1126530 - On Win8, reftest "image-object-position-with-background-2.html" renders with gradient of fuzzy pixels at the bottom of each page, if imgFrame::Optimize is disabled

Status: NEW

(Core :: Graphics: ImageLib, defect)

Description

[Daniel Holbert [:dholbert]]

Attachment: reftest log for failure (w/ data URIs)

Seth pushed a Try run with gDisableOptimize set to "true" in imgFrame:
  https://tbpl.mozilla.org/?tree=Try&rev=a619a8707963

(This was experimental; we should only depend on this optimization for performance, but he's looking into whether we depend on it for correctness as well.)

This Try run had failures for "image-object-position-with-background-2.html", on Windows 8 x64. (both opt + debug).  Win7 & WinXP are all fine. (I'm not sure whether the relevant difference is the Windows version or the 64bit-ness.)

The failure looks like a real bug. The reftest has an opaque image that's split across several pages, and the testcase's reftest-snapshot shows the image & its background gradually blending together at the bottom of each page (with the image fading out & the background fading in). This blending is smeared across the bottom 4-5px of the image's content-box on each page.  I'm attaching the reftest log for this test-failure, for use with reftest-analyzer.xhtml.

I'm guessing what's going on is that we render the image into some buffer, with an antialiased bottom-edge for some reason (so, the bottom edge of pixels in this buffer is semitransparent) -- and then when we scale that up to render, this bottom row of semitransparent pixels get scaled up to several rows.

Anyway, this is a bug. We should fix it.

Comment 1

[Daniel Holbert [:dholbert]]

[ni=seth to tie this to the bug on making this imgFrame optimization pref-controllable, if/when he files that bug]

Comment 2

[Seth Fowler [:seth] [:s2h]]

I talked to Bas about this issue and he suggested that this bug may be specific to the D2D 1.1 backend, which apparently we're only using on the Windows 8 reftest machines right now.

Comment 3

[Seth Fowler [:seth] [:s2h]]

BTW, this is probably in reality a graphics bug, but I think leaving it in this component is fine until someone has time to investigate and identify the specific issue.