Implement drawing an image from a CSS style value into a canvas.

components/script/dom/canvasrenderingcontext2d.rs

@@ -12,12 +12,12 @@ use dom::bindings::cell::DOMRefCell;
 use dom::bindings::codegen::Bindings::CSSStyleDeclarationBinding::CSSStyleDeclarationMethods;
 use dom::bindings::codegen::Bindings::CanvasRenderingContext2DBinding;
 use dom::bindings::codegen::Bindings::CanvasRenderingContext2DBinding::CanvasFillRule;
+use dom::bindings::codegen::Bindings::CanvasRenderingContext2DBinding::CanvasImageSource;
 use dom::bindings::codegen::Bindings::CanvasRenderingContext2DBinding::CanvasLineCap;
 use dom::bindings::codegen::Bindings::CanvasRenderingContext2DBinding::CanvasLineJoin;
 use dom::bindings::codegen::Bindings::CanvasRenderingContext2DBinding::CanvasRenderingContext2DMethods;
 use dom::bindings::codegen::Bindings::ImageDataBinding::ImageDataMethods;
 use dom::bindings::codegen::Bindings::WindowBinding::WindowMethods;
-use dom::bindings::codegen::UnionTypes::HTMLImageElementOrHTMLCanvasElementOrCanvasRenderingContext2D;
 use dom::bindings::codegen::UnionTypes::StringOrCanvasGradientOrCanvasPattern;
 use dom::bindings::error::{Error, ErrorResult, Fallible};
 use dom::bindings::inheritance::Castable;
@@ -29,21 +29,25 @@ use dom::canvasgradient::{CanvasGradient, CanvasGradientStyle, ToFillOrStrokeSty
 use dom::canvaspattern::CanvasPattern;
 use dom::globalscope::GlobalScope;
 use dom::htmlcanvaselement::HTMLCanvasElement;
-use dom::htmlcanvaselement::utils as canvas_utils;
-use dom::htmlimageelement::HTMLImageElement;
 use dom::imagedata::ImageData;
 use dom::node::{document_from_node, Node, NodeDamage, window_from_node};
 use dom_struct::dom_struct;
 use euclid::{Transform2D, Point2D, Vector2D, Rect, Size2D, vec2};
 use ipc_channel::ipc::{self, IpcSender};
 use net_traits::image::base::PixelFormat;
+use net_traits::image_cache::CanRequestImages;
+use net_traits::image_cache::ImageCache;
+use net_traits::image_cache::ImageOrMetadataAvailable;
 use net_traits::image_cache::ImageResponse;
+use net_traits::image_cache::ImageState;
+use net_traits::image_cache::UsePlaceholder;
 use num_traits::ToPrimitive;
 use script_traits::ScriptMsg as ConstellationMsg;
 use servo_url::ServoUrl;
-use std::{cmp, fmt};
+use std::{cmp, fmt, mem};
 use std::cell::Cell;
 use std::str::FromStr;
+use std::sync::Arc;
 use unpremultiplytable::UNPREMULTIPLY_TABLE;
 
 #[must_root]
@@ -61,9 +65,16 @@ pub struct CanvasRenderingContext2D {
     reflector_: Reflector,
     #[ignore_heap_size_of = "Defined in ipc-channel"]
     ipc_renderer: IpcSender<CanvasMsg>,
-    // For rendering contexts created by an HTML canvas element, this is Some,
-    // for ones created by a paint worklet, this is None.
+    /// For rendering contexts created by an HTML canvas element, this is Some,
+    /// for ones created by a paint worklet, this is None.
     canvas: Option<JS<HTMLCanvasElement>>,
+    #[ignore_heap_size_of = "Arc"]
+    image_cache: Arc<ImageCache>,
+    /// Any missing image URLs.
+    missing_image_urls: DOMRefCell<Vec<ServoUrl>>,
+    /// The base URL for resolving CSS image URL values.
+    /// Needed because of https://github.com/servo/servo/issues/17625
+    base_url: ServoUrl,
     state: DOMRefCell<CanvasContextState>,
     saved_states: DOMRefCell<Vec<CanvasContextState>>,
     origin_clean: Cell<bool>,
@@ -113,6 +124,8 @@ impl CanvasContextState {
 impl CanvasRenderingContext2D {
     pub fn new_inherited(global: &GlobalScope,
                          canvas: Option<&HTMLCanvasElement>,
+                         image_cache: Arc<ImageCache>,
+                         base_url: ServoUrl,
                          size: Size2D<i32>)
                          -> CanvasRenderingContext2D {
         debug!("Creating new canvas rendering context.");
@@ -126,6 +139,9 @@ impl CanvasRenderingContext2D {
             reflector_: Reflector::new(),
             ipc_renderer: ipc_renderer,
             canvas: canvas.map(JS::from_ref),
+            image_cache: image_cache,
+            missing_image_urls: DOMRefCell::new(Vec::new()),
+            base_url: base_url,
             state: DOMRefCell::new(CanvasContextState::new()),
             saved_states: DOMRefCell::new(Vec::new()),
             origin_clean: Cell::new(true),
@@ -136,9 +152,11 @@ impl CanvasRenderingContext2D {
                canvas: &HTMLCanvasElement,
                size: Size2D<i32>)
                -> Root<CanvasRenderingContext2D> {
-        reflect_dom_object(box CanvasRenderingContext2D::new_inherited(global, Some(canvas), size),
-                           global,
-                           CanvasRenderingContext2DBinding::Wrap)
+        let window = window_from_node(canvas);
+        let image_cache = window.image_cache();
+        let base_url = window.get_url();
+        let boxed = box CanvasRenderingContext2D::new_inherited(global, Some(canvas), image_cache, base_url, size);
+        reflect_dom_object(boxed, global, CanvasRenderingContext2DBinding::Wrap)
     }
 
     // https://html.spec.whatwg.org/multipage/#concept-canvas-set-bitmap-dimensions
@@ -224,15 +242,15 @@ impl CanvasRenderingContext2D {
 
     // https://html.spec.whatwg.org/multipage/#the-image-argument-is-not-origin-clean
     fn is_origin_clean(&self,
-                       image: HTMLImageElementOrHTMLCanvasElementOrCanvasRenderingContext2D)
+                       image: CanvasImageSource)
                            -> bool {
         match image {
-            HTMLImageElementOrHTMLCanvasElementOrCanvasRenderingContext2D::HTMLCanvasElement(canvas) => {
+            CanvasImageSource::HTMLCanvasElement(canvas) => {
                 canvas.origin_is_clean()
             }
-            HTMLImageElementOrHTMLCanvasElementOrCanvasRenderingContext2D::CanvasRenderingContext2D(image) =>
+            CanvasImageSource::CanvasRenderingContext2D(image) =>
                 image.origin_is_clean(),
-            HTMLImageElementOrHTMLCanvasElementOrCanvasRenderingContext2D::HTMLImageElement(image) => {
+            CanvasImageSource::HTMLImageElement(image) => {
                 let canvas = match self.canvas {
                     Some(ref canvas) => canvas,
                     None => return false,
@@ -241,6 +259,7 @@ impl CanvasRenderingContext2D {
                 let document = document_from_node(&**canvas);
                 document.url().clone().origin() == image_origin
             }
+            CanvasImageSource::CSSStyleValue(_) => true,
         }
     }
 
@@ -266,7 +285,7 @@ impl CanvasRenderingContext2D {
     //
     // https://html.spec.whatwg.org/multipage/#dom-context-2d-drawimage
     fn draw_image(&self,
-                  image: HTMLImageElementOrHTMLCanvasElementOrCanvasRenderingContext2D,
+                  image: CanvasImageSource,
                   sx: f64,
                   sy: f64,
                   sw: Option<f64>,
@@ -277,38 +296,30 @@ impl CanvasRenderingContext2D {
                   dh: Option<f64>)
                   -> ErrorResult {
         let result = match image {
-            HTMLImageElementOrHTMLCanvasElementOrCanvasRenderingContext2D::HTMLCanvasElement(ref canvas) => {
+            CanvasImageSource::HTMLCanvasElement(ref canvas) => {
                 self.draw_html_canvas_element(&canvas,
                                               sx, sy, sw, sh,
                                               dx, dy, dw, dh)
             }
-            HTMLImageElementOrHTMLCanvasElementOrCanvasRenderingContext2D::CanvasRenderingContext2D(ref image) => {
+            CanvasImageSource::CanvasRenderingContext2D(ref image) => {
                 self.draw_html_canvas_element(&image.Canvas(),
                                               sx, sy, sw, sh,
                                               dx, dy, dw, dh)
             }
-            HTMLImageElementOrHTMLCanvasElementOrCanvasRenderingContext2D::HTMLImageElement(ref image) => {
+            CanvasImageSource::HTMLImageElement(ref image) => {
                 // https://html.spec.whatwg.org/multipage/#img-error
                 // If the image argument is an HTMLImageElement object that is in the broken state,
                 // then throw an InvalidStateError exception
-                let (image_data, image_size) = match self.fetch_image_data(image) {
-                    Some((mut data, size)) => {
-                        // Pixels come from cache in BGRA order and drawImage expects RGBA so we
-                        // have to swap the color values
-                        byte_swap_and_premultiply(&mut data);
-                        let size = Size2D::new(size.width as f64, size.height as f64);
-                        (data, size)
-                    },
-                    None => return Err(Error::InvalidState),
-                };
-                let dw = dw.unwrap_or(image_size.width);
-                let dh = dh.unwrap_or(image_size.height);
-                let sw = sw.unwrap_or(image_size.width);
-                let sh = sh.unwrap_or(image_size.height);
-                self.draw_image_data(image_data,
-                                     image_size,
-                                     sx, sy, sw, sh,
-                                     dx, dy, dw, dh)
+                let url = image.get_url().ok_or(Error::InvalidState)?;
+                self.fetch_and_draw_image_data(url,
+                                               sx, sy, sw, sh,
+                                               dx, dy, dw, dh)
+            }
+            CanvasImageSource::CSSStyleValue(ref value) => {
+                let url = value.get_url(self.base_url.clone()).ok_or(Error::InvalidState)?;
+                self.fetch_and_draw_image_data(url,
+                                               sx, sy, sw, sh,
+                                               dx, dy, dw, dh)
             }
         };
 
@@ -386,6 +397,41 @@ impl CanvasRenderingContext2D {
         Ok(())
     }
 
+    fn fetch_and_draw_image_data(&self,
+                                 url: ServoUrl,
+                                 sx: f64,
+                                 sy: f64,
+                                 sw: Option<f64>,
+                                 sh: Option<f64>,
+                                 dx: f64,
+                                 dy: f64,
+                                 dw: Option<f64>,
+                                 dh: Option<f64>)
+                                 -> ErrorResult {
+        debug!("Fetching image {}.", url);
+        // https://html.spec.whatwg.org/multipage/#img-error
+        // If the image argument is an HTMLImageElement object that is in the broken state,
+        // then throw an InvalidStateError exception
+        let (image_data, image_size) = match self.fetch_image_data(url) {
+            Some((mut data, size)) => {
+                // Pixels come from cache in BGRA order and drawImage expects RGBA so we
+                // have to swap the color values
+                byte_swap_and_premultiply(&mut data);
+                let size = Size2D::new(size.width as f64, size.height as f64);
+                (data, size)
+            },
+            None => return Err(Error::InvalidState),
+        };
+        let dw = dw.unwrap_or(image_size.width);
+        let dh = dh.unwrap_or(image_size.height);
+        let sw = sw.unwrap_or(image_size.width);
+        let sh = sh.unwrap_or(image_size.height);
+        self.draw_image_data(image_data,
+                             image_size,
+                             sx, sy, sw, sh,
+                             dx, dy, dw, dh)
+    }
+
     fn draw_image_data(&self,
                        image_data: Vec<u8>,
                        image_size: Size2D<f64>,
@@ -425,12 +471,7 @@ impl CanvasRenderingContext2D {
         Ok(())
     }
 
-    fn fetch_image_data(&self, image_element: &HTMLImageElement) -> Option<(Vec<u8>, Size2D<i32>)> {
-        let url = match image_element.get_url() {
-            Some(url) => url,
-            None => return None,
-        };
-
+    fn fetch_image_data(&self, url: ServoUrl) -> Option<(Vec<u8>, Size2D<i32>)> {
         let img = match self.request_image_from_cache(url) {
             ImageResponse::Loaded(img, _) => img,
             ImageResponse::PlaceholderLoaded(_, _) |
@@ -453,10 +494,26 @@ impl CanvasRenderingContext2D {
 
     #[inline]
     fn request_image_from_cache(&self, url: ServoUrl) -> ImageResponse {
-        self.canvas.as_ref()
-            .map(|canvas| window_from_node(&**canvas))
-            .map(|window| canvas_utils::request_image_from_cache(&window, url))
-            .unwrap_or(ImageResponse::None)
+        let response = self.image_cache
+            .find_image_or_metadata(url.clone(),
+                                    UsePlaceholder::No,
+                                    CanRequestImages::No);
+        match response {
+            Ok(ImageOrMetadataAvailable::ImageAvailable(image, url)) =>
+                ImageResponse::Loaded(image, url),
+            Err(ImageState::Pending(_)) =>
+                ImageResponse::None,
+            _ => {
+                // Rather annoyingly, we get the same response back from
+                // A load which really failed and from a load which hasn't started yet.
+                self.missing_image_urls.borrow_mut().push(url);
+                ImageResponse::None
+            },
+        }
+    }
+
+    pub fn take_missing_image_urls(&self) -> Vec<ServoUrl> {
+        mem::replace(&mut self.missing_image_urls.borrow_mut(), vec![])
     }
 
     fn create_drawable_rect(&self, x: f64, y: f64, w: f64, h: f64) -> Option<Rect<f32>> {
@@ -749,7 +806,7 @@ impl CanvasRenderingContext2DMethods for CanvasRenderingContext2D {
 
     // https://html.spec.whatwg.org/multipage/#dom-context-2d-drawimage
     fn DrawImage(&self,
-                 image: HTMLImageElementOrHTMLCanvasElementOrCanvasRenderingContext2D,
+                 image: CanvasImageSource,
                  dx: f64,
                  dy: f64)
                  -> ErrorResult {
@@ -762,7 +819,7 @@ impl CanvasRenderingContext2DMethods for CanvasRenderingContext2D {
 
     // https://html.spec.whatwg.org/multipage/#dom-context-2d-drawimage
     fn DrawImage_(&self,
-                  image: HTMLImageElementOrHTMLCanvasElementOrCanvasRenderingContext2D,
+                  image: CanvasImageSource,
                   dx: f64,
                   dy: f64,
                   dw: f64,
@@ -777,7 +834,7 @@ impl CanvasRenderingContext2DMethods for CanvasRenderingContext2D {
 
     // https://html.spec.whatwg.org/multipage/#dom-context-2d-drawimage
     fn DrawImage__(&self,
-                   image: HTMLImageElementOrHTMLCanvasElementOrCanvasRenderingContext2D,
+                   image: CanvasImageSource,
                    sx: f64,
                    sy: f64,
                    sw: f64,
@@ -1152,27 +1209,34 @@ impl CanvasRenderingContext2DMethods for CanvasRenderingContext2D {
 
     // https://html.spec.whatwg.org/multipage/#dom-context-2d-createpattern
     fn CreatePattern(&self,
-                     image: HTMLImageElementOrHTMLCanvasElementOrCanvasRenderingContext2D,
+                     image: CanvasImageSource,
                      mut repetition: DOMString)
                      -> Fallible<Root<CanvasPattern>> {
         let (image_data, image_size) = match image {
-            HTMLImageElementOrHTMLCanvasElementOrCanvasRenderingContext2D::HTMLImageElement(ref image) => {
+            CanvasImageSource::HTMLImageElement(ref image) => {
                 // https://html.spec.whatwg.org/multipage/#img-error
                 // If the image argument is an HTMLImageElement object that is in the broken state,
                 // then throw an InvalidStateError exception
-                self.fetch_image_data(image).ok_or(Error::InvalidState)?
+                image.get_url()
+                    .and_then(|url| self.fetch_image_data(url))
+                    .ok_or(Error::InvalidState)?
             },
-            HTMLImageElementOrHTMLCanvasElementOrCanvasRenderingContext2D::HTMLCanvasElement(ref canvas) => {
+            CanvasImageSource::HTMLCanvasElement(ref canvas) => {
                 let _ = canvas.get_or_init_2d_context();
 
                 canvas.fetch_all_data().ok_or(Error::InvalidState)?
             },
-            HTMLImageElementOrHTMLCanvasElementOrCanvasRenderingContext2D::CanvasRenderingContext2D(ref context) => {
+            CanvasImageSource::CanvasRenderingContext2D(ref context) => {
                 let canvas = context.Canvas();
                 let _ = canvas.get_or_init_2d_context();
 
                 canvas.fetch_all_data().ok_or(Error::InvalidState)?
             }
+            CanvasImageSource::CSSStyleValue(ref value) => {
+                value.get_url(self.base_url.clone())
+                    .and_then(|url| self.fetch_image_data(url))
+                    .ok_or(Error::InvalidState)?
+            }
         };
 
         if repetition.is_empty() {

components/script/dom/cssstylevalue.rs

@@ -2,6 +2,8 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
+use cssparser::Parser;
+use cssparser::ParserInput;
 use dom::bindings::codegen::Bindings::CSSStyleValueBinding::CSSStyleValueMethods;
 use dom::bindings::codegen::Bindings::CSSStyleValueBinding::Wrap;
 use dom::bindings::js::Root;
@@ -10,6 +12,7 @@ use dom::bindings::reflector::reflect_dom_object;
 use dom::bindings::str::DOMString;
 use dom::globalscope::GlobalScope;
 use dom_struct::dom_struct;
+use servo_url::ServoUrl;
 
 #[dom_struct]
 pub struct CSSStyleValue {
@@ -44,3 +47,16 @@ impl CSSStyleValueMethods for CSSStyleValue {
         self.Stringifier()
     }
 }
+
+impl CSSStyleValue {
+    /// Parse the value as a `url()`.
+    /// TODO: This should really always be an absolute URL, but we currently
+    /// return relative URLs for computed values, so we pass in a base.
+    /// https://github.com/servo/servo/issues/17625
+    pub fn get_url(&self, base_url: ServoUrl) -> Option<ServoUrl> {
+        let mut input = ParserInput::new(&*self.value);
+        let mut parser = Parser::new(&mut input);
+        parser.expect_url().ok()
+            .and_then(|string| base_url.join(&*string).ok())
+    }
+}

components/script/dom/paintrenderingcontext2d.rs

@@ -11,7 +11,7 @@ use dom::bindings::codegen::Bindings::CanvasRenderingContext2DBinding::CanvasLin
 use dom::bindings::codegen::Bindings::CanvasRenderingContext2DBinding::CanvasRenderingContext2DMethods;
 use dom::bindings::codegen::Bindings::PaintRenderingContext2DBinding;
 use dom::bindings::codegen::Bindings::PaintRenderingContext2DBinding::PaintRenderingContext2DMethods;
-use dom::bindings::codegen::UnionTypes::HTMLImageElementOrHTMLCanvasElementOrCanvasRenderingContext2D;
+use dom::bindings::codegen::UnionTypes::HTMLImageElementOrHTMLCanvasElementOrCanvasRenderingContext2DOrCSSStyleValue;
 use dom::bindings::codegen::UnionTypes::StringOrCanvasGradientOrCanvasPattern;
 use dom::bindings::error::ErrorResult;
 use dom::bindings::error::Fallible;
@@ -24,11 +24,13 @@ use dom::canvasgradient::CanvasGradient;
 use dom::canvaspattern::CanvasPattern;
 use dom::canvasrenderingcontext2d::CanvasRenderingContext2D;
 use dom::paintworkletglobalscope::PaintWorkletGlobalScope;
+use dom::workletglobalscope::WorkletGlobalScope;
 use dom_struct::dom_struct;
 use euclid::ScaleFactor;
 use euclid::Size2D;
 use euclid::TypedSize2D;
 use ipc_channel::ipc::IpcSender;
+use servo_url::ServoUrl;
 use std::cell::Cell;
 use style_traits::CSSPixel;
 use style_traits::DevicePixel;
@@ -42,8 +44,10 @@ pub struct PaintRenderingContext2D {
 impl PaintRenderingContext2D {
     fn new_inherited(global: &PaintWorkletGlobalScope) -> PaintRenderingContext2D {
         let size = Size2D::zero();
+        let image_cache = global.image_cache();
+        let base_url = global.upcast::<WorkletGlobalScope>().base_url();
         PaintRenderingContext2D {
-            context: CanvasRenderingContext2D::new_inherited(global.upcast(), None, size),
+            context: CanvasRenderingContext2D::new_inherited(global.upcast(), None, image_cache, base_url, size),
             device_pixel_ratio: Cell::new(ScaleFactor::new(1.0)),
         }
     }
@@ -59,6 +63,10 @@ impl PaintRenderingContext2D {
         let _ = self.context.ipc_renderer().send(msg);
     }
 
+    pub fn take_missing_image_urls(&self) -> Vec<ServoUrl> {
+        self.context.take_missing_image_urls()
+    }
+
     pub fn set_bitmap_dimensions(&self,
                                  size: TypedSize2D<f32, CSSPixel>,
                                  device_pixel_ratio: ScaleFactor<f32, CSSPixel, DevicePixel>)
@@ -187,7 +195,7 @@ impl PaintRenderingContext2DMethods for PaintRenderingContext2D {
 
     // https://html.spec.whatwg.org/multipage/#dom-context-2d-drawimage
     fn DrawImage(&self,
-                 image: HTMLImageElementOrHTMLCanvasElementOrCanvasRenderingContext2D,
+                 image: HTMLImageElementOrHTMLCanvasElementOrCanvasRenderingContext2DOrCSSStyleValue,
                  dx: f64,
                  dy: f64)
                  -> ErrorResult {
@@ -196,7 +204,7 @@ impl PaintRenderingContext2DMethods for PaintRenderingContext2D {
 
     // https://html.spec.whatwg.org/multipage/#dom-context-2d-drawimage
     fn DrawImage_(&self,
-                  image: HTMLImageElementOrHTMLCanvasElementOrCanvasRenderingContext2D,
+                  image: HTMLImageElementOrHTMLCanvasElementOrCanvasRenderingContext2DOrCSSStyleValue,
                   dx: f64,
                   dy: f64,
                   dw: f64,
@@ -207,7 +215,7 @@ impl PaintRenderingContext2DMethods for PaintRenderingContext2D {
 
     // https://html.spec.whatwg.org/multipage/#dom-context-2d-drawimage
     fn DrawImage__(&self,
-                   image: HTMLImageElementOrHTMLCanvasElementOrCanvasRenderingContext2D,
+                   image: HTMLImageElementOrHTMLCanvasElementOrCanvasRenderingContext2DOrCSSStyleValue,
                    sx: f64,
                    sy: f64,
                    sw: f64,
@@ -309,7 +317,7 @@ impl PaintRenderingContext2DMethods for PaintRenderingContext2D {
 
     // https://html.spec.whatwg.org/multipage/#dom-context-2d-createpattern
     fn CreatePattern(&self,
-                     image: HTMLImageElementOrHTMLCanvasElementOrCanvasRenderingContext2D,
+                     image: HTMLImageElementOrHTMLCanvasElementOrCanvasRenderingContext2DOrCSSStyleValue,
                      repetition: DOMString)
                      -> Fallible<Root<CanvasPattern>> {
         self.context.CreatePattern(image, repetition)

components/script/dom/paintworkletglobalscope.rs

@@ -3,7 +3,6 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 use canvas_traits::CanvasData;
-use canvas_traits::CanvasImageData;
 use dom::bindings::callback::CallbackContainer;
 use dom::bindings::cell::DOMRefCell;
 use dom::bindings::codegen::Bindings::PaintWorkletGlobalScopeBinding;
@@ -28,8 +27,7 @@ use dom::workletglobalscope::WorkletTask;
 use dom_struct::dom_struct;
 use euclid::ScaleFactor;
 use euclid::TypedSize2D;
-use ipc_channel::ipc::IpcSender;
-use ipc_channel::ipc::IpcSharedMemory;
+use ipc_channel::ipc;
 use js::jsapi::Call;
 use js::jsapi::Construct1;
 use js::jsapi::HandleValue;
@@ -45,10 +43,10 @@ use js::jsval::ObjectValue;
 use js::jsval::UndefinedValue;
 use js::rust::Runtime;
 use msg::constellation_msg::PipelineId;
-use net_traits::image::base::Image;
 use net_traits::image::base::PixelFormat;
 use net_traits::image_cache::ImageCache;
 use script_layout_interface::message::Msg;
+use script_traits::DrawAPaintImageResult;
 use script_traits::Painter;
 use servo_atoms::Atom;
 use servo_url::ServoUrl;
@@ -59,6 +57,8 @@ use std::ptr::null_mut;
 use std::rc::Rc;
 use std::sync::Arc;
 use std::sync::Mutex;
+use std::sync::mpsc;
+use std::sync::mpsc::Sender;
 use style_traits::CSSPixel;
 use style_traits::DevicePixel;
 
@@ -67,7 +67,7 @@ use style_traits::DevicePixel;
 pub struct PaintWorkletGlobalScope {
     /// The worklet global for this object
     worklet_global: WorkletGlobalScope,
-    /// The image cache (used for generating invalid images).
+    /// The image cache
     #[ignore_heap_size_of = "Arc"]
     image_cache: Arc<ImageCache>,
     /// https://drafts.css-houdini.org/css-paint-api/#paint-definitions
@@ -94,11 +94,16 @@ impl PaintWorkletGlobalScope {
         unsafe { PaintWorkletGlobalScopeBinding::Wrap(runtime.cx(), global) }
     }
 
+    pub fn image_cache(&self) -> Arc<ImageCache> {
+        self.image_cache.clone()
+    }
+
     pub fn perform_a_worklet_task(&self, task: PaintWorkletTask) {
         match task {
-            PaintWorkletTask::DrawAPaintImage(name, size, device_pixel_ratio, properties, sender) => {
+            PaintWorkletTask::DrawAPaintImage(name, size_in_px, device_pixel_ratio, properties, sender) => {
                 let properties = StylePropertyMapReadOnly::from_iter(self.upcast(), properties);
-                self.draw_a_paint_image(name, size, device_pixel_ratio, &*properties, sender);
+                let result = self.draw_a_paint_image(name, size_in_px, device_pixel_ratio, &*properties);
+                let _ = sender.send(result);
             }
         }
     }
@@ -108,11 +113,11 @@ impl PaintWorkletGlobalScope {
                           name: Atom,
                           size_in_px: TypedSize2D<f32, CSSPixel>,
                           device_pixel_ratio: ScaleFactor<f32, CSSPixel, DevicePixel>,
-                          properties: &StylePropertyMapReadOnly,
-                          sender: IpcSender<CanvasData>)
+                          properties: &StylePropertyMapReadOnly)
+                          -> DrawAPaintImageResult
     {
         // TODO: document paint definitions.
-        self.invoke_a_paint_callback(name, size_in_px, device_pixel_ratio, properties, sender);
+        self.invoke_a_paint_callback(name, size_in_px, device_pixel_ratio, properties)
     }
 
     /// https://drafts.css-houdini.org/css-paint-api/#invoke-a-paint-callback
@@ -121,8 +126,8 @@ impl PaintWorkletGlobalScope {
                                name: Atom,
                                size_in_px: TypedSize2D<f32, CSSPixel>,
                                device_pixel_ratio: ScaleFactor<f32, CSSPixel, DevicePixel>,
-                               properties: &StylePropertyMapReadOnly,
-                               sender: IpcSender<CanvasData>)
+                               properties: &StylePropertyMapReadOnly)
+                               -> DrawAPaintImageResult
     {
         let size_in_dpx = size_in_px * device_pixel_ratio;
         let size_in_dpx = TypedSize2D::new(size_in_dpx.width.abs() as u32, size_in_dpx.height.abs() as u32);
@@ -140,13 +145,13 @@ impl PaintWorkletGlobalScope {
             None => {
                 // Step 2.2.
                 warn!("Drawing un-registered paint definition {}.", name);
-                return self.send_invalid_image(size_in_dpx, sender);
+                return self.invalid_image(size_in_dpx, vec![]);
             }
             Some(definition) => {
                 // Step 5.1
                 if !definition.constructor_valid_flag.get() {
                     debug!("Drawing invalid paint definition {}.", name);
-                    return self.send_invalid_image(size_in_dpx, sender);
+                    return self.invalid_image(size_in_dpx, vec![]);
                 }
                 class_constructor.set(definition.class_constructor.get());
                 paint_function.set(definition.paint_function.get());
@@ -174,7 +179,7 @@ impl PaintWorkletGlobalScope {
                     self.paint_definitions.borrow_mut().get_mut(&name)
                         .expect("Vanishing paint definition.")
                         .constructor_valid_flag.set(false);
-                    return self.send_invalid_image(size_in_dpx, sender);
+                    return self.invalid_image(size_in_dpx, vec![]);
                 }
                 // Step 5.4
                 entry.insert(Box::new(Heap::default())).set(paint_instance.get());
@@ -202,39 +207,42 @@ impl PaintWorkletGlobalScope {
 
         rooted!(in(cx) let mut result = UndefinedValue());
         unsafe { Call(cx, paint_instance.handle(), paint_function.handle(), &args, result.handle_mut()); }
+        let missing_image_urls = rendering_context.take_missing_image_urls();
 
         // Step 13.
         if unsafe { JS_IsExceptionPending(cx) } {
             debug!("Paint function threw an exception {}.", name);
             unsafe { JS_ClearPendingException(cx); }
-            return self.send_invalid_image(size_in_dpx, sender);
+            return self.invalid_image(size_in_dpx, missing_image_urls);
         }
 
+        let (sender, receiver) = ipc::channel().expect("IPC channel creation.");
         rendering_context.send_data(sender);
+        let image_key = match receiver.recv() {
+            Ok(CanvasData::Image(data)) => Some(data.image_key),
+            _ => None,
+        };
+
+        DrawAPaintImageResult {
+            width: size_in_dpx.width,
+            height: size_in_dpx.height,
+            format: PixelFormat::BGRA8,
+            image_key: image_key,
+            missing_image_urls: missing_image_urls,
+        }
     }
 
-    fn send_invalid_image(&self,
-                          size: TypedSize2D<u32, DevicePixel>,
-                          sender: IpcSender<CanvasData>)
-    {
-        debug!("Sending an invalid image.");
-        let width = size.width as u32;
-        let height = size.height as u32;
-        let len = (width as usize) * (height as usize) * 4;
-        let pixel = [0x00, 0x00, 0x00, 0x00];
-        let bytes: Vec<u8> = pixel.iter().cloned().cycle().take(len).collect();
-        let mut image = Image {
-            width: width,
-            height: height,
+    // https://drafts.csswg.org/css-images-4/#invalid-image
+    fn invalid_image(&self, size: TypedSize2D<u32, DevicePixel>, missing_image_urls: Vec<ServoUrl>)
+                     -> DrawAPaintImageResult {
+        debug!("Returning an invalid image.");
+        DrawAPaintImageResult {
+            width: size.width as u32,
+            height: size.height as u32,
             format: PixelFormat::BGRA8,
-            bytes: IpcSharedMemory::from_bytes(&*bytes),
-            id: None,
-        };
-        self.image_cache.set_webrender_image_key(&mut image);
-        let image_key = image.id.expect("Image cache should set image key.");
-        let image_data = CanvasImageData { image_key: image_key };
-        let canvas_data = CanvasData::Image(image_data);
-        let _ = sender.send(canvas_data);
+            image_key: None,
+            missing_image_urls: missing_image_urls,
+        }
     }
 
     fn painter(&self, name: Atom) -> Arc<Painter> {
@@ -244,13 +252,15 @@ impl PaintWorkletGlobalScope {
             fn draw_a_paint_image(&self,
                                   size: TypedSize2D<f32, CSSPixel>,
                                   device_pixel_ratio: ScaleFactor<f32, CSSPixel, DevicePixel>,
-                                  properties: Vec<(Atom, String)>,
-                                  sender: IpcSender<CanvasData>)
+                                  properties: Vec<(Atom, String)>)
+                                  -> DrawAPaintImageResult
             {
                 let name = self.0.clone();
+                let (sender, receiver) = mpsc::channel();
                 let task = PaintWorkletTask::DrawAPaintImage(name, size, device_pixel_ratio, properties, sender);
                 self.1.lock().expect("Locking a painter.")
                     .schedule_a_worklet_task(WorkletTask::Paint(task));
+                receiver.recv().expect("Worklet thread died?")
             }
         }
         Arc::new(WorkletPainter(name, Mutex::new(self.worklet_global.executor())))
@@ -346,7 +356,7 @@ pub enum PaintWorkletTask {
                     TypedSize2D<f32, CSSPixel>,
                     ScaleFactor<f32, CSSPixel, DevicePixel>,
                     Vec<(Atom, String)>,
-                    IpcSender<CanvasData>)
+                    Sender<DrawAPaintImageResult>)
 }
 
 /// A paint definition

components/script/dom/webidls/CanvasRenderingContext2D.webidl

@@ -8,8 +8,11 @@ enum CanvasFillRule { "nonzero", "evenodd" };
 typedef (HTMLImageElement or
          /* HTMLVideoElement or */
          HTMLCanvasElement or
-         CanvasRenderingContext2D /* or
-         ImageBitmap */) CanvasImageSource;
+         CanvasRenderingContext2D or
+         /* ImageBitmap or */
+         // This should probably be a CSSImageValue
+         // https://github.com/w3c/css-houdini-drafts/issues/416
+         CSSStyleValue) CanvasImageSource;
 
 //[Constructor(optional unsigned long width, unsigned long height)]
 interface CanvasRenderingContext2D {