canvas: Make OffscreenCanvas transferable (without placeholder) (#37872)

Follow the specification and make OffscreenCanvas objects are
transferable,
but not in case if there are a weak reference to placeholder canvas
element.
To handle it properly need to implement dedicated frame
provider/dispatcher
between canvas element (script thread) and offscreen canvas (dedicated
worker thread).

https://html.spec.whatwg.org/multipage/#the-offscreencanvas-interface:transferable-objects

Testing: Improvements in the following tests
-
html/canvas/element/drawing-images-to-the-canvas/2d.drawImage.detachedcanvas.html
-
html/canvas/offscreen/manual/convert-to-blob/offscreencanvas.convert.to.blob*
-
html/canvas/offscreen/manual/the-offscreen-canvas/offscreencanvas.transfer*
-
html/infrastructure/safe-passing-of-structured-data/transfer-errors.window.js

Part of #24276

Signed-off-by: Andrei Volykhin <andrei.volykhin@gmail.com>

components/script/canvas_context.rs

@@ -258,6 +258,7 @@ pub(crate) enum OffscreenRenderingContext {
     //WebGL2(Dom<WebGL2RenderingContext>),
     //#[cfg(feature = "webgpu")]
     //WebGPU(Dom<GPUCanvasContext>),
+    Detached,
 }
 
 impl CanvasContext for OffscreenRenderingContext {
@@ -268,54 +269,63 @@ impl CanvasContext for OffscreenRenderingContext {
     fn canvas(&self) -> Option<HTMLCanvasElementOrOffscreenCanvas> {
         match self {
             OffscreenRenderingContext::Context2d(context) => context.canvas(),
+            OffscreenRenderingContext::Detached => None,
         }
     }
 
     fn resize(&self) {
         match self {
             OffscreenRenderingContext::Context2d(context) => context.resize(),
+            OffscreenRenderingContext::Detached => {},
         }
     }
 
     fn reset_bitmap(&self) {
         match self {
             OffscreenRenderingContext::Context2d(context) => context.reset_bitmap(),
+            OffscreenRenderingContext::Detached => {},
         }
     }
 
     fn get_image_data(&self) -> Option<Snapshot> {
         match self {
             OffscreenRenderingContext::Context2d(context) => context.get_image_data(),
+            OffscreenRenderingContext::Detached => None,
         }
     }
 
     fn origin_is_clean(&self) -> bool {
         match self {
             OffscreenRenderingContext::Context2d(context) => context.origin_is_clean(),
+            OffscreenRenderingContext::Detached => true,
         }
     }
 
     fn size(&self) -> Size2D<u32> {
         match self {
             OffscreenRenderingContext::Context2d(context) => context.size(),
+            OffscreenRenderingContext::Detached => Size2D::default(),
         }
     }
 
     fn mark_as_dirty(&self) {
         match self {
             OffscreenRenderingContext::Context2d(context) => context.mark_as_dirty(),
+            OffscreenRenderingContext::Detached => {},
         }
     }
 
     fn update_rendering(&self) {
         match self {
             OffscreenRenderingContext::Context2d(context) => context.update_rendering(),
+            OffscreenRenderingContext::Detached => {},
         }
     }
 
     fn onscreen(&self) -> bool {
         match self {
             OffscreenRenderingContext::Context2d(context) => context.onscreen(),
+            OffscreenRenderingContext::Detached => false,
         }
     }
 }

components/script/canvas_state.rs

@@ -651,6 +651,7 @@ impl CanvasState {
                         smoothing_enabled,
                     ));
                 },
+                OffscreenRenderingContext::Detached => return Err(Error::InvalidState),
             }
         } else {
             self.send_canvas_2d_msg(Canvas2dMsg::DrawEmptyImage(
@@ -719,6 +720,7 @@ impl CanvasState {
                                 source_rect,
                                 smoothing_enabled,
                             )),
+                        OffscreenRenderingContext::Detached => return Err(Error::InvalidState),
                     }
                 },
                 _ => return Err(Error::InvalidState),

components/script/dom/bindings/structuredclone.rs

@@ -11,12 +11,12 @@ use std::ptr;
 
 use base::id::{
     BlobId, DomExceptionId, DomPointId, ImageBitmapId, Index, MessagePortId, NamespaceIndex,
-    PipelineNamespaceId,
+    OffscreenCanvasId, PipelineNamespaceId,
 };
 use constellation_traits::{
     BlobImpl, DomException, DomPoint, MessagePortImpl, Serializable as SerializableInterface,
-    SerializableImageBitmap, StructuredSerializedData, Transferrable as TransferrableInterface,
-    TransformStreamData,
+    SerializableImageBitmap, StructuredSerializedData, TransferableOffscreenCanvas,
+    Transferrable as TransferrableInterface, TransformStreamData,
 };
 use js::gc::RootedVec;
 use js::glue::{
@@ -46,6 +46,7 @@ use crate::dom::dompointreadonly::DOMPointReadOnly;
 use crate::dom::globalscope::GlobalScope;
 use crate::dom::imagebitmap::ImageBitmap;
 use crate::dom::messageport::MessagePort;
+use crate::dom::offscreencanvas::OffscreenCanvas;
 use crate::dom::readablestream::ReadableStream;
 use crate::dom::types::{DOMException, TransformStream};
 use crate::dom::writablestream::WritableStream;
@@ -70,6 +71,7 @@ pub(super) enum StructuredCloneTags {
     WritableStream = 0xFFFF8008,
     TransformStream = 0xFFFF8009,
     ImageBitmap = 0xFFFF800A,
+    OffscreenCanvas = 0xFFFF800B,
     Max = 0xFFFFFFFF,
 }
 
@@ -90,6 +92,7 @@ impl From<TransferrableInterface> for StructuredCloneTags {
         match v {
             TransferrableInterface::ImageBitmap => StructuredCloneTags::ImageBitmap,
             TransferrableInterface::MessagePort => StructuredCloneTags::MessagePort,
+            TransferrableInterface::OffscreenCanvas => StructuredCloneTags::OffscreenCanvas,
             TransferrableInterface::ReadableStream => StructuredCloneTags::ReadableStream,
             TransferrableInterface::WritableStream => StructuredCloneTags::WritableStream,
             TransferrableInterface::TransformStream => StructuredCloneTags::TransformStream,
@@ -274,6 +277,7 @@ fn receiver_for_type(
     match val {
         TransferrableInterface::ImageBitmap => receive_object::<ImageBitmap>,
         TransferrableInterface::MessagePort => receive_object::<MessagePort>,
+        TransferrableInterface::OffscreenCanvas => receive_object::<OffscreenCanvas>,
         TransferrableInterface::ReadableStream => receive_object::<ReadableStream>,
         TransferrableInterface::WritableStream => receive_object::<WritableStream>,
         TransferrableInterface::TransformStream => receive_object::<TransformStream>,
@@ -401,6 +405,7 @@ fn transfer_for_type(val: TransferrableInterface) -> TransferOperation {
     match val {
         TransferrableInterface::ImageBitmap => try_transfer::<ImageBitmap>,
         TransferrableInterface::MessagePort => try_transfer::<MessagePort>,
+        TransferrableInterface::OffscreenCanvas => try_transfer::<OffscreenCanvas>,
         TransferrableInterface::ReadableStream => try_transfer::<ReadableStream>,
         TransferrableInterface::WritableStream => try_transfer::<WritableStream>,
         TransferrableInterface::TransformStream => try_transfer::<TransformStream>,
@@ -451,6 +456,7 @@ unsafe fn can_transfer_for_type(
     match transferable {
         TransferrableInterface::ImageBitmap => can_transfer::<ImageBitmap>(obj, cx),
         TransferrableInterface::MessagePort => can_transfer::<MessagePort>(obj, cx),
+        TransferrableInterface::OffscreenCanvas => can_transfer::<OffscreenCanvas>(obj, cx),
         TransferrableInterface::ReadableStream => can_transfer::<ReadableStream>(obj, cx),
         TransferrableInterface::WritableStream => can_transfer::<WritableStream>(obj, cx),
         TransferrableInterface::TransformStream => can_transfer::<TransformStream>(obj, cx),
@@ -542,6 +548,8 @@ pub(crate) struct StructuredDataReader<'a> {
     pub(crate) image_bitmaps: Option<HashMap<ImageBitmapId, SerializableImageBitmap>>,
     /// A map of transferred image bitmaps.
     pub(crate) transferred_image_bitmaps: Option<HashMap<ImageBitmapId, SerializableImageBitmap>>,
+    /// A map of transferred offscreen canvases.
+    pub(crate) offscreen_canvases: Option<HashMap<OffscreenCanvasId, TransferableOffscreenCanvas>>,
 }
 
 /// A data holder for transferred and serialized objects.
@@ -564,6 +572,8 @@ pub(crate) struct StructuredDataWriter {
     pub(crate) image_bitmaps: Option<HashMap<ImageBitmapId, SerializableImageBitmap>>,
     /// Transferred image bitmaps.
     pub(crate) transferred_image_bitmaps: Option<HashMap<ImageBitmapId, SerializableImageBitmap>>,
+    /// Transferred offscreen canvases.
+    pub(crate) offscreen_canvases: Option<HashMap<OffscreenCanvasId, TransferableOffscreenCanvas>>,
 }
 
 /// Writes a structured clone. Returns a `DataClone` error if that fails.
@@ -620,6 +630,7 @@ pub(crate) fn write(
             blobs: sc_writer.blobs.take(),
             image_bitmaps: sc_writer.image_bitmaps.take(),
             transferred_image_bitmaps: sc_writer.transferred_image_bitmaps.take(),
+            offscreen_canvases: sc_writer.offscreen_canvases.take(),
         };
 
         Ok(data)
@@ -646,6 +657,7 @@ pub(crate) fn read(
         errors: DOMErrorRecord { message: None },
         image_bitmaps: data.image_bitmaps.take(),
         transferred_image_bitmaps: data.transferred_image_bitmaps.take(),
+        offscreen_canvases: data.offscreen_canvases.take(),
     };
     let sc_reader_ptr = &mut sc_reader as *mut _;
     unsafe {

components/script/dom/offscreencanvas.rs

@@ -3,9 +3,11 @@
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
 use std::cell::Cell;
+use std::collections::HashMap;
 use std::rc::Rc;
 
-use constellation_traits::BlobImpl;
+use base::id::{OffscreenCanvasId, OffscreenCanvasIndex};
+use constellation_traits::{BlobImpl, TransferableOffscreenCanvas};
 use dom_struct::dom_struct;
 use euclid::default::Size2D;
 use js::rust::{HandleObject, HandleValue};
@@ -23,6 +25,8 @@ use crate::dom::bindings::refcounted::{Trusted, TrustedPromise};
 use crate::dom::bindings::reflector::{DomGlobal, reflect_dom_object_with_proto};
 use crate::dom::bindings::root::{Dom, DomRoot};
 use crate::dom::bindings::str::DOMString;
+use crate::dom::bindings::structuredclone::StructuredData;
+use crate::dom::bindings::transferable::Transferable;
 use crate::dom::blob::Blob;
 use crate::dom::eventtarget::EventTarget;
 use crate::dom::globalscope::GlobalScope;
@@ -126,6 +130,7 @@ impl OffscreenCanvas {
         if let Some(ctx) = self.context() {
             return match *ctx {
                 OffscreenRenderingContext::Context2d(ref ctx) => Some(DomRoot::from_ref(ctx)),
+                _ => None,
             };
         }
         let context = OffscreenCanvasRenderingContext2D::new(&self.global(), self, can_gc);
@@ -142,6 +147,86 @@ impl OffscreenCanvas {
     }
 }
 
+impl Transferable for OffscreenCanvas {
+    type Index = OffscreenCanvasIndex;
+    type Data = TransferableOffscreenCanvas;
+
+    /// <https://html.spec.whatwg.org/multipage/#the-offscreencanvas-interface:transfer-steps>
+    fn transfer(&self) -> Result<(OffscreenCanvasId, TransferableOffscreenCanvas), ()> {
+        // TODO(#37919) Step 1. If value's context mode is not equal to none,
+        // then throw an "InvalidStateError" DOMException.
+        if !self.context.borrow().is_none() {
+            return Err(());
+        }
+
+        // TODO(#37882): Allow to transfer with a placeholder canvas element.
+        if self.placeholder.is_some() {
+            return Err(());
+        }
+
+        // Step 2. Set value's context mode to detached.
+        *self.context.borrow_mut() = Some(OffscreenRenderingContext::Detached);
+
+        // Step 3. Let width and height be the dimensions of value's bitmap.
+        // Step 5. Unset value's bitmap.
+        let width = self.width.replace(0);
+        let height = self.height.replace(0);
+
+        // TODO(#37918) Step 4. Let language and direction be the values of
+        // value's inherited language and inherited direction.
+
+        // Step 6. Set dataHolder.[[Width]] to width and dataHolder.[[Height]]
+        // to height.
+
+        // TODO(#37918) Step 7. Set dataHolder.[[Language]] to language and
+        // dataHolder.[[Direction]] to direction.
+
+        // TODO(#37882) Step 8. Set dataHolder.[[PlaceholderCanvas]] to be a
+        // weak reference to value's placeholder canvas element, if value has
+        // one, or null if it does not.
+        let transferred = TransferableOffscreenCanvas { width, height };
+
+        Ok((OffscreenCanvasId::new(), transferred))
+    }
+
+    /// <https://html.spec.whatwg.org/multipage/#the-offscreencanvas-interface:transfer-receiving-steps>
+    fn transfer_receive(
+        owner: &GlobalScope,
+        _: OffscreenCanvasId,
+        transferred: TransferableOffscreenCanvas,
+    ) -> Result<DomRoot<Self>, ()> {
+        // Step 1. Initialize value's bitmap to a rectangular array of
+        // transparent black pixels with width given by dataHolder.[[Width]] and
+        // height given by dataHolder.[[Height]].
+
+        // TODO(#37918) Step 2. Set value's inherited language to
+        // dataHolder.[[Language]] and its inherited direction to
+        // dataHolder.[[Direction]].
+
+        // TODO(#37882) Step 3. If dataHolder.[[PlaceholderCanvas]] is not null,
+        // set value's placeholder canvas element to
+        // dataHolder.[[PlaceholderCanvas]] (while maintaining the weak
+        // reference semantics).
+        Ok(OffscreenCanvas::new(
+            owner,
+            None,
+            transferred.width,
+            transferred.height,
+            None,
+            CanGc::note(),
+        ))
+    }
+
+    fn serialized_storage<'a>(
+        data: StructuredData<'a, '_>,
+    ) -> &'a mut Option<HashMap<OffscreenCanvasId, Self::Data>> {
+        match data {
+            StructuredData::Reader(r) => &mut r.offscreen_canvases,
+            StructuredData::Writer(w) => &mut w.offscreen_canvases,
+        }
+    }
+}
+
 impl OffscreenCanvasMethods<crate::DomTypeHolder> for OffscreenCanvas {
     /// <https://html.spec.whatwg.org/multipage/#dom-offscreencanvas>
     fn Constructor(
@@ -151,8 +236,9 @@ impl OffscreenCanvasMethods<crate::DomTypeHolder> for OffscreenCanvas {
         width: u64,
         height: u64,
     ) -> Fallible<DomRoot<OffscreenCanvas>> {
-        let offscreencanvas = OffscreenCanvas::new(global, proto, width, height, None, can_gc);
-        Ok(offscreencanvas)
+        Ok(OffscreenCanvas::new(
+            global, proto, width, height, None, can_gc,
+        ))
     }
 
     /// <https://html.spec.whatwg.org/multipage/#dom-offscreencanvas-getcontext>
@@ -163,6 +249,12 @@ impl OffscreenCanvasMethods<crate::DomTypeHolder> for OffscreenCanvas {
         _options: HandleValue,
         can_gc: CanGc,
     ) -> Fallible<Option<RootedOffscreenRenderingContext>> {
+        // Step 3. Throw an "InvalidStateError" DOMException if the
+        // OffscreenCanvas object's context mode is detached.
+        if let Some(OffscreenRenderingContext::Detached) = *self.context.borrow() {
+            return Err(Error::InvalidState);
+        }
+
         match &*id {
             "2d" => Ok(self
                 .get_or_init_2d_context(can_gc)
@@ -217,9 +309,12 @@ impl OffscreenCanvasMethods<crate::DomTypeHolder> for OffscreenCanvas {
 
     /// <https://html.spec.whatwg.org/multipage/#dom-offscreencanvas-transfertoimagebitmap>
     fn TransferToImageBitmap(&self, can_gc: CanGc) -> Fallible<DomRoot<ImageBitmap>> {
-        // TODO Step 1. If the value of this OffscreenCanvas object's
-        // [[Detached]] internal slot is set to true, then throw an
-        // "InvalidStateError" DOMException.
+        // Step 1. If the value of this OffscreenCanvas object's [[Detached]]
+        // internal slot is set to true, then throw an "InvalidStateError"
+        // DOMException.
+        if let Some(OffscreenRenderingContext::Detached) = *self.context.borrow() {
+            return Err(Error::InvalidState);
+        }
 
         // Step 2. If this OffscreenCanvas object's context mode is set to none,
         // then throw an "InvalidStateError" DOMException.
@@ -255,6 +350,14 @@ impl OffscreenCanvasMethods<crate::DomTypeHolder> for OffscreenCanvas {
         let in_realm_proof = AlreadyInRealm::assert::<crate::DomTypeHolder>();
         let promise = Promise::new_in_current_realm(InRealm::Already(&in_realm_proof), can_gc);
 
+        // Step 1. If the value of this's [[Detached]] internal slot is true,
+        // then return a promise rejected with an "InvalidStateError"
+        // DOMException.
+        if let Some(OffscreenRenderingContext::Detached) = *self.context.borrow() {
+            promise.reject_error(Error::InvalidState, can_gc);
+            return promise;
+        }
+
         // Step 2. If this's context mode is 2d and the rendering context's
         // output bitmap's origin-clean flag is set to false, then return a
         // promise rejected with a "SecurityError" DOMException.