Applet Tutorial: 3D Graphics
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### Exercise 11: 3D Graphics

The source code:

```import java.applet.*;
import java.awt.*;
import java.awt.event.*;
import java.lang.Math;

class Point3D {
public int x, y, z;
public Point3D( int X, int Y, int Z ) {
x = X;  y = Y;  z = Z;
}
}

class Edge {
public int a, b;
public Edge( int A, int B ) {
a = A;  b = B;
}
}

public class WireframeViewer extends Applet
implements MouseListener, MouseMotionListener {

int width, height;
int mx, my;  // the most recently recorded mouse coordinates

Image backbuffer;
Graphics backg;

int azimuth = 35, elevation = 30;

Point3D[] vertices;
Edge[] edges;

public void init() {
width = getSize().width;
height = getSize().height;

vertices = new Point3D[ 8 ];
vertices[0] = new Point3D( -1, -1, -1 );
vertices[1] = new Point3D( -1, -1,  1 );
vertices[2] = new Point3D( -1,  1, -1 );
vertices[3] = new Point3D( -1,  1,  1 );
vertices[4] = new Point3D(  1, -1, -1 );
vertices[5] = new Point3D(  1, -1,  1 );
vertices[6] = new Point3D(  1,  1, -1 );
vertices[7] = new Point3D(  1,  1,  1 );

edges = new Edge[ 12 ];
edges[ 0] = new Edge( 0, 1 );
edges[ 1] = new Edge( 0, 2 );
edges[ 2] = new Edge( 0, 4 );
edges[ 3] = new Edge( 1, 3 );
edges[ 4] = new Edge( 1, 5 );
edges[ 5] = new Edge( 2, 3 );
edges[ 6] = new Edge( 2, 6 );
edges[ 7] = new Edge( 3, 7 );
edges[ 8] = new Edge( 4, 5 );
edges[ 9] = new Edge( 4, 6 );
edges[10] = new Edge( 5, 7 );
edges[11] = new Edge( 6, 7 );

backbuffer = createImage( width, height );
backg = backbuffer.getGraphics();
drawWireframe( backg );

}

void drawWireframe( Graphics g ) {

// compute coefficients for the projection
double theta = Math.PI * azimuth / 180.0;
double phi = Math.PI * elevation / 180.0;
float cosT = (float)Math.cos( theta ), sinT = (float)Math.sin( theta );
float cosP = (float)Math.cos( phi ), sinP = (float)Math.sin( phi );
float cosTcosP = cosT*cosP, cosTsinP = cosT*sinP,
sinTcosP = sinT*cosP, sinTsinP = sinT*sinP;

// project vertices onto the 2D viewport
Point[] points;
points = new Point[ vertices.length ];
int j;
int scaleFactor = width/4;
float near = 3;  // distance from eye to near plane
float nearToObj = 1.5f;  // distance from near plane to center of object
for ( j = 0; j < vertices.length; ++j ) {
int x0 = vertices[j].x;
int y0 = vertices[j].y;
int z0 = vertices[j].z;

// compute an orthographic projection
float x1 = cosT*x0 + sinT*z0;
float y1 = -sinTsinP*x0 + cosP*y0 + cosTsinP*z0;

// now adjust things to get a perspective projection
float z1 = cosTcosP*z0 - sinTcosP*x0 - sinP*y0;
x1 = x1*near/(z1+near+nearToObj);
y1 = y1*near/(z1+near+nearToObj);

// the 0.5 is to round off when converting to int
points[j] = new Point(
(int)(width/2 + scaleFactor*x1 + 0.5),
(int)(height/2 - scaleFactor*y1 + 0.5)
);
}

// draw the wireframe
g.setColor( Color.black );
g.fillRect( 0, 0, width, height );
g.setColor( Color.white );
for ( j = 0; j < edges.length; ++j ) {
g.drawLine(
points[ edges[j].a ].x, points[ edges[j].a ].y,
points[ edges[j].b ].x, points[ edges[j].b ].y
);
}
}

public void mouseEntered( MouseEvent e ) { }
public void mouseExited( MouseEvent e ) { }
public void mouseClicked( MouseEvent e ) { }
public void mousePressed( MouseEvent e ) {
mx = e.getX();
my = e.getY();
e.consume();
}
public void mouseReleased( MouseEvent e ) { }
public void mouseMoved( MouseEvent e ) { }
public void mouseDragged( MouseEvent e ) {
// get the latest mouse position
int new_mx = e.getX();
int new_my = e.getY();

// adjust angles according to the distance travelled by the mouse
// since the last event
azimuth -= new_mx - mx;
elevation += new_my - my;

// update the backbuffer
drawWireframe( backg );

// update our data
mx = new_mx;
my = new_my;

repaint();
e.consume();
}

public void update( Graphics g ) {
g.drawImage( backbuffer, 0, 0, this );
showStatus("Elev: "+elevation+" deg, Azim: "+azimuth+" deg");
}

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

```

Notice that the compiler generates 3 .class files: one for each of the classes defined.

Click and drag on the applet to rotate the cube.

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