Render tests: no OpenGL instance on Windows

Each GPU test made a wgpu instance with every backend, so up to one thread
per core opened Vulkan, DirectX 12 and WGL at once while finished tests'
threads exited. On Windows with an NVIDIA driver the render lib tests hung
most runs (8 of 10 here, RTX 4070; #5238). The tests now take their
instance from gfx::test_gpu, which on Windows opens Vulkan and DirectX 12
only, as the game prefers there; WGPU_BACKEND still overrides. Linux and
macOS are unchanged.

Fixes #5238

Co-Authored-By: Claude Opus 5.5 <[email protected]>

crates/horizon-client-render/src/gfx.rs

@@ -37,6 +37,8 @@ fn entity_shader() -> String {
 mod crumbling_tests;
 mod entity_batch;
 mod entity_outline;
+#[cfg(test)]
+pub(crate) mod test_gpu;
 mod weather;
 use entity_batch::EntityBatch;
 pub use entity_batch::{

crates/horizon-client-render/src/gfx/animate.rs

@@ -735,7 +735,7 @@ mod tests {
     }
 
     fn device() -> Option<(wgpu::Device, wgpu::Queue)> {
-        let instance = wgpu::Instance::new(wgpu::InstanceDescriptor::new_without_display_handle());
+        let instance = crate::gfx::test_gpu::instance();
         let adapter = pollster::block_on(instance.request_adapter(&Default::default())).ok()?;
         pollster::block_on(adapter.request_device(&Default::default())).ok()
     }

crates/horizon-client-render/src/gfx/arena.rs

@@ -526,7 +526,7 @@ mod tests {
 
     /// A device with those of `features` the adapter has.
     fn device_with(features: wgpu::Features) -> Option<(wgpu::Device, wgpu::Queue)> {
-        let instance = wgpu::Instance::new(wgpu::InstanceDescriptor::new_without_display_handle());
+        let instance = crate::gfx::test_gpu::instance();
         let adapter = pollster::block_on(instance.request_adapter(&Default::default())).ok()?;
         eprintln!("arena GPU regression: {}", adapter.get_info().name);
         let required_features = adapter.features() & features;
@@ -540,7 +540,7 @@ mod tests {
     /// A device with the adapter's own limits, as the renderer opens it: page
     /// caps past the default 256 MiB buffer limit show there.
     fn device_at_limits() -> Option<(wgpu::Device, wgpu::Queue)> {
-        let instance = wgpu::Instance::new(wgpu::InstanceDescriptor::new_without_display_handle());
+        let instance = crate::gfx::test_gpu::instance();
         let adapter = pollster::block_on(instance.request_adapter(&Default::default())).ok()?;
         pollster::block_on(adapter.request_device(&wgpu::DeviceDescriptor {
             required_limits: adapter.limits(),

crates/horizon-client-render/src/gfx/crumbling_tests.rs

@@ -4,7 +4,7 @@ use wgpu::util::DeviceExt;
 #[test]
 #[ignore = "requires a Vulkan/Metal/DX12 adapter"]
 fn crack_samples_stay_aligned_between_stages() {
-    let instance = wgpu::Instance::new(wgpu::InstanceDescriptor::new_without_display_handle());
+    let instance = crate::gfx::test_gpu::instance();
     let adapter =
         pollster::block_on(instance.request_adapter(&wgpu::RequestAdapterOptions::default()))
             .unwrap();

crates/horizon-client-render/src/gfx/end_sky/tests.rs

@@ -37,7 +37,7 @@ fn geometry_matches_pre_residency_vertex_snapshots() {
 }
 
 fn device() -> Option<(wgpu::Device, wgpu::Queue)> {
-    let instance = wgpu::Instance::new(wgpu::InstanceDescriptor::new_without_display_handle());
+    let instance = crate::gfx::test_gpu::instance();
     let adapter = pollster::block_on(instance.request_adapter(&Default::default())).ok()?;
     eprintln!("End sky test adapter: {:?}", adapter.get_info());
     pollster::block_on(adapter.request_device(&Default::default())).ok()

crates/horizon-client-render/src/gfx/flat.rs

@@ -982,7 +982,7 @@ mod tests {
     /// of the draws the test saw, in order, and their calls count them.
     #[test]
     fn flatten_writes_the_indices_of_the_per_section_draws() {
-        let instance = wgpu::Instance::new(wgpu::InstanceDescriptor::new_without_display_handle());
+        let instance = crate::gfx::test_gpu::instance();
         let Ok(adapter) = pollster::block_on(instance.request_adapter(&Default::default())) else {
             eprintln!("no GPU adapter: skipped");
             return;

crates/horizon-client-render/src/gfx/frame_gen/optical_flow.rs

@@ -470,7 +470,7 @@ pub(super) mod tests {
     /// A device with WebGPU's default limits (what every GPU wgpu runs on has), or `None`
     /// without a GPU.
     pub fn device() -> Option<(wgpu::Device, wgpu::Queue)> {
-        let instance = wgpu::Instance::new(wgpu::InstanceDescriptor::new_without_display_handle());
+        let instance = crate::gfx::test_gpu::instance();
         let adapter = pollster::block_on(instance.request_adapter(&Default::default())).ok()?;
         pollster::block_on(adapter.request_device(&Default::default())).ok()
     }

crates/horizon-client-render/src/gfx/lightning/tests/mod.rs

@@ -217,7 +217,7 @@ fn long_flash_sequence_keeps_only_active_seeds() {
 #[ignore = "requires GPU; run separately with --ignored --exact"]
 fn retained_gpu_draw_matches_transient_additive_draw() {
     use bytemuck::Zeroable;
-    let instance = wgpu::Instance::new(wgpu::InstanceDescriptor::new_without_display_handle());
+    let instance = crate::gfx::test_gpu::instance();
     let Ok(adapter) = pollster::block_on(instance.request_adapter(&Default::default())) else {
         eprintln!("no GPU adapter: skipped");
         return;
@@ -530,7 +530,7 @@ fn white_uv_is_inside_the_white_sprite() {
 #[test]
 #[ignore = "requires GPU; run separately with --ignored --exact"]
 fn bolt_through_the_atlas_white_sprite_is_fully_drawn() {
-    let instance = wgpu::Instance::new(wgpu::InstanceDescriptor::new_without_display_handle());
+    let instance = crate::gfx::test_gpu::instance();
     let Ok(adapter) = pollster::block_on(instance.request_adapter(&Default::default())) else {
         eprintln!("no GPU adapter: skipped");
         return;

crates/horizon-client-render/src/gfx/native_post.rs

@@ -1294,7 +1294,7 @@ mod tests {
     }
 
     fn device() -> Option<(wgpu::Device, wgpu::Queue)> {
-        let instance = wgpu::Instance::new(wgpu::InstanceDescriptor::new_without_display_handle());
+        let instance = crate::gfx::test_gpu::instance();
         let adapter = pollster::block_on(instance.request_adapter(&Default::default())).ok()?;
         pollster::block_on(adapter.request_device(&Default::default())).ok()
     }

crates/horizon-client-render/src/gfx/native_sky.rs

@@ -211,7 +211,7 @@ mod tests {
     /// vanilla's pixels, one that inverts them draws the inverse (and stays opaque).
     #[test]
     fn a_pack_gets_vanilla_s_colour_and_draws_opaque() {
-        let instance = wgpu::Instance::new(wgpu::InstanceDescriptor::new_without_display_handle());
+        let instance = crate::gfx::test_gpu::instance();
         let Ok(adapter) = pollster::block_on(instance.request_adapter(&Default::default())) else {
             return;
         };

crates/horizon-client-render/src/gfx/pack_atlas.rs

@@ -244,7 +244,7 @@ mod tests {
     /// Two arrays of 2x2 sprites, one layer split; each layer a colour of its own.
     #[test]
     fn layers_land_in_their_cells() {
-        let instance = wgpu::Instance::new(wgpu::InstanceDescriptor::new_without_display_handle());
+        let instance = crate::gfx::test_gpu::instance();
         let Ok(adapter) = pollster::block_on(instance.request_adapter(&Default::default())) else {
             return;
         };

crates/horizon-client-render/src/gfx/pack_post.rs

@@ -3949,7 +3949,7 @@ mod tests {
     /// made. Such a panic skips the pass, as a validation error does, and the device goes on.
     #[test]
     fn a_shader_compiler_panic_skips_the_pass() {
-        let instance = wgpu::Instance::new(wgpu::InstanceDescriptor::new_without_display_handle());
+        let instance = crate::gfx::test_gpu::instance();
         let Ok(adapter) = pollster::block_on(instance.request_adapter(&Default::default())) else {
             return;
         };

crates/horizon-client-render/src/gfx/readback.rs

@@ -85,7 +85,7 @@ mod tests {
     use super::*;
 
     fn device() -> Option<(wgpu::Device, wgpu::Queue)> {
-        let instance = wgpu::Instance::new(wgpu::InstanceDescriptor::new_without_display_handle());
+        let instance = crate::gfx::test_gpu::instance();
         let adapter = pollster::block_on(instance.request_adapter(&Default::default())).ok()?;
         pollster::block_on(adapter.request_device(&Default::default())).ok()
     }

crates/horizon-client-render/src/gfx/submit.rs

@@ -172,7 +172,7 @@ mod tests {
     use super::*;
 
     fn device() -> Option<(wgpu::Device, wgpu::Queue)> {
-        let instance = wgpu::Instance::new(wgpu::InstanceDescriptor::new_without_display_handle());
+        let instance = crate::gfx::test_gpu::instance();
         let adapter = pollster::block_on(instance.request_adapter(&Default::default())).ok()?;
         pollster::block_on(adapter.request_device(&Default::default())).ok()
     }

crates/horizon-client-render/src/gfx/test_gpu.rs

@@ -0,0 +1,14 @@
+//! The GPU tests' `wgpu::Instance`.
+
+/// A new instance for one GPU test. On Windows it opens Vulkan and DirectX 12,
+/// not OpenGL: WGL instances made and dropped from many test threads at once
+/// deadlocked NVIDIA's driver, and the render tests hung most runs (#5238).
+/// The game runs there on Vulkan or DirectX 12 unless neither works.
+/// `WGPU_BACKEND` and the other `WGPU_*` variables still apply, as in the game.
+pub(crate) fn instance() -> wgpu::Instance {
+    let mut descriptor = wgpu::InstanceDescriptor::new_without_display_handle();
+    if cfg!(windows) {
+        descriptor.backends = wgpu::Backends::PRIMARY;
+    }
+    wgpu::Instance::new(descriptor.with_env())
+}

crates/horizon-client-render/src/gfx/upload.rs

@@ -125,7 +125,7 @@ mod tests {
     use super::*;
 
     fn device() -> Option<(wgpu::Device, wgpu::Queue)> {
-        let instance = wgpu::Instance::new(wgpu::InstanceDescriptor::new_without_display_handle());
+        let instance = crate::gfx::test_gpu::instance();
         let adapter = pollster::block_on(instance.request_adapter(&Default::default())).ok()?;
         pollster::block_on(adapter.request_device(&Default::default())).ok()
     }

crates/horizon-client-render/src/gfx/weather.rs

@@ -361,7 +361,7 @@ mod tests {
     #[test]
     #[ignore = "requires a Vulkan/Metal/DX12 adapter"]
     fn weather_shader_uvs_match_legacy_bits() {
-        let instance = wgpu::Instance::new(wgpu::InstanceDescriptor::new_without_display_handle());
+        let instance = crate::gfx::test_gpu::instance();
         let adapter =
             pollster::block_on(instance.request_adapter(&wgpu::RequestAdapterOptions::default()))
                 .unwrap();

crates/horizon-client-render/src/gfx/world_post.rs

@@ -568,8 +568,7 @@ mod tests {
     }
 
     fn test_device() -> Option<(wgpu::Device, wgpu::Queue)> {
-        let instance =
-            wgpu::Instance::new(wgpu::InstanceDescriptor::new_without_display_handle().with_env());
+        let instance = crate::gfx::test_gpu::instance();
         let adapter = pollster::block_on(instance.request_adapter(&Default::default())).ok()?;
         pollster::block_on(adapter.request_device(&Default::default())).ok()
     }

crates/horizon-client-render/src/post_chain.rs

@@ -1659,7 +1659,7 @@ mod tests {
     }
 
     fn device() -> Option<(wgpu::Device, wgpu::Queue)> {
-        let instance = wgpu::Instance::new(wgpu::InstanceDescriptor::new_without_display_handle());
+        let instance = crate::gfx::test_gpu::instance();
         let adapter = pollster::block_on(instance.request_adapter(&Default::default())).ok()?;
         pollster::block_on(adapter.request_device(&Default::default())).ok()
     }