Winit example window not opening on WSL2

Question

My ultimate goal is to use Pixels in WSL to create a data visualization in Rust.

However, I couldn't get the Pixels examples to run and so I first want to make sure Winit can run properly. Downloading the Winit repository from GitHub and running the window example works correctly.

However, if I create a new project and copy-paste the example code to it then running the code does not open a window anymore.

From running gdb, the code appears to get stuck in window.request_redraw() but I couldn't find much else out.

I am not super knowledgeable in windowing systems, but from running echo $DISPLAY and echo $WAYLAND_DISPLAY I get :0 and wayland-0, respectively, which I believe indicates that WSL has both X11 and Wayland functionality installed.

I am using Ubuntu 22.04.3 LTS. Running cat /proc/version prints Linux version 5.15.90.1-microsoft-standard-WSL2 (oe-user@oe-host) (x86_64-msft-linux-gcc (GCC) 9.3.0, GNU ld (GNU Binutils) 2.34.0.20200220) #1 SMP Fri Jan 27 02:56:13 UTC 2023.

I seem to have some misunderstanding of how Cargo manages dependencies, since I don't know why the same code would run inside the Winit source project but not in my own project when I instruct Cargo to download the same version of the Winit source. I have tried Winit v0.29, v0.28, and v0.27 and the same problem persists.

Steps to reproduce:

git clone https://github.com/rust-windowing/winit.git
cd winit
cargo run --example window

window opens fine...

cd ..
cargo new window
cd window
cargo add winit
cargo add simple_logger
cp ../winit/examples/window.rs src/main.rs
mkdir src/util
cp ../winit/examples/util/fill.rs src/util
cargo run

window does not open...

Answer 1

Solved!

TL;DR the example code had a feature flag that I didn't enable in my own project.

---

After fruitlessly debugging the main example code in window.rs I tackled the helper code in fill.rs. There is one function fill_window() with two signatures:

#[cfg(all(feature = "rwh_05", not(any(target_os = "android", target_os = "ios"))))]
pub(super) fn fill_window(window: &Window) {
    ...
}
    
#[cfg(not(all(feature = "rwh_05", not(any(target_os = "android", target_os = "ios")))))]
pub(super) fn fill_window(_window: &Window) {
    // No-op on mobile platforms.
}

The first one should run when the rwh_05 feature is enabled and target_os is not android or ios. Otherwise, the second one should run.

I put a println!() in each and discovered that my window project was compiling to the second (no-op) function while the source winit project was compiling to the first function.

So either target_os == android, target_os == ios, or rwh_05 is not enabled.

I ran some tests by adding code to fill.rs

#[cfg(target_os = "android")]
compile_error!("target_os = android");

#[cfg(target_os = "ios")]
compile_error!("target_os = android");

#[cfg(target_os = "linux")]
compile_error!("target_os = linux");

The output shows that target_os is linux.

error: target_os = linux
  --> src/util/fill.rs:16:1
   |
16 | compile_error!("target_os = linux");
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: could not compile `window` (bin "window") due to previous error

Next,

#[cfg(feature = "rwh_05")]
compile_error!("rwh_05 feature enabled");

#[cfg(not(feature = "rwh_05"))]
compile_error!("rwh_05 feature is not enabled");

The output shows that rwh_05 is not enabled⠀

error: rwh_05 feature is not enabled
  --> src/util/fill.rs:16:1
   |
16 | compile_error!("rwh_05 feature is not enabled");
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: could not compile `window` (bin "window") due to previous error

And this is where I had my revelation.

I had mistakenly put the following in Cargo.toml thinking that it would enable rwh_05 globally, when in reality it only enabled that feature for the winit crate and not my own local project.

[dependencies]
winit = { path = "./winit", features = ["rwh_05"] }

Adding

[features]
rwh_05 = []

to Cargo.toml and running with cargo run --features rwh_05 runs the window example as expected: