cuda conventions (#29)

docs/source/conventions/cuda_conventions.rst

@@ -0,0 +1,44 @@
+CUDA Conventions
+===================================
+
+.. currentmodule:: diff_rast
+
+Here we explain some conventions used for the implementation of the CUDA backend.
+
+Kernel Launch Conventions
+-------------------------
+
+The backend CUDA code consists of several kernel functions that run in parallel for either arbitrary number of gaussians or for arbitrary image dimensions.
+Here we explain some of the conventions used for launching these kernel functions using the ``<<<gridDim, blockDim>>>`` notation.
+
+
+1D Grids
+^^^^^^^^
+
+Kernel functions that depend on the number of input gaussians are organized into one dimensional CUDA grids consisting of 
+
+.. code-block::
+
+    const int gridDim = (num_gaussian_operations + NUM_THREADS - 1) / NUM_THREADS;
+    
+1-D blocks containing ``const int blockDim = NUM_THREADS;`` threads each. An example of a kernel function that depends on the number of gaussians (here denoted by the ``num_gaussian_operations`` variable)
+is the main `ProjectGaussians` kernel that projects an arbitrary number of 3D gaussians into 2D.
+
+
+2D Grids
+^^^^^^^^
+
+Kernel functions that depend on the rendered output image size are organized into two dimensional CUDA grids. The shape of the grid is determined by 
+
+.. code-block:: 
+    
+    const dim3 gridDim = {(img_width + NUM_THREADS_X - 1) / NUM_THREADS_X, (img_height + NUM_THREADS_Y - 1) / NUM_THREADS_Y, 1};
+
+where each individual block within the grid contains a layout of threads defined by ``const dim3 blockDim = {NUM_THREADS_X, NUM_THREADS_Y, 1};``.
+An example of a kernel function that requires two dimensional grids is the main `RasterizeGaussians` kernel that renders an arbitrary number of pixels in an output image.
+
+
+Config Constants
+----------------
+
+We fix the total number of threads within a block to 256. This means that for 1D blocks the block dimension is given by ``const int blockDim = 256;`` and for 2D blocks ``const dim3 blockDim = {16, 16, 1};``.

docs/source/conventions/data_conventions.rst

@@ -3,7 +3,7 @@ Data Conventions
 
 .. currentmodule:: diff_rast
 
-Here we explain the various conventions used in our repo.
+Here we explain the various data conventions used in our repo.
 
 Rotation Convention
 -------------------