RESOLVED FIXED 67216
NRWT dumps text into diff.png files when images are 100% different 
https://bugs.webkit.org/show_bug.cgi?id=67216
Summary NRWT dumps text into diff.png files when images are 100% different
Simon Fraser (smfr)
Reported 2011-08-30 11:58:45 PDT
Created attachment 105661 [details] Zip file; diff image is bad I just ran NRWT with 12 parallel instances, and --pixel. Some of the resulting diff images were corrupted. See attachment.
Attachments
Zip file; diff image is bad (3.02 KB, application/octet-stream)
2011-08-30 11:58 PDT, Simon Fraser (smfr) 		no flags
Details
View All Add attachment proposed patch, testcase, etc.
Eric Seidel (no email)
Comment 1 2011-08-30 12:28:59 PDT
Thank you for the report!
Dirk Pranke
Comment 2 2011-08-30 13:39:45 PDT
I assume this was using the Apple Mac port? Chromium and non-Chromium ports have very different approaches to diffing images, so it probably matters which one you were using.
Simon Fraser (smfr)
Comment 3 2011-08-30 13:45:02 PDT
Apple port, yes. It's not clear that running in parallel is an issue.
Eric Seidel (no email)
Comment 4 2011-09-12 10:55:42 PDT
The backface-visibility-diff.png in his zip file has the content: diff: 100.00% failed it appears we don't handle the case correctly when the diff is 100% different.
Eric Seidel (no email)
Comment 5 2011-10-24 10:43:33 PDT
I feel like this may have been worked on in another bug. But maybe I'm thinking of the "displaying the diff % in results.html" bug.
Eric Seidel (no email)
Comment 6 2011-10-24 11:34:06 PDT
Are you still seeing this? It doesn't look like the current iteration of _read_image_diff could produce this result.
Eric Seidel (no email)
Comment 7 2011-10-24 11:40:16 PDT
I'm not able to reproduce 100% different. I tried with a test.html which just painted black, then changed it to just paint white, and saw only 86% different?? Similarly when changing from red to green, I only got 56% different. In neither case did the diff image actually show me anything useful... Maybe diff images are generally broken in NRWT on Mac?
Eric Seidel (no email)
Comment 8 2011-10-24 15:28:03 PDT
Without a way to reproduce this, there isn't much to do but close this. I believe this was fixed accidentally since filing, since we've been in that code several times. If you see it again, I'm happy to take a crack at it!
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