This new system use transform feedback to compute subdivided hair points
position. For now no smoothing is done between input points.
This new system decouple the strands data (uv, mcol) with the points
position, requiring less update work if only simulation is running.
In the future, we can have compute shader do the work of the feedback
transform pass since it's really what it's meant to. Also we could generate
the child particles during this pass, releasing some CPU time.
draw_hair.c has been created to handle all of the Shading group creations
as well as subdivision shaders.
We store one final batch per settings combination because multiple viewport
or render could use the same particle system with a different subdivision
count or hair shape type.
There are a few places where DerivedMesh is still used, most notably
when calling the (not yet ported) cloth simulation. There is also still
the use of Object.derivedDeform and Object.derivedFinal. Those places are
marked with a TODO.
Some functions in the editors module were copied to accept Mesh. Those
already had 'mesh' in the name; the copies are suffixed with '__real_mesh'
for easy renaming later when the DM-based functionality is removed.
We can not rely on edit->psys, it is not set for particle edit,
and there is some logic deeper inside which does different things
dependent on that.
We need to replace those checks with some some HAIR vs. PARTICLES
flag and always set psys pointer.
The idea is that edit mode structure is owned by original object,
and used for drawing. This is a bit confusing, especially since
path cache is also in that structure and needs evaluated object
to calculate cache.
In the future we should split edit data from visualization data,
but that's bigger refactor.
The depsgraph was always created within a fixed evaluation context. Passing
both risks the depsgraph and evaluation context not matching, and it
complicates the Python API where we'd have to expose both which is not so
easy to understand.
This also removes the global evaluation context in main, which assumed there
to be a single active scene and view layer.
Differential Revision: https://developer.blender.org/D3152
This means fewer indices to store. That being said, it seems to be a little
slower because of the restart index. But that's in the case we would be
vertex bound, which is mostly never going to happen.
The way how particle state is to be accessed or used did not change
in Blender 2.8, so the drawing code should follow old design.
This code is somewhat duplicated from drawobject.c, but old draw
code is on the way to be removed anyway.
This fixes issue with disappearing particles when tweaking number
of particles.
New implementation of hair for Eevee.
Note: A hard coded "transmission" property is being used. This should
eventually be exposed to the UI, possibly in the form of SSS
properties.
This still has a couple of issues:
* Instancing is not working when multiple particle systems use the same
primitive. Only the last particle system to be drawn with a particular
primitive shows up.
* Because of colors being passed as uniforms with static variables, the
color of the collection of the last object to be evauluated is used for
all particles being displayed.
Also, note that while this is being drawn in the clay engine, this might
be moved to the object mode later intead.
Part of T51378
