1221341 - Box-shadow of elements with transform:scale() is rendered incorrectly: with transparent areas between box-shadow and border-box

Status: RESOLVED FIXED

(Core :: Graphics, defect)

Description

[arni2033]

Attachment: testcase 1 - input box-shadow transparent areas.html

STR:   (Win7_64, Nightly 45, 32bit, ID 20151102030241, new profile)
1. Open attached "testcase 1"

Result:
 [see screenshot] Box-shadow is rendered w/ transparent area between box-shadow and border-box

Expectations:
 It should render correctly, w/o transparent areas between box-shadow and border-box

Comment 1

[arni2033]

Attachment: screenshot 1 - Bug 1221341.png

To reproduce the screenshot you may need to maximize the window (because window's width should be an even number). Also, that happens not only on "scale(8)" but also on "scale(2)". It's just more noticeable at "scale(8)"

Comment 2

[j.j.]

Attachment: testcase 2

Simplified testcase
Seems to be a rounding error

Comment 3

[j.j.]

Attachment: screenshot testcase 2

aurora
Mozilla/5.0 (Windows NT 5.1; rv:44.0) Gecko/20100101 Firefox/44.0

Comment 4

[Nicolas Silva [:nical]]

Mason, is this related to the shadow rendering work you have been working on lately ?

Comment 5

[Mason Chang [Inactive] [:mchang]]

(In reply to Nicolas Silva [:nical] from comment #4)
> Mason, is this related to the shadow rendering work you have been working on
> lately ?

Yup, probably.

Comment 6

[Mason Chang [Inactive] [:mchang]]

Attachment: Snap inner clip rect to device pixels

The problem with this bug was that we would clip the inner rect of a box shadow with a pre-transformed rect [1] that was just rounded. Then we'd clip it at [2]. When scaled 8x here, we'd clip too little. This patch snaps the clip rect to device pixels rather than just doing a rounding.

[1] https://dxr.mozilla.org/mozilla-central/source/layout/base/nsCSSRendering.cpp?from=nsCSSRendering.cpp#1289
[2] https://dxr.mozilla.org/mozilla-central/source/layout/base/nsCSSRendering.cpp?from=nsCSSRendering.cpp#1400

Comment 7

[Mason Chang [Inactive] [:mchang]]

Try: https://treeherder.mozilla.org/#/jobs?repo=try&revision=f7b51671f601

Comment 8

[Pulsebot]

https://hg.mozilla.org/integration/mozilla-inbound/rev/ff8ba03eae9c

Comment 9

[Carsten Book [:Tomcat]]

https://hg.mozilla.org/mozilla-central/rev/ff8ba03eae9c