Bug 26747

Summary: REGRESSION (r41238) Repainted portion of a scaled image does not line up with full image
Product: WebKit Reporter: mitz
Component: Layout and RenderingAssignee: mitz
Status: RESOLVED FIXED    
Severity: Normal CC: simon.fraser
Priority: P1 Keywords: InRadar, Regression
Version: 528+ (Nightly build)   
Hardware: Mac   
OS: OS X 10.5   
URL: http://webkit.org/demos/transitions-and-transforms/
Attachments:
Description Flags
Test case
none
Test case
none
Patch
none
Patch simon.fraser: review+

mitz
Reported 2009-06-25 18:24:21 PDT
To reproduce, open the attached test case. If the window size is not an integer multiple of the native size of the background image (so it is scaled), you will notice the background image jiggling as it is undergoes repeated partial repaints (a 50%-height band moves down and up across the image, forcing repainting). The problem goes away if in BitmapImage::draw() in ImageCG.cpp, shouldUseSubimage is forced to false.
Attachments
Test case (757 bytes, text/html)
2009-06-25 18:25 PDT, mitz 		no flags
Details
Test case (759 bytes, text/html)
2009-06-25 18:28 PDT, mitz 		no flags
Details
Patch (4.10 KB, patch)
2009-06-25 22:37 PDT, mitz 		no flags
DetailsFormatted DiffDiff
Patch (221.23 KB, patch)
2009-07-16 16:34 PDT, mitz 		simon.fraser: review+
DetailsFormatted DiffDiff
Show Obsolete (2) View All Add attachment proposed patch, testcase, etc.
mitz
Comment 1 2009-06-25 18:24:43 PDT
<rdar://problem/7009243>
mitz
Comment 2 2009-06-25 18:25:18 PDT
Created attachment 31897 [details] Test case
mitz
Comment 3 2009-06-25 18:28:56 PDT
Created attachment 31898 [details] Test case Fixed typo
mitz
Comment 4 2009-06-25 22:37:10 PDT
Created attachment 31907 [details] Patch Since the subimage is always pixel-aligned in the source image’s coordinate space, it can encompass more than the desired source rect. subimageRect is the actual source rect for the subimage. The adjusted destination rect is… adjusted in order to get the desired mapping. However, there is a problem: this results in drawing outside the desired destination rect. This can be seen in fast/backgrounds/size/backgroundSize15.html . Clipping to destRect solved this, but creates subpixel gaps when the context is transformed, such as in fast/borders/border-image-rotate-transform.html. I am not sure how to resolve this problem.
mitz
Comment 5 2009-06-27 21:15:48 PDT
I broke this in <http://trac.webkit.org/changeset/41238> by making this code path paint only a portion of the image.
mitz
Comment 6 2009-07-15 13:31:45 PDT
*** Bug 27307 has been marked as a duplicate of this bug. ***
mitz
Comment 7 2009-07-16 16:34:47 PDT
Created attachment 32900 [details] Patch Updated the previous patch. Added clipping to the destination rect—drawPattern already does that, so we already have subpixel gaps in that case.
mitz
Comment 8 2009-07-16 17:48:22 PDT
Fixed in <http://trac.webkit.org/projects/webkit/changeset/46002>.
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