Bug 57164

Summary:	Regressions in poppler since cairo 1.12.4
Product:	cairo	Reporter:	Carlos Garcia Campos <carlosgc>
Component:	image backend	Assignee:	Chris Wilson <chris>
Status:	RESOLVED MOVED	QA Contact:	cairo-bugs mailing list <cairo-bugs>
Severity:	normal
Priority:	medium
Version:	1.12.4
Hardware:	Other
OS:	Linux (All)
Whiteboard:
i915 platform:		i915 features:
Attachments:	Expected Actual (since cairo 1.12.4) Diff testcase

Description Carlos Garcia Campos 2012-11-15 17:43:52 UTC

Created attachment 70135 [details]
Expected

git bisect blames this commit:

36536d3eb83a8f942bcf1afba4d0815fbeaca10f is the first bad commit
commit 36536d3eb83a8f942bcf1afba4d0815fbeaca10f
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Thu Sep 27 11:14:18 2012 +0100

    spans-compositor: Use the tight clip-boxes for polygon construction
    
    If we will be reducing the clip intersection to a single clip box check
    during construction, it helps if we use the tight clip box.
    
    Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

The problem can be seen with altona_visual_1v2a_x3.pdf, there's a line in the middle of some radial gradients. I'm attaching the actual, expected and diff images.

Comment 1 Carlos Garcia Campos 2012-11-15 17:45:28 UTC

Created attachment 70136 [details]
Actual (since cairo 1.12.4)

Comment 2 Carlos Garcia Campos 2012-11-15 17:47:18 UTC

Created attachment 70137 [details]
Diff

Comment 3 Uli Schlachter 2013-08-21 13:22:22 UTC

Is this still an issue with latest git?

Comment 4 Massimo 2015-01-09 18:08:03 UTC

Created attachment 112021 [details]
testcase

The problem here is that filling twice the same area including
partially covered pixels results in the first color being blended with
the second in these pixels.

The attached test case shows that the commit above exposed this limitation
in the case of filling two paths clipped by the same vertical edge when
the clip is a rectangle and the edge is not along an integer x and it shows
that the behaviour is now consistent.

It is possible to undo the rekevant effects of that commit by appending a 
'&& 0' to the if condition at line 1138 in src/cairo-spans-compositor.c:

    if (extents->clip->num_boxes == 1 && 0) {

Comment 5 GitLab Migration User 2018-08-25 13:46:45 UTC

-- GitLab Migration Automatic Message --

This bug has been migrated to freedesktop.org's GitLab instance and has been closed from further activity.

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