Java SWT Image 图像 —— 透明度 alpha

原文：http://www.eclipse.org/articles/Article-SWT-images/graphics-resources.html

透明度 alpha可以是所有的像素点拥有同一个，也可以不同的像素点不同。

Shell shell = new Shell(display);
		shell.setLayout(new FillLayout());
		ImageData imageData = new ImageData("C:/temp/Idea_PureWhite.jpg");
		final Image fullImage = new Image(display,imageData);
		imageData.alpha = 128;
		final Image halfImage = new Image(display,imageData);
		imageData.alpha = 64;
		final Image quarterImage = new Image(display,imageData);

		Canvas canvas = new Canvas(shell,SWT.NO_REDRAW_RESIZE);
		canvas.addPaintListener(new PaintListener() {
			public void paintControl(PaintEvent e) {
				e.gc.drawImage(fullImage,0,0);
				e.gc.drawImage(halfImage,140,0);
				e.gc.drawImage(quarterImage,280,0);
			}
		});

ImageData fullImageData = new ImageData("C:/temp/Idea_PureWhite.jpg");
		int width = fullImageData.width;
		int height = fullImageData.height;
		byte[] alphaData = new byte[height * width];
		for(int y=0;y<height;y++){
			byte[] alphaRow = new byte[width];
			for(int x=0;x<width;x++){
				alphaRow[x] = (byte) ((255 * y) /height);
			}
			System.arraycopy(alphaRow,0,alphaData,y*width,width);
		}
		fullImageData.alphaData = alphaData;
		Image fullImage = new Image(display,fullImageData);