450140 - Canvas drawWindow with context.scale adds borders around some images

Status: NEW

(Core :: Graphics: Canvas2D, defect, P3)

Description

[Daniel Holbert [:dholbert]]

Attachment: screenshot 1: borders added around one QMO logo and Google logo.

Steps to Reproduce:
 1. Open these URLs in tabs:
      http://www.google.com/
      http://www.mozilla.org/projects/minefield/
      [anything else]
 2. Use Ctrl-Tab to bring up the new Tab-Switcher
 3. Examine the previews for google and the minefield startup page.

ACTUAL RESULTS:  
  Some images in the previews have borders added around them.  These aren't just JPEG artifacts, AFAICT.

EXPECTED RESULTS:
  No new borders should be added in the previews.

See screenshots for examples. (I've added red arrows to point to the borders.)

I'm testing using a fresh mozilla-central debug build from today.

Comment 1

[Daniel Holbert [:dholbert]]

Attachment: screenshot 2: top-border added to other QMO logo

This screenshot shows that the added borders aren't always the same.  In this case, a top border was added around the Q-shaped QMO logo on the left. (This top border was not present in screenshot 1.)

Comment 2

[Vladimir Vukicevic [:vlad] [:vladv] (needinfo me, slow to respond)]

My guess is that what's happening is that the image is RGB24, with a solid white background.. but we're hitting the EXTEND_PAD failure here, so we're sampling outside of the image bounds and getting solid black (because we're doing RGB24) compositing.  This is kinda broken in a lot of ways, but I really don't know what the right fix should be.

Comment 3

[Vladimir Vukicevic [:vlad] [:vladv] (needinfo me, slow to respond)]

Yep.  This might be fixed by roc's work in bug 458487.

Comment 4

[Dão Gottwald [:dao]]

(In reply to comment #3)
> Yep.  This might be fixed by roc's work in bug 458487.

I'm still seeing the borders around the QMO logos (attachment 333272 [details]).

Comment 5

[Robert O'Callahan (:roc) (email my personal email if necessary)]

Currently we're not pixel-snapping when there's a scale in the context, so these fringes are sure to happen.