Open Bug 1248191 Opened 7 years ago Updated 5 years ago

inconsistent box height between HWA on and off


(Core :: Graphics, defect, P3)

1.9.0 Branch
Windows 7



Tracking Status
firefox47 --- wontfix


(Reporter: alice0775, Assigned: jfkthame)


(Depends on 1 open bug)


(Keywords: regression, Whiteboard: [gfx-noted])


(1 file)

Attached file test.html
When I test Bug 786039, I found the following problem.

I think outer and inner box height should be identical with HWA on/off.

<style type="text/css">
* {
  font: 13px arial, sans-serif;
  text-decoration: none; 
<div id="outer">
    <span id="inner" href="">ZZZZZZZZ</span>

Steps To Reproduce:
1. Open attached with HWA on and off
2. Open Inspector and observe box height

Actual Results:
HWA on
outer box height = 16
inner box height = 15

HWA off
outer box height = 16
inner box height = 16

Expected Results:
outer box height == inner box height

Regression window:
Force enabled HWA

Suspect: 4365eabf7fb0	Jonathan Kew — bug 549190 - round dwrite font vertical metrics to improve rendering/spacing consistency. r=bas
Depends on: 786039
Assignee: nobody → jfkthame
Whiteboard: [gfx-noted]
Jonathan, is this something we should be worrying about?  It's been around for 6 years...
Flags: needinfo?(jfkthame)
I think this is one of a number of issues around font metrics and line height, which would be good to clean up for better consistency and more predictable behavior. Ideally, using the same font across different platforms (GDI and DWrite being in effect two different platforms here) would result in the same metrics, at least vertically (horizontal metrics may depend on the platform's hinting behavior).

The trouble is that touching anything in this area has a high risk of disturbing some legacy quirk that will have unexpected consequences all over the place. And in general sites shouldn't be so fragile that they'll break due to small differences in font metrics, so it's not been a top priority.
Flags: needinfo?(jfkthame)
Thanks.  Note for triage - we should stop tracking and triaging this.
Version: Trunk → 1.9.0 Branch
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