1776928 - [HCM] Avoid backplating whitespace?

Status: RESOLVED FIXED

(Core :: Layout, task)

Description

[Morgan Reschenberg [:morgan]]

This is an issue with various google apps, and I'm not sure it's within our ability to fix but flagging here in case it is:

STR:

1. Open a google sheet
2. Enable HCM (about:preferences > manage colors > always)
3. View the "share" button in the upper right corner of the sheet

Expected: The share icon and text is unobstructed
Actual: A rectangle partially obscures the button content

It looks like google is using a single space in the span that defines the share button, for some reason. And because it's technically text, we backplate it. Is there a way for us to not backplate content that is only whitespace without moving to a "backplate by word" model where we break on every space (which I don't think we should do)?

Comment 1

[Morgan Reschenberg [:morgan]]

Attachment: share button example

Comment 2

[Emilio Cobos Álvarez (:emilio)]

Probably around here we could maybe check nsTextFrame::IsEmpty or so?

Comment 3

[Morgan Reschenberg [:morgan]]

Taking this to save it for a new hire starting in August

Comment 4

[Nathan LaPré]

Here's a minimal reproducer that doesn't require going through google apps (paste into the address bar to view):

data:text/html,<svg width="20" height="20"><circle cx="10" cy="10" r="10" fill="white" /></svg><span style="display:inline-block; position:relative; left:-10px;">&nbsp;</span>

Importantly, the google apps are using   rather than a conventional space. This type of space just so happens to be excluded from the checks in nsTextFrame::IsEmpty (which relies on IsAllWhitespace, defined here). So, nsTextFrame::IsEmpty sees   as non-whitespace. However, we don't even get that far in IsEmpty; instead, we end up failing the check here and returning false before even reaching the invocation of IsAllWhitespace. If you're curious, at the time of failure mState is

NS_FRAME_SIMPLE_DISPLAYLIST | NS_STATE_IS_HORIZONTAL | NS_STATE_MENU_HAS_POPUP_LIST | NS_STATE_BOX_WRAPS_KIDS_IN_BLOCK | NS_STATE_IS_DIRECTION_NORMAL | NS_STATE_FLEX_IS_EMULATING_LEGACY_BOX | TEXT_NO_RENDERED_GLYPHS

according to Visual Studio. It's unclear to me how that's failing, since the check is against TEXT_ISNOT_ONLY_WHITESPACE, but there you have it.

Morgan suggested looking at the text node sitting in the text frame's mContent and checking that whitespace manually, which works. I'm planning to push a changeset with that strategy for discussion soon.

Comment 5

[Nathan LaPré]

Attachment: Bug 1776928 - avoid backplating text that is entirely whitespace in HCM, r?morgan

Some sites use text content that consists entirely of whitespace, which can
lead to unexpected rendering in High Contrast Mode - namely, backplating of
invisible characters. This commit adds logic that detects text nodes consisting
entirely of whitespace and reports their text area as 0. This commit also adds
a test for the behavior, and modifies an existing test to reflect the new
behavior.

Comment 6

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/13ec2080e98a
avoid backplating text that is entirely whitespace in HCM, r=morgan

Comment 7

[Cristian Tuns]

https://hg.mozilla.org/mozilla-central/rev/13ec2080e98a