VTK::RenderingWebGPU#

vtkRenderingWebGPU - WebGPU backend for rendering#

Description#

This module contains the WebGPU native backend for RenderingCore. At the moment, only polygonal geometry can be rendered in different representations with point/cell scalar mapped colors.

Available features#

Here is a list of currently implemented features:

  1. Polygonal geometry rendering with point, line and triangle primitives.

  2. Point scalar mapped coloring of surfaces.

  3. Cell scalar mapped coloring.

  4. Draw actors with the actor representation = VTK_POINTS, VTK_WIREFRAME, VTK_SURFACE and VTK_SURFACE with edge visibility.

  5. Lighting based on VTK headlights and point/cell normals.

  6. Point size adjustments.

  7. Line width adjustments for wireframe and surface with edges.

  8. vtkWebAssemblyWebGPURenderWindow is a reference implementation of vtkWebGPURenderWindow that works on WebAssembly and desktop.

  9. vtkXWebGPURenderWindow is an implementation of vtkWebGPURenderWindow that uses X11 for Linux desktop rendering.

  10. Depth testing.

Compute shader API#

The compute shader API allows offloading work from the CPU onto the GPU using WebGPU compute shaders. User-level information about the usage of the API can be found here. Developper-level information about the API can be found here.

Future work#

Since WebGPU is already an abstraction over graphics APIs, this module doesn’t create another level of abstraction. It uses WebGPU’s C++ flavor for it’s object-oriented API and RAII. There are helper classes in the vtkWebGPUInternals... files for convenience and to make the bind group initialization code look clean.

A lot of work remains to be done. Selections, volume mappers, textures, dual-depth peeling, fancy lights, platform native render windows are few that come to mind.

References#

Here are some very interesting references to learn WebGPU from examples if you prefer code over spec.

  1. https://toji.github.io/webgpu-gltf-case-study/ A case-study that slowly builds up an efficient gltf renderer in WebGPU using javascript. The author describes downfalls in certain methods and proposes alternative ways when applicable.

  2. https://github.com/samdauwe/webgpu-native-examples A curated list of single file examples if you want to see how to do X with Y like constraints using WebGPU C API.

  3. https://eliemichel.github.io/LearnWebGPU/index.html Similar to LearnOpenGL or the vulka-tutorial.com. Walks you through getting a window, triangle, buffers, textures and 3D rendering. This tutorial has good coverage and the author provides a simple to use WebGPU C++ distribution.

  4. https://sotrh.github.io/learn-wgpu/ A very nice coverage of the beginner concepts of webgpu. This tutorial uses wgpu.rs

  5. https://alain.xyz/blog/raw-webgpu Another small tutorial that lets you break the ice with WebGPU and get comfy with the concepts. This tutorial targets javascript API.

  6. https://carmencincotti.com/2022-12-19/how-to-render-a-webgpu-triangle-series-part-three-video/ A detailed, yet fun to read explanation of the swapchain and image presentation process. The author has several other targeted posts on WebGPU concepts.

  7. https://webgpu.rocks/ You want to look at the WebGPU API, but are afraid of reading the spec and do not want to read C headers. This website presents the WebGPU API and WGSL summary in a fancy way with syntax highlights.

Finally, for wgsl, the spec does a good job https://www.w3.org/TR/WGSL/

How to build VTK with Dawn (Highly experimental)#

Things you’ll need:

  1. git

  2. depot_tools

This module uses Dawn-C++ WebGPU implementation when VTK is built outside emscripten. First grab Dawn and follow their build instructions using gn, not CMake.

To build VTK with Dawn, you need to build Dawn at commit 3a00a9e5c4179d789cfe89ba09c329b57d39f947. Subsequent commits have changed the public API of Dawn to a great extent, making it incompatible with VTK. Dawn uses the Chromium build system and dependency management so you need to install depot_tools and add it to the PATH.

# Clone the repo as "dawn"
git clone https://dawn.googlesource.com/dawn dawn && cd dawn
git checkout 3a00a9e5c4

# Bootstrap the gclient configuration
cp scripts/standalone.gclient .gclient

# Fetch external dependencies and toolchains with gclient
gclient sync
Build Dawn with gn and Ninja#

It is important to set is_component_build=true. Otherwise the dawn native shared libraries will not be built.

mkdir -p out/Debug
gn gen out/Debug --target_cpu="x64" --args="is_component_build=true is_debug=true is_clang=true"
autoninja -C out/Debug
Configure and build VTK#
$ cmake \
-S /path/to/vtk/src \
-B /path/to/vtk/build \
-GNinja \
-DVTK_ENABLE_WEBGPU=ON \
-DDAWN_SOURCE_DIR=/path/to/dawn/src \
-DDAWN_INCLUDE_DIR=/path/to/dawn/include \
-DDAWN_BINARY_DIR=/path/to/dawn/out/Debug \
-DVTK_BUILD_TESTING=ON

$ cmake --build
Run the WebGPU tests#

These are not regression tested with image comparisons.

$ ./bin/vtkRenderingWebGPUCxxTests
Available tests:
  0. TestCellScalarMappedColors
  1. TestConesBenchmark
  2. TestLineRendering
  3. TestPointScalarMappedColors
  4. TestSurfacePlusEdges
  5. TestTheQuad
  6. TestTheQuadPointRepresentation
  7. TestTheQuadWireframeRepresentation
  8. TestTheTriangle
  9. TestTheTrianglePointRepresentation
 10. TestTheTriangleWireframeRepresentation
 11. TestVertexRendering
 12. TestWireframe
Run the Rendering Core tests#

The RenderingCore vtk.module can be edited to link the unit tests with VTK::RenderingWebGPU module. After uncommenting the module name under TEST_DEPENDS, rebuild and run the tests. Very few of these pass.

$ export VTK_GRAPHICS_BACKEND=WEBGPU
$ ./bin/vtkRenderingCoreCxxTests