bevy_render: reconfigure surface on Suboptimal present

[rubeniskov]

Bevy 0.18's prepare_windows ignores SurfaceTexture::suboptimal, so when the swapchain reports VK_SUBOPTIMAL_KHR (compositor scale / output reconfig on desktop Linux is the common trigger) wgpu_hal logs

WARN present_frames: wgpu_hal::vulkan: Suboptimal present of frame N

on every present until something flips size_changed and forces a configure_surface. Mirror the SurfaceError::Outdated branch: drop the suboptimal frame, reconfigure, re-acquire.

Objective

• prepare_windows in crates/bevy_render/src/view/window/mod.rs treats wgpu::CurrentSurfaceTexture::Suboptimal exactly like Success: it hands the texture to the renderer and moves on. The swapchain keeps presenting, but it no longer matches the surface (compositor scale change, output reconfiguration, monitor hot-plug on desktop Linux).
• Until something else flips size_changed and triggers configure_surface, wgpu_hal logs one WARN present_frames: wgpu_hal::vulkan: Suboptimal present of frame N per frame. On a 144 Hz display that's ~144 spurious warnings per second filling the log.
• The SurfaceError::Outdated branch already does the right thing for the analogous "swapchain is stale" case — Suboptimal should mirror it.

Solution

• Split Suboptimal out of the combined Success | Suboptimal arm in prepare_windows and mirror the existing Outdated recovery path:
  1. drop(surface_texture) to release the suboptimal frame.
  2. render_device.configure_surface(surface, &surface_data.configuration) so the swapchain re-matches the surface.
  3. Re-acquire via get_current_texture(). If the second acquire still fails, warn!(...) and continue (same pattern as Outdated).

wgpu::CurrentSurfaceTexture::Suboptimal(surface_texture) => {
    // Suboptimal: the swapchain still presents but no longer matches the
    // surface (compositor scale / output reconfig on desktop Linux is the
    // common trigger). wgpu_hal logs a WARN every present until we
    // reconfigure, so mirror the Outdated path: drop the frame,
    // reconfigure, re-acquire.
    drop(surface_texture);
    render_device.configure_surface(surface, &surface_data.configuration);
    let frame = match surface.get_current_texture() {
        wgpu::CurrentSurfaceTexture::Success(surface_texture)
        | wgpu::CurrentSurfaceTexture::Suboptimal(surface_texture) => surface_texture,
        variant => {
            warn!(
                "Couldn't get swap chain texture after suboptimal reconfigure. Cause: '{variant:?}'"
            );
            continue;
        }
    };
    window.set_swapchain_texture(frame);
}

• 21 insertions, 2 deletions in a single file. No trait, API or schedule changes — purely a present-path recovery fix.

Testing

• cargo check -p bevy_render is clean.
• Manually reproduced and verified on Linux + Wayland (KDE Plasma 6, Vulkan backend, mesa-radeonsi). Before the patch: continuous WARN flood after a fractional-scale change. After the patch: a single WARN on the boundary frame, then silence.
• Did not test on macOS / iOS / Windows / WebGPU. The affected variant is the same enum used cross-platform, but Suboptimal is in practice a Vulkan-on-Linux event, so the change is a no-op on platforms that never report it.
• No .stderr or unit-test snapshots reference this code path, so nothing else needs updating.
• Reproduction steps for reviewers (Linux + Wayland is the most reliable; X11/NVIDIA also reproducible):
  1. Create a trivial Bevy app:

     # Cargo.toml
     [package]
     name = "suboptimal_repro"
     version = "0.0.0"
     edition = "2024"
     
     [dependencies]
     bevy = { path = "../bevy" }

     // src/main.rs
     use bevy::prelude::*;
     
     fn main() {
         App::new().add_plugins(DefaultPlugins).run();
     }

  2. RUST_LOG=warn cargo run --release.
  3. Once the window is up, trigger a compositor change that marks the swapchain suboptimal without firing a Bevy resize event — pick one:
     • KDE Plasma / Wayland: System Settings → Display → Scale, bump fractional scale (100 % → 125 %) on the output the window is on.
     • GNOME / Wayland: Settings → Displays → Scale, toggle 100 % to 125 % and apply.
     • Multi-monitor: drag the window from a 100 %-scale output to a 125 %- or 200 %-scale output.
     • Hot-plug: plug or unplug an external display while the window is on the primary.
  4. Without the patch: the terminal floods with one WARN per frame, indefinitely. With the patch: at most a handful of WARNs around the moment of the compositor change, then silence.

---

Showcase

Click to view showcase

Before / after with RUST_LOG=warn cargo run --release on the minimal repro app above, performing a single fractional-scale change at ~3 s:

# Before
[ 3.012 s] WARN present_frames: wgpu_hal::vulkan: Suboptimal present of frame 432
[ 3.019 s] WARN present_frames: wgpu_hal::vulkan: Suboptimal present of frame 433
[ 3.026 s] WARN present_frames: wgpu_hal::vulkan: Suboptimal present of frame 434
... (continues until window closed)

# After
[ 3.012 s] WARN present_frames: wgpu_hal::vulkan: Suboptimal present of frame 432
(silent)

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[IceSentry]

I feel like the shared parts could be extracted to a function but not sure if it's worth it.