Canvas: rotation of 'no-repeat' pattern still has small error

• Component: WebCore Misc.
• Status: RESOLVED FIXED

[Shinichiro Hamaji]

I didn't put expected image into my patch in https://bugs.webkit.org/show_bug.cgi?id=26426

Also, it would be better to use (1<<23)/2 as steps to make the error less than 0.5. I could see the 1 pixel errors with the previous value.

[Shinichiro Hamaji]

Created attachment 31904 [details]
Patch v1

 LayoutTests/ChangeLog                              |   15 +++++++++++++++
 .../image-object-in-canvas-expected.checksum       |    2 +-
 .../canvas/image-object-in-canvas-expected.png     |  Bin 56436 -> 78707 bytes
 WebCore/ChangeLog                                  |   15 +++++++++++++++
 WebCore/platform/graphics/cg/PatternCG.cpp         |    7 +++----
 5 files changed, 34 insertions(+), 5 deletions(-)

[Shinichiro Hamaji]

Adding Oliver into CC list as he reviewed my previous patch.

[Oliver Hunt]

Comment on attachment 31904 [details]
Patch v1

I'm not sure what you're trying to fix here.  If this patch is correct you should just be doing 1<<22, but like i said i'm not sure what you're actually trying to do.

[Shinichiro Hamaji]

Created attachment 32853 [details]
an HTML to describe this bug

[Shinichiro Hamaji]

Created attachment 32854 [details]
Before the patch

[Shinichiro Hamaji]

Created attachment 32855 [details]
After the patch

[Shinichiro Hamaji]

Sorry for the poor description/title of this bug. I've attached an HTML which can describe why I want to use smaller value than before. 1<<23 is the precision of mantissa of floats and using this means that the error is <1px. I think 1px error can be still visible.

The HTML I've attached is putting 3x3 image whose shape is '+' vertically. As it doesn't change the value of X-axis, you should see a vertical straight line like "After the patch". However, with current WebKit, the line is not straight like "Before the patch". If we use 1<<22 as this value, the error should be <0.5px.

As WebKit is doing anti-alias for rotation, the image changes if we use 1<<21 or something smaller value. However, I think no one would be care about such tiny changes. So, I think 1<<22 would be OK.

I'll update the patch with more description and test case.

[Shinichiro Hamaji]

Created attachment 32859 [details]
Patch v2

[Oliver Hunt]

Comment on attachment 32859 [details]
Patch v2

ChangeLog needs to be updated to say 1<<22 not (1<<23)/2 but this is otherwise okay -- can the person who lands fix up the changelog?

[Adam Barth]

(In reply to comment #9)
> (From update of attachment 32859 [details])
> ChangeLog needs to be updated to say 1<<22 not (1<<23)/2 but this is otherwise
> okay -- can the person who lands fix up the changelog?

Ok.  I'll do the fixup.

[Adam Barth]

Sorry, bugzilla-tool isn't awesome enough to handle this PNG.

[Shinichiro Hamaji]

Created attachment 33446 [details]
platform/mac/fast/canvas/image-object-in-canvas-expected.png

[Shinichiro Hamaji]

Created attachment 33447 [details]
platform/mac/fast/canvas/image-pattern-rotate-expected.png

[Shinichiro Hamaji]

Thanks Oliver for your review, and thanks Adam for trying to fix the ChangeLog and  land this patch. I've uploaded png images in this patch. Please use them if you need.

[Adam Barth]

Trying again.

[Adam Barth]

Wow, that was complicated.  Bugzilla-tool validating patch.  Hopefully will be landed shortly.

[Adam Barth]

Committing to http://svn.webkit.org/repository/webkit/trunk ...
	M	LayoutTests/ChangeLog
	A	LayoutTests/fast/canvas/image-pattern-rotate.html
	M	LayoutTests/platform/mac/fast/canvas/image-object-in-canvas-expected.checksum
	M	LayoutTests/platform/mac/fast/canvas/image-object-in-canvas-expected.png
	A	LayoutTests/platform/mac/fast/canvas/image-pattern-rotate-expected.checksum
	A	LayoutTests/platform/mac/fast/canvas/image-pattern-rotate-expected.png
	A	LayoutTests/platform/mac/fast/canvas/image-pattern-rotate-expected.txt
	M	WebCore/ChangeLog
	M	WebCore/platform/graphics/cg/PatternCG.cpp
Committed r46399
	M	WebCore/ChangeLog
	M	WebCore/platform/graphics/cg/PatternCG.cpp
	A	LayoutTests/platform/mac/fast/canvas/image-pattern-rotate-expected.txt
	M	LayoutTests/platform/mac/fast/canvas/image-object-in-canvas-expected.png
	A	LayoutTests/platform/mac/fast/canvas/image-pattern-rotate-expected.checksum
	A	LayoutTests/platform/mac/fast/canvas/image-pattern-rotate-expected.png
	M	LayoutTests/platform/mac/fast/canvas/image-object-in-canvas-expected.checksum
	M	LayoutTests/ChangeLog
	A	LayoutTests/fast/canvas/image-pattern-rotate.html
r46399 = 8574a2ebe1893f5ee6b2b1fb26e1b18debbdf507 (trunk)
No changes between current HEAD and refs/remotes/trunk
Resetting to the latest refs/remotes/trunk
http://trac.webkit.org/changeset/46399

[Adam Barth]

Forgot to fixup the changelog before landing, but I did in the next commit:

Committing to http://svn.webkit.org/repository/webkit/trunk ...
	M	LayoutTests/ChangeLog
	M	WebCore/ChangeLog
Committed r46400