script: Add CanvasContext trait (#35448)

* trait `CanvasContext`

Signed-off-by: sagudev <16504129+sagudev@users.noreply.github.com>

* fixup most stuff

Signed-off-by: sagudev <16504129+sagudev@users.noreply.github.com>

* explain and limit crown `allow(crown::unrooted_must_root)`

Signed-off-by: sagudev <16504129+sagudev@users.noreply.github.com>

---------

Signed-off-by: sagudev <16504129+sagudev@users.noreply.github.com>

components/script/canvas_context.rs

@@ -0,0 +1,77 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+//! Common interfaces for Canvas Contexts
+
+use canvas_traits::canvas::CanvasId;
+use euclid::default::Size2D;
+use ipc_channel::ipc::IpcSharedMemory;
+use script_layout_interface::{HTMLCanvasData, HTMLCanvasDataSource};
+
+use crate::dom::bindings::codegen::UnionTypes::HTMLCanvasElementOrOffscreenCanvas;
+use crate::dom::bindings::inheritance::Castable;
+use crate::dom::node::{Node, NodeDamage};
+
+pub(crate) trait LayoutCanvasRenderingContextHelpers {
+    fn canvas_data_source(self) -> HTMLCanvasDataSource;
+}
+
+pub(crate) trait LayoutHTMLCanvasElementHelpers {
+    fn data(self) -> HTMLCanvasData;
+    fn get_canvas_id_for_layout(self) -> CanvasId;
+}
+
+pub(crate) trait CanvasContext {
+    type ID;
+
+    fn context_id(&self) -> Self::ID;
+
+    fn canvas(&self) -> HTMLCanvasElementOrOffscreenCanvas;
+
+    fn resize(&self);
+
+    fn get_image_data_as_shared_memory(&self) -> Option<IpcSharedMemory>;
+
+    fn get_image_data(&self) -> Option<Vec<u8>> {
+        self.get_image_data_as_shared_memory().map(|sm| sm.to_vec())
+    }
+
+    fn origin_is_clean(&self) -> bool {
+        true
+    }
+
+    fn size(&self) -> Size2D<u64> {
+        self.canvas().size()
+    }
+
+    fn mark_as_dirty(&self) {
+        if let HTMLCanvasElementOrOffscreenCanvas::HTMLCanvasElement(canvas) = &self.canvas() {
+            canvas.upcast::<Node>().dirty(NodeDamage::OtherNodeDamage);
+        }
+    }
+
+    fn update_rendering(&self) {}
+
+    fn onscreen(&self) -> bool {
+        match self.canvas() {
+            HTMLCanvasElementOrOffscreenCanvas::HTMLCanvasElement(ref canvas) => {
+                canvas.upcast::<Node>().is_connected()
+            },
+            // FIXME(34628): Offscreen canvases should be considered offscreen if a placeholder is set.
+            // <https://www.w3.org/TR/webgpu/#abstract-opdef-updating-the-rendering-of-a-webgpu-canvas>
+            HTMLCanvasElementOrOffscreenCanvas::OffscreenCanvas(_) => false,
+        }
+    }
+}
+
+impl HTMLCanvasElementOrOffscreenCanvas {
+    pub(crate) fn size(&self) -> Size2D<u64> {
+        match self {
+            HTMLCanvasElementOrOffscreenCanvas::HTMLCanvasElement(canvas) => {
+                canvas.get_size().cast()
+            },
+            HTMLCanvasElementOrOffscreenCanvas::OffscreenCanvas(canvas) => canvas.get_size(),
+        }
+    }
+}