From c3de161dd2a0144bef1fa740b9ef25166415247a Mon Sep 17 00:00:00 2001
From: Dzmitry Malyshau <kvarkus@gmail.com>
Date: Fri, 27 Aug 2021 12:49:48 -0400
Subject: [PATCH] hal/metal: inherit scaling from NSView

---
 wgpu-hal/src/metal/mod.rs     | 16 ++++++++----
 wgpu-hal/src/metal/surface.rs | 49 +++++++++++++++++++++++++++++++----
 2 files changed, 55 insertions(+), 10 deletions(-)

diff --git a/wgpu-hal/src/metal/mod.rs b/wgpu-hal/src/metal/mod.rs
index 4ebbacce5a..7b95588f46 100644
--- a/wgpu-hal/src/metal/mod.rs
+++ b/wgpu-hal/src/metal/mod.rs
@@ -61,7 +61,9 @@ impl crate::Api for Api {
     type ComputePipeline = ComputePipeline;
 }
 
-pub struct Instance {}
+pub struct Instance {
+    managed_metal_layer_delegate: surface::HalManagedMetalLayerDelegate,
+}
 
 impl Instance {
     pub fn create_surface_from_layer(&self, layer: &mtl::MetalLayerRef) -> Surface {
@@ -72,7 +74,9 @@ impl Instance {
 impl crate::Instance<Api> for Instance {
     unsafe fn init(_desc: &crate::InstanceDescriptor) -> Result<Self, crate::InstanceError> {
         //TODO: enable `METAL_DEVICE_WRAPPER_TYPE` environment based on the flags?
-        Ok(Instance {})
+        Ok(Instance {
+            managed_metal_layer_delegate: surface::HalManagedMetalLayerDelegate::new(),
+        })
     }
 
     unsafe fn create_surface(
@@ -82,12 +86,14 @@ impl crate::Instance<Api> for Instance {
         match has_handle.raw_window_handle() {
             #[cfg(target_os = "ios")]
             raw_window_handle::RawWindowHandle::IOS(handle) => {
+                let _ = &self.managed_metal_layer_delegate;
                 Ok(Surface::from_uiview(handle.ui_view))
             }
             #[cfg(target_os = "macos")]
-            raw_window_handle::RawWindowHandle::MacOS(handle) => {
-                Ok(Surface::from_nsview(handle.ns_view))
-            }
+            raw_window_handle::RawWindowHandle::MacOS(handle) => Ok(Surface::from_nsview(
+                handle.ns_view,
+                &self.managed_metal_layer_delegate,
+            )),
             _ => Err(crate::InstanceError),
         }
     }
diff --git a/wgpu-hal/src/metal/surface.rs b/wgpu-hal/src/metal/surface.rs
index e66a536907..a223d52e4d 100644
--- a/wgpu-hal/src/metal/surface.rs
+++ b/wgpu-hal/src/metal/surface.rs
@@ -1,13 +1,15 @@
-use std::{mem, os::raw::c_void, ptr::NonNull, thread};
+use std::{mem, os::raw::c_void, ptr::NonNull, sync::Once, thread};
 
 use core_graphics_types::{
     base::CGFloat,
     geometry::{CGRect, CGSize},
 };
 use objc::{
-    class, msg_send,
+    class,
+    declare::ClassDecl,
+    msg_send,
     rc::autoreleasepool,
-    runtime::{Object, BOOL, YES},
+    runtime::{Class, Object, Sel, BOOL, YES},
     sel, sel_impl,
 };
 use parking_lot::Mutex;
@@ -19,6 +21,40 @@ extern "C" {
     static kCAGravityTopLeft: *mut Object;
 }
 
+extern "C" fn layer_should_inherit_contents_scale_from_window(
+    _: &Class,
+    _: Sel,
+    _layer: *mut Object,
+    _new_scale: CGFloat,
+    _from_window: *mut Object,
+) -> BOOL {
+    YES
+}
+
+const CAML_DELEGATE_CLASS: &str = "HalManagedMetalLayerDelegate";
+static CAML_DELEGATE_REGISTER: Once = Once::new();
+
+#[derive(Debug)]
+pub struct HalManagedMetalLayerDelegate(&'static Class);
+
+impl HalManagedMetalLayerDelegate {
+    pub fn new() -> Self {
+        CAML_DELEGATE_REGISTER.call_once(|| {
+            type Fun = extern "C" fn(&Class, Sel, *mut Object, CGFloat, *mut Object) -> BOOL;
+            let mut decl = ClassDecl::new(CAML_DELEGATE_CLASS, class!(NSObject)).unwrap();
+            #[allow(trivial_casts)] // false positive
+            unsafe {
+                decl.add_class_method(
+                    sel!(layer:shouldInheritContentsScale:fromWindow:),
+                    layer_should_inherit_contents_scale_from_window as Fun,
+                );
+            }
+            decl.register();
+        });
+        Self(Class::get(CAML_DELEGATE_CLASS).unwrap())
+    }
+}
+
 impl super::Surface {
     fn new(view: Option<NonNull<Object>>, layer: mtl::MetalLayer) -> Self {
         Self {
@@ -74,7 +110,10 @@ impl super::Surface {
 
     #[cfg(target_os = "macos")]
     #[allow(clippy::transmute_ptr_to_ref)]
-    pub unsafe fn from_nsview(nsview: *mut c_void) -> Self {
+    pub unsafe fn from_nsview(
+        nsview: *mut c_void,
+        delegate: &HalManagedMetalLayerDelegate,
+    ) -> Self {
         let view = nsview as *mut Object;
         if view.is_null() {
             panic!("window does not have a valid contentView");
@@ -109,7 +148,7 @@ impl super::Surface {
                 let scale_factor: CGFloat = msg_send![window, backingScaleFactor];
                 let () = msg_send![layer, setContentsScale: scale_factor];
             }
-            //let () = msg_send![layer, setDelegate: self.gfx_managed_metal_layer_delegate.0];
+            let () = msg_send![layer, setDelegate: delegate.0];
             layer
         };