1027580 - Layout of CSS transformed text may be broken when zoom in

Status: NEW

(Core :: Layout: Text and Fonts, defect)

Description

[Duan Yao]

User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:32.0) Gecko/20100101 Firefox/32.0 (Beta/Release)
Build ID: 20140608030203

Steps to reproduce:

Open the attached htm file with firefox, zoom in to maximum ratio by ctr++.

The text lines in this file are specified with large font-size, e.g. 896px (64*14px); and transformed back to normal size, e.g. transform:matrix(0.03125,0,0,0.03125,0,0) (1/64 = 0.03125).

So, these lines should look exactly same as those with font-size:14px.



Actual results:

All the text lines should be rendered properly.


Expected results:

Characters in "[64x]ABCDEFGHIJK" and "[32x]ABCDEFGHIJK" lines are overlapping, and their border box's heights are smaller. While "[16x]ABCDEFGHIJK" and below are normal.

Comment 1

[Duan Yao]

Attachment: transformed text zoom in example

Comment 2

[Duan Yao]

> Actual results:
> 
> All the text lines should be rendered properly.
> 
> 
> Expected results:
> 
> Characters in "[64x]ABCDEFGHIJK" and "[32x]ABCDEFGHIJK" lines are
> overlapping, and their border box's heights are smaller. While
> "[16x]ABCDEFGHIJK" and below are normal.

Well, it should be:

Actual results:

Characters in "[64x]ABCDEFGHIJK" and "[32x]ABCDEFGHIJK" lines are overlapping, and their border box's heights are smaller. While "[16x]ABCDEFGHIJK" and below are normal.

Expected results:

All the text lines should be rendered properly.

Comment 3

[Duan Yao]

firefox 30-33 all have this problem.

Comment 4

[Duan Yao]

Additional experiment shows that:

1. Non-identity CSS transform is required to trigger this bug. A matrix(0.9,0,0,0.9,0,0) is enough. Only a large font-size can't trigger this bug.

2. The font-size value matters, while scaling factor of transform doesn't. The threshold font-size to trigger this bug seems between 336~392px. The bigger the font-size is, the more the characters overlapping.

Comment 5

[Paul Silaghi, QA [:pauly]]

Confirmed in 33.0a1 (2014-07-14), Ubuntu 14.04