Question

I have got my custom widget that changes background when hover. It is working nice but I would like to have smooth transition between no background and hover background. It will work with GC.setAlpha(), but:

Display.getDefault().asyncExec(new Runnable() {
    public void run() {
        for (int i=0;i<255;i++) {
            setBG(BGHelper(imgHover,i)); //i - alpha
            try {
                Thread.sleep(1);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }   
});

This code wait until i == 255, but it doesn’t display a smooth transition. Why?

Answer 1

This can not work, because as long as you are in your Code SWT will not repaint or change the component.

You should do the work in a separate Thread and call Display.asyncExec for every change.

for (int i = 0; i < 255; i++) {
    final int x = i;
    Display.getDefault().asyncExec(new Runnable() {
        public void run() {
            setBG(BGHelper(imgHover,x)); //x - alpha
        }
    });
    try {
        Thread.sleep(1);
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
}