Description Andre Saibel 2006-06-21 09:55:30 EDT

hello..

My test snippet creates a small and simple image (100x100) with a cup of transparent pixels; it also imitates the double buffering mechanism - so this image (testImage) is created once and then drawn into an other image (shadowImage) using a zoom factor.. then the shadowImage is clipped into PaintEvent's GC. 
A mouse click into the shell causes the view to appear zoomed in/out.. but if you try it out, you will notice, that 
1) somewhere along the way nothing more is painted
2) some later an SWTError is thrown: 
org.eclipse.swt.SWTError: No more handles
	at org.eclipse.swt.SWT.error(SWT.java:2968)
	at org.eclipse.swt.SWT.error(SWT.java:2865)
	at org.eclipse.swt.SWT.error(SWT.java:2836)
	at org.eclipse.swt.graphics.GC.drawBitmapAlpha(GC.java:900)
	at org.eclipse.swt.graphics.GC.drawBitmap(GC.java:863)
	at org.eclipse.swt.graphics.GC.drawImage(GC.java:705)
	at org.eclipse.swt.graphics.GC.drawImage(GC.java:665)
	at DIBTest$1.paintControl(DIBTest.java:xx)

import org.eclipse.swt.SWT;
import org.eclipse.swt.events.*;
import org.eclipse.swt.graphics.*;
import org.eclipse.swt.widgets.*;

public class DIBTest {
	static final boolean SHADOWED = true;

	static final int MAX_ZOOM = 512;
	static final int MIN_ZOOM = 1;
	static final int WIDTH = 100;
	static final int HEIGHT = 100;
	static int zoom = MIN_ZOOM;
	static boolean zoomIn = true;

	static Image createTestImage(Display display, int width, int height) {
		ImageData imageData = new ImageData(width, height, 32, new PaletteData(
				255, 255, 255), 1, new byte[height * 4 * width * 4]);
		for (int x = 0; x < width; x++) {
			for (int y = 0; y < height; y++) {
				if (y == x || x == width - y - 1 || x == 0 || x == height - 1
						|| y == 0 || y == width - 1) {
					imageData.setAlpha(x, y, 0xFF);
				}
			}
		}
		return new Image(display, imageData);
	}

	static void test(Composite composite) {
		if (zoomIn) {
			zoom *= 2;
		} else {
			zoom /= 2;
		}
		if (zoom >= MAX_ZOOM) {
			zoomIn = false;
		} else if (zoom <= MIN_ZOOM) {
			zoomIn = true;
		}
		composite.redraw();
	}

	public static void main(String[] args) {
		final Display display = new Display();
		final Shell shell = new Shell(display);

		final Image testImage = createTestImage(display, WIDTH, HEIGHT);
		final Image shadowImage = new Image(display, WIDTH, HEIGHT);
		final GC shadowGc = new GC(shadowImage);
		shell.addPaintListener(new PaintListener() {
			int _i = 0;

			public void paintControl(PaintEvent e) {
				if (SHADOWED == true) {
					shadowGc.fillRectangle(e.gc.getClipping());
					shadowGc.drawImage(testImage, 0, 0, WIDTH, HEIGHT, 0, 0,
							zoom * WIDTH, zoom * HEIGHT);
					e.gc.drawImage(shadowImage, 0, 0);
				} else {
					e.gc.fillRectangle(e.gc.getClipping());
					e.gc.drawImage(testImage, 0, 0, WIDTH, HEIGHT, 0, 0, zoom
							* WIDTH, zoom * HEIGHT);
				}

				System.out.println("zoom: " + zoom + "; " + (++_i)
						+ " paint event");
			}
		});
		shell.addMouseListener(new MouseAdapter() {
			public void mouseDown(MouseEvent e) {
				test(shell);
			}
		});
		shell.setBounds(shell.computeTrim(50, 50, WIDTH, HEIGHT));
		shell.open();
		while (!shell.isDisposed()) {
			if (!display.readAndDispatch()) {
				display.sleep();
			}
		}
	}
}

This code at its own doesn't make sense.. but I have a real application, which has to visualize data from different sources (testImages) at same time.. I'm kinda perplexed, that if I turn off this double buffering hocus-pocus (SHADOWED=false), the problem doesn't occur. Any Idea? 

best regards
Saibel

PS: I would point out that after the initialization no new images (nor any other OS resources) are created -> misleading SWT.ERROR_NO_HANDLES error.