[Bf-viewport] Viewport drawing flow

[Dalai Felinto]

Hi there,

Part of the challenge of the viewport project is to consolidate a
state-of-the-art PBR realitme pipeline with our more mundane drawing
requirements (widgets, image references, outline, ...).

I/we put together a diagram that tries to unify them both, taking as a
reference for PBR the implementation Clément wrote last month [1].

https://docs.google.com/drawings/d/1MGKl2fnZ5h8Z7RyM67ogIUWcFD0A5I5vZhIN2BnawSM/edit?usp=sharing

I hope to address eventual feedbacks soon so we land a final design
for this. Followed by start porting over the already converted plates
(wires, grid, grease pencil)  to the new view3d_draw.c file.

Initially this will be done directly in the color buffer, just to
start compartmentalizing the functions, and later we start worrying
about FBO, other buffers and compositing the plates together.

[1] - https://wiki.blender.org/index.php/Dev:2.8/Viewport/PBR_Pipeline

Thanks,
Dalai
--
blendernetwork.org/dalai-felinto
www.dalaifelinto.com