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Add PresentMode fallbacks #22108

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Add PresentMode fallbacks #22108

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68 changes: 51 additions & 17 deletions crates/bevy_render/src/view/window/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -15,7 +15,7 @@ use core::{
num::NonZero,
ops::{Deref, DerefMut},
};
use tracing::{debug, warn};
use tracing::{debug, info, warn};
use wgpu::{
SurfaceConfiguration, SurfaceTargetUnsafe, TextureFormat, TextureUsages, TextureViewDescriptor,
};
Expand Down Expand Up @@ -348,6 +348,7 @@ pub fn create_surfaces(
.expect("Failed to create wgpu surface")
};
let caps = surface.get_capabilities(&render_adapter);
let present_mode = present_mode(window, &caps);
let formats = caps.formats;
// For future HDR output support, we'll need to request a format that supports HDR,
// but as of wgpu 0.15 that is not yet supported.
Expand All @@ -368,14 +369,7 @@ pub fn create_surfaces(
width: window.physical_width,
height: window.physical_height,
usage: TextureUsages::RENDER_ATTACHMENT,
present_mode: match window.present_mode {
PresentMode::Fifo => wgpu::PresentMode::Fifo,
PresentMode::FifoRelaxed => wgpu::PresentMode::FifoRelaxed,
PresentMode::Mailbox => wgpu::PresentMode::Mailbox,
PresentMode::Immediate => wgpu::PresentMode::Immediate,
PresentMode::AutoVsync => wgpu::PresentMode::AutoVsync,
PresentMode::AutoNoVsync => wgpu::PresentMode::AutoNoVsync,
},
present_mode,
desired_maximum_frame_latency: window
.desired_maximum_frame_latency
.map(NonZero::<u32>::get)
Expand Down Expand Up @@ -413,17 +407,57 @@ pub fn create_surfaces(

data.configuration.width = window.physical_width;
data.configuration.height = window.physical_height;
data.configuration.present_mode = match window.present_mode {
PresentMode::Fifo => wgpu::PresentMode::Fifo,
PresentMode::FifoRelaxed => wgpu::PresentMode::FifoRelaxed,
PresentMode::Mailbox => wgpu::PresentMode::Mailbox,
PresentMode::Immediate => wgpu::PresentMode::Immediate,
PresentMode::AutoVsync => wgpu::PresentMode::AutoVsync,
PresentMode::AutoNoVsync => wgpu::PresentMode::AutoNoVsync,
};
let caps = data.surface.get_capabilities(&render_adapter);
data.configuration.present_mode = present_mode(window, &caps);
render_device.configure_surface(&data.surface, &data.configuration);
}

window_surfaces.configured_windows.insert(window.entity);
}
}

fn present_mode(
window: &mut ExtractedWindow,
caps: &wgpu::SurfaceCapabilities,
) -> wgpu::PresentMode {
let present_mode = match window.present_mode {
PresentMode::Fifo => wgpu::PresentMode::Fifo,
PresentMode::FifoRelaxed => wgpu::PresentMode::FifoRelaxed,
PresentMode::Mailbox => wgpu::PresentMode::Mailbox,
PresentMode::Immediate => wgpu::PresentMode::Immediate,
PresentMode::AutoVsync => wgpu::PresentMode::AutoVsync,
PresentMode::AutoNoVsync => wgpu::PresentMode::AutoNoVsync,
};
let fallbacks = match present_mode {
wgpu::PresentMode::AutoVsync => {
&[wgpu::PresentMode::FifoRelaxed, wgpu::PresentMode::Fifo][..]
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@IQuick143 IQuick143 Dec 13, 2025

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What does the &[][..] syntax do?

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@atlv24 atlv24 Dec 13, 2025

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It turns it into a slice. Rust thinks these are array references if we dont do that, and the match complains about heterogeneous return value.

}
wgpu::PresentMode::AutoNoVsync => &[
wgpu::PresentMode::Immediate,
wgpu::PresentMode::Mailbox,
wgpu::PresentMode::Fifo,
][..],
wgpu::PresentMode::Mailbox => &[
wgpu::PresentMode::Mailbox,
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@IQuick143 IQuick143 Dec 13, 2025

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Is it intentional that in some cases the fallbacks start with the mode they're for, and in other cases not?

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@atlv24 atlv24 Dec 13, 2025

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So, AutoVsync and AutoNoVsync are not actual presentation modes, they never show up in surface caps. Wgpu offers them as a "reasonable defaults" fallback order so that not everyone has to do this cap check type logic in their apps from what i gather. The logic here is the same as in the wgpu source: these two modes convert to this set of fallbacks.

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@IQuick143 IQuick143 Dec 13, 2025

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Ah, okay that explains it, thanks.

wgpu::PresentMode::Immediate,
wgpu::PresentMode::Fifo,
][..],
// Always end in FIFO to make sure it's always supported
x => &[x, wgpu::PresentMode::Fifo][..],
};
let new_present_mode = fallbacks
.iter()
.copied()
.find(|fallback| caps.present_modes.contains(fallback))
.unwrap_or_else(|| {
unreachable!(
"Fallback system failed to choose present mode. \
This is a bug. Mode: {:?}, Options: {:?}",
window.present_mode, &caps.present_modes
);
});
if new_present_mode != present_mode && fallbacks.contains(&present_mode) {
info!("PresentMode {present_mode:?} requested but not available. Falling back to {new_present_mode:?}");
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@janhohenheim janhohenheim Dec 13, 2025

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This may be a little chatty for something like AutoNoVsync where it's not really like you "requested" Immediate, you're more like "just gimme whatever works"

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@atlv24 atlv24 Dec 13, 2025

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AutoNoVsync and AutoVsync will not log because of the fallbacks.contains(&present_mode) check

}
new_present_mode
}