[cairo] win32: Bug in partial redrawing triggered by InvalidateRect

[Andrea Canciani]

On Mon, Jul 25, 2011 at 1:14 PM, Matthias Bolte
<matthias.bolte at googlemail.com> wrote:
> I came across this problem while updating from cairo 1.8 to 1.10.
>
> In 1.8 Triggering partial redraws via InvalidateRect works as
> expected. In 1.10 it doesn't. The size of the rect is correct but the
> offset is lost and the top-left corner of the window is redrawn with
> the wrong content as the content comes from the correct offset.
>
> I tracked the problem down to this commit
>
> b713510f213d0a83cb0575d6870416a0f13786c9
> surface-fallback: Convert to composite rectangles
>
> http://cgit.freedesktop.org/cairo/commit/?id=b713510f213d0a83cb0575d6870416a0f13786c9
>
> But I could not understand why this commit breaks partial redraws.
>
> Today I found a mail on the mailing list about this problem
>
> http://lists.cairographics.org/archives/cairo/2011-March/021800.html
>
> that refers to a bug report from 2010 about this problem
>
> https://bugs.freedesktop.org/show_bug.cgi?id=28541
>
> that has a working patch attached
>
> http://sprunge.us/KOZU
>
> The offending commit seems to have broken the handling of surfaces
> that don't have their origin in (0,0) as it switched to the
> _cairo_composite_rectangles_init* functions that assume that the
> surface has it's origin in (0,0).
>
> The problem seems to be that a BeginPaint call (as a reaction to a
> WM_PAINT message triggered by a InvalidateRect) can return a DC with
> an origin equal to the offset given in the InvalidateRect. So there is
> a DC with an origin different from (0,0).
>
> The referenced patch makes _cairo_composite_rectangles_init* honor
> this offset and fixes the problem.
>
> Now I wonder why this patch from October 2010 has neither been
> reviewed nor been applied yet. This mail is an attempt to finally get
> this problem fixed.

I just updated the bug with some information.
I thought that a discussion about this patch happened on
the mailing lists, but right now I'm unable to find it
(Probably it was actually on IRC)

Sorry for not having updated the bugreport with the nack-review immediately

Andrea

>
> --
> Matthias Bolte
> http://photron.blogspot.com
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