Bug 4476

Summary:	[pixman] non-projective transform optimization can result in wrongly scaled images
Product:	cairo	Reporter:	Bertram Felgenhauer <bertram.felgenhauer>
Component:	image backend	Assignee:	Carl Worth <cworth>
Status:	RESOLVED NOTABUG	QA Contact:	cairo-bugs mailing list <cairo-bugs>
Severity:	minor
Priority:	high
Version:	1.1.1
Hardware:	x86 (IA32)
OS:	Linux (All)
Whiteboard:
i915 platform:		i915 features:
Attachments:	proposed fix proposed patch

Description Bertram Felgenhauer 2005-09-16 11:02:54 UTC

In pixman/fbcompose.c, fbFetchTransformed(), Bool projective  is not set if the
transformation matrix is not projective but contains homogenous components that
are not 1; this will result in wrongly scaled images to be drawn.
The initialization should be done similar to the one in fbFetchSourcePict()
above. I'll attach a patch for this.

NB. I think 'projective' is a misnomer - maybe 'simple_transform' is better?
NB.2. I don't think this gets triggered by cairo's usage of the pixman code,
does it?

Comment 1 Bertram Felgenhauer 2005-09-16 11:07:02 UTC

Created attachment 3297 [details] [review]
proposed fix

[pixman] Changelog

2005-09-16  Bertram Felgenhauer  <int-e@gmx.de>

	Bug #4476

	* src/fbcompose.c (fbFetchTransformed): correct check for
	nonprojective transforms

Comment 2 Bertram Felgenhauer 2005-09-16 13:28:42 UTC

Created attachment 3299 [details] [review]
proposed patch

fixed a stupid typo in the patch - cut&paste coding is evil.

Comment 3 Behdad Esfahbod 2006-06-14 00:07:57 UTC

Can you attach a minimal test case that shows the bug?  That helps confirming
the bug, as well as adding it to the test suite.

Comment 4 Bertram Felgenhauer 2006-06-14 00:48:52 UTC

As far as I know, this is not a bug as far as cairo is concerned; projective
transforms aren't used anywhere. It might affect the X-Server; I've never looked
at what functionality the Render extension exposes. I noticed the bug while
looking at #2488; back then I got the impression that the code might be merged
back into the X-server. I believe that's no longer the case.
(cairo might actually want to get rid of that functionality in pixman)

Comment 5 Bertram Felgenhauer 2006-06-16 15:56:57 UTC

This is fixed in the xorg X server. I'll stick to my analysis about cairo and
close this bug. Thanks.

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