canvasrenderingcontext2d.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 http://mozilla.org/MPL/2.0/. */

use canvas_traits::{Canvas2dMsg, CanvasCommonMsg, CanvasMsg};
use canvas_traits::{CompositionOrBlending, FillOrStrokeStyle, FillRule};
use canvas_traits::{LineCapStyle, LineJoinStyle, LinearGradientStyle};
use canvas_traits::{RadialGradientStyle, RepetitionStyle, byte_swap_and_premultiply};
use cssparser::{Parser, RGBA};
use cssparser::Color as CSSColor;
use dom::bindings::cell::DOMRefCell;
use dom::bindings::codegen::Bindings::CSSStyleDeclarationBinding::CSSStyleDeclarationMethods;
use dom::bindings::codegen::Bindings::CanvasRenderingContext2DBinding;
use dom::bindings::codegen::Bindings::CanvasRenderingContext2DBinding::CanvasFillRule;
use dom::bindings::codegen::Bindings::CanvasRenderingContext2DBinding::CanvasLineCap;
use dom::bindings::codegen::Bindings::CanvasRenderingContext2DBinding::CanvasLineJoin;
use dom::bindings::codegen::Bindings::CanvasRenderingContext2DBinding::CanvasRenderingContext2DMethods;
use dom::bindings::codegen::Bindings::ImageDataBinding::ImageDataMethods;
use dom::bindings::codegen::Bindings::WindowBinding::WindowMethods;
use dom::bindings::codegen::UnionTypes::HTMLImageElementOrHTMLCanvasElementOrCanvasRenderingContext2D;
use dom::bindings::codegen::UnionTypes::StringOrCanvasGradientOrCanvasPattern;
use dom::bindings::error::{Error, ErrorResult, Fallible};
use dom::bindings::inheritance::Castable;
use dom::bindings::js::{JS, LayoutJS, Root};
use dom::bindings::num::Finite;
use dom::bindings::reflector::{DomObject, Reflector, reflect_dom_object};
use dom::bindings::str::DOMString;
use dom::canvasgradient::{CanvasGradient, CanvasGradientStyle, ToFillOrStrokeStyle};
use dom::canvaspattern::CanvasPattern;
use dom::globalscope::GlobalScope;
use dom::htmlcanvaselement::HTMLCanvasElement;
use dom::htmlcanvaselement::utils as canvas_utils;
use dom::htmlimageelement::HTMLImageElement;
use dom::imagedata::ImageData;
use dom::node::{Node, NodeDamage, window_from_node};
use dom_struct::dom_struct;
use euclid::matrix2d::Matrix2D;
use euclid::point::Point2D;
use euclid::rect::Rect;
use euclid::size::Size2D;
use ipc_channel::ipc::{self, IpcSender};
use net_traits::image::base::PixelFormat;
use net_traits::image_cache::ImageResponse;
use num_traits::ToPrimitive;
use script_traits::ScriptMsg as ConstellationMsg;
use servo_url::ServoUrl;
use std::{cmp, fmt};
use std::cell::Cell;
use std::str::FromStr;
use unpremultiplytable::UNPREMULTIPLY_TABLE;

#[must_root]
#[derive(JSTraceable, Clone, HeapSizeOf)]
#[allow(dead_code)]
enum CanvasFillOrStrokeStyle {
    Color(RGBA),
    Gradient(JS<CanvasGradient>),
    Pattern(JS<CanvasPattern>),
}

// https://html.spec.whatwg.org/multipage/#canvasrenderingcontext2d
#[dom_struct]
pub struct CanvasRenderingContext2D {
    reflector_: Reflector,
    #[ignore_heap_size_of = "Defined in ipc-channel"]
    ipc_renderer: IpcSender<CanvasMsg>,
    canvas: JS<HTMLCanvasElement>,
    state: DOMRefCell<CanvasContextState>,
    saved_states: DOMRefCell<Vec<CanvasContextState>>,
    origin_clean: Cell<bool>,
}

#[must_root]
#[derive(JSTraceable, Clone, HeapSizeOf)]
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: Matrix2D<f32>,
    shadow_offset_x: f64,
    shadow_offset_y: f64,
    shadow_blur: f64,
    shadow_color: RGBA,
}

impl CanvasContextState {
    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: Matrix2D::identity(),
            shadow_offset_x: 0.0,
            shadow_offset_y: 0.0,
            shadow_blur: 0.0,
            shadow_color: RGBA::transparent(),
        }
    }
}

impl CanvasRenderingContext2D {
    fn new_inherited(global: &GlobalScope,
                     canvas: &HTMLCanvasElement,
                     size: Size2D<i32>)
                     -> CanvasRenderingContext2D {
        let (sender, receiver) = ipc::channel().unwrap();
        let constellation_chan = global.constellation_chan();
        constellation_chan.send(ConstellationMsg::CreateCanvasPaintThread(size, sender)).unwrap();
        let ipc_renderer = receiver.recv().unwrap();
        CanvasRenderingContext2D {
            reflector_: Reflector::new(),
            ipc_renderer: ipc_renderer,
            canvas: JS::from_ref(canvas),
            state: DOMRefCell::new(CanvasContextState::new()),
            saved_states: DOMRefCell::new(Vec::new()),
            origin_clean: Cell::new(true),
        }
    }

    pub fn new(global: &GlobalScope,
               canvas: &HTMLCanvasElement,
               size: Size2D<i32>)
               -> Root<CanvasRenderingContext2D> {
        reflect_dom_object(box CanvasRenderingContext2D::new_inherited(global, canvas, size),
                           global,
                           CanvasRenderingContext2DBinding::Wrap)
    }

    // https://html.spec.whatwg.org/multipage/#concept-canvas-set-bitmap-dimensions
    pub fn set_bitmap_dimensions(&self, size: Size2D<i32>) {
        self.reset_to_initial_state();
        self.ipc_renderer
            .send(CanvasMsg::Common(CanvasCommonMsg::Recreate(size)))
            .unwrap();
    }

    // https://html.spec.whatwg.org/multipage/#reset-the-rendering-context-to-its-default-state
    fn reset_to_initial_state(&self) {
        self.saved_states.borrow_mut().clear();
        *self.state.borrow_mut() = CanvasContextState::new();
    }

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

    fn mark_as_dirty(&self) {
        self.canvas.upcast::<Node>().dirty(NodeDamage::OtherNodeDamage);
    }

    fn update_transform(&self) {
        self.ipc_renderer
            .send(CanvasMsg::Canvas2d(Canvas2dMsg::SetTransform(self.state.borrow().transform)))
            .unwrap()
    }

    // 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)
    }

    // https://html.spec.whatwg.org/multipage/#the-image-argument-is-not-origin-clean
    fn is_origin_clean(&self,
                       image: HTMLImageElementOrHTMLCanvasElementOrCanvasRenderingContext2D)
                           -> bool {
        match image {
            HTMLImageElementOrHTMLCanvasElementOrCanvasRenderingContext2D::HTMLCanvasElement(canvas) => {
                canvas.origin_is_clean()
            }
            HTMLImageElementOrHTMLCanvasElementOrCanvasRenderingContext2D::CanvasRenderingContext2D(image) =>
                image.origin_is_clean(),
            HTMLImageElementOrHTMLCanvasElementOrCanvasRenderingContext2D::HTMLImageElement(image) =>
                match image.get_url() {
                    None => true,
                    Some(url) => {
                        // TODO(zbarsky): we should check the origin of the image against
                        // the entry settings object, but for now check it against the canvas' doc.
                        let node: &Node = &*self.canvas.upcast();
                        url.origin() == node.owner_doc().url().origin()
                    }
                }
        }
    }

    //
    // 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(&self,
                  image: HTMLImageElementOrHTMLCanvasElementOrCanvasRenderingContext2D,
                  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 {
            HTMLImageElementOrHTMLCanvasElementOrCanvasRenderingContext2D::HTMLCanvasElement(ref canvas) => {
                self.draw_html_canvas_element(&canvas,
                                              sx, sy, sw, sh,
                                              dx, dy, dw, dh)
            }
            HTMLImageElementOrHTMLCanvasElementOrCanvasRenderingContext2D::CanvasRenderingContext2D(ref image) => {
                self.draw_html_canvas_element(&image.Canvas(),
                                              sx, sy, sw, sh,
                                              dx, dy, dw, dh)
            }
            HTMLImageElementOrHTMLCanvasElementOrCanvasRenderingContext2D::HTMLImageElement(ref image) => {
                // https://html.spec.whatwg.org/multipage/#img-error
                // If the image argument is an HTMLImageElement object that is in the broken state,
                // then throw an InvalidStateError exception
                let (image_data, image_size) = match self.fetch_image_data(image) {
                    Some((mut data, size)) => {
                        // Pixels come from cache in BGRA order and drawImage expects RGBA so we
                        // have to swap the color values
                        byte_swap_and_premultiply(&mut data);
                        let size = Size2D::new(size.width as f64, size.height as f64);
                        (data, size)
                    },
                    None => return Err(Error::InvalidState),
                };
                let dw = dw.unwrap_or(image_size.width);
                let dh = dh.unwrap_or(image_size.height);
                let sw = sw.unwrap_or(image_size.width);
                let sh = sh.unwrap_or(image_size.height);
                self.draw_image_data(image_data,
                                     image_size,
                                     sx, sy, sw, sh,
                                     dx, dy, dw, dh)
            }
        };

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

    fn draw_html_canvas_element(&self,
                                canvas: &HTMLCanvasElement,
                                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 &*self.canvas == canvas {
            let msg = CanvasMsg::Canvas2d(Canvas2dMsg::DrawImageSelf(
                image_size, dest_rect, source_rect, smoothing_enabled));
            self.ipc_renderer.send(msg).unwrap();
        } else {
            let context = match canvas.get_or_init_2d_context() {
                Some(context) => context,
                None => return Err(Error::InvalidState),
            };

            let (sender, receiver) = ipc::channel().unwrap();
            let msg = CanvasMsg::Canvas2d(Canvas2dMsg::DrawImageInOther(
                self.ipc_renderer.clone(),
                image_size,
                dest_rect,
                source_rect,
                smoothing_enabled,
                sender));

            let renderer = context.get_ipc_renderer();
            renderer.send(msg).unwrap();
            receiver.recv().unwrap();
        };

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

    fn draw_image_data(&self,
                       image_data: Vec<u8>,
                       image_size: Size2D<f64>,
                       sx: f64,
                       sy: f64,
                       sw: f64,
                       sh: f64,
                       dx: f64,
                       dy: f64,
                       dw: f64,
                       dh: f64)
                       -> ErrorResult {
        // 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.ipc_renderer
            .send(CanvasMsg::Canvas2d(Canvas2dMsg::DrawImage(image_data,
                                                             image_size,
                                                             dest_rect,
                                                             source_rect,
                                                             smoothing_enabled)))
            .unwrap();
        self.mark_as_dirty();
        Ok(())
    }

    fn fetch_image_data(&self, image_element: &HTMLImageElement) -> Option<(Vec<u8>, Size2D<i32>)> {
        let url = match image_element.get_url() {
            Some(url) => url,
            None => return None,
        };

        let img = match self.request_image_from_cache(url) {
            ImageResponse::Loaded(img) => img,
            ImageResponse::PlaceholderLoaded(_) |
            ImageResponse::None |
            ImageResponse::MetadataLoaded(_) => {
                return None;
            }
        };

        let image_size = Size2D::new(img.width as i32, img.height as i32);
        let image_data = match img.format {
            PixelFormat::RGBA8 => img.bytes.to_vec(),
            PixelFormat::K8 => panic!("K8 color type not supported"),
            PixelFormat::RGB8 => panic!("RGB8 color type not supported"),
            PixelFormat::KA8 => panic!("KA8 color type not supported"),
        };

        Some((image_data, image_size))
    }

    #[inline]
    fn request_image_from_cache(&self, url: ServoUrl) -> ImageResponse {
        let window = window_from_node(&*self.canvas);
        canvas_utils::request_image_from_cache(&window, url)
    }

    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)))
    }

    fn parse_color(&self, string: &str) -> Result<RGBA, ()> {
        let mut parser = Parser::new(&string);
        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 window = window_from_node(&*self.canvas);

                    let style = window.GetComputedStyle(&*self.canvas.upcast(), None);

                    let element_not_rendered =
                        !self.canvas.upcast::<Node>().is_in_doc() ||
                        style.GetPropertyValue(DOMString::from("display")) == "none";

                    if element_not_rendered {
                        Ok(RGBA::new(0, 0, 0, 255))
                    } else {
                        self.parse_color(&style.GetPropertyValue(DOMString::from("color")))
                    }
                },
                _ => Err(())
            }
        } else {
            Err(())
        }
    }

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

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

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

pub trait LayoutCanvasRenderingContext2DHelpers {
    #[allow(unsafe_code)]
    unsafe fn get_ipc_renderer(&self) -> IpcSender<CanvasMsg>;
}

impl LayoutCanvasRenderingContext2DHelpers for LayoutJS<CanvasRenderingContext2D> {
    #[allow(unsafe_code)]
    unsafe fn get_ipc_renderer(&self) -> IpcSender<CanvasMsg> {
        (*self.unsafe_get()).ipc_renderer.clone()
    }
}

// We add a guard to each of methods by the spec:
// http://www.w3.org/html/wg/drafts/2dcontext/html5_canvas_CR/
//
// > Except where otherwise specified, for the 2D context interface,
// > any method call with a numeric argument whose value is infinite or a NaN value must be ignored.
//
//  Restricted values are guarded in glue code. Therefore we need not add a guard.
//
// FIXME: this behavior should might be generated by some annotattions to idl.
impl CanvasRenderingContext2DMethods for CanvasRenderingContext2D {
    // https://html.spec.whatwg.org/multipage/#dom-context-2d-canvas
    fn Canvas(&self) -> Root<HTMLCanvasElement> {
        Root::from_ref(&*self.canvas)
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-save
    fn Save(&self) {
        self.saved_states.borrow_mut().push(self.state.borrow().clone());
        self.ipc_renderer.send(CanvasMsg::Canvas2d(Canvas2dMsg::SaveContext)).unwrap();
    }

    #[allow(unrooted_must_root)]
    // https://html.spec.whatwg.org/multipage/#dom-context-2d-restore
    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.ipc_renderer.send(CanvasMsg::Canvas2d(Canvas2dMsg::RestoreContext)).unwrap();
        }
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-scale
    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_scaled(x as f32, y as f32);
        self.update_transform()
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-rotate
    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_mul(
            &Matrix2D::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
    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_translated(x as f32, y as f32);
        self.update_transform()
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-transform
    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_mul(
            &Matrix2D::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-settransform
    fn SetTransform(&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 =
            Matrix2D::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
    fn ResetTransform(&self) {
        self.state.borrow_mut().transform = Matrix2D::identity();
        self.update_transform()
    }

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

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

        self.state.borrow_mut().global_alpha = alpha;
        self.ipc_renderer
            .send(CanvasMsg::Canvas2d(Canvas2dMsg::SetGlobalAlpha(alpha as f32)))
            .unwrap()
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-globalcompositeoperation
    fn GlobalCompositeOperation(&self) -> DOMString {
        let state = self.state.borrow();
        match state.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
    fn SetGlobalCompositeOperation(&self, op_str: DOMString) {
        if let Ok(op) = CompositionOrBlending::from_str(&op_str) {
            self.state.borrow_mut().global_composition = op;
            self.ipc_renderer
                .send(CanvasMsg::Canvas2d(Canvas2dMsg::SetGlobalComposition(op)))
                .unwrap()
        }
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-fillrect
    fn FillRect(&self, x: f64, y: f64, width: f64, height: f64) {
        if let Some(rect) = self.create_drawable_rect(x, y, width, height) {
            self.ipc_renderer.send(CanvasMsg::Canvas2d(Canvas2dMsg::FillRect(rect))).unwrap();
            self.mark_as_dirty();
        }
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-clearrect
    fn ClearRect(&self, x: f64, y: f64, width: f64, height: f64) {
        if let Some(rect) = self.create_drawable_rect(x, y, width, height) {
            self.ipc_renderer
                .send(CanvasMsg::Canvas2d(Canvas2dMsg::ClearRect(rect)))
                .unwrap();
            self.mark_as_dirty();
        }
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-strokerect
    fn StrokeRect(&self, x: f64, y: f64, width: f64, height: f64) {
        if let Some(rect) = self.create_drawable_rect(x, y, width, height) {
            self.ipc_renderer
                .send(CanvasMsg::Canvas2d(Canvas2dMsg::StrokeRect(rect)))
                .unwrap();
            self.mark_as_dirty();
        }
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-beginpath
    fn BeginPath(&self) {
        self.ipc_renderer.send(CanvasMsg::Canvas2d(Canvas2dMsg::BeginPath)).unwrap();
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-closepath
    fn ClosePath(&self) {
        self.ipc_renderer.send(CanvasMsg::Canvas2d(Canvas2dMsg::ClosePath)).unwrap();
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-fill
    fn Fill(&self, _: CanvasFillRule) {
        // TODO: Process fill rule
        self.ipc_renderer.send(CanvasMsg::Canvas2d(Canvas2dMsg::Fill)).unwrap();
        self.mark_as_dirty();
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-stroke
    fn Stroke(&self) {
        self.ipc_renderer.send(CanvasMsg::Canvas2d(Canvas2dMsg::Stroke)).unwrap();
        self.mark_as_dirty();
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-clip
    fn Clip(&self, _: CanvasFillRule) {
        // TODO: Process fill rule
        self.ipc_renderer.send(CanvasMsg::Canvas2d(Canvas2dMsg::Clip)).unwrap();
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-ispointinpath
    fn IsPointInPath(&self, x: f64, y: f64, fill_rule: CanvasFillRule) -> bool {
        let fill_rule = match fill_rule {
            CanvasFillRule::Nonzero => FillRule::Nonzero,
            CanvasFillRule::Evenodd => FillRule::Evenodd,
        };
        let (sender, receiver) = ipc::channel::<bool>().unwrap();
        self.ipc_renderer
            .send(CanvasMsg::Canvas2d(Canvas2dMsg::IsPointInPath(x, y, fill_rule, sender)))
            .unwrap();
        receiver.recv().unwrap()
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-drawimage
    fn DrawImage(&self,
                 image: HTMLImageElementOrHTMLCanvasElementOrCanvasRenderingContext2D,
                 dx: f64,
                 dy: f64)
                 -> ErrorResult {
        if !(dx.is_finite() && dy.is_finite()) {
            return Ok(());
        }

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

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-drawimage
    fn DrawImage_(&self,
                  image: HTMLImageElementOrHTMLCanvasElementOrCanvasRenderingContext2D,
                  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(image, 0f64, 0f64, None, None, dx, dy, Some(dw), Some(dh))
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-drawimage
    fn DrawImage__(&self,
                   image: HTMLImageElementOrHTMLCanvasElementOrCanvasRenderingContext2D,
                   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(image,
                        sx,
                        sy,
                        Some(sw),
                        Some(sh),
                        dx,
                        dy,
                        Some(dw),
                        Some(dh))
    }

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

        let msg = CanvasMsg::Canvas2d(Canvas2dMsg::MoveTo(Point2D::new(x as f32, y as f32)));
        self.ipc_renderer.send(msg).unwrap();
    }

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

        let msg = CanvasMsg::Canvas2d(Canvas2dMsg::LineTo(Point2D::new(x as f32, y as f32)));
        self.ipc_renderer.send(msg).unwrap();
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-rect
    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));
            let msg = CanvasMsg::Canvas2d(Canvas2dMsg::Rect(rect));
            self.ipc_renderer.send(msg).unwrap();
        }
    }

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

        let msg = CanvasMsg::Canvas2d(Canvas2dMsg::QuadraticCurveTo(Point2D::new(cpx as f32,
                                                                                 cpy as f32),
                                                                    Point2D::new(x as f32,
                                                                                 y as f32)));
        self.ipc_renderer.send(msg).unwrap();
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-beziercurveto
    fn BezierCurveTo(&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;
        }

        let msg = CanvasMsg::Canvas2d(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)));
        self.ipc_renderer.send(msg).unwrap();
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-arc
    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);
        }

        let msg = CanvasMsg::Canvas2d(Canvas2dMsg::Arc(Point2D::new(x as f32, y as f32),
                                                       r as f32,
                                                       start as f32,
                                                       end as f32,
                                                       ccw));

        self.ipc_renderer.send(msg).unwrap();
        Ok(())
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-arcto
    fn ArcTo(&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);
        }

        let msg = CanvasMsg::Canvas2d(Canvas2dMsg::ArcTo(Point2D::new(cp1x as f32, cp1y as f32),
                                                         Point2D::new(cp2x as f32, cp2y as f32),
                                                         r as f32));
        self.ipc_renderer.send(msg).unwrap();
        Ok(())
    }

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

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

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-strokestyle
    fn StrokeStyle(&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(Root::from_ref(&*gradient))
            },
            CanvasFillOrStrokeStyle::Pattern(ref pattern) => {
                StringOrCanvasGradientOrCanvasPattern::CanvasPattern(Root::from_ref(&*pattern))
            }
        }
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-strokestyle
    fn SetStrokeStyle(&self, value: StringOrCanvasGradientOrCanvasPattern) {
        match value {
            StringOrCanvasGradientOrCanvasPattern::String(string) => {
                if let Ok(rgba) = self.parse_color(&string) {
                    self.state.borrow_mut().stroke_style = CanvasFillOrStrokeStyle::Color(rgba);
                    self.ipc_renderer
                        .send(CanvasMsg::Canvas2d(Canvas2dMsg::SetStrokeStyle(
                                    FillOrStrokeStyle::Color(rgba))))
                        .unwrap();
                }
            },
            StringOrCanvasGradientOrCanvasPattern::CanvasGradient(gradient) => {
                self.state.borrow_mut().stroke_style =
                    CanvasFillOrStrokeStyle::Gradient(JS::from_ref(&*gradient));
                let msg = CanvasMsg::Canvas2d(
                    Canvas2dMsg::SetStrokeStyle(gradient.to_fill_or_stroke_style()));
                self.ipc_renderer.send(msg).unwrap();
            },
            StringOrCanvasGradientOrCanvasPattern::CanvasPattern(pattern) => {
                self.state.borrow_mut().stroke_style =
                    CanvasFillOrStrokeStyle::Pattern(JS::from_ref(&*pattern));
                let msg = CanvasMsg::Canvas2d(
                    Canvas2dMsg::SetStrokeStyle(pattern.to_fill_or_stroke_style()));
                self.ipc_renderer.send(msg).unwrap();
                if !pattern.origin_is_clean() {
                    self.set_origin_unclean();
                }
            }
        }
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-strokestyle
    fn FillStyle(&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(Root::from_ref(&*gradient))
            },
            CanvasFillOrStrokeStyle::Pattern(ref pattern) => {
                StringOrCanvasGradientOrCanvasPattern::CanvasPattern(Root::from_ref(&*pattern))
            }
        }
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-strokestyle
    fn SetFillStyle(&self, value: StringOrCanvasGradientOrCanvasPattern) {
        match value {
            StringOrCanvasGradientOrCanvasPattern::String(string) => {
                if let Ok(rgba) = self.parse_color(&string) {
                    self.state.borrow_mut().fill_style = CanvasFillOrStrokeStyle::Color(rgba);
                    self.ipc_renderer
                        .send(CanvasMsg::Canvas2d(Canvas2dMsg::SetFillStyle(
                                    FillOrStrokeStyle::Color(rgba))))
                        .unwrap()
                }
            }
            StringOrCanvasGradientOrCanvasPattern::CanvasGradient(gradient) => {
                self.state.borrow_mut().fill_style =
                    CanvasFillOrStrokeStyle::Gradient(JS::from_ref(&*gradient));
                let msg = CanvasMsg::Canvas2d(
                    Canvas2dMsg::SetFillStyle(gradient.to_fill_or_stroke_style()));
                self.ipc_renderer.send(msg).unwrap();
            }
            StringOrCanvasGradientOrCanvasPattern::CanvasPattern(pattern) => {
                self.state.borrow_mut().fill_style =
                    CanvasFillOrStrokeStyle::Pattern(JS::from_ref(&*pattern));
                let msg = CanvasMsg::Canvas2d(
                    Canvas2dMsg::SetFillStyle(pattern.to_fill_or_stroke_style()));
                self.ipc_renderer.send(msg).unwrap();
                if !pattern.origin_is_clean() {
                    self.set_origin_unclean();
                }
            }
        }
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-createimagedata
    fn CreateImageData(&self, sw: Finite<f64>, sh: Finite<f64>) -> Fallible<Root<ImageData>> {
        if *sw == 0.0 || *sh == 0.0 {
            return Err(Error::IndexSize);
        }

        let sw = cmp::max(1, sw.abs().to_u32().unwrap());
        let sh = cmp::max(1, sh.abs().to_u32().unwrap());
        ImageData::new(&self.global(), sw, sh, None)
    }

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

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-getimagedata
    fn GetImageData(&self,
                    sx: Finite<f64>,
                    sy: Finite<f64>,
                    sw: Finite<f64>,
                    sh: Finite<f64>)
                    -> Fallible<Root<ImageData>> {
        if !self.origin_is_clean() {
            return Err(Error::Security)
        }

        let mut sx = *sx;
        let mut sy = *sy;
        let mut sw = *sw;
        let mut sh = *sh;

        if sw == 0.0 || sh == 0.0 {
            return Err(Error::IndexSize);
        }

        if sw < 0.0 {
            sw = -sw;
            sx -= sw;
        }
        if sh < 0.0 {
            sh = -sh;
            sy -= sh;
        }

        let sh = cmp::max(1, sh.to_u32().unwrap());
        let sw = cmp::max(1, sw.to_u32().unwrap());

        let (sender, receiver) = ipc::channel::<Vec<u8>>().unwrap();
        let dest_rect = Rect::new(Point2D::new(sx.to_i32().unwrap(), sy.to_i32().unwrap()),
                                  Size2D::new(sw as i32, sh as i32));
        let canvas_size = self.canvas.get_size();
        let canvas_size = Size2D::new(canvas_size.width as f64, canvas_size.height as f64);
        self.ipc_renderer
            .send(CanvasMsg::Canvas2d(Canvas2dMsg::GetImageData(dest_rect, canvas_size, sender)))
            .unwrap();
        let mut data = receiver.recv().unwrap();

        // Un-premultiply alpha
        for chunk in data.chunks_mut(4) {
            let alpha = chunk[3] as usize;
            chunk[0] = UNPREMULTIPLY_TABLE[256 * alpha + chunk[0] as usize];
            chunk[1] = UNPREMULTIPLY_TABLE[256 * alpha + chunk[1] as usize];
            chunk[2] = UNPREMULTIPLY_TABLE[256 * alpha + chunk[2] as usize];
        }

        ImageData::new(&self.global(), sw, sh, Some(data))
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-putimagedata
    fn PutImageData(&self, imagedata: &ImageData, dx: Finite<f64>, dy: Finite<f64>) {
        self.PutImageData_(imagedata,
                           dx,
                           dy,
                           Finite::wrap(0f64),
                           Finite::wrap(0f64),
                           Finite::wrap(imagedata.Width() as f64),
                           Finite::wrap(imagedata.Height() as f64))
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-putimagedata
    fn PutImageData_(&self,
                     imagedata: &ImageData,
                     dx: Finite<f64>,
                     dy: Finite<f64>,
                     dirty_x: Finite<f64>,
                     dirty_y: Finite<f64>,
                     dirty_width: Finite<f64>,
                     dirty_height: Finite<f64>) {
        let data = imagedata.get_data_array();
        let offset = Point2D::new(*dx, *dy);
        let image_data_size = Size2D::new(imagedata.Width() as f64, imagedata.Height() as f64);

        let dirty_rect = Rect::new(Point2D::new(*dirty_x, *dirty_y),
                                   Size2D::new(*dirty_width, *dirty_height));
        let msg = CanvasMsg::Canvas2d(Canvas2dMsg::PutImageData(data,
                                                                offset,
                                                                image_data_size,
                                                                dirty_rect));
        self.ipc_renderer.send(msg).unwrap();
        self.mark_as_dirty();
    }

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

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

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

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-createpattern
    fn CreatePattern(&self,
                     image: HTMLImageElementOrHTMLCanvasElementOrCanvasRenderingContext2D,
                     mut repetition: DOMString)
                     -> Fallible<Root<CanvasPattern>> {
        let (image_data, image_size) = match image {
            HTMLImageElementOrHTMLCanvasElementOrCanvasRenderingContext2D::HTMLImageElement(ref image) => {
                // https://html.spec.whatwg.org/multipage/#img-error
                // If the image argument is an HTMLImageElement object that is in the broken state,
                // then throw an InvalidStateError exception
                try!(self.fetch_image_data(image).ok_or(Error::InvalidState))
            },
            HTMLImageElementOrHTMLCanvasElementOrCanvasRenderingContext2D::HTMLCanvasElement(ref canvas) => {
                let _ = canvas.get_or_init_2d_context();

                try!(canvas.fetch_all_data().ok_or(Error::InvalidState))
            },
            HTMLImageElementOrHTMLCanvasElementOrCanvasRenderingContext2D::CanvasRenderingContext2D(ref context) => {
                let canvas = context.Canvas();
                let _ = canvas.get_or_init_2d_context();

                try!(canvas.fetch_all_data().ok_or(Error::InvalidState))
            }
        };

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

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

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

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

        self.state.borrow_mut().line_width = width;
        self.ipc_renderer
            .send(CanvasMsg::Canvas2d(Canvas2dMsg::SetLineWidth(width as f32)))
            .unwrap()
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-linecap
    fn LineCap(&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
    fn SetLineCap(&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.ipc_renderer.send(CanvasMsg::Canvas2d(Canvas2dMsg::SetLineCap(line_cap))).unwrap();
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-linejoin
    fn LineJoin(&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
    fn SetLineJoin(&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.ipc_renderer.send(CanvasMsg::Canvas2d(Canvas2dMsg::SetLineJoin(line_join))).unwrap();
    }

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

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

        self.state.borrow_mut().miter_limit = limit;
        self.ipc_renderer
            .send(CanvasMsg::Canvas2d(Canvas2dMsg::SetMiterLimit(limit as f32)))
            .unwrap()
    }

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

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-shadowoffsetx
    fn SetShadowOffsetX(&self, value: f64) {
        if !value.is_finite() || value == self.state.borrow().shadow_offset_x {
            return;
        }
        self.state.borrow_mut().shadow_offset_x = value;
        self.ipc_renderer.send(CanvasMsg::Canvas2d(Canvas2dMsg::SetShadowOffsetX(value))).unwrap()
    }

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

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-shadowoffsety
    fn SetShadowOffsetY(&self, value: f64) {
        if !value.is_finite() || value == self.state.borrow().shadow_offset_y {
            return;
        }
        self.state.borrow_mut().shadow_offset_y = value;
        self.ipc_renderer.send(CanvasMsg::Canvas2d(Canvas2dMsg::SetShadowOffsetY(value))).unwrap()
    }

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

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-shadowblur
    fn SetShadowBlur(&self, value: f64) {
        if !value.is_finite() || value < 0f64 || value == self.state.borrow().shadow_blur {
            return;
        }
        self.state.borrow_mut().shadow_blur = value;
        self.ipc_renderer.send(CanvasMsg::Canvas2d(Canvas2dMsg::SetShadowBlur(value))).unwrap()
    }

    // https://html.spec.whatwg.org/multipage/#dom-context-2d-shadowcolor
    fn ShadowColor(&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
    fn SetShadowColor(&self, value: DOMString) {
        if let Ok(color) = parse_color(&value) {
            self.state.borrow_mut().shadow_color = color;
            self.ipc_renderer
                .send(CanvasMsg::Canvas2d(Canvas2dMsg::SetShadowColor(color)))
                .unwrap()
        }
    }
}

impl Drop for CanvasRenderingContext2D {
    fn drop(&mut self) {
        if let Err(err) = self.ipc_renderer.send(CanvasMsg::Common(CanvasCommonMsg::Close)) {
            warn!("Could not close canvas: {}", err)
        }
    }
}

pub fn parse_color(string: &str) -> Result<RGBA, ()> {
    let mut parser = Parser::new(&string);
    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
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-colour
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())
    }
}