GitLab

Summary:
# Problem
In CT / State Encoding, we expect a scenario where we would like to render a batch of topologies where each of them would have different number of vertices and triangles. Currently the only way to support this with DRTK is to iterate over the batch in a for loop for each topology and render it.
In a series of diffs we would like to solve this issue by making drtk consume a batch of triangles as opposed to just 1 set of triangles. However, we would like to achieve this behavior without affecting the most common single topology case by a lot.

# How do we pass in multiple topologies in a single batch?
We will provide a TopologyBatch structure in xrcia/lib/graphics/structures where we will provide functionality to create a Batch x MaxTriangles x 3 and Batch x MaxVertices x 3.
Padded vertices will be 0s and padded triangles will have MaxVertices - 1 as their value. But these will discarded as degenerate in rasterization / rendering.

# In this diff
- Extend render kernel and render backward kernel to support a batch dimension as default.
- `render` will now unsqueeze the batch dimension when using a single topo
- We access the vertex indices of triangles by walking an additional `batch stride * n` in the triangles data pointer.
- Add an extra condition to check to see if the triangles are degenerate; this happens when padding the batch.
- We show that the we don't cause too much overhead in GPU by introducing these 3 extra operations (Same profiling as in D68423813)

Reviewed By: podgorskiy

Differential Revision: D68423409

fbshipit-source-id: e1007b9844658ef6e1bb2267b6a94804f3b6d13b