This makes brush influence into a tube instead of a sphere.
It can be used along the outline of a mesh to adjust it's silhouette.
Note that all this takes advantage of changes from vertex paint,
from testing this seems useful so exposing from the brush options.
This behavior makes more sense for sculpt, less so for painting.
Restores non PBVH behavior, adding `BKE_pbvh_find_nearest_to_ray` -
similar to ray-cast except it finds the closest point on the surface.
Restoring weights is problematic when the stroke overlaps its mirror.
It's better to simply compute the new weight based on the saved data
rather than restoring things, and check that the change is monotonic.
This way is also closer to how things worked before the merge.
This secondary accumulation option accumulated brush falloff.
The same option in image painting accumulates color
as vertex paiht 'Spray' does.
Giving this option different behavior for vertex paint seems strange.
Also this is basically increasing falloff over time.
Remove the new code, expose existing 'Spray' as 'Accumulate'
to match other paint modes.
Notes:
- Changes in paint_vertex.c were simple to merge, mainly related on passing
evaluation context.
- Conflicts in EditDM and drawmesh.c are solved using code from blender2.8
branch. Those areas are deprecated and not to be used in final release.
However, it's possible that some reference code from master is lost, so
keep attention when adding alpha support for vertex painting.
This makes vertex paint match image painting more closely.
- Add falloff shape option sphere/circle
where sphere uses a 3D radius around the cursor and
circle uses a 2D radius (projected), like previous releases.
- Add normal angle option so you can control the falloff.
- Add Cull option, to paint onto faces pointing away.
Disabling normals, culling and using circle falloff
allows you to paint through the mesh.
When painting with spray disabled - we need to re-apply
on top of the original each time.
Applying the soc-2016-pbvh-painting branch removed this.
While I'd added back a simple previous weight array,
this won't work when multiple groups are painted at once.
This is most pronounced in Auto-Normalize + Multi-Paint. Unlike
vertex paint, the weights being painted on in weight paint mode
don't necessarily correspond to the weight actually stored in
any one vertex group, and may instead be a computed aggregate.
This restores original code behavior lost in rB4f616c93f7cb.
