script/dom/worklet/

paintworkletglobalscope.rs

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at https://mozilla.org/MPL/2.0/. */

use std::cell::Cell;
use std::ptr::{NonNull, null_mut};
use std::sync::atomic::AtomicBool;
use std::sync::{Arc, Mutex};
use std::thread;
use std::time::Duration;

use crossbeam_channel::unbounded;
use dom_struct::dom_struct;
use euclid::{Scale, Size2D};
use js::context::JSContext;
use js::jsapi::{HandleValueArray, Heap, IsCallable, IsConstructor, JSObject, Value};
use js::jsval::{JSVal, ObjectValue, UndefinedValue};
use js::realm::AutoRealm;
use js::rust::wrappers2::{
    Call, Construct1, JS_ClearPendingException, JS_IsExceptionPending, NewArrayObject,
};
use js::rust::{HandleValue, MutableHandle};
use net_traits::image_cache::ImageCache;
use pixels::PixelFormat;
use script_bindings::callback::{HasCallbackHolder, RootedCallback};
use script_bindings::cell::DomRefCell;
use script_bindings::interfaces::HasOrigin;
use script_bindings::reflector::DomObject;
use script_traits::{DrawAPaintImageResult, PaintWorkletError, Painter};
use servo_base::id::PipelineId;
use servo_config::pref;
use servo_url::{MutableOrigin, ServoUrl};
use style_traits::{CSSPixel, SpeculativePainter};
use stylo_atoms::Atom;
use webrender_api::units::DevicePixel;

use crate::dom::bindings::codegen::Bindings::PaintWorkletGlobalScopeBinding;
use crate::dom::bindings::codegen::Bindings::PaintWorkletGlobalScopeBinding::PaintWorkletGlobalScopeMethods;
use crate::dom::bindings::codegen::Bindings::VoidFunctionBinding::VoidFunction;
use crate::dom::bindings::conversions::{get_property, get_property_jsval};
use crate::dom::bindings::error::{Error, Fallible};
use crate::dom::bindings::inheritance::Castable;
use crate::dom::bindings::root::{Dom, DomRoot};
use crate::dom::bindings::str::DOMString;
use crate::dom::bindings::trace::HashMapTracedValues;
use crate::dom::css::cssstylevalue::CSSStyleValue;
use crate::dom::css::stylepropertymapreadonly::StylePropertyMapReadOnly;
use crate::dom::paintrenderingcontext2d::PaintRenderingContext2D;
use crate::dom::paintsize::PaintSize;
use crate::dom::worklet::WorkletExecutor;
use crate::dom::workletglobalscope::{WorkletGlobalScope, WorkletGlobalScopeInit};

/// <https://drafts.css-houdini.org/css-paint-api/#paintworkletglobalscope>
#[dom_struct]
pub(crate) struct PaintWorkletGlobalScope {
    /// The worklet global for this object
    worklet_global: WorkletGlobalScope,
    /// The image cache
    #[ignore_malloc_size_of = "ImageCache"]
    #[no_trace]
    image_cache: Arc<dyn ImageCache>,
    /// <https://drafts.css-houdini.org/css-paint-api/#paint-definitions>
    paint_definitions: DomRefCell<HashMapTracedValues<Atom, Box<PaintDefinition>>>,
    /// <https://drafts.css-houdini.org/css-paint-api/#paint-class-instances>
    #[ignore_malloc_size_of = "mozjs"]
    paint_class_instances: DomRefCell<HashMapTracedValues<Atom, Box<Heap<JSVal>>>>,
    /// The most recent name the worklet was called with
    #[no_trace]
    cached_name: DomRefCell<Atom>,
    /// The most recent size the worklet was drawn at
    #[no_trace]
    cached_size: Cell<Size2D<f32, CSSPixel>>,
    /// The most recent device pixel ratio the worklet was drawn at
    #[no_trace]
    cached_device_pixel_ratio: Cell<Scale<f32, CSSPixel, DevicePixel>>,
    /// The most recent properties the worklet was drawn at
    #[no_trace]
    cached_properties: DomRefCell<Vec<(Atom, String)>>,
    /// The most recent arguments the worklet was drawn at
    cached_arguments: DomRefCell<Vec<String>>,
    /// The most recent result
    #[no_trace]
    cached_result: DomRefCell<DrawAPaintImageResult>,
}

impl PaintWorkletGlobalScope {
    #[allow(clippy::too_many_arguments)]
    pub(crate) fn new(
        cx: &mut JSContext,
        pipeline_id: PipelineId,
        base_url: ServoUrl,
        inherited_secure_context: Option<bool>,
        executor: WorkletExecutor,
        init: &WorkletGlobalScopeInit,
        closing: Arc<AtomicBool>,
    ) -> DomRoot<PaintWorkletGlobalScope> {
        debug!(
            "Creating paint worklet global scope for pipeline {}.",
            pipeline_id
        );
        let global = Box::new(PaintWorkletGlobalScope {
            worklet_global: WorkletGlobalScope::new_inherited(
                pipeline_id,
                base_url,
                inherited_secure_context,
                executor,
                init,
                closing,
            ),
            image_cache: init.image_cache.clone(),
            paint_definitions: Default::default(),
            paint_class_instances: Default::default(),
            cached_name: DomRefCell::new(Atom::from("")),
            cached_size: Cell::new(Size2D::zero()),
            cached_device_pixel_ratio: Cell::new(Scale::new(1.0)),
            cached_properties: Default::default(),
            cached_arguments: Default::default(),
            cached_result: DomRefCell::new(DrawAPaintImageResult {
                width: 0,
                height: 0,
                format: PixelFormat::BGRA8,
                image_key: None,
                missing_image_urls: Vec::new(),
            }),
        });
        PaintWorkletGlobalScopeBinding::Wrap::<crate::DomTypeHolder>(cx, &global.origin(), global)
    }

    pub(crate) fn image_cache(&self) -> Arc<dyn ImageCache> {
        self.image_cache.clone()
    }

    fn has_cached_paint_image(
        &self,
        name: &Atom,
        size: Size2D<f32, CSSPixel>,
        device_pixel_ratio: Scale<f32, CSSPixel, DevicePixel>,
        properties: &[(Atom, String)],
        arguments: &[String],
    ) -> bool {
        (&*self.cached_name.borrow() == name) &&
            (self.cached_size.get() == size) &&
            (self.cached_device_pixel_ratio.get() == device_pixel_ratio) &&
            (*self.cached_properties.borrow() == properties) &&
            (*self.cached_arguments.borrow() == arguments)
    }

    fn set_cached_paint_image(
        &self,
        name: Atom,
        size: Size2D<f32, CSSPixel>,
        device_pixel_ratio: Scale<f32, CSSPixel, DevicePixel>,
        properties: Vec<(Atom, String)>,
        arguments: Vec<String>,
        result: DrawAPaintImageResult,
    ) {
        *self.cached_name.borrow_mut() = name;
        self.cached_size.set(size);
        self.cached_device_pixel_ratio.set(device_pixel_ratio);
        *self.cached_properties.borrow_mut() = properties;
        *self.cached_arguments.borrow_mut() = arguments;
        *self.cached_result.borrow_mut() = result;
    }

    /// <https://drafts.css-houdini.org/css-paint-api/#draw-a-paint-image>
    fn draw_a_paint_image(
        &self,
        cx: &mut JSContext,
        name: &Atom,
        size_in_px: Size2D<f32, CSSPixel>,
        device_pixel_ratio: Scale<f32, CSSPixel, DevicePixel>,
        properties: &StylePropertyMapReadOnly,
        arguments: &[String],
    ) -> DrawAPaintImageResult {
        let size_in_dpx = size_in_px * device_pixel_ratio;
        let size_in_dpx = Size2D::new(
            size_in_dpx.width.abs() as u32,
            size_in_dpx.height.abs() as u32,
        );

        // TODO: Steps 1-5.

        // TODO: document paint definitions.
        self.invoke_a_paint_callback(
            cx,
            name,
            size_in_px,
            size_in_dpx,
            device_pixel_ratio,
            properties,
            arguments,
        )
    }

    #[expect(unsafe_code)]
    /// Gets or creates the `self.paint_class_instances` given by `name` and inserts
    /// the value into the provided `paint_instance` handle. Returns `Err` when this
    /// fails.
    fn get_or_create_paint_instance(
        &self,
        cx: &mut JSContext,
        mut paint_instance: MutableHandle<Value>,
        name: Atom,
        class_constructor: HandleValue,
        size_in_dpx: Size2D<u32, DevicePixel>,
    ) -> Result<(), DrawAPaintImageResult> {
        if let Some(entry) = self.paint_class_instances.borrow().get(&name) {
            paint_instance.set(entry.get());
            return Ok(());
        }

        // Step of <https://drafts.css-houdini.org/css-paint-api/#invoke-a-paint-callback>
        // 5.2 Let paintCtor be the class constructor on definition.
        // 5.3 Let paintInstance be the result of Construct(paintCtor).
        //     If construct throws an exception, set the definition’s constructor valid flag to false,
        //     let the image output be an invalid image and abort all these steps.
        let args = HandleValueArray::empty();
        rooted!(&in(cx) let mut result = null_mut::<JSObject>());
        unsafe {
            Construct1(cx, class_constructor, &args, result.handle_mut());
        }
        paint_instance.set(ObjectValue(result.get()));
        if unsafe { JS_IsExceptionPending(cx) } {
            debug!("Paint constructor threw an exception {}.", name);
            unsafe {
                JS_ClearPendingException(cx);
            }
            self.paint_definitions
                .safe_borrow_mut(cx)
                .get_mut(&name)
                .expect("Vanishing paint definition.")
                .constructor_valid_flag
                .set(false);
            // 1.2 Let the image output be an invalid image and abort all these steps.
            return Err(self.invalid_image(size_in_dpx, vec![]));
        }
        // Step 5.4
        self.paint_class_instances
            .safe_borrow_mut(cx)
            .entry(name)
            .or_default()
            .set(paint_instance.get());
        Ok(())
    }

    /// <https://drafts.css-houdini.org/css-paint-api/#invoke-a-paint-callback>
    #[expect(clippy::too_many_arguments)]
    #[expect(unsafe_code)]
    fn invoke_a_paint_callback(
        &self,
        cx: &mut JSContext,
        name: &Atom,
        size_in_px: Size2D<f32, CSSPixel>,
        size_in_dpx: Size2D<u32, DevicePixel>,
        device_pixel_ratio: Scale<f32, CSSPixel, DevicePixel>,
        properties: &StylePropertyMapReadOnly,
        arguments: &[String],
    ) -> DrawAPaintImageResult {
        debug!(
            "Invoking a paint callback {}({},{}) at {:?}.",
            name, size_in_px.width, size_in_px.height, device_pixel_ratio
        );

        let mut realm = AutoRealm::new(
            cx,
            NonNull::new(self.worklet_global.reflector().get_jsobject().get()).unwrap(),
        );
        let cx = &mut *realm;

        // TODO: Steps 1-2.1.
        // Step 2.2-5.1.
        rooted!(&in(cx) let mut class_constructor = UndefinedValue());
        rooted!(&in(cx) let mut paint_function = UndefinedValue());
        let rendering_context = match self.paint_definitions.borrow().get(name) {
            None => {
                // Step 2.2.
                warn!("Drawing un-registered paint definition {}.", name);
                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.invalid_image(size_in_dpx, vec![]);
                }
                class_constructor.set(definition.class_constructor.get());
                paint_function.set(definition.paint_function.get());
                DomRoot::from_ref(&*definition.context)
            },
        };

        // Steps 5.2-5.4
        // TODO: the spec requires calling the constructor now, but we might want to
        // prepopulate the paint instance in `RegisterPaint`, to avoid calling it in
        // the primary worklet thread.
        // https://github.com/servo/servo/issues/17377
        rooted!(&in(cx) let mut paint_instance = UndefinedValue());
        if let Err(early_return) = self.get_or_create_paint_instance(
            cx,
            paint_instance.handle_mut(),
            name.clone(),
            class_constructor.handle(),
            size_in_dpx,
        ) {
            return early_return;
        }

        // TODO: Steps 6-7
        // Step 8
        // TODO: the spec requires creating a new paint rendering context each time,
        // this code recycles the same one.
        rendering_context.set_bitmap_dimensions(size_in_px, device_pixel_ratio);

        // Step 9
        let paint_size = PaintSize::new(cx, self, size_in_px);

        // TODO: Step 10
        // Steps 11-12
        debug!("Invoking paint function {}.", name);
        rooted_vec!(let mut arguments_values);
        for argument in arguments {
            let style_value = CSSStyleValue::new(cx, self.upcast(), argument.clone());
            arguments_values.push(ObjectValue(style_value.reflector().get_jsobject().get()));
        }
        let arguments_value_array = HandleValueArray::from(&arguments_values);
        rooted!(&in(cx) let argument_object = unsafe { NewArrayObject(cx, &arguments_value_array) });

        rooted_vec!(let mut callback_args);
        callback_args.push(ObjectValue(
            rendering_context.reflector().get_jsobject().get(),
        ));
        callback_args.push(ObjectValue(paint_size.reflector().get_jsobject().get()));
        callback_args.push(ObjectValue(properties.reflector().get_jsobject().get()));
        callback_args.push(ObjectValue(argument_object.get()));
        let args = HandleValueArray::from(&callback_args);

        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.invalid_image(size_in_dpx, missing_image_urls);
        }

        rendering_context.update_rendering();

        DrawAPaintImageResult {
            width: size_in_dpx.width,
            height: size_in_dpx.height,
            format: PixelFormat::BGRA8,
            image_key: Some(rendering_context.image_key()),
            missing_image_urls,
        }
    }

    /// <https://drafts.csswg.org/css-images-4/#invalid-image>
    fn invalid_image(
        &self,
        size: Size2D<u32, DevicePixel>,
        missing_image_urls: Vec<ServoUrl>,
    ) -> DrawAPaintImageResult {
        debug!("Returning an invalid image.");
        DrawAPaintImageResult {
            width: size.width,
            height: size.height,
            format: PixelFormat::BGRA8,
            image_key: None,
            missing_image_urls,
        }
    }

    fn painter(&self, name: Atom) -> Box<dyn Painter> {
        Box::new(WorkletPainter {
            name,
            executor: Mutex::new(self.worklet_global.executor()),
        })
    }
}

// Rather annoyingly we have to use a mutex here to make the painter Sync.
struct WorkletPainter {
    name: Atom,
    executor: Mutex<WorkletExecutor>,
}

impl SpeculativePainter for WorkletPainter {
    fn speculatively_draw_a_paint_image(
        &self,
        properties: Vec<(Atom, String)>,
        arguments: Vec<String>,
    ) {
        let name = self.name.clone();

        let speculatively_draw_a_paint_image_task =
            move |cx: &mut JSContext, global_scope: &WorkletGlobalScope| {
                let paint_worklet_global_scope = global_scope
                    .downcast::<PaintWorkletGlobalScope>()
                    .expect("PaintWorklet's task should be run only on PaintWorkletGlobalScope.");

                let should_speculate = (*paint_worklet_global_scope.cached_name.borrow() != name) ||
                    (*paint_worklet_global_scope.cached_properties.borrow() != properties) ||
                    (*paint_worklet_global_scope.cached_arguments.borrow() != arguments);
                if should_speculate {
                    let size = paint_worklet_global_scope.cached_size.get();
                    let device_pixel_ratio =
                        paint_worklet_global_scope.cached_device_pixel_ratio.get();
                    let map = StylePropertyMapReadOnly::from_iter(
                        cx,
                        paint_worklet_global_scope.upcast(),
                        properties.iter().cloned(),
                    );
                    let result = paint_worklet_global_scope.draw_a_paint_image(
                        cx,
                        &name,
                        size,
                        device_pixel_ratio,
                        &map,
                        &arguments,
                    );
                    if (result.image_key.is_some()) && (result.missing_image_urls.is_empty()) {
                        paint_worklet_global_scope.set_cached_paint_image(
                            name,
                            size,
                            device_pixel_ratio,
                            properties,
                            arguments,
                            result,
                        );
                    }
                }
            };

        self.executor
            .lock()
            .expect("Locking a painter.")
            .schedule_a_worklet_task(Box::new(speculatively_draw_a_paint_image_task));
    }
}

impl Painter for WorkletPainter {
    fn draw_a_paint_image(
        &self,
        size: Size2D<f32, CSSPixel>,
        device_pixel_ratio: Scale<f32, CSSPixel, DevicePixel>,
        properties: Vec<(Atom, String)>,
        arguments: Vec<String>,
    ) -> Result<DrawAPaintImageResult, PaintWorkletError> {
        let name = self.name.clone();
        let (sender, receiver) = unbounded();

        let draw_a_paint_image_task =
            move |cx: &mut JSContext, global_scope: &WorkletGlobalScope| {
                let paint_worklet_global_scope = global_scope
                    .downcast::<PaintWorkletGlobalScope>()
                    .expect("PaintWorklet's task should be run only on PaintWorkletGlobalScope.");

                let cache_hit = paint_worklet_global_scope.has_cached_paint_image(
                    &name,
                    size,
                    device_pixel_ratio,
                    &properties,
                    &arguments,
                );
                let result = if cache_hit {
                    debug!("Cache hit on paint worklet {}!", name);
                    paint_worklet_global_scope.cached_result.borrow().clone()
                } else {
                    debug!("Cache miss on paint worklet {}!", name);
                    let map = StylePropertyMapReadOnly::from_iter(
                        cx,
                        paint_worklet_global_scope.upcast(),
                        properties.iter().cloned(),
                    );
                    let result = paint_worklet_global_scope.draw_a_paint_image(
                        cx,
                        &name,
                        size,
                        device_pixel_ratio,
                        &map,
                        &arguments,
                    );
                    if (result.image_key.is_some()) && (result.missing_image_urls.is_empty()) {
                        paint_worklet_global_scope.set_cached_paint_image(
                            name,
                            size,
                            device_pixel_ratio,
                            properties,
                            arguments,
                            result.clone(),
                        );
                    }
                    result
                };
                let _ = sender.send(result);
            };

        self.executor
            .lock()
            .expect("Locking a painter.")
            .schedule_a_worklet_task(Box::new(draw_a_paint_image_task));

        let timeout = pref!(dom_worklet_timeout_ms) as u64;

        receiver
            .recv_timeout(Duration::from_millis(timeout))
            .map_err(PaintWorkletError::from)
    }
}

/// A paint definition
/// <https://drafts.css-houdini.org/css-paint-api/#paint-definition>
/// This type is dangerous, because it contains uboxed `Heap<JSVal>` values,
/// which can't be moved.
#[derive(JSTraceable, MallocSizeOf)]
#[cfg_attr(crown, crown::unrooted_must_root_lint::must_root)]
struct PaintDefinition {
    #[ignore_malloc_size_of = "mozjs"]
    class_constructor: Heap<JSVal>,
    #[ignore_malloc_size_of = "mozjs"]
    paint_function: Heap<JSVal>,
    constructor_valid_flag: Cell<bool>,
    context_alpha_flag: bool,
    // TODO: this should be a list of CSS syntaxes.
    input_arguments_len: usize,
    // 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,
    // we recycle them.
    context: Dom<PaintRenderingContext2D>,
}

impl PaintDefinition {
    fn new(
        class_constructor: HandleValue,
        paint_function: HandleValue,
        alpha: bool,
        input_arguments_len: usize,
        context: &PaintRenderingContext2D,
    ) -> Box<PaintDefinition> {
        let result = Box::new(PaintDefinition {
            class_constructor: Heap::default(),
            paint_function: Heap::default(),
            constructor_valid_flag: Cell::new(true),
            context_alpha_flag: alpha,
            input_arguments_len,
            context: Dom::from_ref(context),
        });
        result.class_constructor.set(class_constructor.get());
        result.paint_function.set(paint_function.get());
        result
    }
}

impl PaintWorkletGlobalScopeMethods<crate::DomTypeHolder> for PaintWorkletGlobalScope {
    #[expect(unsafe_code)]
    #[cfg_attr(crown, expect(crown::unrooted_must_root))]
    /// <https://drafts.css-houdini.org/css-paint-api/#dom-paintworkletglobalscope-registerpaint>
    fn RegisterPaint(
        &self,
        cx: &mut JSContext,
        name: DOMString,
        paint_ctor: RootedCallback<VoidFunction>,
    ) -> Fallible<()> {
        let name = Atom::from(name);
        rooted!(&in(cx) let paint_obj = paint_ctor.callback_holder().get());
        rooted!(&in(cx) let paint_val = ObjectValue(paint_obj.get()));

        debug!("Registering paint image name {}.", name);

        // Step 1.
        if name.is_empty() {
            return Err(Error::Type(c"Empty paint name.".to_owned()));
        }

        // Step 2-3.
        if self.paint_definitions.borrow().contains_key(&name) {
            return Err(Error::InvalidModification(None));
        }

        // Step 4-6.
        let property_names: Vec<String> =
            get_property(cx, paint_obj.handle(), c"inputProperties", ())?.unwrap_or_default();
        let properties = property_names.into_iter().map(Atom::from).collect();

        // Step 7-9.
        let input_arguments: Vec<String> =
            get_property(cx, paint_obj.handle(), c"inputArguments", ())?.unwrap_or_default();

        // TODO: Steps 10-11.

        // Steps 12-13.
        let alpha: bool = get_property(cx, paint_obj.handle(), c"alpha", ())?.unwrap_or(true);

        // Step 14
        if unsafe { !IsConstructor(paint_obj.get()) } {
            return Err(Error::Type(c"Not a constructor.".to_owned()));
        }

        // Steps 15-16
        rooted!(&in(cx) let mut prototype = UndefinedValue());
        get_property_jsval(cx, paint_obj.handle(), c"prototype", prototype.handle_mut())?;
        if !prototype.is_object() {
            return Err(Error::Type(c"Prototype is not an object.".to_owned()));
        }
        rooted!(&in(cx) let prototype = prototype.to_object());

        // Steps 17-18
        rooted!(&in(cx) let mut paint_function = UndefinedValue());
        get_property_jsval(
            cx,
            prototype.handle(),
            c"paint",
            paint_function.handle_mut(),
        )?;
        if !paint_function.is_object() || unsafe { !IsCallable(paint_function.to_object()) } {
            return Err(Error::Type(c"Paint function is not callable.".to_owned()));
        }

        // Step 19.
        let Some(context) = PaintRenderingContext2D::new(cx, self) else {
            return Err(Error::Operation(None));
        };
        let definition = PaintDefinition::new(
            paint_val.handle(),
            paint_function.handle(),
            alpha,
            input_arguments.len(),
            &context,
        );

        // Step 20.
        debug!("Registering definition {}.", name);
        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());
        self.worklet_global
            .register_paint_worklet(name, properties, painter);

        Ok(())
    }

    /// This is a blocking sleep function available in the paint worklet
    /// global scope behind the dom.worklet.enabled +
    /// dom.worklet.blockingsleep.enabled prefs. It is to be used only for
    /// testing, e.g., timeouts, where otherwise one would need busy waiting
    /// to make sure a certain timeout is triggered.
    /// check-tidy: no specs after this line
    fn Sleep(&self, ms: u64) {
        thread::sleep(Duration::from_millis(ms));
    }
}

impl HasOrigin for PaintWorkletGlobalScope {
    fn origin(&self) -> MutableOrigin {
        self.upcast::<WorkletGlobalScope>().origin()
    }
}