gpui: Enable direct-to-display optimization for metal (#44334)

Marco Mihai Condrache created 1 week ago

When profiling Zed with Instruments, a warning appears indicating that
surfaces cannot be pushed directly to the display as they are
non-opaque. This happens because the metal layer is currently marked as
non-opaque by default, even though the window itself is not transparent.

<img width="590" height="55" alt="image"
src="https://github.com/user-attachments/assets/2647733e-c75b-4aec-aa19-e8b2ffd6194b"
/>

Metal on macOS can bypass compositing and present frames directly to the
display when several conditions are met. One of those conditions is that
the backing layer must be declared opaque. Apple’s documentation notes
that marking layers as opaque allows the system to avoid unnecessary
compositing work, reducing GPU load and improving frame pacing

Ref:
https://developer.apple.com/documentation/metal/managing-your-game-window-for-metal-in-macos

This PR updates the Metal renderer to mark the layer as opaque whenever
the window does not use transparency. This makes Zed eligible for
macOS’s direct-to-display optimization in scenarios where the system can
apply it.

Release Notes:

- gpui: Mark metal layers opaque for non-transparent windows to allow
direct-to-display when supported

---------

Signed-off-by: Marco Mihai Condrache <[e-mail]>

Change summary

crates/gpui/src/platform/mac/metal_renderer.rs | 17 +++++++++++------
1 file changed, 11 insertions(+), 6 deletions(-)

Detailed changes

crates/gpui/src/platform/mac/metal_renderer.rs

@@ -46,9 +46,9 @@ pub unsafe fn new_renderer(
     _native_window: *mut c_void,
     _native_view: *mut c_void,
     _bounds: crate::Size<f32>,
-    _transparent: bool,
+    transparent: bool,
 ) -> Renderer {
-    MetalRenderer::new(context)
+    MetalRenderer::new(context, transparent)
 }
 
 pub(crate) struct InstanceBufferPool {
@@ -128,7 +128,7 @@ pub struct PathRasterizationVertex {
 }
 
 impl MetalRenderer {
-    pub fn new(instance_buffer_pool: Arc<Mutex<InstanceBufferPool>>) -> Self {
+    pub fn new(instance_buffer_pool: Arc<Mutex<InstanceBufferPool>>, transparent: bool) -> Self {
         // Prefer low‐power integrated GPUs on Intel Mac. On Apple
         // Silicon, there is only ever one GPU, so this is equivalent to
         // `metal::Device::system_default()`.
@@ -152,8 +152,13 @@ impl MetalRenderer {
         let layer = metal::MetalLayer::new();
         layer.set_device(&device);
         layer.set_pixel_format(MTLPixelFormat::BGRA8Unorm);
-        layer.set_opaque(false);
+        // Support direct-to-display rendering if the window is not transparent
+        // https://developer.apple.com/documentation/metal/managing-your-game-window-for-metal-in-macos
+        layer.set_opaque(!transparent);
         layer.set_maximum_drawable_count(3);
+        // We already present at display sync with the display link
+        // This allows to use direct-to-display even in window mode
+        layer.set_display_sync_enabled(false);
         unsafe {
             let _: () = msg_send![&*layer, setAllowsNextDrawableTimeout: NO];
             let _: () = msg_send![&*layer, setNeedsDisplayOnBoundsChange: YES];
@@ -352,8 +357,8 @@ impl MetalRenderer {
         }
     }
 
-    pub fn update_transparency(&self, _transparent: bool) {
-        // todo(mac)?
+    pub fn update_transparency(&self, transparent: bool) {
+        self.layer.set_opaque(!transparent);
     }
 
     pub fn destroy(&self) {