compositor: Create a single cross-process compositor API (#33619)

Instead of exposing many different kinds of messages to the compositor
that are routed through the constellation, expose a single message type
which can be sent across IPC channels. In addition, this IPC channel and
the route to the crossbeam channel with the compositor is created along
with the `CompositorProxy`, simplifying what needs to be passed around
during pipeline initialization.

Previously, some image updates (from video) were sent over IPC with a
special serialization routine and some were sent via crossbeam channels
(canvas). Now all updates go over the IPC channel `IpcSharedMemory` is
used to avoid serialization penalties. This should improve performance
and reduce copies for video, but add a memory copy overhead for canvas.
This will improve in the future when canvas renders directly into a
texture.

All-in-all this is a simplification which opens the path toward having a
standard compositor API and reduces the number of duplicate messages and
proxying that had to happen in libservo.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

1 files changed, 7 insertions, 9 deletions

diff --git a/components/script/dom/screen.rs b/components/script/dom/screen.rs
index fcbd84fd061..d7ce8b6b4be 100644
--- a/components/script/dom/screen.rs
+++ b/components/script/dom/screen.rs
@@ -5,16 +5,14 @@
 use dom_struct::dom_struct;
 use euclid::Size2D;
 use profile_traits::ipc;
-use script_traits::ScriptMsg;
 use style_traits::CSSPixel;
 use webrender_api::units::DeviceIntSize;
+use webrender_traits::CrossProcessCompositorMessage;
 
 use crate::dom::bindings::codegen::Bindings::ScreenBinding::ScreenMethods;
-use crate::dom::bindings::inheritance::Castable;
 use crate::dom::bindings::num::Finite;
 use crate::dom::bindings::reflector::{reflect_dom_object, DomObject, Reflector};
 use crate::dom::bindings::root::{Dom, DomRoot};
-use crate::dom::globalscope::GlobalScope;
 use crate::dom::window::Window;
 
 #[dom_struct]
@@ -39,9 +37,9 @@ impl Screen {
         let (send, recv) =
             ipc::channel::<DeviceIntSize>(self.global().time_profiler_chan().clone()).unwrap();
         self.window
-            .upcast::<GlobalScope>()
-            .script_to_constellation_chan()
-            .send(ScriptMsg::GetScreenSize(send))
+            .compositor_api()
+            .sender()
+            .send(CrossProcessCompositorMessage::GetScreenSize(send))
             .unwrap();
         let dpr = self.window.device_pixel_ratio();
         let screen = recv.recv().unwrap_or(Size2D::zero());
@@ -52,9 +50,9 @@ impl Screen {
         let (send, recv) =
             ipc::channel::<DeviceIntSize>(self.global().time_profiler_chan().clone()).unwrap();
         self.window
-            .upcast::<GlobalScope>()
-            .script_to_constellation_chan()
-            .send(ScriptMsg::GetScreenAvailSize(send))
+            .compositor_api()
+            .sender()
+            .send(CrossProcessCompositorMessage::GetAvailableScreenSize(send))
             .unwrap();
         let dpr = self.window.device_pixel_ratio();
         let screen = recv.recv().unwrap_or(Size2D::zero());