gfxContext.h

/* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 * 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 GFX_CONTEXT_H
#define GFX_CONTEXT_H

#include "gfxTypes.h"

#include "gfxASurface.h"
#include "gfxPoint.h"
#include "gfxRect.h"
#include "gfxMatrix.h"
#include "gfxPattern.h"
#include "nsTArray.h"

#include "mozilla/gfx/2D.h"

typedef struct _cairo cairo_t;
class GlyphBufferAzure;

namespace mozilla {
namespace gfx {
struct RectCornerRadii;
} // namespace gfx
} // namespace mozilla

class ClipExporter;

/**
 * This is the main class for doing actual drawing. It is initialized using
 * a surface and can be drawn on. It manages various state information like
 * a current transformation matrix (CTM), a current path, current color,
 * etc.
 *
 * All drawing happens by creating a path and then stroking or filling it.
 * The functions like Rectangle and Arc do not do any drawing themselves.
 * When a path is drawn (stroked or filled), it is filled/stroked with a
 * pattern set by SetPattern, SetColor or SetSource.
 *
 * Note that the gfxContext takes coordinates in device pixels,
 * as opposed to app units.
 */
class gfxContext final {
    typedef mozilla::gfx::CapStyle CapStyle;
    typedef mozilla::gfx::CompositionOp CompositionOp;
    typedef mozilla::gfx::JoinStyle JoinStyle;
    typedef mozilla::gfx::FillRule FillRule;
    typedef mozilla::gfx::Path Path;
    typedef mozilla::gfx::Pattern Pattern;
    typedef mozilla::gfx::Rect Rect;
    typedef mozilla::gfx::RectCornerRadii RectCornerRadii;
    typedef mozilla::gfx::Size Size;

    NS_INLINE_DECL_REFCOUNTING(gfxContext)

public:
    /**
     * Initialize this context from a DrawTarget.
     * Strips any transform from aTarget.
     * aTarget will be flushed in the gfxContext's destructor.
     * If aTarget is null or invalid, nullptr is returned.  The caller
     * is responsible for handling this scenario as appropriate.
     */
    static already_AddRefed<gfxContext>
        CreateOrNull(mozilla::gfx::DrawTarget* aTarget,
                     const mozilla::gfx::Point& aDeviceOffset = mozilla::gfx::Point());

    /**
     * Create a new gfxContext wrapping aTarget and preserving aTarget's
     * transform. Note that the transform is moved from aTarget to the resulting
     * gfxContext, aTarget will no longer have its transform.
     * If aTarget is null or invalid, nullptr is returned.  The caller
     * is responsible for handling this scenario as appropriate.
     */
    static already_AddRefed<gfxContext>
        CreatePreservingTransformOrNull(mozilla::gfx::DrawTarget* aTarget);

    mozilla::gfx::DrawTarget *GetDrawTarget() { return mDT; }

    /**
     ** State
     **/
    // XXX document exactly what bits are saved
    void Save();
    void Restore();

    /**
     ** Paths & Drawing
     **/

    /**
     * Fill the current path according to the current settings.
     *
     * Does not consume the current path.
     */
    void Fill();
    void Fill(const Pattern& aPattern);

    /**
     * Forgets the current path.
     */
    void NewPath();

    /**
     * Closes the path, i.e. connects the last drawn point to the first one.
     *
     * Filling a path will implicitly close it.
     */
    void ClosePath();

    /**
     * Returns the current path.
     */
    already_AddRefed<Path> GetPath();

    /**
     * Sets the given path as the current path.
     */
    void SetPath(Path* path);

    /**
     * Moves the pen to a new point without drawing a line.
     */
    void MoveTo(const gfxPoint& pt);

    /**
     * Returns the current point in the current path.
     */
    gfxPoint CurrentPoint();

    /**
     * Draws a line from the current point to pt.
     *
     * @see MoveTo
     */
    void LineTo(const gfxPoint& pt);

    // path helpers
    /**
     * Draws a line from start to end.
     */
    void Line(const gfxPoint& start, const gfxPoint& end); // XXX snapToPixels option?

    /**
     * Draws the rectangle given by rect.
     * @param snapToPixels ?
     */
    void Rectangle(const gfxRect& rect, bool snapToPixels = false);
    void SnappedRectangle(const gfxRect& rect) { return Rectangle(rect, true); }

    /**
     ** Transformation Matrix manipulation
     **/

    /**
     * Post-multiplies 'other' onto the current CTM, i.e. this
     * matrix's transformation will take place before the previously set
     * transformations.
     */
    void Multiply(const gfxMatrix& other);

    /**
     * Replaces the current transformation matrix with matrix.
     */
    void SetMatrix(const gfxMatrix& matrix);

    /**
     * Returns the current transformation matrix.
     */
    gfxMatrix CurrentMatrix() const;

    /**
     * Converts a point from device to user coordinates using the inverse
     * transformation matrix.
     */
    gfxPoint DeviceToUser(const gfxPoint& point) const;

    /**
     * Converts a size from device to user coordinates. This does not apply
     * translation components of the matrix.
     */
    Size DeviceToUser(const Size& size) const;

    /**
     * Converts a rectangle from device to user coordinates; this has the
     * same effect as using DeviceToUser on both the rectangle's point and
     * size.
     */
    gfxRect DeviceToUser(const gfxRect& rect) const;

    /**
     * Converts a point from user to device coordinates using the transformation
     * matrix.
     */
    gfxPoint UserToDevice(const gfxPoint& point) const;

    /**
     * Converts a size from user to device coordinates. This does not apply
     * translation components of the matrix.
     */
    Size UserToDevice(const Size& size) const;

    /**
     * Converts a rectangle from user to device coordinates.  The
     * resulting rectangle is the minimum device-space rectangle that
     * encloses the user-space rectangle given.
     */
    gfxRect UserToDevice(const gfxRect& rect) const;

    /**
     * Takes the given rect and tries to align it to device pixels.  If
     * this succeeds, the method will return true, and the rect will
     * be in device coordinates (already transformed by the CTM).  If it
     * fails, the method will return false, and the rect will not be
     * changed.
     *
     * If ignoreScale is true, then snapping will take place even if
     * the CTM has a scale applied.  Snapping never takes place if
     * there is a rotation in the CTM.
     */
    bool UserToDevicePixelSnapped(gfxRect& rect, bool ignoreScale = false) const;

    /**
     * Takes the given point and tries to align it to device pixels.  If
     * this succeeds, the method will return true, and the point will
     * be in device coordinates (already transformed by the CTM).  If it
     * fails, the method will return false, and the point will not be
     * changed.
     *
     * If ignoreScale is true, then snapping will take place even if
     * the CTM has a scale applied.  Snapping never takes place if
     * there is a rotation in the CTM.
     */
    bool UserToDevicePixelSnapped(gfxPoint& pt, bool ignoreScale = false) const;

    /**
     ** Painting sources
     **/

    /**
     * Set a solid color to use for drawing.  This color is in the device color space
     * and is not transformed.
     */
    void SetDeviceColor(const mozilla::gfx::Color& aColor);

    /**
     * Gets the current color.  It's returned in the device color space.
     * returns false if there is something other than a color
     *         set as the current source (pattern, surface, etc)
     */
    bool GetDeviceColor(mozilla::gfx::Color& aColorOut);

    /**
     * Set a solid color in the sRGB color space to use for drawing.
     * If CMS is not enabled, the color is treated as a device-space color
     * and this call is identical to SetDeviceColor().
     */
    void SetColor(const mozilla::gfx::Color& aColor);

    /**
     * Uses a surface for drawing. This is a shorthand for creating a
     * pattern and setting it.
     *
     * @param offset from the source surface, to use only part of it.
     *        May need to make it negative.
     */
    void SetSource(gfxASurface *surface, const gfxPoint& offset = gfxPoint(0.0, 0.0));

    /**
     * Uses a pattern for drawing.
     */
    void SetPattern(gfxPattern *pattern);

    /**
     * Set the color that text drawn on top of transparent pixels should be
     * anti-aliased into.
     */
    void SetFontSmoothingBackgroundColor(const mozilla::gfx::Color& aColor);
    mozilla::gfx::Color GetFontSmoothingBackgroundColor();

    /**
     * Get the source pattern (solid color, normal pattern, surface, etc)
     */
    already_AddRefed<gfxPattern> GetPattern();

    /**
     ** Painting
     **/
    /**
     * Paints the current source surface/pattern everywhere in the current
     * clip region.
     */
    void Paint(gfxFloat alpha = 1.0);

    /**
     ** Painting with a Mask
     **/
    /**
     * Like Paint, except that it only draws the source where pattern is
     * non-transparent.
     */
    void Mask(mozilla::gfx::SourceSurface *aSurface, mozilla::gfx::Float aAlpha, const mozilla::gfx::Matrix& aTransform);
    void Mask(mozilla::gfx::SourceSurface *aSurface, const mozilla::gfx::Matrix& aTransform) { Mask(aSurface, 1.0f, aTransform); }
    void Mask(mozilla::gfx::SourceSurface *surface, float alpha = 1.0f, const mozilla::gfx::Point& offset = mozilla::gfx::Point());

    /**
     ** Line Properties
     **/

    void SetDash(gfxFloat *dashes, int ndash, gfxFloat offset);
    // Return true if dashing is set, false if it's not enabled or the
    // context is in an error state.  |offset| can be nullptr to mean
    // "don't care".
    bool CurrentDash(FallibleTArray<gfxFloat>& dashes, gfxFloat* offset) const;
    // Returns 0.0 if dashing isn't enabled.
    gfxFloat CurrentDashOffset() const;

    /**
     * Sets the line width that's used for line drawing.
     */
    void SetLineWidth(gfxFloat width);

    /**
     * Returns the currently set line width.
     *
     * @see SetLineWidth
     */
    gfxFloat CurrentLineWidth() const;

    /**
     * Sets the line caps, i.e. how line endings are drawn.
     */
    void SetLineCap(CapStyle cap);
    CapStyle CurrentLineCap() const;

    /**
     * Sets the line join, i.e. how the connection between two lines is
     * drawn.
     */
    void SetLineJoin(JoinStyle join);
    JoinStyle CurrentLineJoin() const;

    void SetMiterLimit(gfxFloat limit);
    gfxFloat CurrentMiterLimit() const;

    /**
     * Sets the operator used for all further drawing. The operator affects
     * how drawing something will modify the destination. For example, the
     * OVER operator will do alpha blending of source and destination, while
     * SOURCE will replace the destination with the source.
     */
    void SetOp(CompositionOp op);
    CompositionOp CurrentOp() const;

    void SetAntialiasMode(mozilla::gfx::AntialiasMode mode);
    mozilla::gfx::AntialiasMode CurrentAntialiasMode() const;

    /**
     ** Clipping
     **/

    /**
     * Clips all further drawing to the current path.
     * This does not consume the current path.
     */
    void Clip();

    /**
     * Helper functions that will create a rect path and call Clip().
     * Any current path will be destroyed by these functions!
     */
    void Clip(const Rect& rect);
    void Clip(const gfxRect& rect); // will clip to a rect
    void Clip(Path* aPath);

    void PopClip();

    /**
     * This will return the current bounds of the clip region in user
     * space.
     */
    gfxRect GetClipExtents();

    /**
     * Whether the current clip is not a simple rectangle.
     */
    bool HasComplexClip() const;

    /**
     * Returns true if the given rectangle is fully contained in the current clip.
     * This is conservative; it may return false even when the given rectangle is
     * fully contained by the current clip.
     */
    bool ClipContainsRect(const gfxRect& aRect);

     /**
      * Exports the current clip using the provided exporter.
      */
    bool ExportClip(ClipExporter& aExporter);

    /**
     * Groups
     */
    void PushGroupForBlendBack(gfxContentType content, mozilla::gfx::Float aOpacity = 1.0f,
                               mozilla::gfx::SourceSurface* aMask = nullptr,
                               const mozilla::gfx::Matrix& aMaskTransform = mozilla::gfx::Matrix());

    /**
     * Like PushGroupForBlendBack, but if the current surface is gfxContentType::COLOR and
     * content is gfxContentType::COLOR_ALPHA, makes the pushed surface gfxContentType::COLOR
     * instead and copies the contents of the current surface to the pushed
     * surface. This is good for pushing opacity groups, since blending the
     * group back to the current surface with some alpha applied will give
     * the correct results and using an opaque pushed surface gives better
     * quality and performance.
     */
    void PushGroupAndCopyBackground(gfxContentType content = gfxContentType::COLOR,
                                    mozilla::gfx::Float aOpacity = 1.0f,
                                    mozilla::gfx::SourceSurface* aMask = nullptr,
                                    const mozilla::gfx::Matrix& aMaskTransform = mozilla::gfx::Matrix());
    void PopGroupAndBlend();

    mozilla::gfx::Point GetDeviceOffset() const;

#ifdef MOZ_DUMP_PAINTING
    /**
     * Debug functions to encode the current surface as a PNG and export it.
     */

    /**
     * Writes a binary PNG file.
     */
    void WriteAsPNG(const char* aFile);

    /**
     * Write as a PNG encoded Data URL to stdout.
     */
    void DumpAsDataURI();

    /**
     * Copy a PNG encoded Data URL to the clipboard.
     */
    void CopyAsDataURI();
#endif

    static mozilla::gfx::UserDataKey sDontUseAsSourceKey;

private:

    /**
     * Initialize this context from a DrawTarget.
     * Strips any transform from aTarget.
     * aTarget will be flushed in the gfxContext's destructor.  Use the static
     * ContextForDrawTargetNoTransform() when you want this behavior, as that
     * version deals with null DrawTarget better.
     */
    explicit gfxContext(mozilla::gfx::DrawTarget *aTarget,
                        const mozilla::gfx::Point& aDeviceOffset = mozilla::gfx::Point());
    ~gfxContext();

  friend class PatternFromState;
  friend class GlyphBufferAzure;

  typedef mozilla::gfx::Matrix Matrix;
  typedef mozilla::gfx::DrawTarget DrawTarget;
  typedef mozilla::gfx::Color Color;
  typedef mozilla::gfx::StrokeOptions StrokeOptions;
  typedef mozilla::gfx::Float Float;
  typedef mozilla::gfx::PathBuilder PathBuilder;
  typedef mozilla::gfx::SourceSurface SourceSurface;

  struct AzureState {
    AzureState()
      : op(mozilla::gfx::CompositionOp::OP_OVER)
      , color(0, 0, 0, 1.0f)
      , aaMode(mozilla::gfx::AntialiasMode::SUBPIXEL)
      , patternTransformChanged(false)
      , mBlendOpacity(0.0f)
    {}

    mozilla::gfx::CompositionOp op;
    Color color;
    RefPtr<gfxPattern> pattern;
    RefPtr<gfxASurface> sourceSurfCairo;
    RefPtr<SourceSurface> sourceSurface;
    mozilla::gfx::Point sourceSurfaceDeviceOffset;
    Matrix surfTransform;
    Matrix transform;
    struct PushedClip {
      RefPtr<Path> path;
      Rect rect;
      Matrix transform;
    };
    nsTArray<PushedClip> pushedClips;
    nsTArray<Float> dashPattern;
    StrokeOptions strokeOptions;
    RefPtr<DrawTarget> drawTarget;
    mozilla::gfx::AntialiasMode aaMode;
    bool patternTransformChanged;
    Matrix patternTransform;
    Color fontSmoothingBackgroundColor;
    // This is used solely for using minimal intermediate surface size.
    mozilla::gfx::Point deviceOffset;
    // Support groups
    mozilla::gfx::Float mBlendOpacity;
    RefPtr<SourceSurface> mBlendMask;
    Matrix mBlendMaskTransform;
#ifdef DEBUG
    bool mWasPushedForBlendBack;
#endif
  };

  // This ensures mPath contains a valid path (in user space!)
  void EnsurePath();
  // This ensures mPathBuilder contains a valid PathBuilder (in user space!)
  void EnsurePathBuilder();
  void FillAzure(const Pattern& aPattern, mozilla::gfx::Float aOpacity);
  CompositionOp GetOp();
  void ChangeTransform(const mozilla::gfx::Matrix &aNewMatrix, bool aUpdatePatternTransform = true);
  Rect GetAzureDeviceSpaceClipBounds();
  Matrix GetDeviceTransform() const;
  Matrix GetDTTransform() const;

  bool mPathIsRect;
  bool mTransformChanged;
  Matrix mPathTransform;
  Rect mRect;
  RefPtr<PathBuilder> mPathBuilder;
  RefPtr<Path> mPath;
  Matrix mTransform;
  nsTArray<AzureState> mStateStack;

  AzureState &CurrentState() { return mStateStack[mStateStack.Length() - 1]; }
  const AzureState &CurrentState() const { return mStateStack[mStateStack.Length() - 1]; }

  RefPtr<DrawTarget> mDT;
};

/**
 * Sentry helper class for functions with multiple return points that need to
 * call Save() on a gfxContext and have Restore() called automatically on the
 * gfxContext before they return.
 */
class gfxContextAutoSaveRestore
{
public:
  gfxContextAutoSaveRestore() : mContext(nullptr) {}

  explicit gfxContextAutoSaveRestore(gfxContext *aContext) : mContext(aContext) {
    mContext->Save();
  }

  ~gfxContextAutoSaveRestore() {
    Restore();
  }

  void SetContext(gfxContext *aContext) {
    NS_ASSERTION(!mContext, "Not going to call Restore() on some context!!!");
    mContext = aContext;
    mContext->Save();
  }

  void EnsureSaved(gfxContext *aContext) {
    MOZ_ASSERT(!mContext || mContext == aContext, "wrong context");
    if (!mContext) {
        mContext = aContext;
        mContext->Save();
    }
  }

  void Restore() {
    if (mContext) {
      mContext->Restore();
      mContext = nullptr;
    }
  }

private:
  gfxContext *mContext;
};

/**
 * Sentry helper class for functions with multiple return points that need to
 * back up the current matrix of a context and have it automatically restored
 * before they return.
 */
class gfxContextMatrixAutoSaveRestore
{
public:
    gfxContextMatrixAutoSaveRestore() :
      mContext(nullptr)
    {
    }

    explicit gfxContextMatrixAutoSaveRestore(gfxContext *aContext) :
      mContext(aContext), mMatrix(aContext->CurrentMatrix())
    {
    }

    ~gfxContextMatrixAutoSaveRestore()
    {
      if (mContext) {
        mContext->SetMatrix(mMatrix);
      }
    }

    void SetContext(gfxContext *aContext)
    {
      NS_ASSERTION(!mContext,
                   "Not going to restore the matrix on some context!");
      mContext = aContext;
      mMatrix = aContext->CurrentMatrix();
    }

    void Restore()
    {
      if (mContext) {
        mContext->SetMatrix(mMatrix);
        mContext = nullptr;
      }
    }

    const gfxMatrix& Matrix()
    {
      MOZ_ASSERT(mContext, "mMatrix doesn't contain a useful matrix");
      return mMatrix;
    }

    bool HasMatrix() const { return !!mContext; }

private:
    gfxContext *mContext;
    gfxMatrix   mMatrix;
};


class DrawTargetAutoDisableSubpixelAntialiasing {
public:
    typedef mozilla::gfx::DrawTarget DrawTarget;

    DrawTargetAutoDisableSubpixelAntialiasing(DrawTarget *aDT, bool aDisable)
    {
        if (aDisable) {
            mDT = aDT;
            mSubpixelAntialiasingEnabled = mDT->GetPermitSubpixelAA();
            mDT->SetPermitSubpixelAA(false);
        }
    }
    ~DrawTargetAutoDisableSubpixelAntialiasing()
    {
        if (mDT) {
            mDT->SetPermitSubpixelAA(mSubpixelAntialiasingEnabled);
        }
    }

private:
    RefPtr<DrawTarget> mDT;
    bool mSubpixelAntialiasingEnabled;
};

/* This class lives on the stack and allows gfxContext users to easily, and
 * performantly get a gfx::Pattern to use for drawing in their current context.
 */
class PatternFromState
{
public:
  explicit PatternFromState(gfxContext *aContext) : mContext(aContext), mPattern(nullptr) {}
  ~PatternFromState() { if (mPattern) { mPattern->~Pattern(); } }

  operator mozilla::gfx::Pattern&();

private:
  union {
    mozilla::AlignedStorage2<mozilla::gfx::ColorPattern> mColorPattern;
    mozilla::AlignedStorage2<mozilla::gfx::SurfacePattern> mSurfacePattern;
  };

  gfxContext *mContext;
  mozilla::gfx::Pattern *mPattern;
};

/* This interface should be implemented to handle exporting the clip from a context.
 */
class ClipExporter : public mozilla::gfx::PathSink {
public:
  virtual void BeginClip(const mozilla::gfx::Matrix& aMatrix) = 0;
  virtual void EndClip() = 0;
};

#endif /* GFX_CONTEXT_H */