How a font makes its way through the encoding process


Import a DCP containing some subtitles with fonts.

* Examiner

Builds _fonts containing (font-ID, font-TTF-data)
Add to allocator (asset-ID, font-ID)

font-ID will be unique in its own asset, but not more widely.

Use the allocator to set the font ID to N_font-ID where N is an integer unique for all fonts in the DCP.

If there's no fonts in the DCP, add one with an empty ID - we want something in the content for users
to edit.


Now the text content contains fonts with IDs unique within the content.


* DCP Decoder

Some subtitle arrives with an "original" font ID.
Use an allocator (built the same way as in the examiner) to replace the ID with a new one N_font-ID.


Q: Why do we need the allocator?
A: Because we need an ID to refer to each font in the content (to be stored in metadata.xml)
   and we need to turn this ID back into an actual Font C++ object so it must be unique within
   the content.  Also we allow these fonts to have their settings altered so they must have unique
   IDs for that.


* Text Decoder

Calls content->get_font() to get the Font C++ object by the (newly-allocated) ID.  This works because
the allocated font-ID is unique within the content.

The Font C++ object pointer is written to the subtitle.


* Player

Passes subtitles through.


* Writer

Gets all fonts, puts them in the font ID map using the font's original ID.  This is OK because we
don't need uniqueness in the DCP any more.


* Reel Writer

Gets subtitles, uses font ID map to find the ID from the Font C++ object pointer.  Puts this ID in
the font and writes it to the asset.  Ensures the required LoadFont is added.