/* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 2 -*-
 * 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 MOZILLA_GFX_HELPERSD2D_H_
#define MOZILLA_GFX_HELPERSD2D_H_

#include <d2d1_1.h>

#include <vector>

#include <dwrite.h>
#include <versionhelpers.h>
#include "2D.h"
#include "Logging.h"
#include "Tools.h"
#include "ImageScaling.h"

#include "ScaledFontDWrite.h"

#undef min
#undef max

namespace mozilla {
namespace gfx {

ID2D1Factory* D2DFactory();

ID2D1Factory1* D2DFactory1();

static inline D2D1_POINT_2F D2DPoint(const Point &aPoint)
{
  return D2D1::Point2F(aPoint.x, aPoint.y);
}

static inline D2D1_SIZE_U D2DIntSize(const IntSize &aSize)
{
  return D2D1::SizeU(aSize.width, aSize.height);
}

template <typename T>
static inline D2D1_RECT_F D2DRect(const T &aRect)
{
  return D2D1::RectF(aRect.x, aRect.y, aRect.XMost(), aRect.YMost());
}

static inline D2D1_EXTEND_MODE D2DExtend(ExtendMode aExtendMode, Axis aAxis)
{
  D2D1_EXTEND_MODE extend;
  switch (aExtendMode) {
  case ExtendMode::REPEAT:
    extend = D2D1_EXTEND_MODE_WRAP;
    break;
  case ExtendMode::REPEAT_X:
  {
    extend = aAxis == Axis::X_AXIS
             ? D2D1_EXTEND_MODE_WRAP
             : D2D1_EXTEND_MODE_CLAMP;
    break;
  }
  case ExtendMode::REPEAT_Y:
  {
    extend = aAxis == Axis::Y_AXIS
             ? D2D1_EXTEND_MODE_WRAP
             : D2D1_EXTEND_MODE_CLAMP;
    break;
  }
  case ExtendMode::REFLECT:
    extend = D2D1_EXTEND_MODE_MIRROR;
    break;
  default:
    extend = D2D1_EXTEND_MODE_CLAMP;
  }

  return extend;
}

static inline D2D1_BITMAP_INTERPOLATION_MODE D2DFilter(const Filter &aFilter)
{
  switch (aFilter) {
  case Filter::POINT:
    return D2D1_BITMAP_INTERPOLATION_MODE_NEAREST_NEIGHBOR;
  default:
    return D2D1_BITMAP_INTERPOLATION_MODE_LINEAR;
  }
}

static inline D2D1_INTERPOLATION_MODE D2DInterpolationMode(const Filter &aFilter)
{
  switch (aFilter) {
  case Filter::POINT:
    return D2D1_INTERPOLATION_MODE_NEAREST_NEIGHBOR;
  default:
    return D2D1_INTERPOLATION_MODE_LINEAR;
  }
}

static inline D2D1_MATRIX_5X4_F D2DMatrix5x4(const Matrix5x4 &aMatrix)
{
  return D2D1::Matrix5x4F(aMatrix._11, aMatrix._12, aMatrix._13, aMatrix._14,
                          aMatrix._21, aMatrix._22, aMatrix._23, aMatrix._24,
                          aMatrix._31, aMatrix._32, aMatrix._33, aMatrix._34,
                          aMatrix._41, aMatrix._42, aMatrix._43, aMatrix._44,
                          aMatrix._51, aMatrix._52, aMatrix._53, aMatrix._54);
}

static inline D2D1_VECTOR_3F D2DVector3D(const Point3D &aPoint)
{
  return D2D1::Vector3F(aPoint.x, aPoint.y, aPoint.z);
}

static inline D2D1_ANTIALIAS_MODE D2DAAMode(AntialiasMode aMode)
{
  switch (aMode) {
  case AntialiasMode::NONE:
    return D2D1_ANTIALIAS_MODE_ALIASED;
  default:
    return D2D1_ANTIALIAS_MODE_PER_PRIMITIVE;
  }
}

static inline D2D1_MATRIX_3X2_F D2DMatrix(const Matrix &aTransform)
{
  return D2D1::Matrix3x2F(aTransform._11, aTransform._12,
                          aTransform._21, aTransform._22,
                          aTransform._31, aTransform._32);
}

static inline D2D1_COLOR_F D2DColor(const Color &aColor)
{
  return D2D1::ColorF(aColor.r, aColor.g, aColor.b, aColor.a);
}

static inline IntSize ToIntSize(const D2D1_SIZE_U &aSize)
{
  return IntSize(aSize.width, aSize.height);
}

static inline SurfaceFormat ToPixelFormat(const D2D1_PIXEL_FORMAT &aFormat)
{
  switch(aFormat.format) {
  case DXGI_FORMAT_A8_UNORM:
  case DXGI_FORMAT_R8_UNORM:
    return SurfaceFormat::A8;
  case DXGI_FORMAT_B8G8R8A8_UNORM:
    if (aFormat.alphaMode == D2D1_ALPHA_MODE_IGNORE) {
      return SurfaceFormat::B8G8R8X8;
    } else {
      return SurfaceFormat::B8G8R8A8;
    }
  default:
    return SurfaceFormat::B8G8R8A8;
  }
}

static inline Rect ToRect(const D2D1_RECT_F &aRect)
{
  return Rect(aRect.left, aRect.top, aRect.right - aRect.left, aRect.bottom - aRect.top);
}

static inline Matrix ToMatrix(const D2D1_MATRIX_3X2_F &aTransform)
{
  return Matrix(aTransform._11, aTransform._12,
                aTransform._21, aTransform._22,
                aTransform._31, aTransform._32);
}

static inline Point ToPoint(const D2D1_POINT_2F &aPoint)
{
  return Point(aPoint.x, aPoint.y);
}

static inline DXGI_FORMAT DXGIFormat(SurfaceFormat aFormat)
{
  switch (aFormat) {
  case SurfaceFormat::B8G8R8A8:
    return DXGI_FORMAT_B8G8R8A8_UNORM;
  case SurfaceFormat::B8G8R8X8:
    return DXGI_FORMAT_B8G8R8A8_UNORM;
  case SurfaceFormat::A8:
    return DXGI_FORMAT_A8_UNORM;
  default:
    return DXGI_FORMAT_UNKNOWN;
  }
}

static inline D2D1_ALPHA_MODE D2DAlphaModeForFormat(SurfaceFormat aFormat)
{
  switch (aFormat) {
  case SurfaceFormat::B8G8R8X8:
    return D2D1_ALPHA_MODE_IGNORE;
  default:
    return D2D1_ALPHA_MODE_PREMULTIPLIED;
  }
}

static inline D2D1_PIXEL_FORMAT D2DPixelFormat(SurfaceFormat aFormat)
{
  return D2D1::PixelFormat(DXGIFormat(aFormat), D2DAlphaModeForFormat(aFormat));
}

static inline bool D2DSupportsCompositeMode(CompositionOp aOp)
{
  switch(aOp) {
  case CompositionOp::OP_OVER:
  case CompositionOp::OP_ADD:
  case CompositionOp::OP_ATOP:
  case CompositionOp::OP_OUT:
  case CompositionOp::OP_IN:
  case CompositionOp::OP_SOURCE:
  case CompositionOp::OP_DEST_IN:
  case CompositionOp::OP_DEST_OUT:
  case CompositionOp::OP_DEST_OVER:
  case CompositionOp::OP_DEST_ATOP:
  case CompositionOp::OP_XOR:
    return true;
  default:
    return false;
  }
}

static inline D2D1_COMPOSITE_MODE D2DCompositionMode(CompositionOp aOp)
{
  switch(aOp) {
  case CompositionOp::OP_OVER:
    return D2D1_COMPOSITE_MODE_SOURCE_OVER;
  case CompositionOp::OP_ADD:
    return D2D1_COMPOSITE_MODE_PLUS;
  case CompositionOp::OP_ATOP:
    return D2D1_COMPOSITE_MODE_SOURCE_ATOP;
  case CompositionOp::OP_OUT:
    return D2D1_COMPOSITE_MODE_SOURCE_OUT;
  case CompositionOp::OP_IN:
    return D2D1_COMPOSITE_MODE_SOURCE_IN;
  case CompositionOp::OP_SOURCE:
    return D2D1_COMPOSITE_MODE_SOURCE_COPY;
  case CompositionOp::OP_DEST_IN:
    return D2D1_COMPOSITE_MODE_DESTINATION_IN;
  case CompositionOp::OP_DEST_OUT:
    return D2D1_COMPOSITE_MODE_DESTINATION_OUT;
  case CompositionOp::OP_DEST_OVER:
    return D2D1_COMPOSITE_MODE_DESTINATION_OVER;
  case CompositionOp::OP_DEST_ATOP:
    return D2D1_COMPOSITE_MODE_DESTINATION_ATOP;
  case CompositionOp::OP_XOR:
    return D2D1_COMPOSITE_MODE_XOR;
  default:
    return D2D1_COMPOSITE_MODE_SOURCE_OVER;
  }
}

static inline D2D1_BLEND_MODE D2DBlendMode(CompositionOp aOp)
{
  switch (aOp) {
  case CompositionOp::OP_MULTIPLY:
    return D2D1_BLEND_MODE_MULTIPLY;
  case CompositionOp::OP_SCREEN:
    return D2D1_BLEND_MODE_SCREEN;
  case CompositionOp::OP_OVERLAY:
    return D2D1_BLEND_MODE_OVERLAY;
  case CompositionOp::OP_DARKEN:
    return D2D1_BLEND_MODE_DARKEN;
  case CompositionOp::OP_LIGHTEN:
    return D2D1_BLEND_MODE_LIGHTEN;
  case CompositionOp::OP_COLOR_DODGE:
    return D2D1_BLEND_MODE_COLOR_DODGE;
  case CompositionOp::OP_COLOR_BURN:
    return D2D1_BLEND_MODE_COLOR_BURN;
  case CompositionOp::OP_HARD_LIGHT:
    return D2D1_BLEND_MODE_HARD_LIGHT;
  case CompositionOp::OP_SOFT_LIGHT:
    return D2D1_BLEND_MODE_SOFT_LIGHT;
  case CompositionOp::OP_DIFFERENCE:
    return D2D1_BLEND_MODE_DIFFERENCE;
  case CompositionOp::OP_EXCLUSION:
    return D2D1_BLEND_MODE_EXCLUSION;
  case CompositionOp::OP_HUE:
    return D2D1_BLEND_MODE_HUE;
  case CompositionOp::OP_SATURATION:
    return D2D1_BLEND_MODE_SATURATION;
  case CompositionOp::OP_COLOR:
    return D2D1_BLEND_MODE_COLOR;
  case CompositionOp::OP_LUMINOSITY:
    return D2D1_BLEND_MODE_LUMINOSITY;
  default:
    return D2D1_BLEND_MODE_MULTIPLY;
  }
}

static inline bool D2DSupportsPrimitiveBlendMode(CompositionOp aOp)
{
  switch (aOp) {
    case CompositionOp::OP_OVER:
//  case CompositionOp::OP_SOURCE:
      return true;
//  case CompositionOp::OP_DARKEN:
    case CompositionOp::OP_ADD:
      return IsWindows8Point1OrGreater();
    default:
      return false;
  }
}

static inline D2D1_PRIMITIVE_BLEND D2DPrimitiveBlendMode(CompositionOp aOp)
{
  switch (aOp) {
    case CompositionOp::OP_OVER:
      return D2D1_PRIMITIVE_BLEND_SOURCE_OVER;
    // D2D1_PRIMITIVE_BLEND_COPY should leave pixels out of the source's
    // bounds unchanged, but doesn't- breaking unbounded ops.
    // D2D1_PRIMITIVE_BLEND_MIN doesn't quite work like darken either, as it
    // accounts for the source alpha.
    //
    // case CompositionOp::OP_SOURCE:
    //   return D2D1_PRIMITIVE_BLEND_COPY;
    // case CompositionOp::OP_DARKEN:
    //   return D2D1_PRIMITIVE_BLEND_MIN;
    case CompositionOp::OP_ADD:
      return D2D1_PRIMITIVE_BLEND_ADD;
    default:
      return D2D1_PRIMITIVE_BLEND_SOURCE_OVER;
  }
}

static inline bool IsPatternSupportedByD2D(const Pattern &aPattern)
{
  if (aPattern.GetType() != PatternType::RADIAL_GRADIENT) {
    return true;
  }

  const RadialGradientPattern *pat =
    static_cast<const RadialGradientPattern*>(&aPattern);
  
  if (pat->mRadius1 != 0) {
    return false;
  }

  Point diff = pat->mCenter2 - pat->mCenter1;

  if (sqrt(diff.x * diff.x + diff.y * diff.y) >= pat->mRadius2) {
    // Inner point lies outside the circle.
    return false;
  }

  return true;
}

/**
 * This structure is used to pass rectangles to our shader constant. We can use
 * this for passing rectangular areas to SetVertexShaderConstant. In the format
 * of a 4 component float(x,y,width,height). Our vertex shader can then use
 * this to construct rectangular positions from the 0,0-1,1 quad that we source
 * it with.
 */
struct ShaderConstantRectD3D10
{
  float mX, mY, mWidth, mHeight;
  ShaderConstantRectD3D10(float aX, float aY, float aWidth, float aHeight)
    : mX(aX), mY(aY), mWidth(aWidth), mHeight(aHeight)
  { }

  // For easy passing to SetVertexShaderConstantF.
  operator float* () { return &mX; }
};

static inline DWRITE_MATRIX
DWriteMatrixFromMatrix(Matrix &aMatrix)
{
  DWRITE_MATRIX mat;
  mat.m11 = aMatrix._11;
  mat.m12 = aMatrix._12;
  mat.m21 = aMatrix._21;
  mat.m22 = aMatrix._22;
  mat.dx = aMatrix._31;
  mat.dy = aMatrix._32;
  return mat;
}

class AutoDWriteGlyphRun : public DWRITE_GLYPH_RUN
{
    static const unsigned kNumAutoGlyphs = 256;

public:
    AutoDWriteGlyphRun() {
        glyphCount = 0;
    }

    ~AutoDWriteGlyphRun() {
        if (glyphCount > kNumAutoGlyphs) {
            delete[] glyphIndices;
            delete[] glyphAdvances;
            delete[] glyphOffsets;
        }
    }

    void allocate(unsigned aNumGlyphs) {
        glyphCount = aNumGlyphs;
        if (aNumGlyphs <= kNumAutoGlyphs) {
            glyphIndices = &mAutoIndices[0];
            glyphAdvances = &mAutoAdvances[0];
            glyphOffsets = &mAutoOffsets[0];
        } else {
            glyphIndices = new UINT16[aNumGlyphs];
            glyphAdvances = new FLOAT[aNumGlyphs];
            glyphOffsets = new DWRITE_GLYPH_OFFSET[aNumGlyphs];
        }
    }

private:
    DWRITE_GLYPH_OFFSET mAutoOffsets[kNumAutoGlyphs];
    FLOAT               mAutoAdvances[kNumAutoGlyphs];
    UINT16              mAutoIndices[kNumAutoGlyphs];
};

static inline void
DWriteGlyphRunFromGlyphs(const GlyphBuffer &aGlyphs, ScaledFontDWrite *aFont, AutoDWriteGlyphRun *run)
{
  run->allocate(aGlyphs.mNumGlyphs);

  FLOAT *advances = const_cast<FLOAT*>(run->glyphAdvances);
  UINT16 *indices = const_cast<UINT16*>(run->glyphIndices);
  DWRITE_GLYPH_OFFSET *offsets = const_cast<DWRITE_GLYPH_OFFSET*>(run->glyphOffsets);

  memset(advances, 0, sizeof(FLOAT) * aGlyphs.mNumGlyphs);
  for (unsigned int i = 0; i < aGlyphs.mNumGlyphs; i++) {
    indices[i] = aGlyphs.mGlyphs[i].mIndex;
    offsets[i].advanceOffset = aGlyphs.mGlyphs[i].mPosition.x;
    offsets[i].ascenderOffset = -aGlyphs.mGlyphs[i].mPosition.y;
  }
    
  run->bidiLevel = 0;
  run->fontFace = aFont->mFontFace;
  run->fontEmSize = aFont->GetSize();
  run->glyphCount = aGlyphs.mNumGlyphs;
  run->isSideways = FALSE;
}

static inline already_AddRefed<ID2D1Geometry>
ConvertRectToGeometry(const D2D1_RECT_F& aRect)
{
  RefPtr<ID2D1RectangleGeometry> rectGeom;
  D2DFactory()->CreateRectangleGeometry(&aRect, getter_AddRefs(rectGeom));
  return rectGeom.forget();
}

static inline already_AddRefed<ID2D1Geometry>
GetTransformedGeometry(ID2D1Geometry *aGeometry, const D2D1_MATRIX_3X2_F &aTransform)
{
  RefPtr<ID2D1PathGeometry> tmpGeometry;
  D2DFactory()->CreatePathGeometry(getter_AddRefs(tmpGeometry));
  RefPtr<ID2D1GeometrySink> currentSink;
  tmpGeometry->Open(getter_AddRefs(currentSink));
  aGeometry->Simplify(D2D1_GEOMETRY_SIMPLIFICATION_OPTION_CUBICS_AND_LINES,
                      aTransform, currentSink);
  currentSink->Close();
  return tmpGeometry.forget();
}

static inline already_AddRefed<ID2D1Geometry>
IntersectGeometry(ID2D1Geometry *aGeometryA, ID2D1Geometry *aGeometryB)
{
  RefPtr<ID2D1PathGeometry> pathGeom;
  D2DFactory()->CreatePathGeometry(getter_AddRefs(pathGeom));
  RefPtr<ID2D1GeometrySink> sink;
  pathGeom->Open(getter_AddRefs(sink));
  aGeometryA->CombineWithGeometry(aGeometryB, D2D1_COMBINE_MODE_INTERSECT, nullptr, sink);
  sink->Close();

  return pathGeom.forget();
}

static inline already_AddRefed<ID2D1StrokeStyle>
CreateStrokeStyleForOptions(const StrokeOptions &aStrokeOptions)
{
  RefPtr<ID2D1StrokeStyle> style;

  D2D1_CAP_STYLE capStyle;
  D2D1_LINE_JOIN joinStyle;

  switch (aStrokeOptions.mLineCap) {
  case CapStyle::BUTT:
    capStyle = D2D1_CAP_STYLE_FLAT;
    break;
  case CapStyle::ROUND:
    capStyle = D2D1_CAP_STYLE_ROUND;
    break;
  case CapStyle::SQUARE:
    capStyle = D2D1_CAP_STYLE_SQUARE;
    break;
  }

  switch (aStrokeOptions.mLineJoin) {
  case JoinStyle::MITER:
    joinStyle = D2D1_LINE_JOIN_MITER;
    break;
  case JoinStyle::MITER_OR_BEVEL:
    joinStyle = D2D1_LINE_JOIN_MITER_OR_BEVEL;
    break;
  case JoinStyle::ROUND:
    joinStyle = D2D1_LINE_JOIN_ROUND;
    break;
  case JoinStyle::BEVEL:
    joinStyle = D2D1_LINE_JOIN_BEVEL;
    break;
  }


  HRESULT hr;
  // We need to check mDashLength in addition to mDashPattern here since if
  // mDashPattern is set but mDashLength is zero then the stroke will fail to
  // paint.
  if (aStrokeOptions.mDashLength > 0 && aStrokeOptions.mDashPattern) {
    typedef std::vector<Float> FloatVector;
    // D2D "helpfully" multiplies the dash pattern by the line width.
    // That's not what cairo does, or is what <canvas>'s dash wants.
    // So fix the multiplication in advance.
    Float lineWidth = aStrokeOptions.mLineWidth;
    FloatVector dash(aStrokeOptions.mDashPattern,
                     aStrokeOptions.mDashPattern + aStrokeOptions.mDashLength);
    for (FloatVector::iterator it = dash.begin(); it != dash.end(); ++it) {
      *it /= lineWidth;
    }

    hr = D2DFactory()->CreateStrokeStyle(
      D2D1::StrokeStyleProperties(capStyle, capStyle,
                                  capStyle, joinStyle,
                                  aStrokeOptions.mMiterLimit,
                                  D2D1_DASH_STYLE_CUSTOM,
                                  aStrokeOptions.mDashOffset / lineWidth),
      &dash[0], // data() is not C++98, although it's in recent gcc
                // and VC10's STL
      dash.size(),
      getter_AddRefs(style));
  } else {
    hr = D2DFactory()->CreateStrokeStyle(
      D2D1::StrokeStyleProperties(capStyle, capStyle,
                                  capStyle, joinStyle,
                                  aStrokeOptions.mMiterLimit),
      nullptr, 0, getter_AddRefs(style));
  }

  if (FAILED(hr)) {
    gfxWarning() << "Failed to create Direct2D stroke style.";
  }

  return style.forget();
}

// This creates a (partially) uploaded bitmap for a DataSourceSurface. It
// uploads the minimum requirement and possibly downscales. It adjusts the
// input Matrix to compensate.
static inline already_AddRefed<ID2D1Bitmap>
CreatePartialBitmapForSurface(DataSourceSurface *aSurface, const Matrix &aDestinationTransform,
                              const IntSize &aDestinationSize, ExtendMode aExtendMode,
                              Matrix &aSourceTransform, ID2D1RenderTarget *aRT,
                              const IntRect* aSourceRect = nullptr)
{
  RefPtr<ID2D1Bitmap> bitmap;

  // This is where things get complicated. The source surface was
  // created for a surface that was too large to fit in a texture.
  // We'll need to figure out if we can work with a partial upload
  // or downsample in software.

  Matrix transform = aDestinationTransform;
  Matrix invTransform = transform = aSourceTransform * transform;
  if (!invTransform.Invert()) {
    // Singular transform, nothing to be drawn.
    return nullptr;
  }

  Rect rect(0, 0, Float(aDestinationSize.width), Float(aDestinationSize.height));

  // Calculate the rectangle of the source mapped to our surface.
  rect = invTransform.TransformBounds(rect);
  rect.RoundOut();

  IntSize size = aSurface->GetSize();

  Rect uploadRect(0, 0, Float(size.width), Float(size.height));
  if (aSourceRect) {
    uploadRect = Rect(aSourceRect->x, aSourceRect->y, aSourceRect->width, aSourceRect->height);
  }

  // Limit the uploadRect as much as possible without supporting discontiguous uploads 
  //
  //                               region we will paint from
  //   uploadRect
  //   .---------------.              .---------------.         resulting uploadRect
  //   |               |rect          |               |
  //   |          .---------.         .----.     .----.          .---------------.
  //   |          |         |  ---->  |    |     |    |   ---->  |               |
  //   |          '---------'         '----'     '----'          '---------------'
  //   '---------------'              '---------------'
  //
  //

  if (uploadRect.Contains(rect)) {
    // Extend mode is irrelevant, the displayed rect is completely contained
    // by the source bitmap.
    uploadRect = rect;
  } else if (aExtendMode == ExtendMode::CLAMP && uploadRect.Intersects(rect)) {
    // Calculate the rectangle on the source bitmap that touches our
    // surface, and upload that, for ExtendMode::CLAMP we can actually guarantee
    // correct behaviour in this case.
    uploadRect = uploadRect.Intersect(rect);

    // We now proceed to check if we can limit at least one dimension of the
    // upload rect safely without looking at extend mode.
  } else if (rect.x >= 0 && rect.XMost() < size.width) {
    uploadRect.x = rect.x;
    uploadRect.width = rect.width;
  } else if (rect.y >= 0 && rect.YMost() < size.height) {
    uploadRect.y = rect.y;
    uploadRect.height = rect.height;
  }

  if (uploadRect.width <= aRT->GetMaximumBitmapSize() &&
      uploadRect.height <= aRT->GetMaximumBitmapSize()) {
    {
      // Scope to auto-Unmap() |mapping|.
      DataSourceSurface::ScopedMap mapping(aSurface, DataSourceSurface::READ);
      if (MOZ2D_WARN_IF(!mapping.IsMapped())) {
        return nullptr;
      }

      // A partial upload will suffice.
      aRT->CreateBitmap(D2D1::SizeU(uint32_t(uploadRect.width), uint32_t(uploadRect.height)),
                        mapping.GetData() + int(uploadRect.x) * 4 + int(uploadRect.y) * mapping.GetStride(),
                        mapping.GetStride(),
                        D2D1::BitmapProperties(D2DPixelFormat(aSurface->GetFormat())),
                        getter_AddRefs(bitmap));
    }

    aSourceTransform.PreTranslate(uploadRect.x, uploadRect.y);

    return bitmap.forget();
  } else {
    int Bpp = BytesPerPixel(aSurface->GetFormat());

    if (Bpp != 4) {
      // This shouldn't actually happen in practice!
      MOZ_ASSERT(false);
      return nullptr;
    }

    {
      // Scope to auto-Unmap() |mapping|.
      DataSourceSurface::ScopedMap mapping(aSurface, DataSourceSurface::READ);
      if (MOZ2D_WARN_IF(!mapping.IsMapped())) {
        return nullptr;
      }
      ImageHalfScaler scaler(mapping.GetData(), mapping.GetStride(), size);

      // Calculate the maximum width/height of the image post transform.
      Point topRight = transform * Point(Float(size.width), 0);
      Point topLeft = transform * Point(0, 0);
      Point bottomRight = transform * Point(Float(size.width), Float(size.height));
      Point bottomLeft = transform * Point(0, Float(size.height));

      IntSize scaleSize;

      scaleSize.width = int32_t(std::max(Distance(topRight, topLeft),
                                         Distance(bottomRight, bottomLeft)));
      scaleSize.height = int32_t(std::max(Distance(topRight, bottomRight),
                                          Distance(topLeft, bottomLeft)));

      if (unsigned(scaleSize.width) > aRT->GetMaximumBitmapSize()) {
        // Ok, in this case we'd really want a downscale of a part of the bitmap,
        // perhaps we can do this later but for simplicity let's do something
        // different here and assume it's good enough, this should be rare!
        scaleSize.width = 4095;
      }
      if (unsigned(scaleSize.height) > aRT->GetMaximumBitmapSize()) {
        scaleSize.height = 4095;
      }

      scaler.ScaleForSize(scaleSize);

      IntSize newSize = scaler.GetSize();

      if (newSize.IsEmpty()) {
        return nullptr;
      }

      aRT->CreateBitmap(D2D1::SizeU(newSize.width, newSize.height),
                        scaler.GetScaledData(), scaler.GetStride(),
                        D2D1::BitmapProperties(D2DPixelFormat(aSurface->GetFormat())),
                        getter_AddRefs(bitmap));

      aSourceTransform.PreScale(Float(size.width) / newSize.width,
                                Float(size.height) / newSize.height);
    }
    return bitmap.forget();
  }
}

}
}

#endif /* MOZILLA_GFX_HELPERSD2D_H_ */