Bug 286608 – Display all the fonts used in a DOM node

• Component: Web Inspector
• Status: NEW

[Karl Dubost]

Created attachment 474037 [details]
testcase

1. Open the testcase.html with Safari on Desktop
2. Inspect the text 
3. Go to the font Tab

Expected:
Display all the fonts being used

Actual: 
Only the primary defined font is shown

See how Firefox Devtools displays:
* Helvetica
* Hiragino Kaku Gothic ProN

[Radar WebKit Bug Importer]

<rdar://problem/143740107>

[Karl Dubost]

Created attachment 474038 [details]
rendering in safari, firefox

Safari and Firefox with Web Inspector and Dev tools opened on the fonts tab.

[Razvan Caliman]

For clarification, when a font does not have all the necessary glyphs to render a piece of text, fallback fonts will be used for those missing glyphs, going through available fonts declared in `font-family` and down to the default fonts on the system. 

Web Inspector now shows just the "primary font" used to render that node's text:

https://github.com/WebKit/WebKit/blob/b80a2ae51aaf378d3d1de94c0a857f48228ee7fb/Source/WebCore/inspector/agents/InspectorCSSAgent.cpp#L609-L621

There's a getter for this primary font information in `FontCascade`:
https://github.com/WebKit/WebKit/blob/845f0a548125461da779d734a84b15498a4538cb/Source/WebCore/platform/graphics/FontCascade.h#L384-L390

There's no explicit getter for fallback fonts. But a cursory look shows it might be possible to get that information by keeping records while going through `FontCascadeFonts::realizeFallbackRangesAt`:

https://github.com/WebKit/WebKit/blob/845f0a548125461da779d734a84b15498a4538cb/Source/WebCore/platform/graphics/FontCascadeFonts.cpp#L198-L232

[Karl Dubost]

To note that this is essential to be able to investigate some webcompat issues related to fonts.