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Fix macOS wgpu live resize with low-latency surfaces #8229

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Merged
lucasmerlin merged 2 commits into from
Jun 25, 2026
Merged

Fix macOS wgpu live resize with low-latency surfaces #8229

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866367d
Fix macOS wgpu live resize with low latency
yay Jun 5, 2026
d48c90c
Reintroduce feature flag
lucasmerlin Jun 25, 2026
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13 changes: 9 additions & 4 deletions crates/eframe/src/native/wgpu_integration.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -844,13 +844,18 @@ impl WgpuWinitRunning<'_> {
//
// Thus, Painter, responsible for wgpu surfaces and their resize, has to be notified of the
// resize lifecycle, yet winit does not provide any events for that. To work around,
// the last resized viewport is tracked until any next non-resize event is received.
// the last resized viewport is tracked until a later event outside the live resize stream
// is received.
//
// Accidental state change during the resize process due to an unexpected event fire
// is ok, state will switch back upon next resize event.
// AppKit can emit `Moved` events during top/left live resize because the window origin
// changes along with the content size. Treat those as part of live resize on macOS.
//
// See: https://github.com/emilk/egui/issues/903
if let Some(id) = viewport_id
let event_keeps_resize_active = matches!(event, winit::event::WindowEvent::Resized(_))
|| (cfg!(target_os = "macos") && matches!(event, winit::event::WindowEvent::Moved(_)));

if !event_keeps_resize_active
&& let Some(id) = viewport_id
&& shared.resized_viewport == viewport_id
{
shared.painter.on_window_resize_state_change(id, false);
Expand Down
4 changes: 3 additions & 1 deletion crates/egui-wgpu/Cargo.toml
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Expand Up @@ -51,7 +51,9 @@ x11 = ["winit?/x11"]
## Thus that usage is guarded against with compiler errors in wgpu.
fragile-send-sync-non-atomic-wasm = ["wgpu/fragile-send-sync-non-atomic-wasm"]

## Enables `present_with_transaction` surface flag temporary during window resize on MacOS.
## Enables the macOS live-resize jitter fix, which uses `present_with_transaction`.
## This requires the `wgpu/metal` backend. Disable this feature if you want to use egui-wgpu
## with a different backend (e.g. Vulkan or GL) on macOS without pulling in Metal.
macos-window-resize-jitter-fix = ["wgpu/metal"]

[dependencies]
Expand Down
48 changes: 25 additions & 23 deletions crates/egui-wgpu/src/winit.rs
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Expand Up @@ -104,6 +104,15 @@ impl Painter {
desired_maximum_frame_latency,
} = *config;

// Transaction presentation can hold a drawable during AppKit live resize. Keep the
// configured low-latency path normally, but use three Metal drawables while resizing.
#[cfg(all(target_os = "macos", feature = "macos-window-resize-jitter-fix"))]
let desired_maximum_frame_latency = if surface_state.resizing {
Some(desired_maximum_frame_latency.unwrap_or(2).max(2))
} else {
desired_maximum_frame_latency
};

@lucasmerlin lucasmerlin Jun 25, 2026

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Nice, smart way to go about that!

let width = surface_state.width;
let height = surface_state.height;

Expand Down Expand Up @@ -406,6 +415,9 @@ impl Painter {
return;
}

// Set before reconfiguring so macOS live resize uses the temporary latency bump above.
state.resizing = resizing;

// Resizing is a bit tricky on macOS.
// It requires enabling ["present_with_transaction"](https://developer.apple.com/documentation/quartzcore/cametallayer/presentswithtransaction)
// flag to avoid jittering during the resize. Even though resize jittering on macOS
Expand All @@ -414,32 +426,22 @@ impl Painter {
// See https://github.com/emilk/egui/issues/903
#[cfg(all(target_os = "macos", feature = "macos-window-resize-jitter-fix"))]
{
// setPresentsWithTransaction causes hangs when desired_maximum_frame_latency == 1
let is_low_latency = self
.render_state
.as_ref()
.is_some_and(|rs| rs.surface_config.desired_maximum_frame_latency == Some(1));
if !is_low_latency {
// SAFETY: The cast is checked with if condition. If the used backend is not metal
// it gracefully fails.
unsafe {
if let Some(hal_surface) = state.surface.as_hal::<wgpu::hal::api::Metal>() {
hal_surface
.render_layer()
.lock()
.setPresentsWithTransaction(resizing);

Self::configure_surface(
state,
self.render_state.as_ref().unwrap(),
&self.config.surface,
);
}
// SAFETY: `as_hal::<Metal>()` returns `None` unless this surface is backed by wgpu's
// Metal backend.
unsafe {
if let (Some(render_state), Some(hal_surface)) = (
self.render_state.as_ref(),
state.surface.as_hal::<wgpu::hal::api::Metal>(),
) {
hal_surface
.render_layer()
.lock()
.setPresentsWithTransaction(resizing);

Self::configure_surface(state, render_state, &self.config.surface);
}
}
}

state.resizing = resizing;
}

pub fn on_window_resized(
Expand Down
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