Implemented paint worklet properties.

29 files changed, 353 insertions, 118 deletions

diff --git a/Cargo.lock b/Cargo.lock
index 1e1b8d66c47..d1e05813c9f 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1460,6 +1460,7 @@ dependencies = [
  "selectors 0.19.0",
  "serde 1.0.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_json 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "servo_atoms 0.0.1",
  "servo_config 0.0.1",
  "servo_geometry 0.0.1",
  "servo_url 0.0.1",
@@ -1504,6 +1505,7 @@ dependencies = [
  "script_traits 0.0.1",
  "selectors 0.19.0",
  "serde_json 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "servo_atoms 0.0.1",
  "servo_config 0.0.1",
  "servo_geometry 0.0.1",
  "servo_url 0.0.1",
@@ -2506,6 +2508,7 @@ dependencies = [
  "range 0.0.1",
  "script_traits 0.0.1",
  "selectors 0.19.0",
+ "servo_atoms 0.0.1",
  "servo_url 0.0.1",
  "style 0.0.1",
  "webrender_traits 0.44.0 (git+https://github.com/servo/webrender)",
diff --git a/components/layout/Cargo.toml b/components/layout/Cargo.toml
index e3e2c76c2f4..16f82f2236f 100644
--- a/components/layout/Cargo.toml
+++ b/components/layout/Cargo.toml
@@ -34,6 +34,7 @@ script_layout_interface = {path = "../script_layout_interface"}
 script_traits = {path = "../script_traits"}
 selectors = { path = "../selectors" }
 serde = "1.0"
+servo_atoms = {path = "../atoms"}
 servo_geometry = {path = "../geometry"}
 serde_json = "1.0"
 servo_config = {path = "../config"}
diff --git a/components/layout/context.rs b/components/layout/context.rs
index d261fe5d8a7..cda3811421a 100644
--- a/components/layout/context.rs
+++ b/components/layout/context.rs
@@ -4,6 +4,7 @@
 
 //! Data needed by the layout thread.
 
+use fnv::FnvHashMap;
 use fnv::FnvHasher;
 use gfx::display_list::{WebRenderImageInfo, OpaqueNode};
 use gfx::font_cache_thread::FontCacheThread;
@@ -15,8 +16,9 @@ use net_traits::image_cache::{ImageOrMetadataAvailable, UsePlaceholder};
 use opaque_node::OpaqueNodeMethods;
 use parking_lot::RwLock;
 use script_layout_interface::{PendingImage, PendingImageState};
-use script_traits::PaintWorkletExecutor;
+use script_traits::Painter;
 use script_traits::UntrustedNodeAddress;
+use servo_atoms::Atom;
 use servo_url::ServoUrl;
 use std::cell::{RefCell, RefMut};
 use std::collections::HashMap;
@@ -24,6 +26,7 @@ use std::hash::BuildHasherDefault;
 use std::sync::{Arc, Mutex};
 use std::thread;
 use style::context::SharedStyleContext;
+use style::properties::PropertyId;
 
 thread_local!(static FONT_CONTEXT_KEY: RefCell<Option<FontContext>> = RefCell::new(None));
 
@@ -69,8 +72,8 @@ pub struct LayoutContext<'a> {
                                                   WebRenderImageInfo,
                                                   BuildHasherDefault<FnvHasher>>>>,
 
-    /// The executor for worklets
-    pub paint_worklet_executor: Option<Arc<PaintWorkletExecutor>>,
+    /// Paint worklets
+    pub registered_painters: Arc<RwLock<FnvHashMap<Atom, RegisteredPainter>>>,
 
     /// A list of in-progress image loads to be shared with the script thread.
     /// A None value means that this layout was not initiated by the script thread.
@@ -175,3 +178,10 @@ impl<'a> LayoutContext<'a> {
         }
     }
 }
+
+/// A registered paint worklet.
+pub struct RegisteredPainter {
+    pub name: Atom,
+    pub properties: FnvHashMap<Atom, PropertyId>,
+    pub painter: Arc<Painter>,
+}
diff --git a/components/layout/display_list_builder.rs b/components/layout/display_list_builder.rs
index 9aa9301eef8..32439819d9b 100644
--- a/components/layout/display_list_builder.rs
+++ b/components/layout/display_list_builder.rs
@@ -1165,17 +1165,24 @@ impl FragmentDisplayListBuilding for Fragment {
         let size = unbordered_box.size.to_physical(style.writing_mode);
         let name = paint_worklet.name.clone();
 
-        // If the script thread has not added any paint worklet modules, there is nothing to do!
-        let executor = match state.layout_context.paint_worklet_executor {
-            Some(ref executor) => executor,
-            None => return debug!("Worklet {} called before any paint modules are added.", name),
+        // Get the painter, and the computed values for its properties.
+        let (properties, painter) = match state.layout_context.registered_painters.read().get(&name) {
+            Some(registered_painter) => (
+                registered_painter.properties
+                    .iter()
+                    .filter_map(|(name, id)| id.as_shorthand().err().map(|id| (name, id)))
+                    .map(|(name, id)| (name.clone(), style.computed_value_to_string(id)))
+                    .collect(),
+                registered_painter.painter.clone()
+            ),
+            None => return debug!("Worklet {} called before registration.", name),
         };
 
         // TODO: add a one-place cache to avoid drawing the paint image every time.
         // https://github.com/servo/servo/issues/17369
         debug!("Drawing a paint image {}({},{}).", name, size.width.to_px(), size.height.to_px());
         let (sender, receiver) = ipc::channel().unwrap();
-        executor.draw_a_paint_image(name, size, sender);
+        painter.draw_a_paint_image(size, properties, sender);
 
         // TODO: timeout
         let webrender_image = match receiver.recv() {
diff --git a/components/layout/lib.rs b/components/layout/lib.rs
index af108249c42..f7ed79be750 100644
--- a/components/layout/lib.rs
+++ b/components/layout/lib.rs
@@ -37,6 +37,7 @@ extern crate script_layout_interface;
 extern crate script_traits;
 #[macro_use] extern crate serde;
 extern crate serde_json;
+extern crate servo_atoms;
 extern crate servo_config;
 extern crate servo_geometry;
 extern crate servo_url;
diff --git a/components/layout_thread/Cargo.toml b/components/layout_thread/Cargo.toml
index a63b37cfed5..db9c92bb823 100644
--- a/components/layout_thread/Cargo.toml
+++ b/components/layout_thread/Cargo.toml
@@ -31,6 +31,7 @@ script_layout_interface = {path = "../script_layout_interface"}
 script_traits = {path = "../script_traits"}
 selectors = { path = "../selectors" }
 serde_json = "1.0"
+servo_atoms = {path = "../atoms"}
 servo_config = {path = "../config"}
 servo_geometry = {path = "../geometry"}
 servo_url = {path = "../url"}
diff --git a/components/layout_thread/lib.rs b/components/layout_thread/lib.rs
index b063aa0bca6..a51cdb7ac1a 100644
--- a/components/layout_thread/lib.rs
+++ b/components/layout_thread/lib.rs
@@ -33,6 +33,7 @@ extern crate script_layout_interface;
 extern crate script_traits;
 extern crate selectors;
 extern crate serde_json;
+extern crate servo_atoms;
 extern crate servo_config;
 extern crate servo_geometry;
 extern crate servo_url;
@@ -53,6 +54,7 @@ use ipc_channel::router::ROUTER;
 use layout::animation;
 use layout::construct::ConstructionResult;
 use layout::context::LayoutContext;
+use layout::context::RegisteredPainter;
 use layout::context::heap_size_of_persistent_local_context;
 use layout::display_list_builder::ToGfxColor;
 use layout::flow::{self, Flow, ImmutableFlowUtils, MutableFlowUtils, MutableOwnedFlowUtils};
@@ -87,8 +89,8 @@ use script_layout_interface::rpc::TextIndexResponse;
 use script_layout_interface::wrapper_traits::LayoutNode;
 use script_traits::{ConstellationControlMsg, LayoutControlMsg, LayoutMsg as ConstellationMsg};
 use script_traits::{ScrollState, UntrustedNodeAddress};
-use script_traits::PaintWorkletExecutor;
 use selectors::Element;
+use servo_atoms::Atom;
 use servo_config::opts;
 use servo_config::prefs::PREFS;
 use servo_config::resource_files::read_resource_file;
@@ -114,6 +116,7 @@ use style::error_reporting::{NullReporter, RustLogReporter};
 use style::invalidation::element::restyle_hints::RestyleHint;
 use style::logical_geometry::LogicalPoint;
 use style::media_queries::{Device, MediaList, MediaType};
+use style::properties::PropertyId;
 use style::selector_parser::SnapshotMap;
 use style::servo::restyle_damage::{REFLOW, REFLOW_OUT_OF_FLOW, REPAINT, REPOSITION, STORE_OVERFLOW};
 use style::shared_lock::{SharedRwLock, SharedRwLockReadGuard, StylesheetGuards};
@@ -123,6 +126,7 @@ use style::stylist::{ExtraStyleData, Stylist};
 use style::thread_state;
 use style::timer::Timer;
 use style::traversal::{DomTraversal, TraversalDriver, TraversalFlags};
+use style::values::CompactCowStr;
 
 /// Information needed by the layout thread.
 pub struct LayoutThread {
@@ -223,7 +227,7 @@ pub struct LayoutThread {
                                                  WebRenderImageInfo>>>,
     /// The executor for paint worklets.
     /// Will be None if the script thread hasn't added any paint worklet modules.
-    paint_worklet_executor: Option<Arc<PaintWorkletExecutor>>,
+    registered_painters: Arc<RwLock<FnvHashMap<Atom, RegisteredPainter>>>,
 
     /// Webrender interface.
     webrender_api: webrender_traits::RenderApi,
@@ -491,7 +495,7 @@ impl LayoutThread {
             constellation_chan: constellation_chan.clone(),
             time_profiler_chan: time_profiler_chan,
             mem_profiler_chan: mem_profiler_chan,
-            paint_worklet_executor: None,
+            registered_painters: Arc::new(RwLock::new(FnvHashMap::default())),
             image_cache: image_cache.clone(),
             font_cache_thread: font_cache_thread,
             first_reflow: Cell::new(true),
@@ -584,7 +588,7 @@ impl LayoutThread {
             webrender_image_cache: self.webrender_image_cache.clone(),
             pending_images: if script_initiated_layout { Some(Mutex::new(vec![])) } else { None },
             newly_transitioning_nodes: if script_initiated_layout { Some(Mutex::new(vec![])) } else { None },
-            paint_worklet_executor: self.paint_worklet_executor.clone(),
+            registered_painters: self.registered_painters.clone(),
         }
     }
 
@@ -700,10 +704,19 @@ impl LayoutThread {
             Msg::SetFinalUrl(final_url) => {
                 self.url = final_url;
             },
-            Msg::SetPaintWorkletExecutor(executor) => {
-                debug!("Setting the paint worklet executor");
-                debug_assert!(self.paint_worklet_executor.is_none());
-                self.paint_worklet_executor = Some(executor);
+            Msg::RegisterPaint(name, mut properties, painter) => {
+                debug!("Registering the painter");
+                let properties = properties.drain(..)
+                    .filter_map(|name| PropertyId::parse(CompactCowStr::from(&*name)).ok().map(|id| (name.clone(), id)))
+                    .filter(|&(_, ref id)| id.as_shorthand().is_err())
+                    .collect();
+                let registered_painter = RegisteredPainter {
+                    name: name.clone(),
+                    properties: properties,
+                    painter: painter,
+                };
+                self.registered_painters.write()
+                    .insert(name, registered_painter);
             },
             Msg::PrepareToExit(response_chan) => {
                 self.prepare_to_exit(response_chan);
diff --git a/components/script/dom/cssstylevalue.rs b/components/script/dom/cssstylevalue.rs
new file mode 100644
index 00000000000..7ee9d5509f0
--- /dev/null
+++ b/components/script/dom/cssstylevalue.rs
@@ -0,0 +1,46 @@
+/* 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 dom::bindings::codegen::Bindings::CSSStyleValueBinding::CSSStyleValueMethods;
+use dom::bindings::codegen::Bindings::CSSStyleValueBinding::Wrap;
+use dom::bindings::js::Root;
+use dom::bindings::reflector::Reflector;
+use dom::bindings::reflector::reflect_dom_object;
+use dom::bindings::str::DOMString;
+use dom::globalscope::GlobalScope;
+use dom_struct::dom_struct;
+
+#[dom_struct]
+pub struct CSSStyleValue {
+    reflector: Reflector,
+    value: String,
+}
+
+impl CSSStyleValue {
+    fn new_inherited(value: String) -> CSSStyleValue {
+        CSSStyleValue {
+            reflector: Reflector::new(),
+            value: value,
+        }
+    }
+
+    pub fn new(global: &GlobalScope, value: String) -> Root<CSSStyleValue> {
+        reflect_dom_object(box CSSStyleValue::new_inherited(value), global, Wrap)
+    }
+}
+
+impl CSSStyleValueMethods for CSSStyleValue {
+    /// https://drafts.css-houdini.org/css-typed-om-1/#CSSStyleValue-stringification-behavior
+    fn Stringifier(&self) -> DOMString {
+        DOMString::from(&*self.value)
+    }
+
+    /// This attribute is no longer part of the `CSSStyleValue` interface,
+    /// but is still used in some examples.
+    /// https://github.com/GoogleChrome/houdini-samples/issues/16
+    // check-tidy: no specs after this line
+    fn CssText(&self) -> DOMString {
+        self.Stringifier()
+    }
+}
diff --git a/components/script/dom/mod.rs b/components/script/dom/mod.rs
index 1a2a3fc7171..fe17bb712d7 100644
--- a/components/script/dom/mod.rs
+++ b/components/script/dom/mod.rs
@@ -253,6 +253,7 @@ pub mod cssrulelist;
 pub mod cssstyledeclaration;
 pub mod cssstylerule;
 pub mod cssstylesheet;
+pub mod cssstylevalue;
 pub mod csssupportsrule;
 pub mod cssviewportrule;
 pub mod customelementregistry;
@@ -418,6 +419,7 @@ pub mod serviceworkerregistration;
 pub mod servoparser;
 pub mod storage;
 pub mod storageevent;
+pub mod stylepropertymapreadonly;
 pub mod stylesheet;
 pub mod stylesheetlist;
 pub mod svgelement;
diff --git a/components/script/dom/paintworkletglobalscope.rs b/components/script/dom/paintworkletglobalscope.rs
index 5ac021491ad..95f885cd662 100644
--- a/components/script/dom/paintworkletglobalscope.rs
+++ b/components/script/dom/paintworkletglobalscope.rs
@@ -10,19 +10,22 @@ 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::conversions::StringificationBehavior;
 use dom::bindings::conversions::get_property;
 use dom::bindings::conversions::get_property_jsval;
 use dom::bindings::error::Error;
 use dom::bindings::error::Fallible;
+use dom::bindings::inheritance::Castable;
 use dom::bindings::js::JS;
 use dom::bindings::js::Root;
 use dom::bindings::reflector::DomObject;
 use dom::bindings::str::DOMString;
 use dom::paintrenderingcontext2d::PaintRenderingContext2D;
 use dom::paintsize::PaintSize;
+use dom::stylepropertymapreadonly::StylePropertyMapReadOnly;
+use dom::worklet::WorkletExecutor;
 use dom::workletglobalscope::WorkletGlobalScope;
 use dom::workletglobalscope::WorkletGlobalScopeInit;
+use dom::workletglobalscope::WorkletTask;
 use dom_struct::dom_struct;
 use euclid::Size2D;
 use ipc_channel::ipc::IpcSender;
@@ -45,6 +48,8 @@ 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::Painter;
 use servo_atoms::Atom;
 use servo_url::ServoUrl;
 use std::cell::Cell;
@@ -53,6 +58,7 @@ use std::collections::hash_map::Entry;
 use std::ptr::null_mut;
 use std::rc::Rc;
 use std::sync::Arc;
+use std::sync::Mutex;
 
 /// https://drafts.css-houdini.org/css-paint-api/#paintworkletglobalscope
 #[dom_struct]
@@ -73,11 +79,12 @@ impl PaintWorkletGlobalScope {
     pub fn new(runtime: &Runtime,
                pipeline_id: PipelineId,
                base_url: ServoUrl,
+               executor: WorkletExecutor,
                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),
+            worklet_global: WorkletGlobalScope::new_inherited(pipeline_id, base_url, executor, init),
             image_cache: init.image_cache.clone(),
             paint_definitions: Default::default(),
             paint_class_instances: Default::default(),
@@ -87,7 +94,10 @@ impl PaintWorkletGlobalScope {
 
     pub fn perform_a_worklet_task(&self, task: PaintWorkletTask) {
         match task {
-            PaintWorkletTask::DrawAPaintImage(name, size, sender) => self.draw_a_paint_image(name, size, sender),
+            PaintWorkletTask::DrawAPaintImage(name, size, properties, sender) => {
+                let properties = StylePropertyMapReadOnly::from_iter(self.upcast(), properties);
+                self.draw_a_paint_image(name, size, &*properties, sender);
+            }
         }
     }
 
@@ -95,10 +105,11 @@ impl PaintWorkletGlobalScope {
     fn draw_a_paint_image(&self,
                           name: Atom,
                           size: Size2D<Au>,
+                          properties: &StylePropertyMapReadOnly,
                           sender: IpcSender<CanvasData>)
     {
         // TODO: document paint definitions.
-        self.invoke_a_paint_callback(name, size, sender);
+        self.invoke_a_paint_callback(name, size, properties, sender);
     }
 
     /// https://drafts.css-houdini.org/css-paint-api/#invoke-a-paint-callback
@@ -106,6 +117,7 @@ impl PaintWorkletGlobalScope {
     fn invoke_a_paint_callback(&self,
                                name: Atom,
                                size: Size2D<Au>,
+                               properties: &StylePropertyMapReadOnly,
                                sender: IpcSender<CanvasData>)
     {
         let width = size.width.to_px().abs() as u32;
@@ -179,8 +191,10 @@ impl PaintWorkletGlobalScope {
         let args_slice = [
             ObjectValue(rendering_context.reflector().get_jsobject().get()),
             ObjectValue(paint_size.reflector().get_jsobject().get()),
+            ObjectValue(properties.reflector().get_jsobject().get()),
         ];
         let args = unsafe { HandleValueArray::from_rooted_slice(&args_slice) };
+
         rooted!(in(cx) let mut result = UndefinedValue());
         unsafe { Call(cx, paint_instance.handle(), paint_function.handle(), &args, result.handle_mut()); }
 
@@ -194,12 +208,13 @@ impl PaintWorkletGlobalScope {
         rendering_context.send_data(sender);
     }
 
+    // https://drafts.csswg.org/css-images-4/#invalid-image
     fn send_invalid_image(&self, size: Size2D<Au>, sender: IpcSender<CanvasData>) {
         debug!("Sending an invalid image.");
         let width = size.width.to_px().abs() as u32;
         let height = size.height.to_px().abs() as u32;
         let len = (width as usize) * (height as usize) * 4;
-        let pixel = [0xFF, 0x00, 0x00, 0xFF];
+        let pixel = [0x00, 0x00, 0x00, 0x00];
         let bytes: Vec<u8> = pixel.iter().cloned().cycle().take(len).collect();
         let mut image = Image {
             width: width,
@@ -214,6 +229,24 @@ impl PaintWorkletGlobalScope {
         let canvas_data = CanvasData::Image(image_data);
         let _ = sender.send(canvas_data);
     }
+
+    fn painter(&self, name: Atom) -> Arc<Painter> {
+        // Rather annoyingly we have to use a mutex here to make the painter Sync.
+        struct WorkletPainter(Atom, Mutex<WorkletExecutor>);
+        impl Painter for WorkletPainter {
+            fn draw_a_paint_image(&self,
+                                  size: Size2D<Au>,
+                                  properties: Vec<(Atom, String)>,
+                                  sender: IpcSender<CanvasData>)
+            {
+                let name = self.0.clone();
+                let task = PaintWorkletTask::DrawAPaintImage(name, size, properties, sender);
+                self.1.lock().expect("Locking a painter.")
+                    .schedule_a_worklet_task(WorkletTask::Paint(task));
+            }
+        }
+        Arc::new(WorkletPainter(name, Mutex::new(self.worklet_global.executor())))
+    }
 }
 
 impl PaintWorkletGlobalScopeMethods for PaintWorkletGlobalScope {
@@ -239,27 +272,22 @@ impl PaintWorkletGlobalScopeMethods for PaintWorkletGlobalScope {
         }
 
         // Step 4-6.
-        debug!("Getting input properties.");
-        let input_properties: Vec<DOMString> =
-            unsafe { get_property(cx, paint_obj.handle(), "inputProperties", StringificationBehavior::Default) }?
+        let mut property_names: Vec<String> =
+            unsafe { get_property(cx, paint_obj.handle(), "inputProperties", ()) }?
             .unwrap_or_default();
-        debug!("Got {:?}.", input_properties);
+        let properties = property_names.drain(..).map(Atom::from).collect();
 
         // Step 7-9.
-        debug!("Getting input arguments.");
-        let input_arguments: Vec<DOMString> =
-            unsafe { get_property(cx, paint_obj.handle(), "inputArguments", StringificationBehavior::Default) }?
+        let _argument_names: Vec<String> =
+            unsafe { get_property(cx, paint_obj.handle(), "inputArguments", ()) }?
             .unwrap_or_default();
-        debug!("Got {:?}.", input_arguments);
 
         // TODO: Steps 10-11.
 
         // Steps 12-13.
-        debug!("Getting alpha.");
         let alpha: bool =
             unsafe { get_property(cx, paint_obj.handle(), "alpha", ()) }?
             .unwrap_or(true);
-        debug!("Got {:?}.", alpha);
 
         // Step 14
         if unsafe { !IsConstructor(paint_obj.get()) } {
@@ -285,23 +313,28 @@ impl PaintWorkletGlobalScopeMethods for PaintWorkletGlobalScope {
         let context = PaintRenderingContext2D::new(self);
         let definition = PaintDefinition::new(paint_val.handle(),
                                               paint_function.handle(),
-                                              input_properties,
                                               alpha,
                                               &*context);
 
         // Step 20.
         debug!("Registering definition {}.", name);
-        self.paint_definitions.borrow_mut().insert(name, definition);
+        self.paint_definitions.borrow_mut().insert(name.clone(), definition);
 
         // TODO: Step 21.
 
+        // Inform layout that there is a registered paint worklet.
+        // TODO: layout will end up getting this message multiple times.
+        let painter = self.painter(name.clone());
+        let msg = Msg::RegisterPaint(name, properties, painter);
+        self.worklet_global.send_to_layout(msg);
+
         Ok(())
     }
 }
 
 /// Tasks which can be peformed by a paint worklet
 pub enum PaintWorkletTask {
-    DrawAPaintImage(Atom, Size2D<Au>, IpcSender<CanvasData>)
+    DrawAPaintImage(Atom, Size2D<Au>, Vec<(Atom, String)>, IpcSender<CanvasData>)
 }
 
 /// A paint definition
@@ -314,7 +347,6 @@ struct PaintDefinition {
     class_constructor: Heap<JSVal>,
     paint_function: Heap<JSVal>,
     constructor_valid_flag: Cell<bool>,
-    input_properties: Vec<DOMString>,
     context_alpha_flag: bool,
     // TODO: the spec calls for fresh rendering contexts each time a paint image is drawn,
     // but to avoid having the primary worklet thread create a new renering context,
@@ -325,7 +357,6 @@ struct PaintDefinition {
 impl PaintDefinition {
     fn new(class_constructor: HandleValue,
            paint_function: HandleValue,
-           input_properties: Vec<DOMString>,
            alpha: bool,
            context: &PaintRenderingContext2D)
            -> Box<PaintDefinition>
@@ -334,7 +365,6 @@ impl PaintDefinition {
             class_constructor: Heap::default(),
             paint_function: Heap::default(),
             constructor_valid_flag: Cell::new(true),
-            input_properties: input_properties,
             context_alpha_flag: alpha,
             context: JS::from_ref(context),
         });
diff --git a/components/script/dom/stylepropertymapreadonly.rs b/components/script/dom/stylepropertymapreadonly.rs
new file mode 100644
index 00000000000..323f5dae5a9
--- /dev/null
+++ b/components/script/dom/stylepropertymapreadonly.rs
@@ -0,0 +1,66 @@
+/* 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 dom::bindings::codegen::Bindings::StylePropertyMapReadOnlyBinding::StylePropertyMapReadOnlyMethods;
+use dom::bindings::codegen::Bindings::StylePropertyMapReadOnlyBinding::Wrap;
+use dom::bindings::js::JS;
+use dom::bindings::js::Root;
+use dom::bindings::reflector::Reflector;
+use dom::bindings::reflector::reflect_dom_object;
+use dom::bindings::str::DOMString;
+use dom::cssstylevalue::CSSStyleValue;
+use dom::globalscope::GlobalScope;
+use dom_struct::dom_struct;
+use servo_atoms::Atom;
+use std::collections::HashMap;
+use std::iter::Iterator;
+
+#[dom_struct]
+pub struct StylePropertyMapReadOnly {
+    reflector: Reflector,
+    entries: HashMap<Atom, JS<CSSStyleValue>>,
+}
+
+impl StylePropertyMapReadOnly {
+    fn new_inherited<Entries>(entries: Entries) -> StylePropertyMapReadOnly where
+        Entries: IntoIterator<Item=(Atom, JS<CSSStyleValue>)>
+    {
+        StylePropertyMapReadOnly {
+            reflector: Reflector::new(),
+            entries: entries.into_iter().collect(),
+        }
+    }
+
+    pub fn from_iter<Entries>(global: &GlobalScope, entries: Entries) -> Root<StylePropertyMapReadOnly> where
+        Entries: IntoIterator<Item=(Atom, String)>,
+    {
+        let mut keys = Vec::new();
+        rooted_vec!(let mut values);
+        let iter = entries.into_iter();
+        let (lo, _) = iter.size_hint();
+        keys.reserve(lo);
+        values.reserve(lo);
+        for (key, value) in iter {
+            let value = CSSStyleValue::new(global, value);
+            keys.push(key);
+            values.push(JS::from_ref(&*value));
+        }
+        let iter = keys.drain(..).zip(values.iter().cloned());
+        reflect_dom_object(box StylePropertyMapReadOnly::new_inherited(iter), global, Wrap)
+    }
+}
+
+impl StylePropertyMapReadOnlyMethods for StylePropertyMapReadOnly {
+    /// https://drafts.css-houdini.org/css-typed-om-1/#dom-stylepropertymapreadonly-get
+    fn Get(&self, property: DOMString) -> Option<Root<CSSStyleValue>> {
+        // TODO: avoid constructing an Atom
+        self.entries.get(&Atom::from(property)).map(|value| Root::from_ref(&**value))
+    }
+
+    /// https://drafts.css-houdini.org/css-typed-om-1/#dom-stylepropertymapreadonly-has
+    fn Has(&self, property: DOMString) -> bool {
+        // TODO: avoid constructing an Atom
+        self.entries.contains_key(&Atom::from(property))
+    }
+}
diff --git a/components/script/dom/testworkletglobalscope.rs b/components/script/dom/testworkletglobalscope.rs
index dfd000ac5c1..5c9641d5fd2 100644
--- a/components/script/dom/testworkletglobalscope.rs
+++ b/components/script/dom/testworkletglobalscope.rs
@@ -7,6 +7,7 @@ use dom::bindings::codegen::Bindings::TestWorkletGlobalScopeBinding;
 use dom::bindings::codegen::Bindings::TestWorkletGlobalScopeBinding::TestWorkletGlobalScopeMethods;
 use dom::bindings::js::Root;
 use dom::bindings::str::DOMString;
+use dom::worklet::WorkletExecutor;
 use dom::workletglobalscope::WorkletGlobalScope;
 use dom::workletglobalscope::WorkletGlobalScopeInit;
 use dom_struct::dom_struct;
@@ -31,12 +32,13 @@ impl TestWorkletGlobalScope {
     pub fn new(runtime: &Runtime,
                pipeline_id: PipelineId,
                base_url: ServoUrl,
+               executor: WorkletExecutor,
                init: &WorkletGlobalScopeInit)
                -> Root<TestWorkletGlobalScope>
     {
         debug!("Creating test worklet global scope for pipeline {}.", pipeline_id);
         let global = box TestWorkletGlobalScope {
-            worklet_global: WorkletGlobalScope::new_inherited(pipeline_id, base_url, init),
+            worklet_global: WorkletGlobalScope::new_inherited(pipeline_id, base_url, executor, init),
             lookup_table: Default::default(),
         };
         unsafe { TestWorkletGlobalScopeBinding::Wrap(runtime.cx(), global) }
diff --git a/components/script/dom/webidls/CSSStyleValue.webidl b/components/script/dom/webidls/CSSStyleValue.webidl
new file mode 100644
index 00000000000..7f9ab308ff1
--- /dev/null
+++ b/components/script/dom/webidls/CSSStyleValue.webidl
@@ -0,0 +1,14 @@
+/* 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/. */
+
+// https://drafts.css-houdini.org/css-typed-om-1/#cssstylevalue
+// NOTE: should this be exposed to Window?
+[Exposed=(Worklet)]
+interface CSSStyleValue {
+    stringifier;
+    // static CSSStyleValue? parse(DOMString property, DOMString cssText);
+    // static sequence<CSSStyleValue>? parseAll(DOMString property, DOMString cssText);
+    // This is a deprecated property, it's not in the spec any more but is used in houdini-samples
+    readonly attribute DOMString cssText;
+};
diff --git a/components/script/dom/webidls/StylePropertyMapReadOnly.webidl b/components/script/dom/webidls/StylePropertyMapReadOnly.webidl
new file mode 100644
index 00000000000..6ff50ac4be9
--- /dev/null
+++ b/components/script/dom/webidls/StylePropertyMapReadOnly.webidl
@@ -0,0 +1,15 @@
+/* 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/. */
+
+// https://drafts.css-houdini.org/css-typed-om-1/#stylepropertymapreadonly
+// NOTE: should this be exposed to Window?
+[Exposed=(Worklet)]
+interface StylePropertyMapReadOnly {
+    CSSStyleValue? get(DOMString property);
+    // sequence<CSSStyleValue> getAll(DOMString property);
+    boolean has(DOMString property);
+    // iterable<DOMString, (CSSStyleValue or sequence<CSSStyleValue>)>;
+    // sequence<DOMString> getProperties();
+    // stringifier;
+};
diff --git a/components/script/dom/window.rs b/components/script/dom/window.rs
index 59c3c678fb3..89877cd780c 100644
--- a/components/script/dom/window.rs
+++ b/components/script/dom/window.rs
@@ -386,10 +386,7 @@ impl Window {
 
     fn new_paint_worklet(&self) -> Root<Worklet> {
         debug!("Creating new paint worklet.");
-        let worklet = Worklet::new(self, WorkletGlobalScopeType::Paint);
-        let executor = Arc::new(worklet.executor());
-        let _ = self.layout_chan.send(Msg::SetPaintWorkletExecutor(executor));
-        worklet
+        Worklet::new(self, WorkletGlobalScopeType::Paint)
     }
 
     pub fn permission_state_invocation_results(&self) -> &DOMRefCell<HashMap<String, PermissionState>> {
diff --git a/components/script/dom/worklet.rs b/components/script/dom/worklet.rs
index bbcc777ab11..a034ec00f47 100644
--- a/components/script/dom/worklet.rs
+++ b/components/script/dom/worklet.rs
@@ -10,8 +10,6 @@
 //! thread pool implementation, which only performs GC or code loading on
 //! a backup thread, not on the primary worklet thread.
 
-use app_units::Au;
-use canvas_traits::CanvasData;
 use dom::bindings::codegen::Bindings::RequestBinding::RequestCredentials;
 use dom::bindings::codegen::Bindings::WindowBinding::WindowBinding::WindowMethods;
 use dom::bindings::codegen::Bindings::WorkletBinding::WorkletMethods;
@@ -29,7 +27,6 @@ use dom::bindings::str::USVString;
 use dom::bindings::trace::JSTraceable;
 use dom::bindings::trace::RootedTraceableBox;
 use dom::globalscope::GlobalScope;
-use dom::paintworkletglobalscope::PaintWorkletTask;
 use dom::promise::Promise;
 use dom::testworkletglobalscope::TestWorkletTask;
 use dom::window::Window;
@@ -38,8 +35,6 @@ use dom::workletglobalscope::WorkletGlobalScopeInit;
 use dom::workletglobalscope::WorkletGlobalScopeType;
 use dom::workletglobalscope::WorkletTask;
 use dom_struct::dom_struct;
-use euclid::Size2D;
-use ipc_channel::ipc::IpcSender;
 use js::jsapi::JSGCParamKey;
 use js::jsapi::JSTracer;
 use js::jsapi::JS_GC;
@@ -59,8 +54,6 @@ use script_runtime::new_rt_and_cx;
 use script_thread::MainThreadScriptMsg;
 use script_thread::Runnable;
 use script_thread::ScriptThread;
-use script_traits::PaintWorkletExecutor;
-use servo_atoms::Atom;
 use servo_rand;
 use servo_url::ImmutableOrigin;
 use servo_url::ServoUrl;
@@ -69,7 +62,6 @@ use std::collections::HashMap;
 use std::collections::hash_map;
 use std::rc::Rc;
 use std::sync::Arc;
-use std::sync::Mutex;
 use std::sync::atomic::AtomicIsize;
 use std::sync::atomic::Ordering;
 use std::sync::mpsc;
@@ -117,13 +109,6 @@ impl Worklet {
     pub fn worklet_global_scope_type(&self) -> WorkletGlobalScopeType {
         self.global_type
     }
-
-    pub fn executor(&self) -> WorkletExecutor {
-        WorkletExecutor {
-            worklet_id: self.worklet_id,
-            primary_sender: Mutex::new(ScriptThread::worklet_thread_pool().primary_sender.clone()),
-        }
-    }
 }
 
 impl WorkletMethods for Worklet {
@@ -268,7 +253,7 @@ impl Drop for WorkletThreadPool {
 impl WorkletThreadPool {
     /// Create a new thread pool and spawn the threads.
     /// When the thread pool is dropped, the threads will be asked to quit.
-    pub fn spawn(script_sender: Sender<MainThreadScriptMsg>, global_init: WorkletGlobalScopeInit) -> WorkletThreadPool {
+    pub fn spawn(global_init: WorkletGlobalScopeInit) -> WorkletThreadPool {
         let primary_role = WorkletThreadRole::new(false, false);
         let hot_backup_role = WorkletThreadRole::new(true, false);
         let cold_backup_role = WorkletThreadRole::new(false, true);
@@ -276,9 +261,9 @@ impl WorkletThreadPool {
         let hot_backup_sender = hot_backup_role.sender.clone();
         let cold_backup_sender = cold_backup_role.sender.clone();
         let init = WorkletThreadInit {
+            primary_sender: primary_sender.clone(),
             hot_backup_sender: hot_backup_sender.clone(),
             cold_backup_sender: cold_backup_sender.clone(),
-            script_sender: script_sender.clone(),
             global_init: global_init,
         };
         WorkletThreadPool {
@@ -388,9 +373,9 @@ impl WorkletThreadRole {
 #[derive(Clone)]
 struct WorkletThreadInit {
     /// Senders
+    primary_sender: Sender<WorkletData>,
     hot_backup_sender: Sender<WorkletData>,
     cold_backup_sender: Sender<WorkletData>,
-    script_sender: Sender<MainThreadScriptMsg>,
 
     /// Data for initializing new worklet global scopes
     global_init: WorkletGlobalScopeInit,
@@ -406,9 +391,9 @@ struct WorkletThread {
     control_receiver: Receiver<WorkletControl>,
 
     /// Senders
+    primary_sender: Sender<WorkletData>,
     hot_backup_sender: Sender<WorkletData>,
     cold_backup_sender: Sender<WorkletData>,
-    script_sender: Sender<MainThreadScriptMsg>,
 
     /// Data for initializing new worklet global scopes
     global_init: WorkletGlobalScopeInit,
@@ -451,9 +436,9 @@ impl WorkletThread {
             let mut thread = RootedTraceableBox::new(WorkletThread {
                 role: role,
                 control_receiver: control_receiver,
+                primary_sender: init.primary_sender,
                 hot_backup_sender: init.hot_backup_sender,
                 cold_backup_sender: init.cold_backup_sender,
-                script_sender: init.script_sender,
                 global_init: init.global_init,
                 global_scopes: HashMap::new(),
                 control_buffer: None,
@@ -562,7 +547,8 @@ impl WorkletThread {
             hash_map::Entry::Occupied(entry) => Root::from_ref(entry.get()),
             hash_map::Entry::Vacant(entry) => {
                 debug!("Creating new worklet global scope.");
-                let result = global_type.new(&self.runtime, pipeline_id, base_url, &self.global_init);
+                let executor = WorkletExecutor::new(worklet_id, self.primary_sender.clone());
+                let result = global_type.new(&self.runtime, pipeline_id, base_url, executor, &self.global_init);
                 entry.insert(JS::from_ref(&*result));
                 result
             },
@@ -626,7 +612,7 @@ impl WorkletThread {
             if old_counter == 1 {
                 debug!("Resolving promise.");
                 let msg = MainThreadScriptMsg::WorkletLoaded(pipeline_id);
-                self.script_sender.send(msg).expect("Worklet thread outlived script thread.");
+                self.global_init.script_sender.send(msg).expect("Worklet thread outlived script thread.");
                 self.run_in_script_thread(promise.resolve_runnable(()));
             }
         }
@@ -668,35 +654,28 @@ impl WorkletThread {
     {
         let msg = CommonScriptMsg::RunnableMsg(ScriptThreadEventCategory::WorkletEvent, box runnable);
         let msg = MainThreadScriptMsg::Common(msg);
-        self.script_sender.send(msg).expect("Worklet thread outlived script thread.");
+        self.global_init.script_sender.send(msg).expect("Worklet thread outlived script thread.");
     }
 }
 
 /// An executor of worklet tasks
+#[derive(Clone, JSTraceable, HeapSizeOf)]
 pub struct WorkletExecutor {
     worklet_id: WorkletId,
-    // Rather annoyingly, we have to use a mutex here because
-    // layout threads share their context rather than cloning it.
-    primary_sender: Mutex<Sender<WorkletData>>,
+    #[ignore_heap_size_of = "channels are hard"]
+    primary_sender: Sender<WorkletData>,
 }
 
 impl WorkletExecutor {
-    /// Schedule a worklet task to be peformed by the worklet thread pool.
-    fn schedule_a_worklet_task(&self, task: WorkletTask) {
-        let _ = self.primary_sender.lock()
-            .expect("Locking the worklet channel.")
-            .send(WorkletData::Task(self.worklet_id, task));
+    fn new(worklet_id: WorkletId, primary_sender: Sender<WorkletData>) -> WorkletExecutor {
+        WorkletExecutor {
+            worklet_id: worklet_id,
+            primary_sender: primary_sender,
+        }
     }
-}
 
-impl PaintWorkletExecutor for WorkletExecutor {
-    /// https://drafts.css-houdini.org/css-paint-api/#draw-a-paint-image
-    fn draw_a_paint_image(&self,
-                          name: Atom,
-                          concrete_object_size: Size2D<Au>,
-                          sender: IpcSender<CanvasData>)
-    {
-        let task = WorkletTask::Paint(PaintWorkletTask::DrawAPaintImage(name, concrete_object_size, sender));
-        self.schedule_a_worklet_task(task);
+    /// Schedule a worklet task to be peformed by the worklet thread pool.
+    pub fn schedule_a_worklet_task(&self, task: WorkletTask) {
+        let _ = self.primary_sender.send(WorkletData::Task(self.worklet_id, task));
     }
 }
diff --git a/components/script/dom/workletglobalscope.rs b/components/script/dom/workletglobalscope.rs
index bbe3c47e3f8..d8b5fdac22d 100644
--- a/components/script/dom/workletglobalscope.rs
+++ b/components/script/dom/workletglobalscope.rs
@@ -10,6 +10,7 @@ use dom::paintworkletglobalscope::PaintWorkletGlobalScope;
 use dom::paintworkletglobalscope::PaintWorkletTask;
 use dom::testworkletglobalscope::TestWorkletGlobalScope;
 use dom::testworkletglobalscope::TestWorkletTask;
+use dom::worklet::WorkletExecutor;
 use dom_struct::dom_struct;
 use ipc_channel::ipc;
 use ipc_channel::ipc::IpcSender;
@@ -23,12 +24,19 @@ use net_traits::ResourceThreads;
 use net_traits::image_cache::ImageCache;
 use profile_traits::mem;
 use profile_traits::time;
+use script_layout_interface::message::Msg;
+use script_runtime::CommonScriptMsg;
+use script_runtime::ScriptThreadEventCategory;
+use script_thread::MainThreadScriptMsg;
+use script_thread::Runnable;
+use script_thread::ScriptThread;
 use script_traits::ScriptMsg;
 use script_traits::TimerSchedulerMsg;
 use servo_url::ImmutableOrigin;
 use servo_url::MutableOrigin;
 use servo_url::ServoUrl;
 use std::sync::Arc;
+use std::sync::mpsc::Sender;
 
 #[dom_struct]
 /// https://drafts.css-houdini.org/worklets/#workletglobalscope
@@ -39,12 +47,18 @@ pub struct WorkletGlobalScope {
     base_url: ServoUrl,
     /// The microtask queue for this worklet
     microtask_queue: MicrotaskQueue,
+    /// Sender back to the script thread
+    #[ignore_heap_size_of = "channels are hard"]
+    script_sender: Sender<MainThreadScriptMsg>,
+    /// Worklet task executor
+    executor: WorkletExecutor,
 }
 
 impl WorkletGlobalScope {
     /// Create a new stack-allocated `WorkletGlobalScope`.
     pub fn new_inherited(pipeline_id: PipelineId,
                          base_url: ServoUrl,
+                         executor: WorkletExecutor,
                          init: &WorkletGlobalScopeInit)
                          -> WorkletGlobalScope {
         // Any timer events fired on this global are ignored.
@@ -61,6 +75,8 @@ impl WorkletGlobalScope {
                                                     MutableOrigin::new(ImmutableOrigin::new_opaque())),
             base_url: base_url,
             microtask_queue: MicrotaskQueue::default(),
+            script_sender: init.script_sender.clone(),
+            executor: executor,
         }
     }
 
@@ -76,11 +92,37 @@ impl WorkletGlobalScope {
         self.globalscope.evaluate_js_on_global_with_result(&*script, rval.handle_mut())
     }
 
+    /// Run a runnable in the main script thread.
+    pub fn run_in_script_thread<R>(&self, runnable: R) where
+        R: 'static + Send + Runnable,
+    {
+        let msg = CommonScriptMsg::RunnableMsg(ScriptThreadEventCategory::WorkletEvent, box runnable);
+        let msg = MainThreadScriptMsg::Common(msg);
+        self.script_sender.send(msg).expect("Worklet thread outlived script thread.");
+    }
+
+    /// Send a message to layout.
+    pub fn send_to_layout(&self, msg: Msg) {
+        struct RunnableMsg(PipelineId, Msg);
+        impl Runnable for RunnableMsg {
+            fn main_thread_handler(self: Box<Self>, script_thread: &ScriptThread) {
+                script_thread.send_to_layout(self.0, self.1);
+            }
+        }
+        let pipeline_id = self.globalscope.pipeline_id();
+        self.run_in_script_thread(RunnableMsg(pipeline_id, msg));
+    }
+
     /// The base URL of this global.
     pub fn base_url(&self) -> ServoUrl {
         self.base_url.clone()
     }
 
+    /// The worklet executor.
+    pub fn executor(&self) -> WorkletExecutor {
+        self.executor.clone()
+    }
+
     /// Queue up a microtask to be executed in this global.
     pub fn enqueue_microtask(&self, job: Microtask) {
         self.microtask_queue.enqueue(job);
@@ -113,6 +155,8 @@ impl WorkletGlobalScope {
 /// Resources required by workletglobalscopes
 #[derive(Clone)]
 pub struct WorkletGlobalScopeInit {
+    /// Channel to the main script thread
+    pub script_sender: Sender<MainThreadScriptMsg>,
     /// Channel to a resource thread
     pub resource_threads: ResourceThreads,
     /// Channel to the memory profiler
@@ -144,14 +188,15 @@ impl WorkletGlobalScopeType {
                runtime: &Runtime,
                pipeline_id: PipelineId,
                base_url: ServoUrl,
+               executor: WorkletExecutor,
                init: &WorkletGlobalScopeInit)
                -> Root<WorkletGlobalScope>
     {
         match *self {
             WorkletGlobalScopeType::Test =>
-                Root::upcast(TestWorkletGlobalScope::new(runtime, pipeline_id, base_url, init)),
+                Root::upcast(TestWorkletGlobalScope::new(runtime, pipeline_id, base_url, executor, init)),
             WorkletGlobalScopeType::Paint =>
-                Root::upcast(PaintWorkletGlobalScope::new(runtime, pipeline_id, base_url, init)),
+                Root::upcast(PaintWorkletGlobalScope::new(runtime, pipeline_id, base_url, executor, init)),
         }
     }
 }
diff --git a/components/script/script_thread.rs b/components/script/script_thread.rs
index 94318472b50..641d761b373 100644
--- a/components/script/script_thread.rs
+++ b/components/script/script_thread.rs
@@ -79,7 +79,7 @@ use net_traits::request::{CredentialsMode, Destination, RedirectMode, RequestIni
 use net_traits::storage_thread::StorageType;
 use profile_traits::mem::{self, OpaqueSender, Report, ReportKind, ReportsChan};
 use profile_traits::time::{self, ProfilerCategory, profile};
-use script_layout_interface::message::{self, NewLayoutThreadInfo, ReflowQueryType};
+use script_layout_interface::message::{self, Msg, NewLayoutThreadInfo, ReflowQueryType};
 use script_runtime::{CommonScriptMsg, ScriptChan, ScriptThreadEventCategory};
 use script_runtime::{ScriptPort, StackRootTLS, get_reports, new_rt_and_cx};
 use script_traits::{CompositorEvent, ConstellationControlMsg};
@@ -718,8 +718,8 @@ impl ScriptThread {
         SCRIPT_THREAD_ROOT.with(|root| {
             let script_thread = unsafe { &*root.get().unwrap() };
             script_thread.worklet_thread_pool.borrow_mut().get_or_insert_with(|| {
-                let chan = script_thread.chan.0.clone();
                 let init = WorkletGlobalScopeInit {
+                    script_sender: script_thread.chan.0.clone(),
                     resource_threads: script_thread.resource_threads.clone(),
                     mem_profiler_chan: script_thread.mem_profiler_chan.clone(),
                     time_profiler_chan: script_thread.time_profiler_chan.clone(),
@@ -728,11 +728,20 @@ impl ScriptThread {
                     scheduler_chan: script_thread.scheduler_chan.clone(),
                     image_cache: script_thread.image_cache.clone(),
                 };
-                Rc::new(WorkletThreadPool::spawn(chan, init))
+                Rc::new(WorkletThreadPool::spawn(init))
             }).clone()
         })
     }
 
+    pub fn send_to_layout(&self, pipeline_id: PipelineId, msg: Msg) {
+        let window = self.documents.borrow().find_window(pipeline_id);
+        let window = match window {
+            Some(window) => window,
+            None => return warn!("Message sent to layout after pipeline {} closed.", pipeline_id),
+        };
+        let _ = window.layout_chan().send(msg);
+    }
+
     /// Creates a new script thread.
     pub fn new(state: InitialScriptState,
                port: Receiver<MainThreadScriptMsg>,
diff --git a/components/script_layout_interface/Cargo.toml b/components/script_layout_interface/Cargo.toml
index 6a74eeda086..8a4c66c9e0d 100644
--- a/components/script_layout_interface/Cargo.toml
+++ b/components/script_layout_interface/Cargo.toml
@@ -28,6 +28,7 @@ profile_traits = {path = "../profile_traits"}
 range = {path = "../range"}
 script_traits = {path = "../script_traits"}
 selectors = { path = "../selectors" }
+servo_atoms = {path = "../atoms"}
 servo_url = {path = "../url"}
 style = {path = "../style"}
 webrender_traits = {git = "https://github.com/servo/webrender", features = ["ipc"]}
diff --git a/components/script_layout_interface/lib.rs b/components/script_layout_interface/lib.rs
index 3e0a258aa7d..ebdb4a59b7a 100644
--- a/components/script_layout_interface/lib.rs
+++ b/components/script_layout_interface/lib.rs
@@ -30,6 +30,7 @@ extern crate profile_traits;
 extern crate range;
 extern crate script_traits;
 extern crate selectors;
+extern crate servo_atoms;
 extern crate servo_url;
 extern crate style;
 extern crate webrender_traits;
diff --git a/components/script_layout_interface/message.rs b/components/script_layout_interface/message.rs
index 84b93c527aa..4b1648bb6a2 100644
--- a/components/script_layout_interface/message.rs
+++ b/components/script_layout_interface/message.rs
@@ -13,7 +13,8 @@ use profile_traits::mem::ReportsChan;
 use rpc::LayoutRPC;
 use script_traits::{ConstellationControlMsg, LayoutControlMsg, LayoutMsg as ConstellationMsg};
 use script_traits::{ScrollState, UntrustedNodeAddress, WindowSizeData};
-use script_traits::PaintWorkletExecutor;
+use script_traits::Painter;
+use servo_atoms::Atom;
 use servo_url::ServoUrl;
 use std::sync::Arc;
 use std::sync::mpsc::{Receiver, Sender};
@@ -86,7 +87,7 @@ pub enum Msg {
     UpdateScrollStateFromScript(ScrollState),
 
     /// Tells layout that script has added some paint worklet modules.
-    SetPaintWorkletExecutor(Arc<PaintWorkletExecutor>),
+    RegisterPaint(Atom, Vec<Atom>, Arc<Painter>),
 }
 
 
diff --git a/components/script_traits/lib.rs b/components/script_traits/lib.rs
index 540bf7b47fc..85189c29229 100644
--- a/components/script_traits/lib.rs
+++ b/components/script_traits/lib.rs
@@ -828,11 +828,11 @@ impl From<RecvTimeoutError> for PaintWorkletError {
 }
 
 /// Execute paint code in the worklet thread pool.
-pub trait PaintWorkletExecutor: Sync + Send {
+pub trait Painter: Sync + Send {
     /// https://drafts.css-houdini.org/css-paint-api/#draw-a-paint-image
     fn draw_a_paint_image(&self,
-                          name: Atom,
                           concrete_object_size: Size2D<Au>,
+                          properties: Vec<(Atom, String)>,
                           sender: IpcSender<CanvasData>);
 }
 
diff --git a/components/style/servo/restyle_damage.rs b/components/style/servo/restyle_damage.rs
index 0d3a4b00092..1e9cae4ea08 100644
--- a/components/style/servo/restyle_damage.rs
+++ b/components/style/servo/restyle_damage.rs
@@ -64,16 +64,7 @@ impl ServoRestyleDamage {
                                     new: &ServoComputedValues)
                                     -> StyleDifference {
         let damage = compute_damage(old, new);
-        // If computed values for custom properties changed, we should cascade these changes to
-        // children (custom properties are all inherited).
-        // https://www.w3.org/TR/css-variables/#defining-variables
-        // (With Properties & Values, not all custom properties will be inherited!)
-        let variable_values_changed = old.get_custom_properties() != new.get_custom_properties();
-        let change = if damage.is_empty() && !variable_values_changed {
-            StyleChange::Unchanged
-        } else {
-            StyleChange::Changed
-        };
+        let change = if damage.is_empty() { StyleChange::Unchanged } else { StyleChange::Changed };
         StyleDifference::new(damage, change)
     }
 
@@ -285,6 +276,13 @@ fn compute_damage(old: &ServoComputedValues, new: &ServoComputedValues) -> Servo
         get_inheritedbox.visibility
     ]);
 
+
+    // Paint worklets may depend on custom properties,
+    // so if they have changed we should repaint.
+    if old.get_custom_properties() != new.get_custom_properties() {
+        damage.insert(REPAINT);
+    }
+
     // If the layer requirements of this flow have changed due to the value
     // of the transform, then reflow is required to rebuild the layers.
     if old.transform_requires_layer() != new.transform_requires_layer() {
diff --git a/tests/wpt/mozilla/meta/MANIFEST.json b/tests/wpt/mozilla/meta/MANIFEST.json
index e9a237feec4..7947a375509 100644
--- a/tests/wpt/mozilla/meta/MANIFEST.json
+++ b/tests/wpt/mozilla/meta/MANIFEST.json
@@ -9966,6 +9966,11 @@
      {}
     ]
    ],
+   "mozilla/css-paint-api/resources/html5.png": [
+    [
+     {}
+    ]
+   ],
    "mozilla/css-paint-api/valid-image-after-load-ref.html": [
     [
      {}
@@ -26158,6 +26163,10 @@
    "e4b544068821f6f8882f05836a07a19891fc85b8",
    "reftest"
   ],
+  "mozilla/css-paint-api/resources/html5.png": [
+   "83ef56b6e4d0dcb0d2dcecfb3fc78035051e8627",
+   "support"
+  ],
   "mozilla/css-paint-api/valid-image-after-load-ref.html": [
    "b0c34ee1480fe1108fe8dc53f2bbb2f3ffa1c408",
    "support"
diff --git a/tests/wpt/mozilla/meta/mozilla/css-paint-api/background-image-tiled.html.ini b/tests/wpt/mozilla/meta/mozilla/css-paint-api/background-image-tiled.html.ini
deleted file mode 100644
index 70236851502..00000000000
--- a/tests/wpt/mozilla/meta/mozilla/css-paint-api/background-image-tiled.html.ini
+++ /dev/null
@@ -1,4 +0,0 @@
-[background-image-tiled.html]
-  type: reftest
-  expected: FAIL
-  bug: https://github.com/servo/servo/issues/17598
diff --git a/tests/wpt/mozilla/meta/mozilla/css-paint-api/invalid-image-constructor-error.html.ini b/tests/wpt/mozilla/meta/mozilla/css-paint-api/invalid-image-constructor-error.html.ini
deleted file mode 100644
index b8b8b6a43fa..00000000000
--- a/tests/wpt/mozilla/meta/mozilla/css-paint-api/invalid-image-constructor-error.html.ini
+++ /dev/null
@@ -1,4 +0,0 @@
-[invalid-image-constructor-error.html]
-  type: reftest
-  expected: FAIL
-  bug: https://github.com/servo/servo/issues/17595
diff --git a/tests/wpt/mozilla/meta/mozilla/css-paint-api/invalid-image-paint-error.html.ini b/tests/wpt/mozilla/meta/mozilla/css-paint-api/invalid-image-paint-error.html.ini
deleted file mode 100644
index 12ed50a9383..00000000000
--- a/tests/wpt/mozilla/meta/mozilla/css-paint-api/invalid-image-paint-error.html.ini
+++ /dev/null
@@ -1,4 +0,0 @@
-[invalid-image-paint-error.html]
-  type: reftest
-  expected: FAIL
-  bug: https://github.com/servo/servo/issues/17595
diff --git a/tests/wpt/mozilla/meta/mozilla/css-paint-api/invalid-image-pending-script.html.ini b/tests/wpt/mozilla/meta/mozilla/css-paint-api/invalid-image-pending-script.html.ini
deleted file mode 100644
index 41e6a2089d7..00000000000
--- a/tests/wpt/mozilla/meta/mozilla/css-paint-api/invalid-image-pending-script.html.ini
+++ /dev/null
@@ -1,4 +0,0 @@
-[invalid-image-pending-script.html]
-  type: reftest
-  expected: FAIL
-  bug: https://github.com/servo/servo/issues/17595
diff --git a/tests/wpt/mozilla/tests/mozilla/css-paint-api/resources/html5.png b/tests/wpt/mozilla/tests/mozilla/css-paint-api/resources/html5.png
new file mode 100644
index 00000000000..bfc98fdc062
--- /dev/null
+++ b/tests/wpt/mozilla/tests/mozilla/css-paint-api/resources/html5.png