12.4 Transforms

The AffineTransform class can transform a shape (or coordinate system) by translating, scaling, rotating, or shearing it, using any combination of these individual transformation types. Figure 12-5 illustrates the results of various types of coordinate-system transformations on the appearance of one shape, drawn multiple times. Example 12-7 shows the Java code that generates the figure.

Figure 12-5. Transformed shapes

An affine transformation is a linear transformation that has two important properties: all straight lines remain straight, and all parallel lines remain parallel. The AffineTransform class can perform a great variety of transformations, but it can't produce nonlinear effects, such as distorting a figure as through a fisheye lens. That kind of effect can be achieved only with image-processing techniques. For a further discussion of transformations and the linear algebra behind the AffineTransform class, see Chapter 4 of Java Foundation Classes in a Nutshell.

Example 12-7. Transforms.java

package je3.graphics; import java.awt.*; import java.awt.geom.*; /** A demonstration of Java2D transformations */ public class Transforms implements GraphicsExample {     public String getName( ) { return "Transforms"; } // From GraphicsExample     public int getWidth( ) { return 750; }            // From GraphicsExample     public int getHeight( ) { return 250; }           // From GraphicsExample     Shape shape;                   // The shape to draw     AffineTransform[  ] transforms;  // The ways to transform it     String[  ] transformLabels;      // Labels for each transform     /**       * This constructor sets up the Shape and AffineTransform objects we need      **/     public Transforms( ) {         GeneralPath path = new GeneralPath( );   // Create a shape to draw         path.append(new Line2D.Float(0.0f, 0.0f, 0.0f, 100.0f), false);         path.append(new Line2D.Float(-10.0f, 50.0f, 10.0f, 50.0f), false);         path.append(new Polygon(new int[  ] { -5, 0, 5 },                                 new int[  ] { 5, 0, 5 }, 3), false);         this.shape = path;  // Remember this shape         // Set up some transforms to alter the shape         this.transforms = new AffineTransform[6];         // 1) the identity transform         transforms[0] = new AffineTransform( );           // 2) A scale tranform: 3/4 size         transforms[1] = AffineTransform.getScaleInstance(0.75, 0.75);         // 3) A shearing transform         transforms[2] = AffineTransform.getShearInstance(-0.4, 0.0);         // 4) A 30 degree clockwise rotation about the origin of the shape         transforms[3] = AffineTransform.getRotateInstance(Math.PI*2/12);         // 5) A 180 degree rotation about the midpoint of the shape         transforms[4] = AffineTransform.getRotateInstance(Math.PI, 0.0, 50.0);         // 6) A combination transform         transforms[5] = AffineTransform.getScaleInstance(0.5, 1.5);         transforms[5].shear(0.0, 0.4);         transforms[5].rotate(Math.PI/2, 0.0, 50.0);  // 90 degrees         // Define names for the transforms         transformLabels = new String[  ] {             "identity", "scale", "shear", "rotate", "rotate", "combo"         };     }     /** Draw the defined shape and label, using each transform */     public void draw(Graphics2D g, Component c) {         // Define basic drawing attributes         g.setColor(Color.black);                                   // black         g.setStroke(new BasicStroke(2.0f, BasicStroke.CAP_SQUARE,  // 2-pixel                                     BasicStroke.JOIN_BEVEL));         g.setRenderingHint(RenderingHints.KEY_ANTIALIASING,        // antialias                            RenderingHints.VALUE_ANTIALIAS_ON);         // Now draw the shape once using each of the transforms we've defined         for(int i = 0; i < transforms.length; i++) {             AffineTransform save = g.getTransform( );    // save current state             g.translate(i*125 + 50, 50);                // move origin             g.transform(transforms[i]);                 // apply transform             g.draw(shape);                              // draw shape             g.drawString(transformLabels[i], -25, 125); // draw label             g.drawRect(-40, -10, 80, 150);              // draw box             g.setTransform(save);                       // restore transform         }     } }