Drawing on a transparent image using Java SWT

Question

How do I create an in-memory fully transparent SWT image and draw a black line on it with antialias enabled?

I expect the result to include only black color and alph

Answer 1

I made it by allocating an ImageData, making it transparent then creating the Image from the data :

static Image createTransparentImage(Display display, int width, int height) {
    // allocate an image data
    ImageData imData = new ImageData(width, height, 24, new PaletteData(0xff0000,0x00ff00, 0x0000ff));
    imData.setAlpha(0, 0, 0); // just to force alpha array allocation with the right size
    Arrays.fill(imData.alphaData, (byte) 0); // set whole image as transparent

    // Initialize image from transparent image data
    return new Image(display, imData);
}