Pango is in clearly maintenance mode — Behdad and I have a Pango work day once every few months, whenever we get together somewhere.
But thats about it. Things that we don’t get done in a day often sit unfinished for long times in git branches or issues. Examples for this are the color Emoji support that took many years to land, or the subpixel positioning work that is still unfinished.
This doesn’t mean that text rendering is in decline. Far from it. In fact, Harfbuzz is more active than ever and has had unprecedented success: All major Web browsers, toolkits, and applications are using it.
We’ve discussed for a while how to best take advantage of Harfbuzz’ success for text rendering on the desktop. Our conclusion is that we have to keep Pango from getting in the way. It should be a thin and translucent layer, and not require us to plumb APIs for every new feature through several internal abstractions.
We have identified several steps that will let us make progress towards this goal.
Many libraries provide subsets of Unicode data and APIs: GLib has some. ICU has some, fribidi has some. Even Harfbuzz has some.
Pango really does not need to provide its own wrappers for text direction or Unicode scripts. Not doing so means we don’t have to update Pango when there is a new version of Unicode.
New font features land regularly in Harfbuzz. By providing direct access to Harfbuzz objects, we can make these available to GTK and applications without adding APIs to Pango.
Stop using freetype
Freetypes FT_Face object has locking semantics that are broken and hard to work with; they are constantly getting in the way as we are juggling hb_fonts, FT_Face and cairo scaled font objects.
We’ve concluded that the best way forward is to stop using freetype for font loading or accessing font and glyph metrics. We can use Harfbuzz for all of these (a small gap will be closed soon).
Using Harfbuzz for font loading means that we will lose support for bitmap and type1 fonts. We think this is an acceptable trade-off, but others might disagree. Note that Harfbuzz does support loading bitmap-only OpenType fonts.
Shaping is the process of turning a paragraph of text and fonts into a sequence of positioned glyphs for rendering. Historically, Pango has used a different implementation on each platforms.
Going forward, we want to use Harfbuzz for shaping on all platforms. The web browsers already do this, and it works well. This will let us clean up a lot of old, unused shaping engine abstractions in Pango.
As a general direction, we want to move Pango towards (horizontally) unhinted rendering, combined with subpixel positioning. Other platforms are already doing this. And it gives us resolution-independent layout that is better suited for scalable apis and OpenGL rendering.