fix: Allow unknown bit-depth on macOS (#4190)

It is unclear what values CGDisplayModeCopyPixelEncoding is allowed to
return, so let's make sure to handle unknown cases.

src/changelog/unreleased.md

@@ -248,3 +248,4 @@ changelog entry.
 - On macOS, fixed the scancode conversion for audio volume keys.
 - On macOS, fixed the scancode conversion for `IntlBackslash`.
 - On macOS, fixed redundant `SurfaceResized` event at window creation.
+- On macOS, don't panic on monitors with unknown bit-depths.

src/platform_impl/apple/appkit/ffi.rs

@@ -11,8 +11,8 @@ use objc2_core_graphics::CGDirectDisplayID;
 
 pub const IO16BitDirectPixels: &str = "-RRRRRGGGGGBBBBB";
 pub const IO32BitDirectPixels: &str = "--------RRRRRRRRGGGGGGGGBBBBBBBB";
-
 pub const kIO30BitDirectPixels: &str = "--RRRRRRRRRRGGGGGGGGGGBBBBBBBBBB";
+pub const kIO64BitDirectPixels: &str = "-16R16G16B16";
 
 // `CGDisplayCreateUUIDFromDisplayID` comes from the `ColorSync` framework.
 // However, that framework was only introduced "publicly" in macOS 10.13.

src/platform_impl/apple/appkit/monitor.rs

@@ -66,17 +66,21 @@ impl VideoModeHandle {
         refresh_rate_millihertz: Option<NonZeroU32>,
     ) -> Self {
         unsafe {
+            // The bit-depth is basically always 32 since macOS 10.12.
             #[allow(deprecated)]
             let pixel_encoding =
                 CGDisplayMode::pixel_encoding(Some(&native_mode.0)).unwrap().to_string();
             let bit_depth = if pixel_encoding.eq_ignore_ascii_case(ffi::IO32BitDirectPixels) {
-                32
+                NonZeroU16::new(32)
             } else if pixel_encoding.eq_ignore_ascii_case(ffi::IO16BitDirectPixels) {
-                16
+                NonZeroU16::new(16)
             } else if pixel_encoding.eq_ignore_ascii_case(ffi::kIO30BitDirectPixels) {
-                30
+                NonZeroU16::new(30)
+            } else if pixel_encoding.eq_ignore_ascii_case(ffi::kIO64BitDirectPixels) {
+                NonZeroU16::new(64)
             } else {
-                unimplemented!()
+                warn!(?pixel_encoding, "unknown bit depth");
+                None
             };
 
             let mode = VideoMode::new(
@@ -84,7 +88,7 @@ impl VideoModeHandle {
                     CGDisplayMode::pixel_width(Some(&native_mode.0)) as u32,
                     CGDisplayMode::pixel_height(Some(&native_mode.0)) as u32,
                 ),
-                NonZeroU16::new(bit_depth),
+                bit_depth,
                 refresh_rate_millihertz,
             );
 

winit-core/src/monitor.rs

@@ -151,6 +151,13 @@ impl VideoMode {
     /// Returns the bit depth of this video mode, as in how many bits you have
     /// available per color. This is generally 24 bits or 32 bits on modern
     /// systems, depending on whether the alpha channel is counted or not.
+    ///
+    /// # Platform-specific
+    ///
+    /// - **macOS**: Video modes do not control the bit depth of the monitor, so this often defaults
+    ///   to 32.
+    /// - **iOS**: Always returns `None`.
+    /// - **Wayland**: Always returns `None`.
     pub fn bit_depth(&self) -> Option<NonZeroU16> {
         self.bit_depth
     }