rendering.
RE_BlenderFrame() and RE_BlenderAnim() are Blender's internal
top-level rendering API functions for a single frame and a series of
frames, respectively. These functions rely on global variables to
keep render pipeline states. Freestyle's stroke rendering was also
using RE_BlenderFrame to render a temporary scene of stroke meshes.
These nested calls of the top-level rendering API functions were
causing broken render pipeline states and eventually led to a crash.
This commit is intended to fix the issue, by introducing an rendering
API function RE_RenderFreestyleStrokes specifically used for stroke
rendering in Freestyle. The new function does not do anything with
regard to the global variables in the rendering API implementation.
6a681bca45