Bug 51609 – Accumulated pixel rounding of 'left' results in jumps when transitioning it

• Component: CSS
• Status: RESOLVED FIXED

[Vincent Meurisse]

Created attachment 77438 [details]
Testcase

When combining CSS transitions (eg. an animated div inside another animated div), I expect the resulting animation to be smooth. Instead, each position is rounded to the closest pixel before the final sum. Please look at the attachment for a demo (and open it in Firefox4 for the expected result).

Please note that using floating point arithmetic for calulation would solve both this bug and #15827 as the lack of synchronization will then result in less than 1px of error.

[Luke Macpherson]

Levi & Emil, do you think this will be fixed by the switch to floating point everywhere that you guys are working on?

[Emil A Eklund]

Yeah, seems likely. I'll try the attached test case on our build and report back.

[Emil A Eklund]

Turns it it's still failing when running our patched browser with sub-pixel precision.
From looking at the test case the desired behavior isn't obvious. I assume you expect the divs to snap one at a time resulting in a smoother transition?

[Levi Weintraub]

Yeah, you can see the proper expected results in FFX7. This should be solvable with our patch, but unfortunately still seems to a problem at the moment.

[Emil A Eklund]

The attached test case now works as expected with SUBPIXEL_LAYOUT enabled.