289 Commits

Author SHA1 Message Date
Georgia Gkioxari
e651a4299c add texture vertex sampling functionality to textures
Summary: Enhance every texture type with `faces_verts_textures_packed` that allows users to query the texture of each vertex in mesh

Reviewed By: nikhilaravi

Differential Revision: D24058778

fbshipit-source-id: 19d0e3a244fa96aae462c47bf52e07dfd3b7c6f0
2020-10-06 10:44:33 -07:00
Georgia Gkioxari
327bd2b976 extend sample_points_from_meshes with texture
Summary:
Enhanced `sample_points_from_meshes` with texture sampling

* This new feature is used to return textures corresponding to the sampled points in `sample_points_from_meshes`

Reviewed By: nikhilaravi

Differential Revision: D24031525

fbshipit-source-id: 8e5d8f784cc38aa391aa8e84e54423bd9fad7ad1
2020-10-06 09:17:58 -07:00
Amitav Baruah
8f1e9e1f06 Plotly figure for visualizing pointclouds
Summary:
Visualize a pointcloud in plotly.
- customize lighting and light position
- customizable axis arguments
- customizable height and width of plotly figure
- render batches in subplots or the same plot

Reviewed By: nikhilaravi

Differential Revision: D23872391

fbshipit-source-id: 9b1e1fd417500521be9d0eb85d71c77a538fa77c
2020-10-01 16:49:19 -07:00
Amitav Baruah
8b6310359f plotly figure for visualizing a mesh
Summary:
Visualize a mesh in a plotly figure.
- customize lighting and light position
- customizable axis arguments (x, y, z)
- customizable height and width of plotly figure
- render batches of meshes in subplots or in a singular plot

Reviewed By: nikhilaravi

Differential Revision: D22611960

fbshipit-source-id: 5dc5c55e599d5b0d9c38f22e156c662654099e11
2020-10-01 16:49:19 -07:00
Patrick Labatut
8219a52ccc Fix a few linting warnings
Summary: Fix a few linting warnings

Reviewed By: nikhilaravi

Differential Revision: D20720810

fbshipit-source-id: c5b6a25fdd7971cc8743b54bbe162464a874071d
2020-10-01 02:39:27 -07:00
Eduardo Henrique Arnold
4f8a2f1979 Fixing look_at_view_transform documentation, azim angle definition was incorrect (#251)
Summary:
…between the projection on the y=0 plane and reference vector (0,0,1).

Fixes https://github.com/facebookresearch/pytorch3d/issues/229

Pull Request resolved: https://github.com/facebookresearch/pytorch3d/pull/251

Reviewed By: gkioxari

Differential Revision: D23967073

Pulled By: nikhilaravi

fbshipit-source-id: fb6f10d4b7f5e319d17e28b4316837205b637f5e
2020-09-29 09:47:09 -07:00
generatedunixname89002005307016
d902a96ca2 suppress errors in vision - batch 1
Differential Revision: D23970214

fbshipit-source-id: b6a328f53178304b36556b5cf96584467a7d2ce4
2020-09-28 13:33:20 -07:00
Nikhila Ravi
e5ac38aa87 fix docs for FOVPerspectiveCamera
Summary: Small documentation fix for FOVPerspectiveCamera. The error pointed out in the GitHub issue was due to the docs referring to the OpenGL z parameterization from [-1, 1] whereas we use the [0, 1] range.

Reviewed By: gkioxari

Differential Revision: D23857312

fbshipit-source-id: 2d20677ec614c935e76f67e100a41a23df708d59
2020-09-23 17:28:15 -07:00
Nikhila Ravi
956d3a010c Support for moving the renderer to a new device
Summary:
Support for moving all the tensors of the renderer to another device by calling `renderer.to(new_device)`

Currently the `MeshRenderer`, `MeshRasterizer` and `SoftPhongShader` (and other shaders) are all of type `nn.Module` which already supports easily moving tensors of submodules (defined as class attributes) to a different device. However the class attributes of the rasterizer and shader (e.g. cameras, lights, materials), are of type `TensorProperties`, not nn.Module so we need to explicity create a `to` method to move these tensors to device. Note that the `TensorProperties` class already has a `to` method so we only need to call `cameras.to(device)` and don't need to worry about the internal tensors.

The other option is of course making these other classes (cameras, lights etc) also of type nn.Module.

Reviewed By: gkioxari

Differential Revision: D23885107

fbshipit-source-id: d71565c442181f739de4d797076ed5d00fb67f8e
2020-09-23 17:13:07 -07:00
andrijazz
b1eee579fd resouces filenames with spaces (#358)
Summary:
I'm constantly encountering 3D models with resources that have spaces in their filenames (especially on Windows) and therefore they can't be loaded in pytorch3d. Let me know what you think.

Thanks

Pull Request resolved: https://github.com/facebookresearch/pytorch3d/pull/358

Reviewed By: bottler

Differential Revision: D23798492

Pulled By: nikhilaravi

fbshipit-source-id: 4d85b7ee05339486d2e5ef53a531f8e6052251c5
2020-09-23 12:12:20 -07:00
Nikhila Ravi
93d3d8feda Tidy OBJ / MTL parsing
Summary: Tidy OBJ / MTL parsing: remove redundant calls to tokenize, factor out parsing and texture loading

Reviewed By: gkioxari

Differential Revision: D20720768

fbshipit-source-id: fb1713106d4ff99a4a9147afcc3da74ae013d8dc
2020-09-23 12:12:20 -07:00
Jeremy Reizenstein
ea0e762c36 Fix TexturesUV doc
Summary: Fix map size in the comment.

Reviewed By: gkioxari

Differential Revision: D23813431

fbshipit-source-id: e0777beadd7473014c1b79ad9f850d10f3549599
2020-09-21 11:39:35 -07:00
Jeremy Reizenstein
197f1d6217 save_ply binary
Summary:
Make save_ply save to binary instead of ascii. An option makes the previous functionality available. save_ply's API accepts a stream, but this is undocumented; that stream must now be a binary stream not a text stream.

Avoiding warnings about making tensors from immutable numpy arrays.

Possible performance improvement when reading binary files.

Fix reading zero-length binary lists.

Reviewed By: nikhilaravi

Differential Revision: D22333118

fbshipit-source-id: b423dfd3da46e047bead200255f47a7707306811
2020-09-21 05:16:31 -07:00
Nikhila Ravi
ebe2693b11 Support variable size radius for points in rasterizer
Summary:
Support variable size pointclouds in the renderer API to allow compatibility with Pulsar rasterizer.

If radius is provided as a float, it is converted to a tensor of shape (P). Otherwise radius is expected to be an (N, P_padded) dimensional tensor where P_padded is the max number of points in the batch (following the convention from pulsar: https://our.intern.facebook.com/intern/diffusion/FBS/browse/master/fbcode/frl/gemini/pulsar/pulsar/renderer.py?commit=ee0342850210e5df441e14fd97162675c70d147c&lines=50)

Reviewed By: jcjohnson, gkioxari

Differential Revision: D21429400

fbshipit-source-id: 65de7d9cd2472b27fc29f96160c33687e88098a2
2020-09-18 18:48:18 -07:00
z003yctd
e40c2167ae fix incorrect variable naming (#362)
Summary: Pull Request resolved: https://github.com/facebookresearch/pytorch3d/pull/362

Reviewed By: bottler

Differential Revision: D23712242

Pulled By: nikhilaravi

fbshipit-source-id: 1c4184c8482049991356be7dbc9755b0c2018a1d
2020-09-17 16:50:34 -07:00
OrHayat
de77e426eb typo in docstring (#322)
Summary:
fixed small typo in update_padded function docstring.

Pull Request resolved: https://github.com/facebookresearch/pytorch3d/pull/322

Reviewed By: gkioxari

Differential Revision: D23712324

Pulled By: nikhilaravi

fbshipit-source-id: fea3b68039644b236897c6f465cbb322c5c48085
2020-09-16 16:22:28 -07:00
Amitav Baruah
872ff8c796 Add background color support to compositors
Summary: Support rendering different color backgrounds for pointclouds for both compositors

Reviewed By: nikhilaravi

Differential Revision: D23611043

fbshipit-source-id: ab029650d51349340372c5bd66700e6577d48851
2020-09-14 10:39:08 -07:00
David Novotny
dc40adfa24 Bugfix: Wrong default T in SfMCameras
Summary: Fixes a bug that initializes default SfMCameras with a default _R instead of default _T

Reviewed By: gkioxari

Differential Revision: D23654583

fbshipit-source-id: ccfb7235b2fb6df5a2e402b9fb4b194e97d78dc6
2020-09-11 15:32:25 -07:00
Amitav Baruah
eb517dd70b Fix look_at corner case
Summary: When the camera is vertically oriented, calculating the look_at x-axis (also known as the "right" vector) does not succeed, resulting in the x-axis being placed at the origin. Adds a check to correctly calculate the x-axis if this case occurs.

Reviewed By: nikhilaravi, sbranson

Differential Revision: D23511859

fbshipit-source-id: ee5145cdbecdbe2f7c7d288588bd0899480cb327
2020-09-10 12:53:08 -07:00
Steve Branson
f8ea5906c0 Fix softmax_rgb_blend() when mesh is outside zfar
Summary:
This fixes two small issues with blending.py:softmax_rgb_blend():
  1) zfar and znear attributes are propagated from the camera settings instead of just using default settings of znear=1.0 and zfar=100.0
  2) A check is added to prevent arithmetic overflow in softmax_rgb_blend()

This is a fix in response to https://github.com/facebookresearch/pytorch3d/issues/334
where meshes rendererd using a SoftPhongShader with faces_per_pixel=1 appear black.  This only occurs when the scale of the mesh is large (vertex values > 100, where 100 is the default value of zfar).  This fix allows the caller to increase the value of cameras.zfar to match the scale of her/his mesh.

Reviewed By: nikhilaravi

Differential Revision: D23517541

fbshipit-source-id: ab8631ce9e5f2149f140b67b13eff857771b8807
2020-09-09 13:22:25 -07:00
generatedunixname89002005307016
6eb158e548 suppress errors in vision/fair/pytorch3d
Differential Revision: D23521117

fbshipit-source-id: 8e11e91aaa2a91b7ca1fa4c00a3db86ab8648f7f
2020-09-03 18:17:49 -07:00
David Novotny
316b77782e Camera alignment
Summary:
adds `corresponding_cameras_alignment` function that estimates a similarity transformation between two sets of cameras.

The function is essential for computing camera errors in SfM pipelines.

```
Benchmark                                                   Avg Time(μs)      Peak Time(μs) Iterations
--------------------------------------------------------------------------------
CORRESPONDING_CAMERAS_ALIGNMENT_10_centers_False                32219           36211             16
CORRESPONDING_CAMERAS_ALIGNMENT_10_centers_True                 32429           36063             16
CORRESPONDING_CAMERAS_ALIGNMENT_10_extrinsics_False              5548            8782             91
CORRESPONDING_CAMERAS_ALIGNMENT_10_extrinsics_True               6153            9752             82
CORRESPONDING_CAMERAS_ALIGNMENT_100_centers_False               33344           40398             16
CORRESPONDING_CAMERAS_ALIGNMENT_100_centers_True                34528           37095             15
CORRESPONDING_CAMERAS_ALIGNMENT_100_extrinsics_False             5576            7187             90
CORRESPONDING_CAMERAS_ALIGNMENT_100_extrinsics_True              6256            9166             80
CORRESPONDING_CAMERAS_ALIGNMENT_1000_centers_False              32020           37247             16
CORRESPONDING_CAMERAS_ALIGNMENT_1000_centers_True               32776           37644             16
CORRESPONDING_CAMERAS_ALIGNMENT_1000_extrinsics_False            5336            8795             94
CORRESPONDING_CAMERAS_ALIGNMENT_1000_extrinsics_True             6266            9929             80
--------------------------------------------------------------------------------
```

Reviewed By: shapovalov

Differential Revision: D22946415

fbshipit-source-id: 8caae7ee365b304d8aa1f8133cf0dd92c35bc0dd
2020-09-03 13:27:14 -07:00
Adly Templeton
14f015d8bf Add pyre typeshed information for Tensor.ndim and nn.ConvTranspose2d
Summary: Adding some appropriate methods into pyre typeshed. Removing corresponding pyre-ignore and pyre-fixme messages.

Differential Revision: D22949138

fbshipit-source-id: add8acdd4611ab698954868832594d062cd58f88
2020-09-02 06:52:30 -07:00
Jeremy Reizenstein
701bbef4f3 version number for version 0.2.5
Reviewed By: jcjohnson

Differential Revision: D23244140

fbshipit-source-id: 8f95c817637162350b61b1b0fc3d2de66087250e
2020-08-27 17:15:51 -07:00
Steve Branson
46c0e83461 Change default settings of clip_barycentric_coords
Summary: When raster_settings.clip_barycentric_coords is unspecified, clip_barycentric_coords is turned on if blur_radius is greater than 0.  This matches the behavior prior to D21705503 (cc70950f40).

Reviewed By: gkioxari

Differential Revision: D23375257

fbshipit-source-id: 4b87588aabb69d4d835d4dcceb11153628121d30
2020-08-27 16:44:12 -07:00
Jeremy Reizenstein
9aeb88b48e tutorial fixes. validate #cameras
Summary:
Update the installation cells to import torch.
Replace use of deprecated Textures in deform tutorial.
Correct the deform tutorial's idea of its own name.
Fix typo in batched part of render_textured_meshes which meant only one mesh was being rendered with a batch of cameras.
Add an error check in the rasterizer to make the error friendly from such a mistake elsewhere.

Reviewed By: gkioxari

Differential Revision: D23345462

fbshipit-source-id: 1d5bd25db052f7ef687b7168d7aee5cc4dce8952
2020-08-26 08:27:53 -07:00
Jeremy Reizenstein
909dc83505 amalgamate meshes with texture into a single scene
Summary:
Add a join_scene method to all the textures to allow the join_mesh function to include textures. Rename the join_mesh function to join_meshes_as_scene.

For TexturesAtlas, we now interpolate if the user attempts to have the resolution vary across the batch. This doesn't look great if the resolution is already very low.

For TexturesUV, a rectangle packing function is required, this does something simple.

Reviewed By: gkioxari

Differential Revision: D23188773

fbshipit-source-id: c013db061a04076e13e90ccc168a7913e933a9c5
2020-08-25 11:28:40 -07:00
Jeremy Reizenstein
e25ccab3d9 align_corners and padding for TexturesUV
Summary:
Allow, and make default, align_corners=True for texture maps. Allow changing the padding_mode and set the default to be "border" which produces more logical results. Some new documentation.

The previous behavior corresponds to padding_mode="zeros" and align_corners=False.

Reviewed By: gkioxari

Differential Revision: D23268775

fbshipit-source-id: 58d6229baa591baa69705bcf97471c80ba3651de
2020-08-25 11:28:40 -07:00
Eduardo Henrique Arnold
d0cec028c7 Fix look_at_view_transform when object location is not (0,0,0) (#230)
Summary:
The look_at_view_transform did not give the correct results when the object location `at` was not (0,0,0).

The problem was on computing the cameras' location in world's coordinate `C`. It only took into account the camera position from spherical angles, but ignored the object location in the world's coordinate system. I simply modified the C tensor to take into account the object's location which is not necessarily in the origin.

I ran unit tests and all but 4 failed with the same error message: `RuntimeError: CUDA error: invalid device ordinal`. However the same happens before this patch, so I believe these errors are unrelated.

Pull Request resolved: https://github.com/facebookresearch/pytorch3d/pull/230

Reviewed By: gkioxari

Differential Revision: D23278126

Pulled By: nikhilaravi

fbshipit-source-id: c06e891bc46de8222325ee7b37aa43cde44648e8
2020-08-21 23:43:47 -07:00
Nikhila Ravi
778383eef7 Texture loading and rendering in ShapeNetCore and R2N2 data loaders
Summary:
- Add support for loading textures from ShapeNet Obj files as a texture atlas.
- Support textured rendering of shapenet models

Reviewed By: gkioxari

Differential Revision: D23141143

fbshipit-source-id: 26eb81758d4cdbd6d820b072b58f5c6c08cb90bc
2020-08-21 20:42:17 -07:00
Nikhila Ravi
90f6a005b0 Tutorials textures updates and fix bug in extending meshes with uv textures
Summary:
Found a bug in extending textures with vertex uv coordinates. This was due to the padded -> list conversion of vertex uv coordinates i.e.                 The number of vertices in the mesh and in verts_uvs can differ
e.g. if a vertex is shared between 3 faces, it can
have up to 3 different uv coordinates. Therefore we cannot convert directly from padded to list using _num_verts_per_mesh

Reviewed By: bottler

Differential Revision: D23233595

fbshipit-source-id: 0c66d15baae697ead0bdc384f74c27d4c6539fc9
2020-08-21 19:20:09 -07:00
Jeremy Reizenstein
9a50cf800e Fix batching bug from TexturesUV packed ambiguity, other textures tidyup
Summary:
faces_uvs_packed and verts_uvs_packed were only used in one place and the definition of the former was ambiguous. This meant that the wrong coordinates could be used for meshes other than the first in the batch. I have therefore removed both functions and build their common result inline. Added a test that a simple batch of two meshes is rendered consistently with the rendering of each alone. This test would have failed before.

I hope this fixes https://github.com/facebookresearch/pytorch3d/issues/283.

Some other small improvements to the textures code.

Reviewed By: nikhilaravi

Differential Revision: D23161936

fbshipit-source-id: f99b560a46f6b30262e07028b049812bc04350a7
2020-08-21 05:53:29 -07:00
Steve Branson
9aaba0483c Temporary fix for mesh rasterization bug for traingles partially behind the camera
Summary: A triangle is culled if any vertex in a triangle is behind the camera.  This fixes incorrect rendering of triangles that are partially behind the camera, where screen coordinate calculations are strange.  It doesn't work for triangles that are partially behind the camera but still intersect with the view frustum.

Reviewed By: nikhilaravi

Differential Revision: D22856181

fbshipit-source-id: a9cbaa1327d89601b83d0dfd3e4a04f934a4a213
2020-08-20 22:24:19 -07:00
Georgia Gkioxari
57a22e7306 camera refactoring
Summary:
Refactor cameras
* CamerasBase was enhanced with `transform_points_screen` that transforms projected points from NDC to screen space
* OpenGLPerspective, OpenGLOrthographic -> FoVPerspective, FoVOrthographic
* SfMPerspective, SfMOrthographic -> Perspective, Orthographic
* PerspectiveCamera can optionally be constructred with screen space parameters
* Note on Cameras and coordinate systems was added

Reviewed By: nikhilaravi

Differential Revision: D23168525

fbshipit-source-id: dd138e2b2cc7e0e0d9f34c45b8251c01266a2063
2020-08-20 22:22:06 -07:00
root@sandcastle5743.frc3.facebook.com
f03aa5803b suppress errors in vision/fair/pytorch3d
Differential Revision: D23180198

fbshipit-source-id: cad1fa7ba9935f3ca20410a2575e173999c04be1
2020-08-17 18:08:19 -07:00
Georgia Gkioxari
7f2f95f225 detach for meshes, pointclouds, textures
Summary: Add `detach` for Meshes, Pointclouds, Textures

Reviewed By: nikhilaravi

Differential Revision: D23070418

fbshipit-source-id: 68671124ce114c4495d7ef3c944c9aac3d0db2d8
2020-08-17 14:55:54 -07:00
Nikhila Ravi
5852b74d12 Softmax blending small fix
Summary:
Small fix to the softmax blending function.

To avoid overflow in the exponential for the softmax, the exponent is shifted by the maximum value. In the final calculation of the color there is a weighted sum between the pixel color and the background color - in order for the sum to be correct, the background color also needs to be handled in the same way witt the shifted exponent.

Reviewed By: gkioxari

Differential Revision: D23148301

fbshipit-source-id: 86066586ee7d3ce7bd4a2076b12ce191fbd151a7
2020-08-17 11:59:53 -07:00
Patrick Labatut
6d76336501 Extract more reusable I/O functions
Summary: Continue extracting reusable I/O functions to a separate utils module (and remove duplication).

Reviewed By: nikhilaravi

Differential Revision: D20720433

fbshipit-source-id: e82b19560a5dc8a506c4c4d098da69c202790c4f
2020-08-11 15:51:30 -07:00
Luya Gao
63ba74f1a8 Return R2N2 voxel coordinates
Summary: Return R2N2's voxel coordinates.

Reviewed By: nikhilaravi

Differential Revision: D22462530

fbshipit-source-id: a995cfa0957b2561eb3b0f4591cb1db42170bc68
2020-08-07 13:22:26 -07:00
Luya Gao
326e4ccb5b Return R2N2 R,T,K
Summary: Return rotation, translation and intrinsic matrices necessary to reproduce R2N2's own renderings.

Reviewed By: nikhilaravi

Differential Revision: D22462520

fbshipit-source-id: 46a3859743ebc43c7a24f75827d2be3adf3f486b
2020-08-07 13:22:26 -07:00
Jeremy Reizenstein
7944d24d48 gather_scatter on CPU
Summary: CPU implementation of the graph convolution op.

Reviewed By: nikhilaravi, gkioxari

Differential Revision: D21384361

fbshipit-source-id: bc96730e9727bb9aa1b0a232dcb82f0c0d12fe6b
2020-08-05 07:00:20 -07:00
generatedunixname89002005307016
07d7e12644 suppress errors in vision/fair/pytorch3d
Differential Revision: D22834017

fbshipit-source-id: 441124c67a2bbfe086e2983d5c4c845b58fc965c
2020-07-29 18:24:04 -07:00
Nikhila Ravi
a3932960b3 Texturing API updates
Summary:
A fairly big refactor of the texturing API with some breaking changes to how textures are defined.

Main changes:
- There are now 3 types of texture classes: `TexturesUV`, `TexturesAtlas` and `TexturesVertex`. Each class:
   - has a `sample_textures` function which accepts the `fragments` from rasterization and returns `texels`. This means that the shaders will not need to know the type of the mesh texture which will resolve several issues people were reporting on GitHub.
  -  has a `join_batch` method for joining multiple textures of the same type into a batch

Reviewed By: gkioxari

Differential Revision: D21067427

fbshipit-source-id: 4b346500a60181e72fdd1b0dd89b5505c7a33926
2020-07-29 16:11:23 -07:00
Luya Gao
722c2b7149 Add BlenderCamera
Summary: Adding BlenderCamera (for rendering with R2N2 Blender transformations in the next diff).

Reviewed By: nikhilaravi

Differential Revision: D22462515

fbshipit-source-id: 4b40ee9bba8b6d56788dd3c723036ec704668153
2020-07-23 10:17:12 -07:00
Luya Gao
483e538dae Test R2N2 loads correct numbers of instances
Summary:
Sample/Get all views at the loading phase instead of returning phase;
Load only views from the split instead of all 24 views;
Test the numbers of views loaded are correct for each category.

Reviewed By: nikhilaravi

Differential Revision: D22631414

fbshipit-source-id: 1c5ce99fe2bdf6618c1aa0b69bb6899473376bc2
2020-07-23 10:17:12 -07:00
generatedunixname89002005307016
7cb9d8ea86 suppress errors in vision - batch 1
Reviewed By: pradeep90

Differential Revision: D22628883

fbshipit-source-id: a19c271b4025c0e3c61408604a7e0f9fbcbdfa5b
2020-07-20 17:13:59 -07:00
Nikhila Ravi
4f78af6170 pyre and lint fixes
Summary: Fixing several unused imports and pyre/linter warnings.

Reviewed By: bottler

Differential Revision: D22592491

fbshipit-source-id: 463383b9b73a545949475044fb5c531712f8482c
2020-07-17 10:28:53 -07:00
Roman Shapovalov
cdaac5f9c5 Bumping the threshold to allow leeway for CI testing randomness.
Summary:
1. CircleCI tests fail because of different randomisation. I was able to reproduce it on devfair (with an older version of pytorch3d though), but with a new threshold, it works. Let’s push and see if it will work in CircleCI.
2. Fixing linter’s issue with `l` variable name.

Reviewed By: bottler

Differential Revision: D22573244

fbshipit-source-id: 32cebc8981883a3411ed971eb4a617469376964d
2020-07-16 10:19:43 -07:00
Nikhila Ravi
cc70950f40 barycentric clipping in cuda/c++
Summary:
Added support for barycentric clipping in the C++/CUDA rasterization kernels which can be switched on/off via a rasterization setting.

Added tests and a benchmark to compare with the current implementation in PyTorch - for some cases of large image size/faces per pixel the cuda version is 10x faster.

Reviewed By: gkioxari

Differential Revision: D21705503

fbshipit-source-id: e835c0f927f1e5088ca89020aef5ff27ac3a8769
2020-07-16 10:17:28 -07:00
Nikhila Ravi
bce396df93 C++/CUDA implementation of sigmoid alpha blend
Summary:
C++/CUDA implementation of forward and backward passes for the sigmoid alpha blending function.

This is slightly faster than the vectorized implementation in Python, but more importantly uses less memory due to fewer tensors being created.

Reviewed By: gkioxari

Differential Revision: D19980671

fbshipit-source-id: 0779055d2c68b1f20fb0870e60046077ef4613ff
2020-07-16 10:17:28 -07:00