Blender Git Loki

Import changes from development branch

Merge branch 'master' into subdivision_work

Fix missing subdivision evaluation when modifier is applied.

Merge changes from development branches.

Merge branch 'master' into subdivision_work

Merge branch 'master' into subdivision_work

Vertex crease: import changes from code review

Merge branch 'master' into subdivision_work

Subdivision: basic GPU subdivision for OpenGL

This implements GPU subdivision via OpenSubDiv for OpenGL based render
engines. At the moment only uniform subdivision is supported. Adaptive
subdivision still lacks a way to render triangles from the subdivision
patches.

The GPUBatch is extended with a new VBO and a new IBO to gather
subdivided points and indices. This allows to render the subdivided
surface and the original control cage in edit mode without disrupting
too much the code.

To generate triangles from the subdivided index buffer, a compute
shader is used. Although, at the moment normals are not computed there
so a CPU fallback is used, where data is read from the GPU, processed
on the CPU to generate triangles and normals, and then sent back to
the GPU. To compute normals, a secondary compute shader might be used.
This is not ideal for performance, but allows to validate that
subdivision is indeed performed properly on the GPU.

Attributes (including UVs and vertex colors) are not supported yet.

For performance, some proper caching mechanism will need to be used.
There currently is some logic to cache the subdivision structures that
can be reused between updates. However, it is deactivated as it does
not properly detect when changes occur, and causes crashes in edit
mode.

Performance can be further improved by reducing data transfer to the
GPU, since OpenSubDiv asks us to allocate buffers big enough for the
refined and coarse mesh we also allocate such buffer on the host, and
transfer the entier buffer worth of data to the device, although only
the coarse part need to be truly allocated on the host and sent to the
device. This will require some change to the vertex buffer structure.

Subdivision: store settings in the Mesh datablock

This stores the subdivision settings in the Mesh datablock in order to simplify
detection of whether subdivision is needed, especially for rendering to avoid
subdividing a Mesh twice, one on the Blender side, and once on the render engine
side.

Ref T68891

Subdivision: initial support for face holes

Subdivision: add support for vertex creasing

This adds vertex creasing support for modeling, rendering, and Alembic IO. This is only implemented for OpenSubDiv.

For modeling, vertex creasing follows the edge creasing implementation with an operator accessed through the Vertex menu in Edit Mode, and some parameter in the properties panel.

Also added options to the Subsurf and Multires modifiers to disable vertex creasing, the existing option is only affecting edge creasing. Not sure if this is desirable, but I think it makes sense to separate them, as it can help people understand and study the effects of each of them.

For Cycles this adds a couple of sockets on the Mesh node to hold data about which vertices are creased (one socket for the indices, one for the weigths). We could have a single socket with a value for every vertex, but this helps reducing memory usage a bit. Crease weights for vertices are then merged with the ones for edge creasing when setting up data for OpenSubDiv.

For rendering vertex creasing in the viewport in Edit Mode, I tried to have a similar rendering as for edge creasing, that is with a colored outline, but I could not get it to work properly, so I resorted to mixing the vertex selected color with the edge crease color so the creasing is shown to emanate from the vertices, along the edges. If both vertices of an edge are creased, this would render the edge as creased. This needs improvement.

To support rendering vertex and edge creases differently, `EditLoopData` was modified to hold `ushorts` instead of `uchars` in order to store more bit flags as all available bits in `EditLoopData.e_flag` were used. (For those unaware, this structure maps to an `ivec4` in the GLSL shader, so adding another member to hold vertex creasing is not really possible.)

For Alembic, vertex creases are read and written in a similar fashion as edge creases (vertex creases are called "corners" in Alembic), so this is only written if a subdivision modifier is present on the Blender Mesh.