black window on nixos+nvidia+vulkan

[ozkutuk]

I am trying to run the example as explained in the project's landing page. However, the triangle is not displayed:

Corresponding terminal output:

$ zig build run-example
found Vulkan backend on Discrete GPU adapter: NVIDIA GeForce GTX 1060 with Max-Q Design, NVIDIA: 510.54

I am on NixOS, so I have prepared a Nix flake to satisfy the system dependencies (i.e. X11 and Vulkan). I think there may be an implicit dependency I didn't capture within the Nix flake that does not cause a failure but is necessary to display the triangle? Again, nothing else is reported through standard output except from the above, so I couldn't go any further. If it would help, I can provide the Nix flake I am trying to get this working with.

$ zig version
0.10.0-dev.1453+9f25c8140

[emidoots]

Hmm, sorry to hear that - it found the Vulkan driver, so I would've expected it to just work.

Could you try with GPU_BACKEND=opengl zig build run-example ?

I'd also be curious if you can install a vulkan-tools package and see if vkcube runs on your system or not.

[ozkutuk]

Interestingly enough, with GPU_BACKEND=opengl it stills picks up Vulkan backend but rather than displaying black window, it immediately segfaults.

$ GPU_BACKEND=opengl zig build run-example
found Vulkan backend on Discrete GPU adapter: NVIDIA GeForce GTX 1060 with Max-Q Design, NVIDIA: 510.54
Segmentation fault at address 0x2100000620
???:?:?: 0x7f73345bfbdb in ??? (???)

vkcube works without any issues.

[emidoots]

OK, I see, it looks like we've got a bug in the gpu/ example with the OpenGL backend detection - I can repro on my Linux machine and am working on a fix.

Could you see if this other example works for you?

cd mach/gpu-dawn/
GPU_BACKEND=opengl zig build run-dawn-example

[ozkutuk]

That still reports Vulkan being found, and the output is a black window as it was the case initially:

$ GPU_BACKEND=opengl zig build run-dawn-example
found Vulkan adapter: NVIDIA GeForce GTX 1060 with Max-Q Design, NVIDIA: 510.54
Warning: clearColor is deprecated, prefer using clearValue instead.

If I remove the Vulkan stuff from the running environment through Nix, it fails to find Vulkan and panics:

$ GPU_BACKEND=opengl zig build run-dawn-example
Error: Couldn't load Vulkan. Searched /home/ozkutuk/dev/mach/gpu-dawn/zig-out/bin/libvulkan.so.1, /home/ozkutuk/dev/mach/gpu-dawn/zig-out/bin/libvulkan.so.1, libvulkan.so.1.
    at operator() (/home/runner/work/mach-gpu-dawn/mach-gpu-dawn/libs/dawn/src/dawn/native/vulkan/BackendVk.cpp:198)
    at Initialize (/home/runner/work/mach-gpu-dawn/mach-gpu-dawn/libs/dawn/src/dawn/native/vulkan/BackendVk.cpp:203)
    at Create (/home/runner/work/mach-gpu-dawn/mach-gpu-dawn/libs/dawn/src/dawn/native/vulkan/BackendVk.cpp:165)
    at operator() (/home/runner/work/mach-gpu-dawn/mach-gpu-dawn/libs/dawn/src/dawn/native/vulkan/BackendVk.cpp:420)

thread 5452 panic: reached unreachable code
/nix/store/pimq56ywpwy8wargg8byj29yydd70gyw-zig-0.10.0-dev.1453+9f25c8140/lib/std/debug.zig:234:14: 0x477358 in std.debug.assert (dawn-example)
    if (!ok) unreachable; // assertion failure
             ^
/home/ozkutuk/dev/mach/gpu-dawn/src/dawn/sample_utils.zig:92:11: 0x479e5d in sample_utils.setup (dawn-example)
    assert(backend_adapter != null);
          ^
/home/ozkutuk/dev/mach/gpu-dawn/src/dawn/hello_triangle.zig:10:41: 0x478522 in main (dawn-example)
    const setup = try sample_utils.setup(allocator);
                                        ^
/nix/store/pimq56ywpwy8wargg8byj29yydd70gyw-zig-0.10.0-dev.1453+9f25c8140/lib/std/start.zig:575:37: 0x487017 in std.start.callMain (dawn-example)
            const result = root.main() catch |err| {
                                    ^
/nix/store/pimq56ywpwy8wargg8byj29yydd70gyw-zig-0.10.0-dev.1453+9f25c8140/lib/std/start.zig:509:12: 0x47b467 in std.start.callMainWithArgs (dawn-example)
    return @call(.{ .modifier = .always_inline }, callMain, .{});
           ^
/nix/store/pimq56ywpwy8wargg8byj29yydd70gyw-zig-0.10.0-dev.1453+9f25c8140/lib/std/start.zig:474:12: 0x47b212 in std.start.main (dawn-example)
    return @call(.{ .modifier = .always_inline }, callMainWithArgs, .{ @intCast(usize, c_argc), c_argv, envp });

[emidoots]

@ozkutuk I can't believe I messed this up, so sorry, the env var is WGPU_BACKEND not GPU_BACKEND when running from the gpu-dawn/ directory, my bad! The correct commands are:

cd mach/gpu-dawn/
WGPU_BACKEND=opengl zig build run-dawn-example

Would be very curious to know if that works on your system or not.

---

In case it helps, the following shell.nix is what Mitchell Hashimoto needed (putting X11/GL on the LD_LIBRARY_PATH):

with import <nixpkgs> {};

pkgs.mkShell {
  nativeBuildInputs = with pkgs; [
    xorg.libX11
    libGL

    vulkan-tools
    glxinfo
  ];

  LD_LIBRARY_PATH="${pkgs.vulkan-loader}/lib:${pkgs.libGL}/lib";
}

I'd be keen to know if that fixes the black window issue or not. If not, it's likely the black screen issue is a bug in Dawn upstream

[ozkutuk]

It works! I have a somewhat similar Nix config, though I have migrated to Nix flakes so here is my flake.nix in case anyone else needs (it also provides a 0.10.x version of the Zig compiler through zig-overlay):

{
  description = "Mach is a game engine & graphics toolkit for the future.";

  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
    zig.url = "github:roarkanize/zig-overlay";
  };

  outputs = { self, zig, nixpkgs }:
    let
      pkgs = nixpkgs.legacyPackages.x86_64-linux;
      lib = pkgs.lib;
    in {
      devShell.x86_64-linux = pkgs.mkShell {
        packages = [
          # As of 2022-03-20, 0.10.x is only available in nightly builds.
          # Any build with 0.10.x is okay.
          zig.packages.x86_64-linux.master."2022-03-20"
          pkgs.xorg.libX11
          pkgs.libGL
        ];
        LD_LIBRARY_PATH = "${lib.makeLibraryPath [ pkgs.libGL ]}";
      };
    };
}

I initially had Vulkan related parts in the config, but later removed them as it didn't work for me (I'm still curious as to why it didn't though).

[emidoots]

Just to clarify, was it the OpenGL backend that worked? Or Vulkan also worked after that?

[ozkutuk]

OpenGL backend worked with the correct commands you have provided. Unfortunately, still no triangle with the Vulkan backend.

[emidoots]

Thanks! I fixed the issue where GPU_BACKEND in the standard gpu/ example was not working, so this should work now.

Regarding Vulkan, I see two possibilities here:

1. This is a NixOS-specific issue. If so, it would have to be a configuration difference between vkcube (perhaps it's dynamically linking vulkan?) and our binary (which loads vulkan at runtime, not dynamically linked.) Perhaps ${pkgs.vulkan-loader}/lib missing from your LD_LIBRARY_PATH could make a difference?
2. This is a bug in Dawn <-> your graphics driver. I would find this really surprising, because I have verified this all works on laptop NVIDIA GPU drivers very similar to yours (on Elementary OS.) - and your GPU is similarly capable to mine.

Unfortunately, short of installing NixOS on my laptop I'm not sure there's any other way to debug here. I may try that in the future but it'd be a few months.

[desttinghim]

I have an updated nix flake:

{
  description = "Mach is a game engine & graphics toolkit for the future.";

  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
    zig.url = "github:mitchellh/zig-overlay";
  };

  outputs = { self, zig, nixpkgs }:
    let
      pkgs = nixpkgs.legacyPackages.x86_64-linux;
      lib = pkgs.lib;
    in {
      devShell.x86_64-linux = pkgs.mkShell {
        packages = [
          zig.packages.x86_64-linux.master
          pkgs.xorg.libX11
          pkgs.libGL
          pkgs.libsoundio
          pkgs.alsa-lib
        ];
        LD_LIBRARY_PATH = "${lib.makeLibraryPath [ pkgs.libGL pkgs.vulkan-loader ]}";
      };
    };
}