1713199 - Italic variant not selected but defined in style

Status: RESOLVED INVALID

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

Description

[Calixte Denizet (:calixte)]

Attachment: toto.html

The attached html contains 2 fonts Arial:

• one with property font-style: oblique -12deg;
• one with property font-style: oblique 0deg.

and at the end <span style="font-family: Arial; font-style: italic;">Hello world</span>.
The text is rendered with the normal variant and not the italic one.
It works correctly in Chrome (unstable at least).
I met this bug when implementing XFA stuff in pdf.js.

:jfkthame, could help here ?

Comment 1

[Calixte Denizet (:calixte)]

If an info is missing in the font itself, please tell me, it's likely caused by an issue in pdf.js where fonts are parsed and rewrote.

Comment 2

[Jonathan Kew [:jfkthame]]

This looks like correct behavior, according to the CSS font-matching algorithm.

oblique -12deg is a poor match for italic; the face with oblique: 0deg is preferred. If the <span> were actually styled with a negative oblique style, then the oblique -12deg face would be used.

I think the root of this is a misunderstanding in handling the mapping between italic/oblique angles as found in the OpenType font and the values used in CSS. OpenType measures the angle counter-clockwise, so that a "normal" right-leaning italic font has a negative angle; but CSS measures clockwise, so the default oblique angle is 14deg, and a negative angle would represent a left-leaning font. See https://drafts.csswg.org/css-fonts-4/#valdef-font-style-oblique-angle.

Comment 3

[Calixte Denizet (:calixte)]

And adding a minus to the angle fixes the issue, thanks a lot.