Re: refresh problem when resizing split panes

[Fred Kiefer]

I had almost forgotten about this old problem, as we no longer use XOR
operations directly in the normal GNUstep code. There are at least to 
different issues here. First the Cocoa documentation states that 
NSCompositeHighlight gets mapped to NSCompositeSourceOver just as we do 
in the cairo backend. But on the other hand gui still uses this operator 
as XOR, which of course wont work.
As far as I am aware we only use this in the function NSHighlightRect() 
in gui and we should come up with an operation here that just inverts 
the colour values. I vaguely remember some discussion on the cairo 
mailing list about subtracting the current colour from white
Something like:

cairo_set_operator (cr, CAIRO_OPERATOR_DIFFERENCE);
cairo_set_source_rgb (cr, 1, 1, 1);

We should introduce a new operator for this GSCompositeXOR and implement 
it with the old NSCompositeHighlight code in the other backends. Not 
sure whether we should add this now in the middle of a code freeze. We 
need somebody to remind us to do it afterwards though.

I just looked at the currently available composite operators in cairo 
(http://cairographics.org/operators/) and they have extended a lot since 
we started to use it. Maybe we should recheck some of our operator 
mappings now.

Fred

On 24.01.2012 22:39, Eric Wasylishen wrote:
> I get this too with GSUseGhostResize YES. It's not clear to me how
> the ghost resize code in NSSplitView is supposed to work. Is that
> code expecting NSHighlightRect to be a bitwise XOR where drawing the
> same rect twice gives you the original image back? NSHighlightRect
> doesn't appear to do that, at least with cairo.
>
> e.g. see
> http://lists.cairographics.org/archives/cairo/2004-July/001593.html
>
> On 2012-01-24, at 8:44 AM, Riccardo Mottola wrote:
> > when resizing split panes we have some sort of refresh problem
> > where the "grey" of the moving bar just erases what's in the view.
> > I can verify this in Grr and its reading panes but also in Vespucci
> > when viewing pages with frames.