| Backscreen Scrolling [message #467050] |
Mon, 23 January 2006 19:09 |
 Dominic Cubitt
Messages: 2
Registered: July 2009 |
Junior Member |
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Hi,
I am developing an app on the Pocket PC and am having serious problems when
scrolling. There is much flickering and partial redraw when scrolling a
composite containing a few labels and such. This is because the redraw is
called every time.
I am using J9 with 3.2 M4 PPC j2se.
I have tinkered extensively with DOUBLE_BUFFERED and NO_BACKGROUND that do
make some difference, but by no means enough.
I have investigated further; and scrolling of an image seems to work very
well.
So what i want to do is render my component(s) to a backscreen and copy the
appropriate image segment to a canvas for normal drawing.
I have had some success with this using code like:
public void setContent(Composite c){
this.content = c;
content.setVisible(true);
}
void paintControl(PaintEvent e) {
Point contentSize = content.getSize();
GC gc = new GC(content);
Image image = new Image(content.getDisplay(), contentSize.x,
contentSize.y);
gc.copyArea(image, 0, 0);
gc.dispose();
gc = e.gc;
gc.drawImage(image, 100, offsetY);
image.dispose();
gc.dispose();
}
The problem here is that the content component needs to be visible for me to
take an image - this defeats the point in the first place. However the image
to the right scrolls very smoothly despite me taking a new image every time!
I would very much like to build a generic solution to this as scrolling is a
significant feature of the application.
Any advice on how to correctly render component(s) to a backscreen would be
much appreciated.
Regards,
Dominic,
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