p[1][y]-p[2][y])*(p[3][x]-p[2][x]) > 0) {
            // |2->1 x 2->3| > 0
            int xCoords123[] = {(int)(p[1][x])+w,(int)(p[2][x])+w,(int)(p[3][x])+w};
            int yCoords123[] = {(int)(p[1][y])+w,(int)(p[2][y])+w,(int)(p[3][y])+w};
            gBuffer.setColor(new Color(255,0,0));
            gBuffer.fillPolygon(new Polygon(xCoords123,yCoords123,3));
        }
        if((p[3][x]-p[2][x])*(p[4][y]-p[2][y])-(p[3][y]-p[2][y])*(p[4][x]-p[2][x]) > 0) {
            // |2->3 x 2->4| > 0
            int xCoords324[] = {(int)(p[3][x])+w,(int)(p[2][x])+w,(int)(p[4][x])+w};
            int yCoords324[] = {(int)(p[3][y])+w,(int)(p[2][y])+w,(int)(p[4][y])+w};
            gBuffer.setColor(new Color(0,255,0));
            gBuffer.fillPolygon(new Polygon(xCoords324,yCoords324,3));
        }
        if((p[4][x]-p[2][x])*(p[1][y]-p[2][y])-(p[4][y]-p[2][y])*(p[1][x]-p[2][x]) > 0) {
            // |2->4 x 2->1| > 0
            int xCoords421[] = {(int)(p[4][x])+w,(int)(p[2][x])+w,(int)(p[1][x])+w};
            int yCoords421[] = {(int)(p[4][y])+w,(int)(p[2][y])+w,(int)(p[1][y])+w};
            gBuffer.setColor(new Color(0,0,255));
            gBuffer.fillPolygon(new Polygon(xCoords421,yCoords421,3));
        }
        if((p[3][x]-p[4][x])*(p[1][y]-p[4][y])-(p[3][y]-p[4][y])*(p[1][x]-p[4][x]) > 0) {
            // |4->3 x 4->1| > 0
            int xCoords341[] = {(int)(p[3][x])+w,(int)(p[4][x])+w,(int)(p[1][x])+w};
            int yCoords341[] = {(int)(p[3][y])+w,(int)(p[4][y])+w,(int)(p[1][y])+w};
            gBuffer.setColor(new Color(255,255,0));
            gBuffer.fillPolygon(new Polygon(xCoords341,yCoords341,3));
        }

        g.drawImage (buffer, 0, 0, this);

        // Verzögerung
        try {Thread.sleep(10);}
        catch (InterruptedException e) {}

        double px, py, pz;

        for (int i=1;i<5;i++) {

            px = p[i][x];
            py = p[i][y];
            pz = p[i][z];

            // Rotation um x-Achse
            p[i][y] = py*Math.cos(angle_x)-pz*Math.sin(angle_x);
            p[i][z] = py*Math.sin(angle_x)+pz*Math.cos(angle_x);

            py = p[i][y];
            pz = p[i][z];

            // Rotation um y-Achse
            p[i][x] = px*Math.cos(angle_y)+pz*Math.sin(angle_y);
            p[i][z] =-px*Math.sin(angle_y)+pz*Math.cos(angle_y);

            px = p[i][x];

            // Rotation um z-Achse
            p[i][x] = px*Math.cos(angle_z)-py*Math.sin(angle_z);
            p[i][y] = py*Math.cos(angle_z)+px*Math.sin(angle_z);
        }

        repaint();
    }

    public void update(Graphics g) {paint(g);}
}

Download  Tetraeder_2.zip (Applet und Code, ca. 3,5 kb)

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