User:Qmatillat/GSoC2019/FinalReport

GSoC 2019 Embree on GPU

Example performance gain on a scene with motion blur

This is the final report for the GSoC 2019 project: Embree on GPU.

All of the code can be found in this branch: soc-2019-embree-gpu, and in this diff D5522. It contain a patch that summarize all the change to Embree. Those change can also be found in this repository : github.com/tinou98/embree.

Work done

The creation of all the BVH structure are extracted from Embree internal structure, and support the existing following traversal features :

• instanced mesh
• motion blur
• curves (without motion blur)

Embree also support these new features that have been added to the traversal code :

• node that are only valid for a range of time
• linear interpolation of bounding box at traversal time

Remaining work

• Support for motion blur on curves
• The convert step is currently single threaded, and can benefit from multithreading.
• Improvement to creation of leaf: Creation of leaf still require some access to blender object data, and thus is slow.
• The shrink step can be optimized :

Embree has a BVH4 tree, but GPU expect a BVH2 tree, thus the conversion step create two inner node :

Original BVH4 tree

Converted tree (BVH2)

The computation of the two bounding box for the inner node, can be optimized (especially with unaligned node), see bvh_shrink.

Try it yourself

• Clone blender and checkout the soc-2019-embree-gpu.

git clone git://git.blender.org/blender.git
git checkout soc-2019-embree-gpu

• Install dependencies, but force to build embree from source :

./blender/build_files/build_environment/install_deps.sh --with-embree --build--embree

• Install dependencies, but force to build embree from source :

mkdir build; cd build
cmake -DWITH_CYCLES_EMBREE=ON ../blender
make -j <N> install

• Enable Embree converter from Render panel : Performance » Acceleration Structure » BVH Builder » Embree, then convert
• Then render

Benchmark

The converter shows the best performances on the scenes with a deformation motion blur, but on other scene, it is usually around 10% slower.

• 

  test/cycles/deformation_motion.blend

• 

  Scene with deformation blur

• 

  benchmarks/cycles/classroom_gpu.blend

• 

  test/cycles/motion_blur.blend