Improve ScopedEnvironmentVar to distinguish between null and empty

Found while investigating Swiftshader support. Some Vulkan loaders
fail to create an instance if VK_ICD_FILENAMES is empty string
rather than entirely absent. It was set to empty string because
Dawn did not distinguish between nonexistent environment variables
and the empty string. This CL adds distinguishing between the two,
including tests for the behavior.

Bug: chromium:1266550
Change-Id: I1680a281f62e6b340009e01da65db9d485e2975e
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/69520
Auto-Submit: Austin Eng <enga@chromium.org>
Reviewed-by: Loko Kung <lokokung@google.com>
Commit-Queue: Austin Eng <enga@chromium.org>
5 files changed
tree: a9e577cda3a015b4d292c7f5ec04e9ec1779698f
  1. .vscode/
  2. build_overrides/
  3. docs/
  4. examples/
  5. generator/
  6. infra/
  7. scripts/
  8. src/
  9. third_party/
  10. tools/
  11. .clang-format
  12. .gitattributes
  13. .gitignore
  14. .gn
  15. AUTHORS
  16. BUILD.gn
  17. CMakeLists.txt
  18. codereview.settings
  19. dawn.json
  20. dawn_wire.json
  21. DEPS
  22. DIR_METADATA
  23. LICENSE
  24. OWNERS
  25. PRESUBMIT.py
  26. README.chromium
  27. README.md
README.md

Dawn's logo: a sun rising behind a stylized mountain inspired by the WebGPU logo. The text Dawn is written below it.

Dawn, a WebGPU implementation

Dawn is an open-source and cross-platform implementation of the work-in-progress WebGPU standard. More precisely it implements webgpu.h that is a one-to-one mapping with the WebGPU IDL. Dawn is meant to be integrated as part of a larger system and is the underlying implementation of WebGPU in Chromium.

Dawn provides several WebGPU building blocks:

  • WebGPU C/C++ headers that applications and other building blocks use.
    • The webgpu.h version that Dawn implements.
    • A C++ wrapper for the webgpu.h.
  • A “native” implementation of WebGPU using platforms' GPU APIs:
    • D3D12 on Windows 10
    • Metal on macOS and iOS
    • Vulkan on Windows, Linux, ChromeOS, Android and Fuchsia
    • OpenGL as best effort where available
  • A client-server implementation of WebGPU for applications that are in a sandbox without access to native drivers

Helpful links:

Documentation table of content

Developer documentation:

User documentation: (TODO, figure out what overlaps with the webgpu.h docs)

Status

(TODO)

License

Apache 2.0 Public License, please see LICENSE.

Disclaimer

This is not an officially supported Google product.