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UIKit: detect GL and Metal backing layers #4621

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brianconnoly wants to merge 3 commits into from
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UIKit: detect GL and Metal backing layers #4621

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UIKit: detect GL and Metal backing layers
brianconnoly Jul 8, 2026
483a186
UIKit: remove unused foundation protocol import
brianconnoly Jul 8, 2026
7f0bc83
Remove unsafe UIKit backing layer lookup
brianconnoly Jul 27, 2026
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11 changes: 8 additions & 3 deletions winit-uikit/src/window.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -9,9 +9,10 @@ use dpi::{
Position, Size,
};
use objc2::rc::Retained;
use objc2::runtime::AnyObject;
use objc2::{MainThreadMarker, available, class, define_class, msg_send};
use objc2_core_foundation::{CGFloat, CGPoint, CGRect, CGSize};
use objc2_foundation::{NSObject, NSObjectProtocol};
use objc2_foundation::NSObject;
use objc2_ui_kit::{
UIApplication, UICoordinateSpace, UIEdgeInsets, UIResponder, UIScreen,
UIScreenOverscanCompensation, UIViewController, UIWindow,
Expand Down Expand Up @@ -535,8 +536,12 @@ impl Window {

let view = WinitView::new(mtm, ios_attributes.scale_factor, frame);

let gl_or_metal_backed =
view.isKindOfClass(class!(CAMetalLayer)) || view.isKindOfClass(class!(CAEAGLLayer));
let gl_or_metal_backed = unsafe {
let view_layer: *mut AnyObject = msg_send![&*view, layer];
let metal_backed: bool = msg_send![view_layer, isKindOfClass: class!(CAMetalLayer)];
let gl_backed: bool = msg_send![view_layer, isKindOfClass: class!(CAEAGLLayer)];

@tronical tronical Jul 27, 2026 •
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I must be missing something, but ... isn't this new code doing the same as the old code? (except that it introduces the use of unsafe)

Edit: nevermind, I see now that it performs the check on the layer, not the view.

@tronical tronical Jul 27, 2026

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Instead of this unsafe, block, would it be possible to use https://docs.rs/objc2-ui-kit/latest/objc2_ui_kit/struct.UIView.html#method.layerClass to obtain the class and then perform the check?

@brianconnoly brianconnoly Jul 27, 2026

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Good suggestion to avoid the handwritten unsafe block. A direct UIView::layerClass call would inspect the base UIView class, while subclasses may override it, so it is not equivalent to checking the actual backing-layer instance. I enabled the objc2-quartz-core bindings and now use the safe typed view.layer() result followed by isKindOfClass checks. This removes the raw pointer and the entire unsafe block.

Verification: cargo check -p winit-uikit --target aarch64-apple-ios passes on macOS. I also tested the same typed access pattern through our 0.30 patch lineage on a physical iPad: signed install and launch passed, rendering looked correct, and the app remained alive through a controlled suspend/resume.

metal_backed || gl_backed
};

let view_controller = WinitViewController::new(mtm, &ios_attributes, &view);
let window = WinitUIWindow::new(mtm, &window_attributes, frame, &view_controller);
Expand Down
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