Re: [platform-swt-dev] GC on native components and painting

[Carolyn MacLeod <Carolyn_MacLeod@xxxxxxxxxx>]

The following snippet is the best I
can do.
Hope it helps.
Carolyn

import
org.eclipse.swt.*;
import
org.eclipse.swt.graphics.*;
import
org.eclipse.swt.layout.*;
import
org.eclipse.swt.widgets.*;

/**
 *
Buttons
on
Windows
don't
like
transparent
images.
 *
So
you
have
to
simulate
transparency
by
setting
the
image's
 *
transparent
pixel
to
the
button's
background
color.
 */
public
class
Main {
        
public
static
void
main (String [] args) {
        Display
display = new
Display();
        
        /*
Create a shell with a button. */
        Shell
shell = new
Shell (display);
        shell.setLayout
(new
FillLayout ());
        Button
button = new
Button (shell, SWT.PUSH | SWT.BORDER);

        /*
Create an image data with a 2-color palette (red, white). */
        PaletteData
palette = new
PaletteData (new
RGB[] {
         
      display.getSystemColor (SWT.COLOR_RED).getRGB
(),   // pixel
0 = red
         
      display.getSystemColor (SWT.COLOR_WHITE).getRGB
(), // pixel 1 = white
        });
        ImageData
imageData = new
ImageData (24, 24, 1, palette);
        imageData.transparentPixel
= 1; // set the transparent
color to white
        
        /*
Create an image from the image data, and draw on it. */
        Image
image = new
Image (display, imageData);
        GC
gc = new
GC (image);
        gc.setBackground
(display.getSystemColor (SWT.COLOR_WHITE));
        gc.fillRectangle
(0, 0, 24, 24); //
fill with white
        gc.setBackground
(display.getSystemColor (SWT.COLOR_RED));
        gc.fillArc
(2, 2, 20, 20, 0, 360); //
draw a red circle in the middle
        gc.dispose
();
        
        /*
Tell the image to use the button's background color for transparent pixels.
*/
        image.setBackground
(button.getBackground ());
        button.setImage
(image);
        
        shell.pack
();
        shell.open
();
        while
(!shell.isDisposed ()) {
         
      if
(!display.readAndDispatch ()) display.sleep ();
        }
        image.dispose
();
        display.dispose
();
}
}

Minh Chiem <minhchiem@xxxxxxxxxxxx>
Sent by: platform-swt-dev-admin@xxxxxxxxxxx

11/26/2003 03:13 AM

Please respond to
platform-swt-dev

To	platform-swt-dev@xxxxxxxxxxx
cc
Subject	[platform-swt-dev] GC on native components and painting

Hi.

I've followed the guide on 
http://www.eclipse.org/articles/Article-SWT-images/graphics-resources.html#Transparency
to find out how to do transparency.

I've added a paintlistener on a button however, when you go to click on
the button there seems to be no refresh so it appears as if a image as
disappeared.

It looks like there's another paint listener when the button is pressed
so what I've done is made the button repaint everytime the mouse down 
and mouse up event occurs and that seems to be a nice work around. 
However, I've got lots of buttons/toolbar items that have images and 
adding mouse listeners to all the buttons makes code look really messy
IMHO. Since I can't just extend the Button so that it encapsulates the
extra repainting behaviour, is another way to approach this problem?

BTW, I'm running this on the windows version of SWT.

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