Description Rob Grzywinski 2005-06-26 17:17:27 EDT

If advanced graphics (GC.setAdvanced(true)) is enabled on a graphics context
then calling GC.drawImage(Image image, int srcX, int srcY, int srcWidth, int
srcHeight, int destX, int destY, int destWidth, int destHeight) where the
destination width and/or height is greater than that of the source image will
draw an image with an alpha gradient.  Specially, the drawn image will be the
desired color at its center but have an alpha graient applied towards its edges
(as if the act of stretching implies an alpha shift).

An example can be quickly cooked up using SWT image snippet #112:

    public static void main (String [] args) {
        Display display = new Display ();
        final Image image = new Image(display, 2, 10);
            final Color color = display.getSystemColor(SWT.COLOR_BLUE);
            final GC gc = new GC (image);
                gc.setBackground(color);
                gc.fillRectangle(image.getBounds());
            gc.dispose ();
            color.dispose ();

        Shell shell = new Shell (display);
        shell.setLayout (new FillLayout ());
        Group group = new Group (shell, SWT.NONE);
        group.setLayout (new FillLayout ());
        group.setText ("a square");
        Canvas canvas = new Canvas (group, SWT.NONE);
        canvas.addPaintListener (new PaintListener () {
            public void paintControl (PaintEvent e) {
                // NOTE: turning on advanced graphics here (regardless of any
                //       alpha value set) will cause the stretched image to have
                //       an alpha gradient applied
                // NOTE: this same effect can be seen by performing any function
                //       that would enabled advanced graphics such as:
                //           e.gc.setAlpha(0xFE);
                //       or:
                //           e.gc.setAntialias(SWT.ON);
                e.gc.setAdvanced(true);
                // NOTE: the image is stretched in both dimensions
                e.gc.drawImage(image, 0, 0, 2, 10, 0, 0, 300, 300);
            }
        });

        shell.pack ();
        shell.open ();
        while (!shell.isDisposed ()) {
            if (!display.readAndDispatch ())
                display.sleep ();
        }
        image.dispose ();
        display.dispose ();
    }

This gradient occurs regardless of the source of the source image (e.g. a loaded
image or a created image as in the snippet above).

(This bug becomes more severe with the use of GEF as there is no way to disable
the use of advanced graphics on a Graphics object after it has been enabled. 
(And it hasn't been shown that disabling advanced graphics will even solve the
problem.))