canvas_state.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 crate::dom::bindings::cell::DomRefCell;
use crate::dom::bindings::codegen::Bindings::CanvasRenderingContext2DBinding::CanvasDirection;
use crate::dom::bindings::codegen::Bindings::CanvasRenderingContext2DBinding::CanvasFillRule;
use crate::dom::bindings::codegen::Bindings::CanvasRenderingContext2DBinding::CanvasImageSource;
use crate::dom::bindings::codegen::Bindings::CanvasRenderingContext2DBinding::CanvasLineCap;
use crate::dom::bindings::codegen::Bindings::CanvasRenderingContext2DBinding::CanvasLineJoin;
use crate::dom::bindings::codegen::Bindings::CanvasRenderingContext2DBinding::CanvasTextAlign;
use crate::dom::bindings::codegen::Bindings::CanvasRenderingContext2DBinding::CanvasTextBaseline;
use crate::dom::bindings::codegen::Bindings::ImageDataBinding::ImageDataMethods;
use crate::dom::bindings::codegen::UnionTypes::StringOrCanvasGradientOrCanvasPattern;
use crate::dom::bindings::error::{Error, ErrorResult, Fallible};
use crate::dom::bindings::inheritance::Castable;
use crate::dom::bindings::num::Finite;
use crate::dom::bindings::root::{Dom, DomRoot};
use crate::dom::bindings::str::DOMString;
use crate::dom::canvasgradient::{CanvasGradient, CanvasGradientStyle, ToFillOrStrokeStyle};
use crate::dom::canvaspattern::CanvasPattern;
use crate::dom::dommatrix::DOMMatrix;
use crate::dom::element::cors_setting_for_element;
use crate::dom::element::Element;
use crate::dom::globalscope::GlobalScope;
use crate::dom::htmlcanvaselement::{CanvasContext, HTMLCanvasElement};
use crate::dom::imagedata::ImageData;
use crate::dom::node::{window_from_node, Node, NodeDamage};
use crate::dom::offscreencanvas::{OffscreenCanvas, OffscreenCanvasContext};
use crate::dom::paintworkletglobalscope::PaintWorkletGlobalScope;
use crate::dom::textmetrics::TextMetrics;
use crate::unpremultiplytable::UNPREMULTIPLY_TABLE;
use canvas_traits::canvas::{Canvas2dMsg, CanvasId, CanvasMsg, Direction, TextAlign, TextBaseline};
use canvas_traits::canvas::{CompositionOrBlending, FillOrStrokeStyle, FillRule};
use canvas_traits::canvas::{LineCapStyle, LineJoinStyle, LinearGradientStyle};
use canvas_traits::canvas::{RadialGradientStyle, RepetitionStyle};
use cssparser::Color as CSSColor;
use cssparser::{Parser, ParserInput, RGBA};
use euclid::{
    default::{Point2D, Rect, Size2D, Transform2D},
    vec2,
};
use ipc_channel::ipc::{self, IpcSender};
use net_traits::image_cache::{ImageCache, ImageResponse};
use net_traits::request::CorsSettings;
use pixels::PixelFormat;
use profile_traits::ipc as profiled_ipc;
use script_traits::ScriptMsg;
use serde_bytes::ByteBuf;
use servo_url::{ImmutableOrigin, ServoUrl};
use std::cell::Cell;
use std::fmt;
use std::str::FromStr;
use std::sync::Arc;
use style::properties::longhands::font_variant_caps::computed_value::T as FontVariantCaps;
use style::properties::style_structs::Font;
use style::values::computed::font::FontStyle;
use style_traits::values::ToCss;

#[unrooted_must_root_lint::must_root]
#[derive(Clone, JSTraceable, MallocSizeOf)]
#[allow(dead_code)]
pub(crate) enum CanvasFillOrStrokeStyle {
    Color(RGBA),
    Gradient(Dom<CanvasGradient>),
    Pattern(Dom<CanvasPattern>),
}

impl CanvasFillOrStrokeStyle {
    fn to_fill_or_stroke_style(&self) -> FillOrStrokeStyle {
        match self {
            CanvasFillOrStrokeStyle::Color(rgba) => FillOrStrokeStyle::Color(*rgba),
            CanvasFillOrStrokeStyle::Gradient(gradient) => gradient.to_fill_or_stroke_style(),
            CanvasFillOrStrokeStyle::Pattern(pattern) => pattern.to_fill_or_stroke_style(),
        }
    }
}

#[unrooted_must_root_lint::must_root]
#[derive(Clone, JSTraceable, MallocSizeOf)]
pub(crate) struct CanvasContextState {
    global_alpha: f64,
    global_composition: CompositionOrBlending,
    image_smoothing_enabled: bool,
    fill_style: CanvasFillOrStrokeStyle,
    stroke_style: CanvasFillOrStrokeStyle,
    line_width: f64,
    line_cap: LineCapStyle,
    line_join: LineJoinStyle,
    miter_limit: f64,
    transform: Transform2D<f32>,
    shadow_offset_x: f64,
    shadow_offset_y: f64,
    shadow_blur: f64,
    shadow_color: RGBA,
    font_style: Option<Font>,
    text_align: TextAlign,
    text_baseline: TextBaseline,
    direction: Direction,
}

impl CanvasContextState {
    const DEFAULT_FONT_STYLE: &'static str = "10px sans-serif";

    pub(crate) fn new() -> CanvasContextState {
        let black = RGBA::new(0, 0, 0, 255);
        CanvasContextState {
            global_alpha: 1.0,
            global_composition: CompositionOrBlending::default(),
            image_smoothing_enabled: true,
            fill_style: CanvasFillOrStrokeStyle::Color(black),
            stroke_style: CanvasFillOrStrokeStyle::Color(black),
            line_width: 1.0,
            line_cap: LineCapStyle::Butt,
            line_join: LineJoinStyle::Miter,
            miter_limit: 10.0,
            transform: Transform2D::identity(),
            shadow_offset_x: 0.0,
            shadow_offset_y: 0.0,
            shadow_blur: 0.0,
            shadow_color: RGBA::transparent(),
            font_style: None,
            text_align: Default::default(),
            text_baseline: Default::default(),
            direction: Default::default(),
        }
    }
}

#[unrooted_must_root_lint::must_root]
#[derive(JSTraceable, MallocSizeOf)]
pub(crate) struct CanvasState {
    #[ignore_malloc_size_of = "Defined in ipc-channel"]
    ipc_renderer: IpcSender<CanvasMsg>,
    canvas_id: CanvasId,
    state: DomRefCell<CanvasContextState>,
    origin_clean: Cell<bool>,
    #[ignore_malloc_size_of = "Arc"]
    image_cache: Arc<dyn ImageCache>,
    /// The base URL for resolving CSS image URL values.
    /// Needed because of https://github.com/servo/servo/issues/17625
    base_url: ServoUrl,
    origin: ImmutableOrigin,
    /// Any missing image URLs.
    missing_image_urls: DomRefCell<Vec<ServoUrl>>,
    saved_states: DomRefCell<Vec<CanvasContextState>>,
}

impl CanvasState {
    pub(crate) fn new(global: &GlobalScope, size: Size2D<u64>) -> CanvasState {
        debug!("Creating new canvas rendering context.");
        let (sender, receiver) =
            profiled_ipc::channel(global.time_profiler_chan().clone()).unwrap();
        let script_to_constellation_chan = global.script_to_constellation_chan();
        debug!("Asking constellation to create new canvas thread.");
        script_to_constellation_chan
            .send(ScriptMsg::CreateCanvasPaintThread(size, sender))
            .unwrap();
        let (ipc_renderer, canvas_id) = receiver.recv().unwrap();
        debug!("Done.");
        // Worklets always receive a unique origin. This messes with fetching
        // cached images in the case of paint worklets, since the image cache
        // is keyed on the origin requesting the image data.
        let origin = if global.is::<PaintWorkletGlobalScope>() {
            global.api_base_url().origin()
        } else {
            global.origin().immutable().clone()
        };
        CanvasState {
            ipc_renderer: ipc_renderer,
            canvas_id: canvas_id,
            state: DomRefCell::new(CanvasContextState::new()),
            origin_clean: Cell::new(true),
            image_cache: global.image_cache(),
            base_url: global.api_base_url(),
            missing_image_urls: DomRefCell::new(Vec::new()),
            saved_states: DomRefCell::new(Vec::new()),
            origin,
        }
    }

    pub fn get_ipc_renderer(&self) -> &IpcSender<CanvasMsg> {
        &self.ipc_renderer
    }

    pub fn get_missing_image_urls(&self) -> &DomRefCell<Vec<ServoUrl>> {
        &self.missing_image_urls
    }

    pub fn get_canvas_id(&self) -> CanvasId {
        self.canvas_id.clone()
    }

    pub fn send_canvas_2d_msg(&self, msg: Canvas2dMsg) {
        self.ipc_renderer
            .send(CanvasMsg::Canvas2d(msg, self.get_canvas_id()))
            .unwrap()
    }

    // https://html.spec.whatwg.org/multipage/#concept-canvas-set-bitmap-dimensions
    pub fn set_bitmap_dimensions(&self, size: Size2D<u64>) {
        self.reset_to_initial_state();
        self.ipc_renderer
            .send(CanvasMsg::Recreate(size, self.get_canvas_id()))
            .unwrap();
    }

    pub fn reset_to_initial_state(&self) {
        self.saved_states.borrow_mut().clear();
        *self.state.borrow_mut() = CanvasContextState::new();
    }

    fn create_drawable_rect(&self, x: f64, y: f64, w: f64, h: f64) -> Option<Rect<f32>> {
        if !([x, y, w, h].iter().all(|val| val.is_finite())) {
            return None;
        }

        if w == 0.0 && h == 0.0 {
            return None;
        }

        Some(Rect::new(
            Point2D::new(x as f32, y as f32),
            Size2D::new(w as f32, h as f32),
        ))
    }

    pub fn origin_is_clean(&self) -> bool {
        self.origin_clean.get()
    }

    fn set_origin_unclean(&self) {
        self.origin_clean.set(false)
    }

    // https://html.spec.whatwg.org/multipage/#the-image-argument-is-not-origin-clean
    fn is_origin_clean(&self, image: CanvasImageSource) -> bool {
        match image {
            CanvasImageSource::HTMLCanvasElement(canvas) => canvas.origin_is_clean(),
            CanvasImageSource::OffscreenCanvas(canvas) => canvas.origin_is_clean(),
            CanvasImageSource::HTMLImageElement(image) => {
                image.same_origin(GlobalScope::entry().origin())
            },
            CanvasImageSource::CSSStyleValue(_) => true,
        }
    }

    fn fetch_image_data(
        &self,
        url: ServoUrl,
        cors_setting: Option<CorsSettings>,
    ) -> Option<(Vec<u8>, Size2D<u32>)> {
        let img = match self.request_image_from_cache(url, cors_setting) {
            ImageResponse::Loaded(img, _) => img,
            ImageResponse::PlaceholderLoaded(_, _) |
            ImageResponse::None |
            ImageResponse::MetadataLoaded(_) => {
                return None;
            },
        };

        let image_size = Size2D::new(img.width, img.height);
        let image_data = match img.format {
            PixelFormat::BGRA8 => img.bytes.to_vec(),
            pixel_format => unimplemented!("unsupported pixel format ({:?})", pixel_format),
        };

        Some((image_data, image_size))
    }

    fn request_image_from_cache(
        &self,
        url: ServoUrl,
        cors_setting: Option<CorsSettings>,
    ) -> ImageResponse {
        match self
            .image_cache
            .get_image(url.clone(), self.origin.clone(), cors_setting)
        {
            Some(image) => ImageResponse::Loaded(image, url),
            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
            },
        }
    }

    fn parse_color(&self, canvas: Option<&HTMLCanvasElement>, string: &str) -> Result<RGBA, ()> {
        let mut input = ParserInput::new(string);
        let mut parser = Parser::new(&mut input);
        let color = CSSColor::parse(&mut parser);
        if parser.is_exhausted() {
            match color {
                Ok(CSSColor::RGBA(rgba)) => Ok(rgba),
                Ok(CSSColor::CurrentColor) => {
                    // TODO: https://github.com/whatwg/html/issues/1099
                    // Reconsider how to calculate currentColor in a display:none canvas

                    // TODO: will need to check that the context bitmap mode is fixed
                    // once we implement CanvasProxy
                    let canvas = match canvas {
                        // https://drafts.css-houdini.org/css-paint-api/#2d-rendering-context
                        // Whenever "currentColor" is used as a color in the PaintRenderingContext2D API,
                        // it is treated as opaque black.
                        None => return Ok(RGBA::new(0, 0, 0, 255)),
                        Some(ref canvas) => &**canvas,
                    };

                    let canvas_element = canvas.upcast::<Element>();

                    match canvas_element.style() {
                        Some(ref s) if canvas_element.has_css_layout_box() => {
                            Ok(s.get_inherited_text().color)
                        },
                        _ => Ok(RGBA::new(0, 0, 0, 255)),
                    }
                },
                _ => Err(()),
            }
        } else {
            Err(())
        }
    }

    pub fn get_rect(&self, canvas_size: Size2D<u64>, rect: Rect<u64>) -> Vec<u8> {
        assert!(self.origin_is_clean());

        assert!(Rect::from_size(canvas_size).contains_rect(&rect));

        let (sender, receiver) = ipc::bytes_channel().unwrap();
        self.send_canvas_2d_msg(Canvas2dMsg::GetImageData(rect, canvas_size, sender));
        let mut pixels = receiver.recv().unwrap().to_vec();

        for chunk in pixels.chunks_mut(4) {
            let b = chunk[0];
            chunk[0] = UNPREMULTIPLY_TABLE[256 * (chunk[3] as usize) + chunk[2] as usize];
            chunk[1] = UNPREMULTIPLY_TABLE[256 * (chunk[3] as usize) + chunk[1] as usize];
            chunk[2] = UNPREMULTIPLY_TABLE[256 * (chunk[3] as usize) + b as usize];
        }

        pixels
    }

    //
    // drawImage coordinates explained
    //
    //  Source Image      Destination Canvas
    // +-------------+     +-------------+
    // |             |     |             |
    // |(sx,sy)      |     |(dx,dy)      |
    // |   +----+    |     |   +----+    |
    // |   |    |    |     |   |    |    |
    // |   |    |sh  |---->|   |    |dh  |
    // |   |    |    |     |   |    |    |
    // |   +----+    |     |   +----+    |
    // |     sw      |     |     dw      |
    // |             |     |             |
    // +-------------+     +-------------+
    //
    //
    // The rectangle (sx, sy, sw, sh) from the source image
    // is copied on the rectangle (dx, dy, dh, dw) of the destination canvas
    //
    // https://html.spec.whatwg.org/multipage/#dom-context-2d-drawimage
    fn draw_image_internal(
        &self,
        htmlcanvas: Option<&HTMLCanvasElement>,
        image: CanvasImageSource,
        sx: f64,
        sy: f64,
        sw: Option<f64>,
        sh: Option<f64>,
        dx: f64,
        dy: f64,
        dw: Option<f64>,
        dh: Option<f64>,
    ) -> ErrorResult {
        let result = match image {
            CanvasImageSource::HTMLCanvasElement(ref canvas) => {
                // https://html.spec.whatwg.org/multipage/#check-the-usability-of-the-image-argument
                if !canvas.is_valid() {
                    return Err(Error::InvalidState);
                }

                self.draw_html_canvas_element(&canvas, htmlcanvas, sx, sy, sw, sh, dx, dy, dw, dh)
            },
            CanvasImageSource::OffscreenCanvas(ref canvas) => {
                // https://html.spec.whatwg.org/multipage/#check-the-usability-of-the-image-argument
                if !canvas.is_valid() {
                    return Err(Error::InvalidState);
                }

                self.draw_offscreen_canvas(&canvas, htmlcanvas, sx, sy, sw, sh, dx, dy, dw, dh)
            },
            CanvasImageSource::HTMLImageElement(ref image) => {
                // https://html.spec.whatwg.org/multipage/#drawing-images
                // 2. Let usability be the result of checking the usability of image.
                // 3. If usability is bad, then return (without drawing anything).
                if !image.is_usable()? {
                    return Ok(());
                }

                // TODO(pylbrecht): is it possible for image.get_url() to return None after the usability check?
                // 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 url = image.get_url().ok_or(Error::InvalidState)?;
                let cors_setting = cors_setting_for_element(image.upcast());
                self.fetch_and_draw_image_data(
                    htmlcanvas,
                    url,
                    cors_setting,
                    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(
                    htmlcanvas, url, None, sx, sy, sw, sh, dx, dy, dw, dh,
                )
            },
        };

        if result.is_ok() && !self.is_origin_clean(image) {
            self.set_origin_unclean()
        }
        result
    }

    fn draw_offscreen_canvas(
        &self,
        canvas: &OffscreenCanvas,
        htmlcanvas: Option<&HTMLCanvasElement>,
        sx: f64,
        sy: f64,
        sw: Option<f64>,
        sh: Option<f64>,
        dx: f64,
        dy: f64,
        dw: Option<f64>,
        dh: Option<f64>,
    ) -> ErrorResult {
        let canvas_size = canvas.get_size();
        let dw = dw.unwrap_or(canvas_size.width as f64);
        let dh = dh.unwrap_or(canvas_size.height as f64);
        let sw = sw.unwrap_or(canvas_size.width as f64);
        let sh = sh.unwrap_or(canvas_size.height as f64);

        let image_size = Size2D::new(canvas_size.width as f64, canvas_size.height as f64);
        // 2. Establish the source and destination rectangles
        let (source_rect, dest_rect) =
            self.adjust_source_dest_rects(image_size, sx, sy, sw, sh, dx, dy, dw, dh);

        if !is_rect_valid(source_rect) || !is_rect_valid(dest_rect) {
            return Ok(());
        }

        let smoothing_enabled = self.state.borrow().image_smoothing_enabled;

        if let Some(context) = canvas.context() {
            match *context {
                OffscreenCanvasContext::OffscreenContext2d(ref context) => {
                    context.send_canvas_2d_msg(Canvas2dMsg::DrawImageInOther(
                        self.get_canvas_id(),
                        image_size,
                        dest_rect,
                        source_rect,
                        smoothing_enabled,
                    ));
                },
            }
        } else {
            self.send_canvas_2d_msg(Canvas2dMsg::DrawImage(
                None,
                image_size,
                dest_rect,
                source_rect,
                smoothing_enabled,
            ));
        }

        self.mark_as_dirty(htmlcanvas);
        Ok(())
    }

    fn draw_html_canvas_element(
        &self,
        canvas: &HTMLCanvasElement,             // source canvas
        htmlcanvas: Option<&HTMLCanvasElement>, // destination canvas
        sx: f64,
        sy: f64,
        sw: Option<f64>,
        sh: Option<f64>,
        dx: f64,
        dy: f64,
        dw: Option<f64>,
        dh: Option<f64>,
    ) -> ErrorResult {
        // 1. Check the usability of the image argument
        if !canvas.is_valid() {
            return Err(Error::InvalidState);
        }

        let canvas_size = canvas.get_size();
        let dw = dw.unwrap_or(canvas_size.width as f64);
        let dh = dh.unwrap_or(canvas_size.height as f64);
        let sw = sw.unwrap_or(canvas_size.width as f64);
        let sh = sh.unwrap_or(canvas_size.height as f64);

        let image_size = Size2D::new(canvas_size.width as f64, canvas_size.height as f64);
        // 2. Establish the source and destination rectangles
        let (source_rect, dest_rect) =
            self.adjust_source_dest_rects(image_size, sx, sy, sw, sh, dx, dy, dw, dh);

        if !is_rect_valid(source_rect) || !is_rect_valid(dest_rect) {
            return Ok(());
        }

        let smoothing_enabled = self.state.borrow().image_smoothing_enabled;

        if let Some(context) = canvas.context() {
            match *context {
                CanvasContext::Context2d(ref context) => {
                    context.send_canvas_2d_msg(Canvas2dMsg::DrawImageInOther(
                        self.get_canvas_id(),
                        image_size,
                        dest_rect,
                        source_rect,
                        smoothing_enabled,
                    ));
                },
                _ => return Err(Error::InvalidState),
            }
        } else {
            self.send_canvas_2d_msg(Canvas2dMsg::DrawImage(
                None,
                image_size,
                dest_rect,
                source_rect,
                smoothing_enabled,
            ));
        }

        self.mark_as_dirty(htmlcanvas);
        Ok(())
    }

    fn fetch_and_draw_image_data(
        &self,
        canvas: Option<&HTMLCanvasElement>,
        url: ServoUrl,
        cors_setting: Option<CorsSettings>,
        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);
        let (mut image_data, image_size) = self
            .fetch_image_data(url, cors_setting)
            .ok_or(Error::InvalidState)?;
        pixels::rgba8_premultiply_inplace(&mut image_data);
        let image_size = image_size.to_f64();

        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);

        // Establish the source and destination rectangles
        let (source_rect, dest_rect) =
            self.adjust_source_dest_rects(image_size, sx, sy, sw, sh, dx, dy, dw, dh);

        if !is_rect_valid(source_rect) || !is_rect_valid(dest_rect) {
            return Ok(());
        }

        let smoothing_enabled = self.state.borrow().image_smoothing_enabled;
        self.send_canvas_2d_msg(Canvas2dMsg::DrawImage(
            Some(ByteBuf::from(image_data)),
            image_size,
            dest_rect,
            source_rect,
            smoothing_enabled,
        ));
        self.mark_as_dirty(canvas);
        Ok(())
    }

    pub fn mark_as_dirty(&self, canvas: Option<&HTMLCanvasElement>) {
        if let Some(ref canvas) = canvas {
            canvas.upcast::<Node>().dirty(NodeDamage::OtherNodeDamage);
        }
    }

    // It is used by DrawImage to calculate the size of the source and destination rectangles based
    // on the drawImage call arguments
    // source rectangle = area of the original image to be copied
    // destination rectangle = area of the destination canvas where the source image is going to be drawn
    fn adjust_source_dest_rects(
        &self,
        image_size: Size2D<f64>,
        sx: f64,
        sy: f64,
        sw: f64,
        sh: f64,
        dx: f64,
        dy: f64,
        dw: f64,
        dh: f64,
    ) -> (Rect<f64>, Rect<f64>) {
        let image_rect = Rect::new(
            Point2D::new(0f64, 0f64),
            Size2D::new(image_size.width as f64, image_size.height as f64),
        );

        // The source rectangle is the rectangle whose corners are the four points (sx, sy),
        // (sx+sw, sy), (sx+sw, sy+sh), (sx, sy+sh).
        let source_rect = Rect::new(
            Point2D::new(sx.min(sx + sw), sy.min(sy + sh)),
            Size2D::new(sw.abs(), sh.abs()),
        );

        // When the source rectangle is outside the source image,
        // the source rectangle must be clipped to the source image
        let source_rect_clipped = source_rect
            .intersection(&image_rect)
            .unwrap_or(Rect::zero());

        // Width and height ratios between the non clipped and clipped source rectangles
        let width_ratio: f64 = source_rect_clipped.size.width / source_rect.size.width;
        let height_ratio: f64 = source_rect_clipped.size.height / source_rect.size.height;

        // When the source rectangle is outside the source image,
        // the destination rectangle must be clipped in the same proportion.
        let dest_rect_width_scaled: f64 = dw * width_ratio;
        let dest_rect_height_scaled: f64 = dh * height_ratio;

        // The destination rectangle is the rectangle whose corners are the four points (dx, dy),
        // (dx+dw, dy), (dx+dw, dy+dh), (dx, dy+dh).
        let dest_rect = Rect::new(
            Point2D::new(
                dx.min(dx + dest_rect_width_scaled),
                dy.min(dy + dest_rect_height_scaled),
            ),
            Size2D::new(dest_rect_width_scaled.abs(), dest_rect_height_scaled.abs()),
        );

        let source_rect = Rect::new(
            Point2D::new(source_rect_clipped.origin.x, source_rect_clipped.origin.y),
            Size2D::new(
                source_rect_clipped.size.width,
                source_rect_clipped.size.height,
            ),
        );

        (source_rect, dest_rect)
    }

    fn update_transform(&self) {
        self.send_canvas_2d_msg(Canvas2dMsg::SetTransform(self.state.borrow().transform))
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-fillrect
    pub fn fill_rect(&self, x: f64, y: f64, width: f64, height: f64) {
        if let Some(rect) = self.create_drawable_rect(x, y, width, height) {
            let style = self.state.borrow().fill_style.to_fill_or_stroke_style();
            self.send_canvas_2d_msg(Canvas2dMsg::FillRect(rect, style));
        }
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-clearrect
    pub fn clear_rect(&self, x: f64, y: f64, width: f64, height: f64) {
        if let Some(rect) = self.create_drawable_rect(x, y, width, height) {
            self.send_canvas_2d_msg(Canvas2dMsg::ClearRect(rect));
        }
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-strokerect
    pub fn stroke_rect(&self, x: f64, y: f64, width: f64, height: f64) {
        if let Some(rect) = self.create_drawable_rect(x, y, width, height) {
            let style = self.state.borrow().stroke_style.to_fill_or_stroke_style();
            self.send_canvas_2d_msg(Canvas2dMsg::StrokeRect(rect, style));
        }
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-shadowoffsetx
    pub fn shadow_offset_x(&self) -> f64 {
        self.state.borrow().shadow_offset_x
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-shadowoffsetx
    pub fn set_shadow_offset_x(&self, value: f64) {
        if !value.is_finite() || value == self.state.borrow().shadow_offset_x {
            return;
        }
        self.state.borrow_mut().shadow_offset_x = value;
        self.send_canvas_2d_msg(Canvas2dMsg::SetShadowOffsetX(value))
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-shadowoffsety
    pub fn shadow_offset_y(&self) -> f64 {
        self.state.borrow().shadow_offset_y
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-shadowoffsety
    pub fn set_shadow_offset_y(&self, value: f64) {
        if !value.is_finite() || value == self.state.borrow().shadow_offset_y {
            return;
        }
        self.state.borrow_mut().shadow_offset_y = value;
        self.send_canvas_2d_msg(Canvas2dMsg::SetShadowOffsetY(value))
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-shadowblur
    pub fn shadow_blur(&self) -> f64 {
        self.state.borrow().shadow_blur
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-shadowblur
    pub fn set_shadow_blur(&self, value: f64) {
        if !value.is_finite() || value < 0f64 || value == self.state.borrow().shadow_blur {
            return;
        }
        self.state.borrow_mut().shadow_blur = value;
        self.send_canvas_2d_msg(Canvas2dMsg::SetShadowBlur(value))
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-shadowcolor
    pub fn shadow_color(&self) -> DOMString {
        let mut result = String::new();
        serialize(&self.state.borrow().shadow_color, &mut result).unwrap();
        DOMString::from(result)
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-shadowcolor
    pub fn set_shadow_color(&self, value: DOMString) {
        if let Ok(color) = parse_color(&value) {
            self.state.borrow_mut().shadow_color = color;
            self.send_canvas_2d_msg(Canvas2dMsg::SetShadowColor(color))
        }
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-strokestyle
    pub fn stroke_style(&self) -> StringOrCanvasGradientOrCanvasPattern {
        match self.state.borrow().stroke_style {
            CanvasFillOrStrokeStyle::Color(ref rgba) => {
                let mut result = String::new();
                serialize(rgba, &mut result).unwrap();
                StringOrCanvasGradientOrCanvasPattern::String(DOMString::from(result))
            },
            CanvasFillOrStrokeStyle::Gradient(ref gradient) => {
                StringOrCanvasGradientOrCanvasPattern::CanvasGradient(DomRoot::from_ref(&*gradient))
            },
            CanvasFillOrStrokeStyle::Pattern(ref pattern) => {
                StringOrCanvasGradientOrCanvasPattern::CanvasPattern(DomRoot::from_ref(&*pattern))
            },
        }
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-strokestyle
    pub fn set_stroke_style(
        &self,
        canvas: Option<&HTMLCanvasElement>,
        value: StringOrCanvasGradientOrCanvasPattern,
    ) {
        match value {
            StringOrCanvasGradientOrCanvasPattern::String(string) => {
                if let Ok(rgba) = self.parse_color(canvas, &string) {
                    self.state.borrow_mut().stroke_style = CanvasFillOrStrokeStyle::Color(rgba);
                }
            },
            StringOrCanvasGradientOrCanvasPattern::CanvasGradient(gradient) => {
                self.state.borrow_mut().stroke_style =
                    CanvasFillOrStrokeStyle::Gradient(Dom::from_ref(&*gradient));
            },
            StringOrCanvasGradientOrCanvasPattern::CanvasPattern(pattern) => {
                self.state.borrow_mut().stroke_style =
                    CanvasFillOrStrokeStyle::Pattern(Dom::from_ref(&*pattern));
                if !pattern.origin_is_clean() {
                    self.set_origin_unclean();
                }
            },
        }
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-strokestyle
    pub fn fill_style(&self) -> StringOrCanvasGradientOrCanvasPattern {
        match self.state.borrow().fill_style {
            CanvasFillOrStrokeStyle::Color(ref rgba) => {
                let mut result = String::new();
                serialize(rgba, &mut result).unwrap();
                StringOrCanvasGradientOrCanvasPattern::String(DOMString::from(result))
            },
            CanvasFillOrStrokeStyle::Gradient(ref gradient) => {
                StringOrCanvasGradientOrCanvasPattern::CanvasGradient(DomRoot::from_ref(&*gradient))
            },
            CanvasFillOrStrokeStyle::Pattern(ref pattern) => {
                StringOrCanvasGradientOrCanvasPattern::CanvasPattern(DomRoot::from_ref(&*pattern))
            },
        }
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-strokestyle
    pub fn set_fill_style(
        &self,
        canvas: Option<&HTMLCanvasElement>,
        value: StringOrCanvasGradientOrCanvasPattern,
    ) {
        match value {
            StringOrCanvasGradientOrCanvasPattern::String(string) => {
                if let Ok(rgba) = self.parse_color(canvas, &string) {
                    self.state.borrow_mut().fill_style = CanvasFillOrStrokeStyle::Color(rgba);
                }
            },
            StringOrCanvasGradientOrCanvasPattern::CanvasGradient(gradient) => {
                self.state.borrow_mut().fill_style =
                    CanvasFillOrStrokeStyle::Gradient(Dom::from_ref(&*gradient));
            },
            StringOrCanvasGradientOrCanvasPattern::CanvasPattern(pattern) => {
                self.state.borrow_mut().fill_style =
                    CanvasFillOrStrokeStyle::Pattern(Dom::from_ref(&*pattern));
                if !pattern.origin_is_clean() {
                    self.set_origin_unclean();
                }
            },
        }
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-createlineargradient
    pub fn create_linear_gradient(
        &self,
        global: &GlobalScope,
        x0: Finite<f64>,
        y0: Finite<f64>,
        x1: Finite<f64>,
        y1: Finite<f64>,
    ) -> DomRoot<CanvasGradient> {
        CanvasGradient::new(
            global,
            CanvasGradientStyle::Linear(LinearGradientStyle::new(*x0, *y0, *x1, *y1, Vec::new())),
        )
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-createradialgradient
    pub fn create_radial_gradient(
        &self,
        global: &GlobalScope,
        x0: Finite<f64>,
        y0: Finite<f64>,
        r0: Finite<f64>,
        x1: Finite<f64>,
        y1: Finite<f64>,
        r1: Finite<f64>,
    ) -> Fallible<DomRoot<CanvasGradient>> {
        if *r0 < 0. || *r1 < 0. {
            return Err(Error::IndexSize);
        }

        Ok(CanvasGradient::new(
            global,
            CanvasGradientStyle::Radial(RadialGradientStyle::new(
                *x0,
                *y0,
                *r0,
                *x1,
                *y1,
                *r1,
                Vec::new(),
            )),
        ))
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-createpattern
    pub fn create_pattern(
        &self,
        global: &GlobalScope,
        image: CanvasImageSource,
        mut repetition: DOMString,
    ) -> Fallible<Option<DomRoot<CanvasPattern>>> {
        let (image_data, image_size) = match image {
            CanvasImageSource::HTMLImageElement(ref image) => {
                // https://html.spec.whatwg.org/multipage/#check-the-usability-of-the-image-argument
                if !image.is_usable()? {
                    return Ok(None);
                }

                image
                    .get_url()
                    .and_then(|url| {
                        self.fetch_image_data(url, cors_setting_for_element(image.upcast()))
                    })
                    .ok_or(Error::InvalidState)?
            },
            CanvasImageSource::HTMLCanvasElement(ref canvas) => {
                let (data, size) = canvas.fetch_all_data().ok_or(Error::InvalidState)?;
                let data = data
                    .map(|data| data.to_vec())
                    .unwrap_or_else(|| vec![0; size.area() as usize * 4]);
                (data, size)
            },
            CanvasImageSource::OffscreenCanvas(ref canvas) => {
                let (data, size) = canvas.fetch_all_data().ok_or(Error::InvalidState)?;
                let data = data
                    .map(|data| data.to_vec())
                    .unwrap_or_else(|| vec![0; size.area() as usize * 4]);
                (data, size)
            },
            CanvasImageSource::CSSStyleValue(ref value) => value
                .get_url(self.base_url.clone())
                .and_then(|url| self.fetch_image_data(url, None))
                .ok_or(Error::InvalidState)?,
        };

        if repetition.is_empty() {
            repetition.push_str("repeat");
        }

        if let Ok(rep) = RepetitionStyle::from_str(&repetition) {
            Ok(Some(CanvasPattern::new(
                global,
                image_data,
                image_size,
                rep,
                self.is_origin_clean(image),
            )))
        } else {
            Err(Error::Syntax)
        }
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-save
    pub fn save(&self) {
        self.saved_states
            .borrow_mut()
            .push(self.state.borrow().clone());
        self.send_canvas_2d_msg(Canvas2dMsg::SaveContext);
    }

    #[allow(unrooted_must_root)]
    // https://html.spec.whatwg.org/multipage/#dom-context-2d-restore
    pub fn restore(&self) {
        let mut saved_states = self.saved_states.borrow_mut();
        if let Some(state) = saved_states.pop() {
            self.state.borrow_mut().clone_from(&state);
            self.send_canvas_2d_msg(Canvas2dMsg::RestoreContext);
        }
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-globalalpha
    pub fn global_alpha(&self) -> f64 {
        self.state.borrow().global_alpha
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-globalalpha
    pub fn set_global_alpha(&self, alpha: f64) {
        if !alpha.is_finite() || alpha > 1.0 || alpha < 0.0 {
            return;
        }

        self.state.borrow_mut().global_alpha = alpha;
        self.send_canvas_2d_msg(Canvas2dMsg::SetGlobalAlpha(alpha as f32))
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-globalcompositeoperation
    pub fn global_composite_operation(&self) -> DOMString {
        match self.state.borrow().global_composition {
            CompositionOrBlending::Composition(op) => DOMString::from(op.to_str()),
            CompositionOrBlending::Blending(op) => DOMString::from(op.to_str()),
        }
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-globalcompositeoperation
    pub fn set_global_composite_operation(&self, op_str: DOMString) {
        if let Ok(op) = CompositionOrBlending::from_str(&op_str) {
            self.state.borrow_mut().global_composition = op;
            self.send_canvas_2d_msg(Canvas2dMsg::SetGlobalComposition(op))
        }
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-imagesmoothingenabled
    pub fn image_smoothing_enabled(&self) -> bool {
        self.state.borrow().image_smoothing_enabled
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-imagesmoothingenabled
    pub fn set_image_smoothing_enabled(&self, value: bool) {
        self.state.borrow_mut().image_smoothing_enabled = value;
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-filltext
    pub fn fill_text(
        &self,
        canvas: Option<&HTMLCanvasElement>,
        text: DOMString,
        x: f64,
        y: f64,
        max_width: Option<f64>,
    ) {
        if !x.is_finite() || !y.is_finite() {
            return;
        }
        if max_width.map_or(false, |max_width| !max_width.is_finite() || max_width <= 0.) {
            return;
        }
        if self.state.borrow().font_style.is_none() {
            self.set_font(canvas, CanvasContextState::DEFAULT_FONT_STYLE.into())
        }

        let is_rtl = match self.state.borrow().direction {
            Direction::Ltr => false,
            Direction::Rtl => true,
            Direction::Inherit => false, // TODO: resolve direction wrt to canvas element
        };

        let style = self.state.borrow().fill_style.to_fill_or_stroke_style();
        self.send_canvas_2d_msg(Canvas2dMsg::FillText(
            text.into(),
            x,
            y,
            max_width,
            style,
            is_rtl,
        ));
    }

    // https://html.spec.whatwg.org/multipage/#textmetrics
    pub fn measure_text(&self, global: &GlobalScope, _text: DOMString) -> DomRoot<TextMetrics> {
        // FIXME: for now faking the implementation of MeasureText().
        // See https://github.com/servo/servo/issues/5411#issuecomment-533776291
        TextMetrics::new(
            global, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0,
        )
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-font
    pub fn set_font(&self, canvas: Option<&HTMLCanvasElement>, value: DOMString) {
        let canvas = match canvas {
            Some(element) => element,
            None => return, // offscreen canvas doesn't have a placeholder canvas
        };
        let node = canvas.upcast::<Node>();
        let window = window_from_node(&*canvas);
        let resolved_font_style = match window.resolved_font_style_query(&node, value.to_string()) {
            Some(value) => value,
            None => return, // syntax error
        };
        self.state.borrow_mut().font_style = Some((*resolved_font_style).clone());
        self.send_canvas_2d_msg(Canvas2dMsg::SetFont((*resolved_font_style).clone()));
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-font
    pub fn font(&self) -> DOMString {
        self.state.borrow().font_style.as_ref().map_or_else(
            || CanvasContextState::DEFAULT_FONT_STYLE.into(),
            |style| {
                let mut result = String::new();
                serialize_font(style, &mut result).unwrap();
                DOMString::from(result)
            },
        )
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-textalign
    pub fn text_align(&self) -> CanvasTextAlign {
        match self.state.borrow().text_align {
            TextAlign::Start => CanvasTextAlign::Start,
            TextAlign::End => CanvasTextAlign::End,
            TextAlign::Left => CanvasTextAlign::Left,
            TextAlign::Right => CanvasTextAlign::Right,
            TextAlign::Center => CanvasTextAlign::Center,
        }
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-textalign
    pub fn set_text_align(&self, value: CanvasTextAlign) {
        let text_align = match value {
            CanvasTextAlign::Start => TextAlign::Start,
            CanvasTextAlign::End => TextAlign::End,
            CanvasTextAlign::Left => TextAlign::Left,
            CanvasTextAlign::Right => TextAlign::Right,
            CanvasTextAlign::Center => TextAlign::Center,
        };
        self.state.borrow_mut().text_align = text_align;
        self.send_canvas_2d_msg(Canvas2dMsg::SetTextAlign(text_align));
    }

    pub fn text_baseline(&self) -> CanvasTextBaseline {
        match self.state.borrow().text_baseline {
            TextBaseline::Top => CanvasTextBaseline::Top,
            TextBaseline::Hanging => CanvasTextBaseline::Hanging,
            TextBaseline::Middle => CanvasTextBaseline::Middle,
            TextBaseline::Alphabetic => CanvasTextBaseline::Alphabetic,
            TextBaseline::Ideographic => CanvasTextBaseline::Ideographic,
            TextBaseline::Bottom => CanvasTextBaseline::Bottom,
        }
    }

    pub fn set_text_baseline(&self, value: CanvasTextBaseline) {
        let text_baseline = match value {
            CanvasTextBaseline::Top => TextBaseline::Top,
            CanvasTextBaseline::Hanging => TextBaseline::Hanging,
            CanvasTextBaseline::Middle => TextBaseline::Middle,
            CanvasTextBaseline::Alphabetic => TextBaseline::Alphabetic,
            CanvasTextBaseline::Ideographic => TextBaseline::Ideographic,
            CanvasTextBaseline::Bottom => TextBaseline::Bottom,
        };
        self.state.borrow_mut().text_baseline = text_baseline;
        self.send_canvas_2d_msg(Canvas2dMsg::SetTextBaseline(text_baseline));
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-direction
    pub fn direction(&self) -> CanvasDirection {
        match self.state.borrow().direction {
            Direction::Ltr => CanvasDirection::Ltr,
            Direction::Rtl => CanvasDirection::Rtl,
            Direction::Inherit => CanvasDirection::Inherit,
        }
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-direction
    pub fn set_direction(&self, value: CanvasDirection) {
        let direction = match value {
            CanvasDirection::Ltr => Direction::Ltr,
            CanvasDirection::Rtl => Direction::Rtl,
            CanvasDirection::Inherit => Direction::Inherit,
        };
        self.state.borrow_mut().direction = direction;
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-linewidth
    pub fn line_width(&self) -> f64 {
        self.state.borrow().line_width
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-linewidth
    pub fn set_line_width(&self, width: f64) {
        if !width.is_finite() || width <= 0.0 {
            return;
        }

        self.state.borrow_mut().line_width = width;
        self.send_canvas_2d_msg(Canvas2dMsg::SetLineWidth(width as f32))
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-linecap
    pub fn line_cap(&self) -> CanvasLineCap {
        match self.state.borrow().line_cap {
            LineCapStyle::Butt => CanvasLineCap::Butt,
            LineCapStyle::Round => CanvasLineCap::Round,
            LineCapStyle::Square => CanvasLineCap::Square,
        }
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-linecap
    pub fn set_line_cap(&self, cap: CanvasLineCap) {
        let line_cap = match cap {
            CanvasLineCap::Butt => LineCapStyle::Butt,
            CanvasLineCap::Round => LineCapStyle::Round,
            CanvasLineCap::Square => LineCapStyle::Square,
        };
        self.state.borrow_mut().line_cap = line_cap;
        self.send_canvas_2d_msg(Canvas2dMsg::SetLineCap(line_cap));
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-linejoin
    pub fn line_join(&self) -> CanvasLineJoin {
        match self.state.borrow().line_join {
            LineJoinStyle::Round => CanvasLineJoin::Round,
            LineJoinStyle::Bevel => CanvasLineJoin::Bevel,
            LineJoinStyle::Miter => CanvasLineJoin::Miter,
        }
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-linejoin
    pub fn set_line_join(&self, join: CanvasLineJoin) {
        let line_join = match join {
            CanvasLineJoin::Round => LineJoinStyle::Round,
            CanvasLineJoin::Bevel => LineJoinStyle::Bevel,
            CanvasLineJoin::Miter => LineJoinStyle::Miter,
        };
        self.state.borrow_mut().line_join = line_join;
        self.send_canvas_2d_msg(Canvas2dMsg::SetLineJoin(line_join));
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-miterlimit
    pub fn miter_limit(&self) -> f64 {
        self.state.borrow().miter_limit
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-miterlimit
    pub fn set_miter_limit(&self, limit: f64) {
        if !limit.is_finite() || limit <= 0.0 {
            return;
        }

        self.state.borrow_mut().miter_limit = limit;
        self.send_canvas_2d_msg(Canvas2dMsg::SetMiterLimit(limit as f32))
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-createimagedata
    pub fn create_image_data(
        &self,
        global: &GlobalScope,
        sw: i32,
        sh: i32,
    ) -> Fallible<DomRoot<ImageData>> {
        if sw == 0 || sh == 0 {
            return Err(Error::IndexSize);
        }
        ImageData::new(global, sw.abs() as u32, sh.abs() as u32, None)
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-createimagedata
    pub fn create_image_data_(
        &self,
        global: &GlobalScope,
        imagedata: &ImageData,
    ) -> Fallible<DomRoot<ImageData>> {
        ImageData::new(global, imagedata.Width(), imagedata.Height(), None)
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-getimagedata
    pub fn get_image_data(
        &self,
        canvas_size: Size2D<u64>,
        global: &GlobalScope,
        sx: i32,
        sy: i32,
        sw: i32,
        sh: i32,
    ) -> Fallible<DomRoot<ImageData>> {
        // FIXME(nox): There are many arithmetic operations here that can
        // overflow or underflow, this should probably be audited.

        if sw == 0 || sh == 0 {
            return Err(Error::IndexSize);
        }

        if !self.origin_is_clean() {
            return Err(Error::Security);
        }

        let (origin, size) = adjust_size_sign(Point2D::new(sx, sy), Size2D::new(sw, sh));
        let read_rect = match pixels::clip(origin, size.to_u64(), canvas_size) {
            Some(rect) => rect,
            None => {
                // All the pixels are outside the canvas surface.
                return ImageData::new(global, size.width, size.height, None);
            },
        };

        ImageData::new(
            global,
            size.width,
            size.height,
            Some(self.get_rect(canvas_size, read_rect)),
        )
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-putimagedata
    pub fn put_image_data(
        &self,
        canvas_size: Size2D<u64>,
        imagedata: &ImageData,
        dx: i32,
        dy: i32,
    ) {
        self.put_image_data_(
            canvas_size,
            imagedata,
            dx,
            dy,
            0,
            0,
            imagedata.Width() as i32,
            imagedata.Height() as i32,
        )
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-putimagedata
    #[allow(unsafe_code)]
    pub fn put_image_data_(
        &self,
        canvas_size: Size2D<u64>,
        imagedata: &ImageData,
        dx: i32,
        dy: i32,
        dirty_x: i32,
        dirty_y: i32,
        dirty_width: i32,
        dirty_height: i32,
    ) {
        // FIXME(nox): There are many arithmetic operations here that can
        // overflow or underflow, this should probably be audited.

        let imagedata_size = Size2D::new(imagedata.Width(), imagedata.Height());
        if imagedata_size.area() == 0 {
            return;
        }

        // Step 1.
        // Done later.

        // Step 2.
        // TODO: throw InvalidState if buffer is detached.

        // Steps 3-6.
        let (src_origin, src_size) = adjust_size_sign(
            Point2D::new(dirty_x, dirty_y),
            Size2D::new(dirty_width, dirty_height),
        );
        let src_rect = match pixels::clip(src_origin, src_size.to_u64(), imagedata_size.to_u64()) {
            Some(rect) => rect,
            None => return,
        };
        let (dst_origin, _) = adjust_size_sign(
            Point2D::new(dirty_x.saturating_add(dx), dirty_y.saturating_add(dy)),
            Size2D::new(dirty_width, dirty_height),
        );
        // By clipping to the canvas surface, we avoid sending any pixel
        // that would fall outside it.
        let dst_rect = match pixels::clip(dst_origin, src_rect.size, canvas_size) {
            Some(rect) => rect,
            None => return,
        };

        // Step 7.
        let (sender, receiver) = ipc::bytes_channel().unwrap();
        let pixels = unsafe { &imagedata.get_rect(Rect::new(src_rect.origin, dst_rect.size)) };
        self.send_canvas_2d_msg(Canvas2dMsg::PutImageData(dst_rect, receiver));
        sender.send(pixels).unwrap();
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-drawimage
    pub fn draw_image(
        &self,
        canvas: Option<&HTMLCanvasElement>,
        image: CanvasImageSource,
        dx: f64,
        dy: f64,
    ) -> ErrorResult {
        if !(dx.is_finite() && dy.is_finite()) {
            return Ok(());
        }

        self.draw_image_internal(canvas, image, 0f64, 0f64, None, None, dx, dy, None, None)
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-drawimage
    pub fn draw_image_(
        &self,
        canvas: Option<&HTMLCanvasElement>,
        image: CanvasImageSource,
        dx: f64,
        dy: f64,
        dw: f64,
        dh: f64,
    ) -> ErrorResult {
        if !(dx.is_finite() && dy.is_finite() && dw.is_finite() && dh.is_finite()) {
            return Ok(());
        }

        self.draw_image_internal(
            canvas,
            image,
            0f64,
            0f64,
            None,
            None,
            dx,
            dy,
            Some(dw),
            Some(dh),
        )
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-drawimage
    pub fn draw_image__(
        &self,
        canvas: Option<&HTMLCanvasElement>,
        image: CanvasImageSource,
        sx: f64,
        sy: f64,
        sw: f64,
        sh: f64,
        dx: f64,
        dy: f64,
        dw: f64,
        dh: f64,
    ) -> ErrorResult {
        if !(sx.is_finite() &&
            sy.is_finite() &&
            sw.is_finite() &&
            sh.is_finite() &&
            dx.is_finite() &&
            dy.is_finite() &&
            dw.is_finite() &&
            dh.is_finite())
        {
            return Ok(());
        }

        self.draw_image_internal(
            canvas,
            image,
            sx,
            sy,
            Some(sw),
            Some(sh),
            dx,
            dy,
            Some(dw),
            Some(dh),
        )
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-beginpath
    pub fn begin_path(&self) {
        self.send_canvas_2d_msg(Canvas2dMsg::BeginPath);
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-fill
    pub fn fill(&self, _fill_rule: CanvasFillRule) {
        // TODO: Process fill rule
        let style = self.state.borrow().fill_style.to_fill_or_stroke_style();
        self.send_canvas_2d_msg(Canvas2dMsg::Fill(style));
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-stroke
    pub fn stroke(&self) {
        let style = self.state.borrow().stroke_style.to_fill_or_stroke_style();
        self.send_canvas_2d_msg(Canvas2dMsg::Stroke(style));
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-clip
    pub fn clip(&self, _fill_rule: CanvasFillRule) {
        // TODO: Process fill rule
        self.send_canvas_2d_msg(Canvas2dMsg::Clip);
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-ispointinpath
    pub fn is_point_in_path(
        &self,
        global: &GlobalScope,
        x: f64,
        y: f64,
        fill_rule: CanvasFillRule,
    ) -> bool {
        if !(x.is_finite() && y.is_finite()) {
            return false;
        }

        let fill_rule = match fill_rule {
            CanvasFillRule::Nonzero => FillRule::Nonzero,
            CanvasFillRule::Evenodd => FillRule::Evenodd,
        };
        let (sender, receiver) =
            profiled_ipc::channel::<bool>(global.time_profiler_chan().clone()).unwrap();
        self.send_canvas_2d_msg(Canvas2dMsg::IsPointInPath(x, y, fill_rule, sender));
        receiver.recv().unwrap()
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-scale
    pub fn scale(&self, x: f64, y: f64) {
        if !(x.is_finite() && y.is_finite()) {
            return;
        }

        let transform = self.state.borrow().transform;
        self.state.borrow_mut().transform = transform.pre_scale(x as f32, y as f32);
        self.update_transform()
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-rotate
    pub fn rotate(&self, angle: f64) {
        if angle == 0.0 || !angle.is_finite() {
            return;
        }

        let (sin, cos) = (angle.sin(), angle.cos());
        let transform = self.state.borrow().transform;
        self.state.borrow_mut().transform = transform.pre_transform(&Transform2D::row_major(
            cos as f32,
            sin as f32,
            -sin as f32,
            cos as f32,
            0.0,
            0.0,
        ));
        self.update_transform()
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-translate
    pub fn translate(&self, x: f64, y: f64) {
        if !(x.is_finite() && y.is_finite()) {
            return;
        }

        let transform = self.state.borrow().transform;
        self.state.borrow_mut().transform = transform.pre_translate(vec2(x as f32, y as f32));
        self.update_transform()
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-transform
    pub fn transform(&self, a: f64, b: f64, c: f64, d: f64, e: f64, f: f64) {
        if !(a.is_finite() &&
            b.is_finite() &&
            c.is_finite() &&
            d.is_finite() &&
            e.is_finite() &&
            f.is_finite())
        {
            return;
        }

        let transform = self.state.borrow().transform;
        self.state.borrow_mut().transform = transform.pre_transform(&Transform2D::row_major(
            a as f32, b as f32, c as f32, d as f32, e as f32, f as f32,
        ));
        self.update_transform()
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-gettransform
    pub fn get_transform(&self, global: &GlobalScope) -> DomRoot<DOMMatrix> {
        let (sender, receiver) = ipc::channel::<Transform2D<f32>>().unwrap();
        self.send_canvas_2d_msg(Canvas2dMsg::GetTransform(sender));
        let transform = receiver.recv().unwrap();

        DOMMatrix::new(global, true, transform.cast::<f64>().to_3d())
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-settransform
    pub fn set_transform(&self, a: f64, b: f64, c: f64, d: f64, e: f64, f: f64) {
        if !(a.is_finite() &&
            b.is_finite() &&
            c.is_finite() &&
            d.is_finite() &&
            e.is_finite() &&
            f.is_finite())
        {
            return;
        }

        self.state.borrow_mut().transform =
            Transform2D::row_major(a as f32, b as f32, c as f32, d as f32, e as f32, f as f32);
        self.update_transform()
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-resettransform
    pub fn reset_transform(&self) {
        self.state.borrow_mut().transform = Transform2D::identity();
        self.update_transform()
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-closepath
    pub fn close_path(&self) {
        self.send_canvas_2d_msg(Canvas2dMsg::ClosePath);
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-moveto
    pub fn move_to(&self, x: f64, y: f64) {
        if !(x.is_finite() && y.is_finite()) {
            return;
        }
        self.send_canvas_2d_msg(Canvas2dMsg::MoveTo(Point2D::new(x as f32, y as f32)));
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-lineto
    pub fn line_to(&self, x: f64, y: f64) {
        if !(x.is_finite() && y.is_finite()) {
            return;
        }
        self.send_canvas_2d_msg(Canvas2dMsg::LineTo(Point2D::new(x as f32, y as f32)));
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-rect
    pub fn rect(&self, x: f64, y: f64, width: f64, height: f64) {
        if [x, y, width, height].iter().all(|val| val.is_finite()) {
            let rect = Rect::new(
                Point2D::new(x as f32, y as f32),
                Size2D::new(width as f32, height as f32),
            );
            self.send_canvas_2d_msg(Canvas2dMsg::Rect(rect));
        }
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-quadraticcurveto
    pub fn quadratic_curve_to(&self, cpx: f64, cpy: f64, x: f64, y: f64) {
        if !(cpx.is_finite() && cpy.is_finite() && x.is_finite() && y.is_finite()) {
            return;
        }
        self.send_canvas_2d_msg(Canvas2dMsg::QuadraticCurveTo(
            Point2D::new(cpx as f32, cpy as f32),
            Point2D::new(x as f32, y as f32),
        ));
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-beziercurveto
    pub fn bezier_curve_to(&self, cp1x: f64, cp1y: f64, cp2x: f64, cp2y: f64, x: f64, y: f64) {
        if !(cp1x.is_finite() &&
            cp1y.is_finite() &&
            cp2x.is_finite() &&
            cp2y.is_finite() &&
            x.is_finite() &&
            y.is_finite())
        {
            return;
        }
        self.send_canvas_2d_msg(Canvas2dMsg::BezierCurveTo(
            Point2D::new(cp1x as f32, cp1y as f32),
            Point2D::new(cp2x as f32, cp2y as f32),
            Point2D::new(x as f32, y as f32),
        ));
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-arc
    pub fn arc(&self, x: f64, y: f64, r: f64, start: f64, end: f64, ccw: bool) -> ErrorResult {
        if !([x, y, r, start, end].iter().all(|x| x.is_finite())) {
            return Ok(());
        }

        if r < 0.0 {
            return Err(Error::IndexSize);
        }

        self.send_canvas_2d_msg(Canvas2dMsg::Arc(
            Point2D::new(x as f32, y as f32),
            r as f32,
            start as f32,
            end as f32,
            ccw,
        ));
        Ok(())
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-arcto
    pub fn arc_to(&self, cp1x: f64, cp1y: f64, cp2x: f64, cp2y: f64, r: f64) -> ErrorResult {
        if !([cp1x, cp1y, cp2x, cp2y, r].iter().all(|x| x.is_finite())) {
            return Ok(());
        }
        if r < 0.0 {
            return Err(Error::IndexSize);
        }

        self.send_canvas_2d_msg(Canvas2dMsg::ArcTo(
            Point2D::new(cp1x as f32, cp1y as f32),
            Point2D::new(cp2x as f32, cp2y as f32),
            r as f32,
        ));
        Ok(())
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-ellipse
    pub fn ellipse(
        &self,
        x: f64,
        y: f64,
        rx: f64,
        ry: f64,
        rotation: f64,
        start: f64,
        end: f64,
        ccw: bool,
    ) -> ErrorResult {
        if !([x, y, rx, ry, rotation, start, end]
            .iter()
            .all(|x| x.is_finite()))
        {
            return Ok(());
        }
        if rx < 0.0 || ry < 0.0 {
            return Err(Error::IndexSize);
        }

        self.send_canvas_2d_msg(Canvas2dMsg::Ellipse(
            Point2D::new(x as f32, y as f32),
            rx as f32,
            ry as f32,
            rotation as f32,
            start as f32,
            end as f32,
            ccw,
        ));
        Ok(())
    }
}

pub fn parse_color(string: &str) -> Result<RGBA, ()> {
    let mut input = ParserInput::new(string);
    let mut parser = Parser::new(&mut input);
    match CSSColor::parse(&mut parser) {
        Ok(CSSColor::RGBA(rgba)) => {
            if parser.is_exhausted() {
                Ok(rgba)
            } else {
                Err(())
            }
        },
        _ => Err(()),
    }
}

// Used by drawImage to determine if a source or destination rectangle is valid
// Origin coordinates and size cannot be negative. Size has to be greater than zero
pub fn is_rect_valid(rect: Rect<f64>) -> bool {
    rect.size.width > 0.0 && rect.size.height > 0.0
}

// https://html.spec.whatwg.org/multipage/#serialisation-of-a-color
pub fn serialize<W>(color: &RGBA, dest: &mut W) -> fmt::Result
where
    W: fmt::Write,
{
    let red = color.red;
    let green = color.green;
    let blue = color.blue;

    if color.alpha == 255 {
        write!(
            dest,
            "#{:x}{:x}{:x}{:x}{:x}{:x}",
            red >> 4,
            red & 0xF,
            green >> 4,
            green & 0xF,
            blue >> 4,
            blue & 0xF
        )
    } else {
        write!(
            dest,
            "rgba({}, {}, {}, {})",
            red,
            green,
            blue,
            color.alpha_f32()
        )
    }
}

pub fn adjust_size_sign(
    mut origin: Point2D<i32>,
    mut size: Size2D<i32>,
) -> (Point2D<i32>, Size2D<u32>) {
    if size.width < 0 {
        size.width = -size.width;
        origin.x = origin.x.saturating_sub(size.width);
    }
    if size.height < 0 {
        size.height = -size.height;
        origin.y = origin.y.saturating_sub(size.height);
    }
    (origin, size.to_u32())
}

fn serialize_font<W>(style: &Font, dest: &mut W) -> fmt::Result
where
    W: fmt::Write,
{
    if style.font_style == FontStyle::Italic {
        write!(dest, "{} ", style.font_style.to_css_string())?;
    }
    if style.font_weight.is_bold() {
        write!(dest, "{} ", style.font_weight.to_css_string())?;
    }
    if style.font_variant_caps == FontVariantCaps::SmallCaps {
        write!(dest, "{} ", style.font_variant_caps.to_css_string())?;
    }
    write!(
        dest,
        "{} {}",
        style.font_size.to_css_string(),
        style.font_family.to_css_string()
    )
}