Re: supportsDrawGState

[Fred Kiefer]

On 13.06.2011 20:19, Quentin Mathé wrote:
> Le 13 juin 2011 à 14:41, Fred Kiefer a écrit :
>
> > I had to restrict the usage of the new image drawing mechanism for
> > the cairo backend to the cases where the clipping region is
> > representable as a list of rectangles. With the new drawing code we
> > store and restore the GState and this only works correctly when the
> > clipping region is composed of rectangles.
>
> I don't see where the gstate is saved/restored in the new drawing
> code and not in the old code path. I checked both Back and  Gui.
> Which lines are you referring to precisely? In Back cairo_save() and
> cairo_restore() seems to be used in both cases. On the Gui side,
> PSgsave(), DPSgsave(), PSgrestore() or DPSgrestore() seems to be used
> in the same way in the two drawing methods.
>
> > The problem became obvious in the JigSaw Application which is now
> > part of GAP and which does use non-rectangular shapes for its
> > pieces. These pieces where drawn incorrectly with the new drawing
> > mechanism but correctly with the old one.
>
> Are they drawn correctly on Mac OS X?
>
> > I would love to see a better solution for this, so feel free to
> > suggest one.
>
> Agreed :-)

Quentin,

I would have expected a little trust in my analysis here :-)
But anyway you are free to ask and not just take my word for it. The
difference is between the methods guiDrawInRect:... and
nativeDrawInRect:... If you carefully count the PSgsave calls you will
see that each has exactly one in each call path. The difference is that
in guiDrawInRect:.. the save happens while drawing on the cache surface
whereas for nativeDrawInRect:.. we use the save while drawing on the
main surface. This may look only slightly different but changed the 
whole thing.

The annoying bit here is that we now know that we have a general 
problem. For this image drawing issue I was able to resolve it, but if 
somebody manually sets a non rectangular clip and than uses PSsave we 
are in trouble.

Fred