hello_triangle_c panics while unwrapping power preference about wgpu

[grovesNL]

I can't confirm right now but I believe we don't assume any backend by default, so you'll need to specify cargo build --features metal or cargo build --features gfx-backend-metal depending on which crate you build.

We could probably provide an error when no backend has been selected.

[grovesNL]

To clarify my understanding, is it correct to say that I've compiled wgpu with no backend, and then the C code calls correctly into the rust library which was compiled incorrectly?

That's right, the library needs to be compiled with a particular backend specified (most functions will fail when they hit an unimplemented somewhere).

The Makefile is probably out of date because it existed before we switched to cmake for the C example.

I also don't see gfx-backend-metal in the features section of wgpu-native's Cargo.toml

I don't think this should be required because it's an optional crate (i.e. --features gfx-backend-metal should work).

You should be able to run the command (including all of the cds) we just added to Travis: https://github.com/gfx-rs/wgpu/blob/master/.travis.yml#L47 I also forgot to mention the local flag when building wgpu-native directly.

Edit: We also have a Gitter to chat if it's easier to discuss there.

[cshenton]

Brilliant! The command from travis builds a binary that works on my machine.

Thanks so much for being so responsive on this. Now I can start experimenting against the C API.

[cshenton]

I suspected it was something to do with selecting a backend. To clarify my understanding, is it correct to say that I've compiled wgpu with no backend, and then the C code calls correctly into the rust library which was compiled incorrectly?

[cshenton]

I've just cloned a fresh copy of the repo and built with cargo build --features metal using the same repro steps above and am getting the same error.

[cshenton]

In addition, running the following from the root of a fresh copy of the repo:

make lib-native
cd examples/hello_triangle_c/
cmake .
make hello_triangle
./hello_triangle

Results in a Segmentation fault: 11

[cshenton]

I also don't see gfx-backend-metal in the features section of wgpu-native's Cargo.toml, which could explain why the conditional compilation of the metal backend is working for the rust example but not the C one.

[kvark]

@cshenton don't hesitate to visit us on gitter or elsewhere! We'd be happy to showcase your screenshots in the gallery.

[mokpi]

The link provided above by grovesNL no longer works, but I believe it refers to this line found here in 508b724.

  - if [[ $TRAVIS_OS_NAME == "osx" ]]; then (brew update && brew upgrade cmake && brew install glfw3 && cd wgpu-native && cargo build --features=local,gfx-backend-metal && cd ../examples/hello_triangle_c && mkdir build && cd build && cmake .. && make); fi

However, it seems such a long ago answer is no longer applicable if one faces the same issue in 2023 or onwards, at least in my own experience that's the case.