gtk4: Add support for GL on macOS

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs/-/merge_requests/1025>

video/gtk4/Cargo.toml

@@ -24,6 +24,10 @@ gst_gl_egl = { package = "gstreamer-gl-egl", git = "https://gitlab.freedesktop.o
 
 once_cell = "1.0"
 
+[target.'cfg(target_os = "macos")'.dependencies]
+gtk = { package = "gtk4", git = "https://github.com/gtk-rs/gtk4-rs", features = ["v4_6"] }
+gst_gl = { package = "gstreamer-gl", git = "https://gitlab.freedesktop.org/gstreamer/gstreamer-rs", features = ["v1_16"] }
+
 [lib]
 name = "gstgtk4"
 crate-type = ["cdylib", "rlib"]

video/gtk4/src/sink/imp.rs

@@ -598,6 +598,8 @@ impl PaintableSink {
                 "GdkX11GLContextGLX" => (),
                 #[cfg(all(target_os = "linux", feature = "wayland"))]
                 "GdkWaylandGLContext" => (),
+                #[cfg(all(target_os = "macos", feature = "gst_gl"))]
+                "GdkMacosGLContext" => (),
                 display => {
                     gst::error!(CAT, imp: self_, "Unsupported GDK display {display} for GL");
                     return None;
@@ -654,6 +656,10 @@ impl PaintableSink {
             "GdkWaylandGLContext" => {
                 self.initialize_waylandegl(display, &mut display_ctx_guard, &mut app_ctx_guard);
             }
+            #[cfg(all(target_os = "macos", feature = "gst_gl"))]
+            "GdkMacosGLContext" => {
+                self.initialize_macosgl(display, &mut display_ctx_guard, &mut app_ctx_guard);
+            }
             _ => {
                 unreachable!("Unsupported GDK display {display} for GL");
             }
@@ -851,4 +857,38 @@ impl PaintableSink {
             app_ctx_guard.replace(gst_app_context.unwrap());
         }
     }
+
+    #[cfg(all(target_os = "macos", feature = "gst_gl"))]
+    fn initialize_macosgl(
+        &self,
+        display: gdk::Display,
+        display_ctx_guard: &mut Option<gst_gl::GLDisplay>,
+        app_ctx_guard: &mut Option<gst_gl::GLContext>,
+    ) {
+        gst::info!(
+            CAT,
+            imp: self,
+            "Initializing GL with for macOS backend and display."
+        );
+
+        let platform = gst_gl::GLPlatform::CGL;
+        let (gl_api, _, _) = gst_gl::GLContext::current_gl_api(platform);
+        let gl_ctx = gst_gl::GLContext::current_gl_context(platform);
+
+        if gl_ctx == 0 {
+            gst::error!(CAT, imp: self, "Failed to get handle from GdkGLContext",);
+            return;
+        }
+
+        let gst_display = gst_gl::GLDisplay::new();
+        unsafe {
+            let gst_app_context =
+                gst_gl::GLContext::new_wrapped(&gst_display, gl_ctx, platform, gl_api);
+
+            assert!(gst_app_context.is_some());
+
+            display_ctx_guard.replace(gst_display);
+            app_ctx_guard.replace(gst_app_context.unwrap());
+        }
+    }
 }