Name: bb33257 Date: 03/16/99


The following program displays two Images. One was produced
with a clipped Graphics; the other with a translated and clipped
Graphics. The Images should be identical but they aren't. It
looks like clipping is applied to the wrong portion of the Image.

import java.awt.event.*;
import java.awt.*;
import java.awt.geom.Rectangle2D;

/**
 * This test exposes a bug in JDK 1.2. If you get a Graphics from an
 * Image, translate the Graphics and then set clipping on the Graphics,
 * the wrong area of the graphics gets clipped.
 *
 * The strategy used in this test is to translate a Graphics by (-dx, -dy),
 * set a clipping region at (dx, dy), and then draw something at (dx, dy).
 * If the output changes with changes in dx or dy, there is a bug.
 */
public final class ClipBug extends Component {

    private static final int squareSize = 80;

    /**
     * This method draws a red square inside of a blue square.
     * The topleft corner of the blue square is at (0, 0). In
     * a correctly functioning Graphics, dx and dy should not affect
     * the result of this method at all.
     */
    private void drawIt(Graphics2D g,
                        int dx,
                        int dy) {

        g.translate(-dx, -dy);

        g.setColor(Color.blue);
        g.fillRect(dx, dy, squareSize, squareSize);

        g.setColor(Color.red);

        // This clipping should not affect the appearance of
        // the image, but it does if dx and dy are nonzero.
        g.setClip(new Rectangle2D.Float(dx, dy, squareSize, squareSize));

        g.fillRect(dx, dy, squareSize, squareSize);
    }

    /**
     * Return an Image with the squares draw in it. (dx, dy) is the
     * amount to translate by - their values should not affect the
     * outcome.
     */
    private Image makeImage(int dx, int dy) {

        Image image = createImage(squareSize, squareSize);
        Graphics2D g = (Graphics2D) image.getGraphics();
        drawIt(g, dx, dy);
        return image;
    }

    public void paint(Graphics g) {

        Image buffer = makeImage(0, 0);
        g.drawImage(buffer, 10, 10, this);

        buffer = makeImage(60, 40);
        g.drawImage(buffer, 30 + squareSize, 10, this);
    }

    public static void main(String[] args) {

        Frame f = new Frame("You shouldn't see any blue");
        f.addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent e) {
                System.exit(0);
            }
        });
        f.add(new ClipBug());
        f.setSize(50 + 2*squareSize, 60 + squareSize);
        f.show();
    }
}

(Review ID: 55671)

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