rototiller: add threaded rendering

This is a simple worker thread implementation derived from the ray_threads
code in the ray module.  The ray_threads code should be discarded in a
future commit now that rototiller can render fragments using threads.

If a module supplies a prepare_frame() method, then it is called
per-frame to prepare a rototiller_frame_t which specifies how to divvy
up the page into fragments.  Those fragments are then dispatched to a
thread per CPU which call the module's rendering function in parallel.

There is no coupling of the number of fragments in a frame to the number of
threads/CPUs.  Some modules may benefit from the locality of tile-based
rendering, so the fragments are simply dispatched across the available CPUs
in a striped fashion.

Helpers will be added later to the fb interface for tiling fragments, which
modules desiring tiled rendering may utilize in their prepare_frame()
methods.

This commit does not modify any modules to become threaded, it only adds
the scaffolding.

0 files changed, 0 insertions, 0 deletions