TODO

# Expose performance counters

# depth-based shading pipeline

Use depth rather than stencil to occlude objects (as in fast ui draw):
- simpler for stroke and convex fill, similar for complex fill 
- opaque draw can benefit of Z rejection
- might be possible to implement a `frame` combinator to clip in/out. should be
  combined with a stroke to hide the lack of antialiasing :P

# Abstract the GL backend.

The two promising approaches are:
- [Lit](http://erratique.ch/software/lit), however it is not actively developed
- [Bgfx](https://github.com/bkaradzic/bgfx), a bit overkill and in C++ (which paradoxically, worsen the portability, especially if considering Web GL)
  
## OSX target

Proper support for OSX platform is a must.

# Better Font management

The strategy for allocating and collecting font buffers is quite naive... It
deserves more work.

# Spatial and temporal sharing

Something very naive would deliver most of the benefits...

# Integration with VG and abstraction for reusing buffers.

...

# Document

Wall API could benefit from some doc comments (especially fonts and tasks)