Implemented the plumbing for paint worklets.

components/script/dom/paintworkletglobalscope.rs

@@ -0,0 +1,97 @@
+/* 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 http://mozilla.org/MPL/2.0/. */
+
+use app_units::Au;
+use dom::bindings::cell::DOMRefCell;
+use dom::bindings::codegen::Bindings::PaintWorkletGlobalScopeBinding;
+use dom::bindings::codegen::Bindings::PaintWorkletGlobalScopeBinding::PaintWorkletGlobalScopeMethods;
+use dom::bindings::codegen::Bindings::VoidFunctionBinding::VoidFunction;
+use dom::bindings::js::Root;
+use dom::bindings::str::DOMString;
+use dom::workletglobalscope::WorkletGlobalScope;
+use dom::workletglobalscope::WorkletGlobalScopeInit;
+use dom_struct::dom_struct;
+use euclid::Size2D;
+use ipc_channel::ipc::IpcSharedMemory;
+use js::rust::Runtime;
+use msg::constellation_msg::PipelineId;
+use net_traits::image::base::Image;
+use net_traits::image::base::PixelFormat;
+use script_traits::PaintWorkletError;
+use servo_atoms::Atom;
+use servo_url::ServoUrl;
+use std::rc::Rc;
+use std::sync::mpsc::Sender;
+
+#[dom_struct]
+/// https://drafts.css-houdini.org/css-paint-api/#paintworkletglobalscope
+pub struct PaintWorkletGlobalScope {
+    /// The worklet global for this object
+    worklet_global: WorkletGlobalScope,
+    /// A buffer to draw into
+    buffer: DOMRefCell<Vec<u8>>,
+}
+
+impl PaintWorkletGlobalScope {
+    #[allow(unsafe_code)]
+    pub fn new(runtime: &Runtime,
+               pipeline_id: PipelineId,
+               base_url: ServoUrl,
+               init: &WorkletGlobalScopeInit)
+               -> Root<PaintWorkletGlobalScope> {
+        debug!("Creating paint worklet global scope for pipeline {}.", pipeline_id);
+        let global = box PaintWorkletGlobalScope {
+            worklet_global: WorkletGlobalScope::new_inherited(pipeline_id, base_url, init),
+            buffer: Default::default(),
+        };
+        unsafe { PaintWorkletGlobalScopeBinding::Wrap(runtime.cx(), global) }
+    }
+
+    pub fn perform_a_worklet_task(&self, task: PaintWorkletTask) {
+        match task {
+            PaintWorkletTask::DrawAPaintImage(name, size, sender) => self.draw_a_paint_image(name, size, sender),
+        }
+    }
+
+    fn draw_a_paint_image(&self,
+                          name: Atom,
+                          concrete_object_size: Size2D<Au>,
+                          sender: Sender<Result<Image, PaintWorkletError>>) {
+        let width = concrete_object_size.width.to_px().abs() as u32;
+        let height = concrete_object_size.height.to_px().abs() as u32;
+        let area = (width as usize) * (height as usize);
+        let old_buffer_size = self.buffer.borrow().len();
+        let new_buffer_size = area * 4;
+        debug!("Drawing a paint image {}({},{}).", name, width, height);
+        // TODO: call into script to create the image.
+        // For now, we just build a dummy.
+        if new_buffer_size > old_buffer_size {
+            let pixel = [0xFF, 0x00, 0x00, 0xFF];
+            self.buffer.borrow_mut().extend(pixel.iter().cycle().take(new_buffer_size - old_buffer_size));
+        } else {
+            self.buffer.borrow_mut().truncate(new_buffer_size);
+        }
+        let image = Image {
+            width: width,
+            height: height,
+            format: PixelFormat::RGBA8,
+            bytes: IpcSharedMemory::from_bytes(&*self.buffer.borrow()),
+            id: None,
+        };
+        let _ = sender.send(Ok(image));
+    }
+}
+
+impl PaintWorkletGlobalScopeMethods for PaintWorkletGlobalScope {
+    /// https://drafts.css-houdini.org/css-paint-api/#dom-paintworkletglobalscope-registerpaint
+    fn RegisterPaint(&self, name: DOMString, _paintCtor: Rc<VoidFunction>) {
+        debug!("Registering paint image name {}.", name);
+        // TODO
+    }
+}
+
+/// Tasks which can be peformed by a paint worklet
+pub enum PaintWorkletTask {
+    DrawAPaintImage(Atom, Size2D<Au>, Sender<Result<Image, PaintWorkletError>>)
+}