gecko-dev/dom/canvas/CanvasRenderingContext2D.h

/* 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/. */

#ifndef CanvasRenderingContext2D_h
#define CanvasRenderingContext2D_h

#include "mozilla/Attributes.h"
#include <vector>
#include "nsICanvasRenderingContextInternal.h"
#include "mozilla/RefPtr.h"
#include "nsColor.h"
#include "mozilla/dom/HTMLCanvasElement.h"
#include "mozilla/dom/HTMLVideoElement.h"
#include "mozilla/ErrorResult.h"
#include "mozilla/dom/BasicRenderingContext2D.h"
#include "mozilla/dom/CanvasGradient.h"
#include "mozilla/dom/CanvasRenderingContext2DBinding.h"
#include "mozilla/dom/CanvasPattern.h"
#include "mozilla/gfx/Rect.h"
#include "mozilla/gfx/2D.h"
#include "mozilla/PresShell.h"
#include "mozilla/UniquePtr.h"
#include "gfx2DGlue.h"
#include "imgIEncoder.h"
#include "nsLayoutUtils.h"
#include "mozilla/EnumeratedArray.h"
#include "FilterSupport.h"
#include "SVGObserverUtils.h"
#include "Layers.h"
#include "nsBidi.h"

class gfxFontGroup;
class nsGlobalWindowInner;
class nsXULElement;

namespace mozilla {
namespace gl {
class SourceSurface;
}  // namespace gl

namespace dom {
class
    HTMLImageElementOrSVGImageElementOrHTMLCanvasElementOrHTMLVideoElementOrImageBitmap;
typedef HTMLImageElementOrSVGImageElementOrHTMLCanvasElementOrHTMLVideoElementOrImageBitmap
    CanvasImageSource;
class ImageBitmap;
class ImageData;
class StringOrCanvasGradientOrCanvasPattern;
class OwningStringOrCanvasGradientOrCanvasPattern;
class TextMetrics;
class CanvasPath;

extern const mozilla::gfx::Float SIGMA_MAX;

template <typename T>
class Optional;

struct CanvasBidiProcessor;
class CanvasRenderingContext2DUserData;
class CanvasDrawObserver;
class CanvasShutdownObserver;

class DOMMatrix;
class DOMMatrixReadOnly;
struct DOMMatrix2DInit;

/**
 ** CanvasRenderingContext2D
 **/
class CanvasRenderingContext2D final : public nsICanvasRenderingContextInternal,
                                       public nsWrapperCache,
                                       public BasicRenderingContext2D {
  virtual ~CanvasRenderingContext2D();

 public:
  explicit CanvasRenderingContext2D(layers::LayersBackend aCompositorBackend);

  virtual JSObject* WrapObject(JSContext* aCx,
                               JS::Handle<JSObject*> aGivenProto) override;

  HTMLCanvasElement* GetCanvas() const {
    if (!mCanvasElement || mCanvasElement->IsInNativeAnonymousSubtree()) {
      return nullptr;
    }

    // corresponds to changes to the old bindings made in bug 745025
    return mCanvasElement->GetOriginalCanvas();
  }

  void Save() override;
  void Restore() override;
  void Scale(double aX, double aY, mozilla::ErrorResult& aError) override;
  void Rotate(double aAngle, mozilla::ErrorResult& aError) override;
  void Translate(double aX, double aY, mozilla::ErrorResult& aError) override;
  void Transform(double aM11, double aM12, double aM21, double aM22, double aDx,
                 double aDy, mozilla::ErrorResult& aError) override;
  already_AddRefed<DOMMatrix> GetTransform(
      mozilla::ErrorResult& aError) override;
  void SetTransform(double aM11, double aM12, double aM21, double aM22,
                    double aDx, double aDy,
                    mozilla::ErrorResult& aError) override;
  void SetTransform(const DOMMatrix2DInit& aInit,
                    mozilla::ErrorResult& aError) override;
  void ResetTransform(mozilla::ErrorResult& aError) override;

  double GlobalAlpha() override { return CurrentState().globalAlpha; }

  // Useful for silencing cast warnings
  static mozilla::gfx::Float ToFloat(double aValue) {
    return mozilla::gfx::Float(aValue);
  }

  void SetGlobalAlpha(double aGlobalAlpha) override {
    if (aGlobalAlpha >= 0.0 && aGlobalAlpha <= 1.0) {
      CurrentState().globalAlpha = ToFloat(aGlobalAlpha);
    }
  }

  void GetGlobalCompositeOperation(nsAString& aOp,
                                   mozilla::ErrorResult& aError) override;
  void SetGlobalCompositeOperation(const nsAString& aOp,
                                   mozilla::ErrorResult& aError) override;

  void GetStrokeStyle(
      OwningStringOrCanvasGradientOrCanvasPattern& aValue) override {
    GetStyleAsUnion(aValue, Style::STROKE);
  }

  void SetStrokeStyle(
      const StringOrCanvasGradientOrCanvasPattern& aValue) override {
    SetStyleFromUnion(aValue, Style::STROKE);
  }

  void GetFillStyle(
      OwningStringOrCanvasGradientOrCanvasPattern& aValue) override {
    GetStyleAsUnion(aValue, Style::FILL);
  }

  void SetFillStyle(
      const StringOrCanvasGradientOrCanvasPattern& aValue) override {
    SetStyleFromUnion(aValue, Style::FILL);
  }

  already_AddRefed<CanvasGradient> CreateLinearGradient(double aX0, double aY0,
                                                        double aX1,
                                                        double aY1) override;
  already_AddRefed<CanvasGradient> CreateRadialGradient(
      double aX0, double aY0, double aR0, double aX1, double aY1, double aR1,
      ErrorResult& aError) override;
  already_AddRefed<CanvasPattern> CreatePattern(
      const CanvasImageSource& aElement, const nsAString& aRepeat,
      ErrorResult& aError) override;

  double ShadowOffsetX() override { return CurrentState().shadowOffset.x; }

  void SetShadowOffsetX(double aShadowOffsetX) override {
    CurrentState().shadowOffset.x = ToFloat(aShadowOffsetX);
  }

  double ShadowOffsetY() override { return CurrentState().shadowOffset.y; }

  void SetShadowOffsetY(double aShadowOffsetY) override {
    CurrentState().shadowOffset.y = ToFloat(aShadowOffsetY);
  }

  double ShadowBlur() override { return CurrentState().shadowBlur; }

  void SetShadowBlur(double aShadowBlur) override {
    if (aShadowBlur >= 0.0) {
      CurrentState().shadowBlur = ToFloat(aShadowBlur);
    }
  }

  void GetShadowColor(nsAString& aShadowColor) override {
    StyleColorToString(CurrentState().shadowColor, aShadowColor);
  }

  void GetFilter(nsAString& aFilter) { aFilter = CurrentState().filterString; }

  void SetShadowColor(const nsAString& aShadowColor) override;
  void SetFilter(const nsAString& aFilter, mozilla::ErrorResult& aError);
  void ClearRect(double aX, double aY, double aW, double aH) override;
  void FillRect(double aX, double aY, double aW, double aH) override;
  void StrokeRect(double aX, double aY, double aW, double aH) override;
  void BeginPath();
  void Fill(const CanvasWindingRule& aWinding);
  void Fill(const CanvasPath& aPath, const CanvasWindingRule& aWinding);
  void Stroke();
  void Stroke(const CanvasPath& aPath);
  void DrawFocusIfNeeded(mozilla::dom::Element& aElement, ErrorResult& aRv);
  bool DrawCustomFocusRing(mozilla::dom::Element& aElement);
  void Clip(const CanvasWindingRule& aWinding);
  void Clip(const CanvasPath& aPath, const CanvasWindingRule& aWinding);
  bool IsPointInPath(JSContext* aCx, double aX, double aY,
                     const CanvasWindingRule& aWinding,
                     nsIPrincipal& aSubjectPrincipal);
  bool IsPointInPath(JSContext* aCx, const CanvasPath& aPath, double aX,
                     double aY, const CanvasWindingRule& aWinding,
                     nsIPrincipal&);
  bool IsPointInStroke(JSContext* aCx, double aX, double aY,
                       nsIPrincipal& aSubjectPrincipal);
  bool IsPointInStroke(JSContext* aCx, const CanvasPath& aPath, double aX,
                       double aY, nsIPrincipal&);
  void FillText(const nsAString& aText, double aX, double aY,
                const Optional<double>& aMaxWidth,
                mozilla::ErrorResult& aError);
  void StrokeText(const nsAString& aText, double aX, double aY,
                  const Optional<double>& aMaxWidth,
                  mozilla::ErrorResult& aError);
  TextMetrics* MeasureText(const nsAString& aRawText,
                           mozilla::ErrorResult& aError);

  void AddHitRegion(const HitRegionOptions& aOptions,
                    mozilla::ErrorResult& aError);
  void RemoveHitRegion(const nsAString& aId);
  void ClearHitRegions();

  void DrawImage(const CanvasImageSource& aImage, double aDx, double aDy,
                 mozilla::ErrorResult& aError) override {
    DrawImage(aImage, 0.0, 0.0, 0.0, 0.0, aDx, aDy, 0.0, 0.0, 0, aError);
  }

  void DrawImage(const CanvasImageSource& aImage, double aDx, double aDy,
                 double aDw, double aDh,
                 mozilla::ErrorResult& aError) override {
    DrawImage(aImage, 0.0, 0.0, 0.0, 0.0, aDx, aDy, aDw, aDh, 2, aError);
  }

  void DrawImage(const CanvasImageSource& aImage, double aSx, double aSy,
                 double aSw, double aSh, double aDx, double aDy, double aDw,
                 double aDh, mozilla::ErrorResult& aError) override {
    DrawImage(aImage, aSx, aSy, aSw, aSh, aDx, aDy, aDw, aDh, 6, aError);
  }

  already_AddRefed<ImageData> CreateImageData(JSContext* aCx, double aSw,
                                              double aSh,
                                              mozilla::ErrorResult& aError);
  already_AddRefed<ImageData> CreateImageData(JSContext* aCx,
                                              ImageData& aImagedata,
                                              mozilla::ErrorResult& aError);
  already_AddRefed<ImageData> GetImageData(JSContext* aCx, double aSx,
                                           double aSy, double aSw, double aSh,
                                           nsIPrincipal& aSubjectPrincipal,
                                           mozilla::ErrorResult& aError);
  void PutImageData(ImageData& aImageData, double aDx, double aDy,
                    mozilla::ErrorResult& aError);
  void PutImageData(ImageData& aImageData, double aDx, double aDy,
                    double aDirtyX, double aDirtyY, double aDirtyWidth,
                    double aDirtyHeight, mozilla::ErrorResult& aError);

  double LineWidth() override { return CurrentState().lineWidth; }

  void SetLineWidth(double aWidth) override {
    if (aWidth > 0.0) {
      CurrentState().lineWidth = ToFloat(aWidth);
    }
  }
  void GetLineCap(nsAString& aLinecapStyle) override;
  void SetLineCap(const nsAString& aLinecapStyle) override;
  void GetLineJoin(nsAString& aLinejoinStyle,
                   mozilla::ErrorResult& aError) override;
  void SetLineJoin(const nsAString& aLinejoinStyle) override;

  double MiterLimit() override { return CurrentState().miterLimit; }

  void SetMiterLimit(double aMiter) override {
    if (aMiter > 0.0) {
      CurrentState().miterLimit = ToFloat(aMiter);
    }
  }

  void GetFont(nsAString& aFont) { aFont = GetFont(); }

  void SetFont(const nsAString& aFont, mozilla::ErrorResult& aError);
  void GetTextAlign(nsAString& aTextAlign);
  void SetTextAlign(const nsAString& aTextAlign);
  void GetTextBaseline(nsAString& aTextBaseline);
  void SetTextBaseline(const nsAString& aTextBaseline);

  void ClosePath() override {
    EnsureWritablePath();

    if (mPathBuilder) {
      mPathBuilder->Close();
    } else {
      mDSPathBuilder->Close();
    }
  }

  void MoveTo(double aX, double aY) override {
    EnsureWritablePath();

    if (mPathBuilder) {
      mPathBuilder->MoveTo(mozilla::gfx::Point(ToFloat(aX), ToFloat(aY)));
    } else {
      mDSPathBuilder->MoveTo(mTarget->GetTransform().TransformPoint(
          mozilla::gfx::Point(ToFloat(aX), ToFloat(aY))));
    }
  }

  void LineTo(double aX, double aY) override {
    EnsureWritablePath();

    LineTo(mozilla::gfx::Point(ToFloat(aX), ToFloat(aY)));
  }

  void QuadraticCurveTo(double aCpx, double aCpy, double aX,
                        double aY) override {
    EnsureWritablePath();

    if (mPathBuilder) {
      mPathBuilder->QuadraticBezierTo(
          mozilla::gfx::Point(ToFloat(aCpx), ToFloat(aCpy)),
          mozilla::gfx::Point(ToFloat(aX), ToFloat(aY)));
    } else {
      mozilla::gfx::Matrix transform = mTarget->GetTransform();
      mDSPathBuilder->QuadraticBezierTo(
          transform.TransformPoint(
              mozilla::gfx::Point(ToFloat(aCpx), ToFloat(aCpy))),
          transform.TransformPoint(
              mozilla::gfx::Point(ToFloat(aX), ToFloat(aY))));
    }
  }

  void BezierCurveTo(double aCp1x, double aCp1y, double aCp2x, double aCp2y,
                     double aX, double aY) override {
    EnsureWritablePath();

    BezierTo(mozilla::gfx::Point(ToFloat(aCp1x), ToFloat(aCp1y)),
             mozilla::gfx::Point(ToFloat(aCp2x), ToFloat(aCp2y)),
             mozilla::gfx::Point(ToFloat(aX), ToFloat(aY)));
  }

  void ArcTo(double aX1, double aY1, double aX2, double aY2, double aRadius,
             mozilla::ErrorResult& aError) override;
  void Rect(double aX, double aY, double aW, double aH) override;
  void Arc(double aX, double aY, double aRadius, double aStartAngle,
           double aEndAngle, bool aAnticlockwise,
           mozilla::ErrorResult& aError) override;
  void Ellipse(double aX, double aY, double aRadiusX, double aRadiusY,
               double aRotation, double aStartAngle, double aEndAngle,
               bool aAnticlockwise, ErrorResult& aError) override;

  void GetMozCurrentTransform(JSContext* aCx,
                              JS::MutableHandle<JSObject*> aResult,
                              mozilla::ErrorResult& aError);
  void SetMozCurrentTransform(JSContext* aCx,
                              JS::Handle<JSObject*> aCurrentTransform,
                              mozilla::ErrorResult& aError);
  void GetMozCurrentTransformInverse(JSContext* aCx,
                                     JS::MutableHandle<JSObject*> aResult,
                                     mozilla::ErrorResult& aError);
  void SetMozCurrentTransformInverse(JSContext* aCx,
                                     JS::Handle<JSObject*> aCurrentTransform,
                                     mozilla::ErrorResult& aError);
  void GetFillRule(nsAString& aFillRule);
  void SetFillRule(const nsAString& aFillRule);

  void SetLineDash(const Sequence<double>& aSegments,
                   mozilla::ErrorResult& aRv) override;
  void GetLineDash(nsTArray<double>& aSegments) const override;

  void SetLineDashOffset(double aOffset) override;
  double LineDashOffset() const override;

  void GetMozTextStyle(nsAString& aMozTextStyle) { GetFont(aMozTextStyle); }

  void SetMozTextStyle(const nsAString& aMozTextStyle,
                       mozilla::ErrorResult& aError) {
    SetFont(aMozTextStyle, aError);
  }

  bool ImageSmoothingEnabled() override {
    return CurrentState().imageSmoothingEnabled;
  }

  void SetImageSmoothingEnabled(bool aImageSmoothingEnabled) override {
    if (aImageSmoothingEnabled != CurrentState().imageSmoothingEnabled) {
      CurrentState().imageSmoothingEnabled = aImageSmoothingEnabled;
    }
  }

  void DrawWindow(nsGlobalWindowInner& aWindow, double aX, double aY, double aW,
                  double aH, const nsAString& aBgColor, uint32_t aFlags,
                  mozilla::ErrorResult& aError);

  // Eventually this should be deprecated. Keeping for now to keep the binding
  // functional.
  void Demote();

  nsresult Redraw();

  gfx::IntSize GetSize() const { return gfx::IntSize(mWidth, mHeight); }
  virtual int32_t GetWidth() override { return GetSize().width; }
  virtual int32_t GetHeight() override { return GetSize().height; }

  // nsICanvasRenderingContextInternal
  /**
   * Gets the pres shell from either the canvas element or the doc shell
   */
  PresShell* GetPresShell() final {
    if (mCanvasElement) {
      return mCanvasElement->OwnerDoc()->GetPresShell();
    }
    if (mDocShell) {
      return mDocShell->GetPresShell();
    }
    return nullptr;
  }
  NS_IMETHOD SetDimensions(int32_t aWidth, int32_t aHeight) override;
  NS_IMETHOD InitializeWithDrawTarget(
      nsIDocShell* aShell, NotNull<gfx::DrawTarget*> aTarget) override;

  NS_IMETHOD GetInputStream(const char* aMimeType,
                            const nsAString& aEncoderOptions,
                            nsIInputStream** aStream) override;

  already_AddRefed<mozilla::gfx::SourceSurface> GetSurfaceSnapshot(
      gfxAlphaType* aOutAlphaType = nullptr) override;

  virtual void SetOpaqueValueFromOpaqueAttr(bool aOpaqueAttrValue) override;
  bool GetIsOpaque() override { return mOpaque; }
  NS_IMETHOD Reset() override;
  already_AddRefed<Layer> GetCanvasLayer(nsDisplayListBuilder* aBuilder,
                                         Layer* aOldLayer,
                                         LayerManager* aManager) override;

  bool UpdateWebRenderCanvasData(nsDisplayListBuilder* aBuilder,
                                 WebRenderCanvasData* aCanvasData) override;

  bool InitializeCanvasRenderer(nsDisplayListBuilder* aBuilder,
                                CanvasRenderer* aRenderer) override;
  virtual bool ShouldForceInactiveLayer(LayerManager* aManager) override;
  void MarkContextClean() override;
  void MarkContextCleanForFrameCapture() override;
  bool IsContextCleanForFrameCapture() override;
  NS_IMETHOD SetIsIPC(bool aIsIPC) override;
  // this rect is in canvas device space
  void Redraw(const mozilla::gfx::Rect& aR);
  NS_IMETHOD Redraw(const gfxRect& aR) override {
    Redraw(ToRect(aR));
    return NS_OK;
  }
  NS_IMETHOD SetContextOptions(JSContext* aCx, JS::Handle<JS::Value> aOptions,
                               ErrorResult& aRvForDictionaryInit) override;

  /**
   * An abstract base class to be implemented by callers wanting to be notified
   * that a refresh has occurred. Callers must ensure an observer is removed
   * before it is destroyed.
   */
  virtual void DidRefresh() override;

  // this rect is in mTarget's current user space
  void RedrawUser(const gfxRect& aR);

  // nsISupports interface + CC
  NS_DECL_CYCLE_COLLECTING_ISUPPORTS

  NS_DECL_CYCLE_COLLECTION_SKIPPABLE_SCRIPT_HOLDER_CLASS(
      CanvasRenderingContext2D)

  enum class CanvasMultiGetterType : uint8_t {
    STRING = 0,
    PATTERN = 1,
    GRADIENT = 2
  };

  enum class Style : uint8_t { STROKE = 0, FILL, MAX };

  nsINode* GetParentObject() { return mCanvasElement; }

  void LineTo(const mozilla::gfx::Point& aPoint) {
    if (mPathBuilder) {
      mPathBuilder->LineTo(aPoint);
    } else {
      mDSPathBuilder->LineTo(mTarget->GetTransform().TransformPoint(aPoint));
    }
  }

  void BezierTo(const mozilla::gfx::Point& aCP1,
                const mozilla::gfx::Point& aCP2,
                const mozilla::gfx::Point& aCP3) {
    if (mPathBuilder) {
      mPathBuilder->BezierTo(aCP1, aCP2, aCP3);
    } else {
      mozilla::gfx::Matrix transform = mTarget->GetTransform();
      mDSPathBuilder->BezierTo(transform.TransformPoint(aCP1),
                               transform.TransformPoint(aCP2),
                               transform.TransformPoint(aCP3));
    }
  }

  friend class CanvasRenderingContext2DUserData;

  virtual UniquePtr<uint8_t[]> GetImageBuffer(int32_t* aFormat) override;

  // Given a point, return hit region ID if it exists
  nsString GetHitRegion(const mozilla::gfx::Point& aPoint) override;

  // return true and fills in the bound rect if element has a hit region.
  bool GetHitRegionRect(Element* aElement, nsRect& aRect) override;

  void OnShutdown();

  /**
   * Update CurrentState().filter with the filter description for
   * CurrentState().filterChain.
   * Flushes the PresShell, so the world can change if you call this function.
   */
  MOZ_CAN_RUN_SCRIPT_BOUNDARY void UpdateFilter();

 protected:
  nsresult GetImageDataArray(JSContext* aCx, int32_t aX, int32_t aY,
                             uint32_t aWidth, uint32_t aHeight,
                             nsIPrincipal& aSubjectPrincipal,
                             JSObject** aRetval);

  nsresult PutImageData_explicit(int32_t aX, int32_t aY, uint32_t aW,
                                 uint32_t aH, dom::Uint8ClampedArray* aArray,
                                 bool aHasDirtyRect, int32_t aDirtyX,
                                 int32_t aDirtyY, int32_t aDirtyWidth,
                                 int32_t aDirtyHeight);

  bool CopyBufferProvider(layers::PersistentBufferProvider& aOld,
                          gfx::DrawTarget& aTarget, gfx::IntRect aCopyRect);

  /**
   * Internal method to complete initialisation, expects mTarget to have been
   * set
   */
  nsresult Initialize(int32_t aWidth, int32_t aHeight);

  nsresult InitializeWithTarget(mozilla::gfx::DrawTarget* aSurface,
                                int32_t aWidth, int32_t aHeight);

  /**
   * The number of living nsCanvasRenderingContexts.  When this goes down to
   * 0, we free the premultiply and unpremultiply tables, if they exist.
   */
  static uintptr_t sNumLivingContexts;

  static mozilla::gfx::DrawTarget* sErrorTarget;

  void SetTransformInternal(const mozilla::gfx::Matrix& aTransform);

  // Some helpers.  Doesn't modify a color on failure.
  void SetStyleFromUnion(const StringOrCanvasGradientOrCanvasPattern& aValue,
                         Style aWhichStyle);
  void SetStyleFromString(const nsAString& aStr, Style aWhichStyle);

  void SetStyleFromGradient(CanvasGradient& aGradient, Style aWhichStyle) {
    CurrentState().SetGradientStyle(aWhichStyle, &aGradient);
  }

  void SetStyleFromPattern(CanvasPattern& aPattern, Style aWhichStyle) {
    CurrentState().SetPatternStyle(aWhichStyle, &aPattern);
  }

  void GetStyleAsUnion(OwningStringOrCanvasGradientOrCanvasPattern& aValue,
                       Style aWhichStyle);

  // Returns whether a color was successfully parsed.
  bool ParseColor(const nsAString& aString, nscolor* aColor);

  static void StyleColorToString(const nscolor& aColor, nsAString& aStr);

  // Returns whether a filter was successfully parsed.
  bool ParseFilter(const nsAString& aString,
                   StyleOwnedSlice<StyleFilter>& aFilterChain,
                   ErrorResult& aError);

  // Returns whether the font was successfully updated.
  bool SetFontInternal(const nsAString& aFont, mozilla::ErrorResult& aError);

  // Clears the target and updates mOpaque based on mOpaqueAttrValue and
  // mContextAttributesHasAlpha.
  void UpdateIsOpaque();

  /**
   * Creates the error target, if it doesn't exist
   */
  static void EnsureErrorTarget();

  /* This function ensures there is a writable pathbuilder available, this
   * pathbuilder may be working in user space or in device space or
   * device space.
   * After calling this function mPathTransformWillUpdate will be false
   */
  void EnsureWritablePath();

  // Ensures a path in UserSpace is available.
  void EnsureUserSpacePath(
      const CanvasWindingRule& aWinding = CanvasWindingRule::Nonzero);

  /**
   * Needs to be called before updating the transform. This makes a call to
   * EnsureTarget() so you don't have to.
   */
  void TransformWillUpdate();

  // Report the fillRule has changed.
  void FillRuleChanged();

  /**
   * Create the backing surfacing, if it doesn't exist. If there is an error
   * in creating the target then it will put sErrorTarget in place. If there
   * is in turn an error in creating the sErrorTarget then they would both
   * be null so IsTargetValid() would still return null.
   *
   * Returns true on success.
   */
  bool EnsureTarget(const gfx::Rect* aCoveredRect = nullptr,
                    bool aWillClear = false);

  void RestoreClipsAndTransformToTarget();

  bool TrySharedTarget(RefPtr<gfx::DrawTarget>& aOutDT,
                       RefPtr<layers::PersistentBufferProvider>& aOutProvider);

  bool TryBasicTarget(RefPtr<gfx::DrawTarget>& aOutDT,
                      RefPtr<layers::PersistentBufferProvider>& aOutProvider);

  void RegisterAllocation();

  void SetInitialState();

  void SetErrorState();

  /**
   * This method is run at the end of the event-loop spin where
   * ScheduleStableStateCallback was called.
   *
   * We use it to unlock resources that need to be locked while drawing.
   */
  void OnStableState();

  /**
   * Cf. OnStableState.
   */
  void ScheduleStableStateCallback();

  /**
   * Disposes an old target and prepares to lazily create a new target.
   *
   * Parameters are the new dimensions to be used, or if either is negative,
   * existing dimensions will be left unchanged.
   */
  void ClearTarget(int32_t aWidth = -1, int32_t aHeight = -1);

  /*
   * Returns the target to the buffer provider. i.e. this will queue a frame for
   * rendering.
   */
  void ReturnTarget(bool aForceReset = false);

  /**
   * Check if the target is valid after calling EnsureTarget.
   */
  bool IsTargetValid() const { return !!mTarget && mTarget != sErrorTarget; }

  /**
   * Returns the surface format this canvas should be allocated using. Takes
   * into account mOpaque, platform requirements, etc.
   */
  mozilla::gfx::SurfaceFormat GetSurfaceFormat() const;

  /**
   * Returns true if we know for sure that the pattern for a given style is
   * opaque. Usefull to know if we can discard the content below in certain
   * situations. Optionally checks if the pattern is a color pattern.
   */
  bool PatternIsOpaque(Style aStyle, bool* aIsColor = nullptr) const;

  nsLayoutUtils::SurfaceFromElementResult CachedSurfaceFromElement(
      Element* aElement);

  void DrawImage(const CanvasImageSource& aImgElt, double aSx, double aSy,
                 double aSw, double aSh, double aDx, double aDy, double aDw,
                 double aDh, uint8_t aOptional_argc,
                 mozilla::ErrorResult& aError);

  void DrawDirectlyToCanvas(const nsLayoutUtils::DirectDrawInfo& aImage,
                            mozilla::gfx::Rect* aBounds,
                            mozilla::gfx::Rect aDest, mozilla::gfx::Rect aSrc,
                            gfx::IntSize aImgSize);

  nsString& GetFont() {
    /* will initilize the value if not set, else does nothing */
    GetCurrentFontStyle();

    return CurrentState().font;
  }

  // Member vars
  int32_t mWidth, mHeight;

  // This is true when the canvas is valid, but of zero size, this requires
  // specific behavior on some operations.
  bool mZero;

  // The two ways to set the opaqueness of the canvas.
  // mOpaqueAttrValue: Whether the <canvas> element has the moz-opaque attribute
  // set. Can change during the lifetime of the context. Non-standard, should
  // hopefully go away soon.
  // mContextAttributesHasAlpha: The standard way of setting canvas opaqueness.
  // Set at context initialization time and never changes.
  bool mOpaqueAttrValue;
  bool mContextAttributesHasAlpha;

  // Determines the context's opaqueness. Is computed from mOpaqueAttrValue and
  // mContextAttributesHasAlpha in UpdateIsOpaque().
  bool mOpaque;

  // This is true when the next time our layer is retrieved we need to
  // recreate it (i.e. our backing surface changed)
  bool mResetLayer;
  // This is needed for drawing in drawAsyncXULElement
  bool mIPC;

  bool mHasPendingStableStateCallback;

  nsTArray<CanvasRenderingContext2DUserData*> mUserDatas;

  // If mCanvasElement is not provided, then a docshell is
  nsCOMPtr<nsIDocShell> mDocShell;

  // This is created lazily so it is necessary to call EnsureTarget before
  // accessing it. In the event of an error it will be equal to
  // sErrorTarget.
  RefPtr<mozilla::gfx::DrawTarget> mTarget;

  RefPtr<mozilla::layers::PersistentBufferProvider> mBufferProvider;

  RefPtr<CanvasShutdownObserver> mShutdownObserver;
  void RemoveShutdownObserver();
  bool AlreadyShutDown() const { return !mShutdownObserver; }

  /**
   * Flag to avoid duplicate calls to InvalidateFrame. Set to true whenever
   * Redraw is called, reset to false when Render is called.
   */
  bool mIsEntireFrameInvalid;
  /**
   * When this is set, the first call to Redraw(gfxRect) should set
   * mIsEntireFrameInvalid since we expect it will be followed by
   * many more Redraw calls.
   */
  bool mPredictManyRedrawCalls;

  /**
   * Flag to avoid unnecessary surface copies to FrameCaptureListeners in the
   * case when the canvas is not currently being drawn into and not rendered
   * but canvas capturing is still ongoing.
   */
  bool mIsCapturedFrameInvalid;

  /**
   * We also have a device space pathbuilder. The reason for this is as
   * follows, when a path is being built, but the transform changes, we
   * can no longer keep a single path in userspace, considering there's
   * several 'user spaces' now. We therefore transform the current path
   * into device space, and add all operations to this path in device
   * space.
   *
   * When then finally executing a render, the Azure drawing API expects
   * the path to be in userspace. We could then set an identity transform
   * on the DrawTarget and do all drawing in device space. This is
   * undesirable because it requires transforming patterns, gradients,
   * clips, etc. into device space and it would not work for stroking.
   * What we do instead is convert the path back to user space when it is
   * drawn, and draw it with the current transform. This makes all drawing
   * occur correctly.
   *
   * There's never both a device space path builder and a user space path
   * builder present at the same time. There is also never a path and a
   * path builder present at the same time. When writing proceeds on an
   * existing path the Path is cleared and a new builder is created.
   *
   * mPath is always in user-space.
   */
  RefPtr<mozilla::gfx::Path> mPath;
  RefPtr<mozilla::gfx::PathBuilder> mDSPathBuilder;
  RefPtr<mozilla::gfx::PathBuilder> mPathBuilder;
  bool mPathTransformWillUpdate;
  mozilla::gfx::Matrix mPathToDS;

  /**
   * Number of times we've invalidated before calling redraw
   */
  uint32_t mInvalidateCount;
  static const uint32_t kCanvasMaxInvalidateCount = 100;

  /**
   * State information for hit regions
   */
  struct RegionInfo {
    nsString mId;
    // fallback element for a11y
    RefPtr<Element> mElement;
    // Path of the hit region in the 2d context coordinate space (not user
    // space)
    RefPtr<gfx::Path> mPath;
  };

  nsTArray<RegionInfo> mHitRegionsOptions;

  nsBidi mBidiEngine;

  /**
   * Returns true if a shadow should be drawn along with a
   * drawing operation.
   */
  bool NeedToDrawShadow() {
    const ContextState& state = CurrentState();

    // The spec says we should not draw shadows if the operator is OVER.
    // If it's over and the alpha value is zero, nothing needs to be drawn.
    return NS_GET_A(state.shadowColor) != 0 &&
           (state.shadowBlur != 0.f || state.shadowOffset.x != 0.f ||
            state.shadowOffset.y != 0.f);
  }

  /**
   * Returns true if the result of a drawing operation should be
   * drawn with a filter.
   */
  bool NeedToApplyFilter() {
    return EnsureUpdatedFilter().mPrimitives.Length() > 0;
  }

  /**
   * Calls UpdateFilter if the canvas's WriteOnly state has changed between the
   * last call to UpdateFilter and now.
   */
  const gfx::FilterDescription& EnsureUpdatedFilter() {
    bool isWriteOnly = mCanvasElement && mCanvasElement->IsWriteOnly();
    if (CurrentState().filterSourceGraphicTainted != isWriteOnly) {
      UpdateFilter();
      EnsureTarget();
    }
    MOZ_ASSERT(CurrentState().filterSourceGraphicTainted == isWriteOnly);
    return CurrentState().filter;
  }

  bool NeedToCalculateBounds() {
    return NeedToDrawShadow() || NeedToApplyFilter();
  }

  mozilla::gfx::CompositionOp UsedOperation() {
    if (NeedToDrawShadow() || NeedToApplyFilter()) {
      // In this case the shadow or filter rendering will use the operator.
      return mozilla::gfx::CompositionOp::OP_OVER;
    }

    return CurrentState().op;
  }

  // text

 protected:
  enum class TextAlign : uint8_t { START, END, LEFT, RIGHT, CENTER };

  enum class TextBaseline : uint8_t {
    TOP,
    HANGING,
    MIDDLE,
    ALPHABETIC,
    IDEOGRAPHIC,
    BOTTOM
  };

  enum class TextDrawOperation : uint8_t { FILL, STROKE, MEASURE };

 protected:
  gfxFontGroup* GetCurrentFontStyle();

  /**
   * Implementation of the fillText, strokeText, and measure functions with
   * the operation abstracted to a flag.
   */
  nsresult DrawOrMeasureText(const nsAString& aText, float aX, float aY,
                             const Optional<double>& aMaxWidth,
                             TextDrawOperation aOp, float* aWidth);

  // A clip or a transform, recorded and restored in order.
  struct ClipState {
    explicit ClipState(mozilla::gfx::Path* aClip) : clip(aClip) {}

    explicit ClipState(const mozilla::gfx::Matrix& aTransform)
        : transform(aTransform) {}

    bool IsClip() const { return !!clip; }

    RefPtr<mozilla::gfx::Path> clip;
    mozilla::gfx::Matrix transform;
  };

  // state stack handling
  class ContextState {
   public:
    ContextState();
    ContextState(const ContextState& aOther);
    ~ContextState();

    void SetColorStyle(Style aWhichStyle, nscolor aColor) {
      colorStyles[aWhichStyle] = aColor;
      gradientStyles[aWhichStyle] = nullptr;
      patternStyles[aWhichStyle] = nullptr;
    }

    void SetPatternStyle(Style aWhichStyle, CanvasPattern* aPat) {
      gradientStyles[aWhichStyle] = nullptr;
      patternStyles[aWhichStyle] = aPat;
    }

    void SetGradientStyle(Style aWhichStyle, CanvasGradient* aGrad) {
      gradientStyles[aWhichStyle] = aGrad;
      patternStyles[aWhichStyle] = nullptr;
    }

    /**
     * returns true iff the given style is a solid color.
     */
    bool StyleIsColor(Style aWhichStyle) const {
      return !(patternStyles[aWhichStyle] || gradientStyles[aWhichStyle]);
    }

    int32_t ShadowBlurRadius() const {
      static const gfxFloat GAUSSIAN_SCALE_FACTOR =
          (3 * sqrt(2 * M_PI) / 4) * 1.5;
      return (int32_t)floor(ShadowBlurSigma() * GAUSSIAN_SCALE_FACTOR + 0.5);
    }

    mozilla::gfx::Float ShadowBlurSigma() const {
      return std::min(SIGMA_MAX, shadowBlur / 2.0f);
    }

    nsTArray<ClipState> clipsAndTransforms;

    RefPtr<gfxFontGroup> fontGroup;
    RefPtr<nsAtom> fontLanguage;
    nsFont fontFont;

    EnumeratedArray<Style, Style::MAX, RefPtr<CanvasGradient>> gradientStyles;
    EnumeratedArray<Style, Style::MAX, RefPtr<CanvasPattern>> patternStyles;
    EnumeratedArray<Style, Style::MAX, nscolor> colorStyles;

    nsString font;
    TextAlign textAlign = TextAlign::START;
    TextBaseline textBaseline = TextBaseline::ALPHABETIC;

    nscolor shadowColor = 0;

    mozilla::gfx::Matrix transform;
    mozilla::gfx::Point shadowOffset;
    mozilla::gfx::Float lineWidth = 1.0f;
    mozilla::gfx::Float miterLimit = 10.0f;
    mozilla::gfx::Float globalAlpha = 1.0f;
    mozilla::gfx::Float shadowBlur = 0.0f;

    nsTArray<mozilla::gfx::Float> dash;
    mozilla::gfx::Float dashOffset = 0.0f;

    mozilla::gfx::CompositionOp op = mozilla::gfx::CompositionOp::OP_OVER;
    mozilla::gfx::FillRule fillRule = mozilla::gfx::FillRule::FILL_WINDING;
    mozilla::gfx::CapStyle lineCap = mozilla::gfx::CapStyle::BUTT;
    mozilla::gfx::JoinStyle lineJoin = mozilla::gfx::JoinStyle::MITER_OR_BEVEL;

    nsString filterString = nsString(u"none");
    StyleOwnedSlice<StyleFilter> filterChain;
    // RAII object that we obtain when we start to observer SVG filter elements
    // for rendering changes.  When released we stop observing the SVG elements.
    nsCOMPtr<nsISupports> autoSVGFiltersObserver;
    mozilla::gfx::FilterDescription filter;
    nsTArray<RefPtr<mozilla::gfx::SourceSurface>> filterAdditionalImages;

    // This keeps track of whether the canvas was "tainted" or not when
    // we last used a filter. This is a security measure, whereby the
    // canvas is flipped to write-only if a cross-origin image is drawn to it.
    // This is to stop bad actors from reading back data they shouldn't have
    // access to.
    //
    // This also limits what filters we can apply to the context; in particular
    // feDisplacementMap is restricted.
    //
    // We keep track of this to ensure that if this gets out of sync with the
    // tainted state of the canvas itself, we update our filters accordingly.
    bool filterSourceGraphicTainted = false;

    bool imageSmoothingEnabled = true;
    bool fontExplicitLanguage = false;
  };

  AutoTArray<ContextState, 3> mStyleStack;

  inline ContextState& CurrentState() {
    return mStyleStack[mStyleStack.Length() - 1];
  }

  inline const ContextState& CurrentState() const {
    return mStyleStack[mStyleStack.Length() - 1];
  }

  friend class CanvasGeneralPattern;
  friend class AdjustedTarget;
  friend class AdjustedTargetForShadow;
  friend class AdjustedTargetForFilter;

  // other helpers
  void GetAppUnitsValues(int32_t* aPerDevPixel, int32_t* aPerCSSPixel) {
    // If we don't have a canvas element, we just return something generic.
    if (aPerDevPixel) {
      *aPerDevPixel = 60;
    }
    if (aPerCSSPixel) {
      *aPerCSSPixel = 60;
    }
    PresShell* presShell = GetPresShell();
    if (!presShell) {
      return;
    }
    nsPresContext* presContext = presShell->GetPresContext();
    if (!presContext) {
      return;
    }
    if (aPerDevPixel) {
      *aPerDevPixel = presContext->AppUnitsPerDevPixel();
    }
    if (aPerCSSPixel) {
      *aPerCSSPixel = AppUnitsPerCSSPixel();
    }
  }

  friend struct CanvasBidiProcessor;
  friend class CanvasDrawObserver;
  friend class ImageBitmap;

  void SetWriteOnly();

  bool IsWriteOnly() const { return mWriteOnly; }

  bool mWriteOnly;
};

size_t BindingJSObjectMallocBytes(CanvasRenderingContext2D* aContext);

}  // namespace dom
}  // namespace mozilla

#endif /* CanvasRenderingContext2D_h */