Bug 102036

Summary:	[PATCH] Arthur backend renders highlight annotations wrongly
Product:	poppler	Reporter:	oliver.sander
Component:	arthur backend	Assignee:	poppler-bugs <poppler-bugs>
Status:	RESOLVED FIXED	QA Contact:
Severity:	normal
Priority:	medium	CC:	m.weghorn, oliver.sander
Version:	unspecified
Hardware:	Other
OS:	All
Whiteboard:
i915 platform:		i915 features:
Attachments:	Patch that implements ArthurOutputDev::updateBlendMode Test document: a short text that is partially highlighted New test file Patch that implements ArthurOutputDev::updateBlendMode Patch that replaces the QPainter by a stack of QPainters Patch implementing rudimentary transparency group support

Description oliver.sander 2017-08-04 13:00:29 UTC

Created attachment 133245 [details] [review]
Patch that implements ArthurOutputDev::updateBlendMode

The Arthur backend renders highlight annotations wrongly.  The yellow rectangles are simply rendered on top of the highlighted text, hiding that text completely.

The obvious explanation was that the updateBlendMode method is not implemented in ArthurOutputDev.  I therefore prepared a patch that implements that method.  It is simple and self-contained.

Full disclosure: I actually took the implementation from the much larger patch that Mihai Niculescu posted to the mailing list in

  https://lists.freedesktop.org/archives/poppler/2013-June/010370.html

That's why the patch contains Mihai's name in the copyright list.

Only, it doesn't solve the problem: With it, the yellow rectangles still hide the text.  And I don't understand why this is.  When the ArthurOutputDev::fill method that draws the yellow rectangle is called, the blend mode is gfxBlendNormal, which I suppose means "draw right on top of it".  I need a hint here.  What is the mechanism that allows me to see the highlighted text through the rectangle, if it isn't the blend mode?  It doesn't seem to be opacity, either.

Comment 1 oliver.sander 2017-08-04 13:01:25 UTC

Created attachment 133246 [details]
Test document: a short text that is partially highlighted

Comment 2 Albert Astals Cid 2017-08-07 21:39:41 UTC

If you want i can commit this, but honestly i don't have time to sink on ArthurOutputDev trying to help you

Comment 3 oliver.sander 2017-10-20 10:17:48 UTC

Created attachment 134934 [details]
New test file

Updated the test file.  For some reason I don't see a highlight at all any more in the old one.

Comment 4 oliver.sander 2017-10-28 19:24:05 UTC

Created attachment 135143 [details] [review]
Patch that implements ArthurOutputDev::updateBlendMode

Rebased the patch, and removed a stray debugging output.

Comment 5 oliver.sander 2017-10-28 19:31:59 UTC

I finally figured out how to make Arthur render highlight annotations properly.
(Thanks to Adrian for his advice---I should have listened earlier.)  These annotations need support for transparency groups.  My implementation comes as three separate patches:

1) The implementation of updateBlendMode.  Please commit this, it is definitely needed.

2) A patch that replaces the single QPainter object by a stack of QPainters. That one is a bit invasive, that's why I'm submitting it separately.  All references to the current painter are now m_painter.top() rather than simple m_painter. Having a getter method for that may be nice---I am undecided.

3) The actual implementations of {begin|end|paint}TransparenceGroup.  These are short and rudimentary.  Transparency groups can do much more than just highlights, but that has to wait until later.

Thanks for your review.

Comment 6 oliver.sander 2017-10-28 19:32:29 UTC

Created attachment 135144 [details] [review]
Patch that replaces the QPainter by a stack of QPainters

Comment 7 oliver.sander 2017-10-28 19:33:13 UTC

Created attachment 135145 [details] [review]
Patch implementing rudimentary transparency group support

Comment 8 Albert Astals Cid 2017-12-28 23:19:32 UTC

pushed

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