This means that rendering clay with AO only needs 1 geometry pass.
Thus greatly improving performance of poly heavy scene.
This also fix a self shadow issue in the AO, making low sample count
way better.
We also do not need to blit the depth anymore since we
are doing a fullscreen shading pass.
The constant cost of running the a deferred shading pass is negligeable.
This include quite a bit of code cleanup inside clay_engine.c.
The deferred pipeline is only enabled if at least one material needs it.
Multisampling is not supported yet.
Small hacks when doing deferred:
- We invert the normal before encoding it for precision.
- We put the facing direction into the sign of the mat_id.
- We dither the normal to fight the low bitdepth artifacts of the normal
buffer (which is 8bits per channel to reduce bandwidth usage).
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