在SWT上具有透明度的PNG图像

Question

I've got a Composite and would like to use a png file as background image. I can do that, the problem is when the image uses transparency it doesn't work and shows a white colour instead. Any thoughts on how to get this to work?

Thanks!

Answer 1

Does this article help?

Taking a look at SWT Images

It talks about drawing an image (albeit a GIF) to a Canvas with transparency ( Canvas extends Composite ).

Answer 2

SOLVED! I've solved exactly this problem - displaying PNG files that contain transparent areas. I could not get it to work with Labels (in fact the article quoted states "Label does not support native transparency") so I put the image directly into a canvas instead. The other key to success is to use the Image constructor that includes a 3rd parameter, which is the transparency mask. An extra step I did is to call setRegion, which means that mouse events (such as mouse clicks) only fire when they occur over visible pixels.

ImageData id = new ImageData("basket.png");
Image image = new Image (display, id, id); //3rd parameter is transparency mask
Canvas c = new Canvas (shell, SWT.TRANSPARENT);
c.addPaintListener(
    new PaintListener(){
        public void paintControl(PaintEvent e) 
        {
            e.gc.drawImage(image, 0, 0);
        }
    }
);

//the image has been created, with transparent regions. Now set the active region
//so that mouse click (enter, exit etc) events only fire when they occur over
//visible pixels. If you're not worried about this ignore the code that follows
Region region = new Region();
Rectangle pixel = new Rectangle(0, 0, 1, 1);
for (int y = 0; y < id.height; y++)
{
    for (int x = 0; x < id.width; x++)
    {
        if (id.getAlpha(x,y) > 0)
        {
            pixel.x = id.x + x;
            pixel.y = id.y + y;
            region.add(pixel);
        }
    }
}
c.setRegion(region);