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Issue 1445 Prescaling images loses subpixel precision in translation
Starred by 5 users Project Member Reported by humper@google.com, Jul 24 2013 Back to list
Status: New
Owner:
Cc:
Area: Bitmap
Priority: Medium
Type: Defect



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What steps will reproduce the problem?
1. Draw a bitmap with a non-trivial scale and a fractional translation

What is the expected output? What do you see instead?

The fractional translation should persist through to the per-scanline bilerp code.  Instead, we remove the scale factor from the matrix after scaling, causing us to think that the matrix is translation-only.  

Unfortunately, for translation-only matrices, we round the translation amounts to the nearest integer.

Need to have a discussion with the right people about why translations are quantized in these cases, and what I should do about it.
 
Project Member Comment 1 by skia-commit-bot@chromium.org, May 29 2014
Cc: humper@google.com
Commit: https://skia.googlesource.com/skia/+/1803f4e
 Email: commit-bot@chromium.org@2bbb7eff-a529-9590-31e7-b0007b416f81

new animated sample to show subpixel translate bug with high quality scaling

BUG=1445
R=reed@google.com, robertphillips@google.com

Author: humper@google.com

Review URL: https://codereview.chromium.org/303123003

git-svn-id: http://skia.googlecode.com/svn/trunk@14981 2bbb7eff-a529-9590-31e7-b0007b416f81

Thu May 29 22:01:08 2014 +0000
M	gyp/SampleApp.gyp
A	samplecode/SampleSubpixelTranslate.cpp
Project Member Comment 2 by humper@google.com, May 30 2014
Status: Started
Project Member Comment 3 by hcm@google.com, Oct 13 2014
Labels: Area-Bitmap
Project Member Comment 4 by halcanary@google.com, Sep 5 2015
Owner: reed@google.com
Project Member Comment 5 by caryclark@google.com, Mar 2 2016
Status: New
Confirmed that the example mentioned above still shows the whole pixel jumps described above. However, whole pixel jumps may be desirable in scrolling and zooming applications. Does this bug still have legs?
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