Hello,

Is it possible (to write a Firefox extension, say) to find out what
font a particular block of text is being rendered in?

Asking on IRC, I learnt of the "Font Finder" extension [http://
bendodson.com/extensions/] and window.getComputedStyle, but both of
them display the font that *should* have been there, and do not handle
substitutions that were performed in case a font was unavailable.

Is information available somewhere about the actual font that is being
used?

Thanks,

Note that it could be a different font for every character (or at least glyph
cluster) in the text....

Basically, no.  At least not exposed to anything outside gfx, last I checked.

-Boris

I would like to see this too.

We should add something to inIDOMUtils for this.

Patches accepted.

Rob

As others have mentioned several fonts can be used within a single text run due to font fallback.  Since the font matching code is platform specific, the logging is different on each platform.

Under Windows, font matching logs can be dumped even from production builds. Open up a command shell and set the following environment variable:

  set NSPR_LOG_MODULES=winfonts:5

Change directories to the one containing Firefox 3 and run the executable directly:

  firefox -console

You'll see the details of all font matching operations spewed to a console window on a character-by-character basis.

On the Mac you'll need to set up your own build and uncomment the // #define DUMP_TEXT_RUNS in gfx/thebes/src/gfxAtsuiFonts.cpp.  Rebuild, then open up a Terminal window and use:

  export NSPR_LOG_MODULES=atsuiTextRun:5
  cd <obj-dir>/dist/MinefieldDebug.app/Contents/MacOS
  firefox

Each text run will be dumped with a record of the fonts that were matched.

Beyond simple logging that works on all platforms we should probably have a way of inspecting this information so that Firebug can display this information directly.

Cheers,

John