gecko-dev/layout/style/nsStyleTransformMatrix.h

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* 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/. */

/*
 * A class representing three matrices that can be used for style transforms.
 */

#ifndef nsStyleTransformMatrix_h_
#define nsStyleTransformMatrix_h_

#include "gfxPoint.h"
#include "mozilla/gfx/Matrix.h"
#include "mozilla/EnumeratedArray.h"
#include "nsSize.h"

#include <limits>

class nsIFrame;
class nsPresContext;
struct gfxQuaternion;
struct nsRect;

namespace mozilla {
struct MotionPathData;
}

/**
 * A helper to generate gfxMatrixes from css transform functions.
 */
namespace nsStyleTransformMatrix {
// The operator passed to Servo backend.
enum class MatrixTransformOperator : uint8_t { Interpolate, Accumulate };

// Function for applying perspective() transform function. We treat
// any value smaller than epsilon as perspective(infinity), which
// follows CSSWG's resolution on perspective(0). See bug 1316236.
inline void ApplyPerspectiveToMatrix(mozilla::gfx::Matrix4x4& aMatrix,
                                     float aDepth) {
  if (aDepth >= std::numeric_limits<float>::epsilon()) {
    aMatrix.Perspective(aDepth);
  }
}

/**
 * This class provides on-demand access to the 'reference box' for CSS
 * transforms (needed to resolve percentage values in 'transform',
 * 'transform-origin', etc.):
 *
 *    http://dev.w3.org/csswg/css-transforms/#reference-box
 *
 * This class helps us to avoid calculating the reference box unless and
 * until it is actually needed. This is important for performance when
 * transforms are applied to SVG elements since the reference box for SVG is
 * much more expensive to calculate (than for elements with a CSS layout box
 * where we can use the nsIFrame's cached mRect), much more common (than on
 * HTML), and yet very rarely have percentage values that require the
 * reference box to be resolved. We also don't want to cause SVG frames to
 * cache lots of ObjectBoundingBoxProperty objects that aren't needed.
 *
 * If UNIFIED_CONTINUATIONS (experimental, and currently broke) is defined,
 * we consider the reference box for non-SVG frames to be the smallest
 * rectangle containing a frame and all of its continuations.  For example,
 * if there is a <span> element with several continuations split over
 * several lines, this function will return the rectangle containing all of
 * those continuations. (This behavior is not currently in a spec.)
 */
class MOZ_STACK_CLASS TransformReferenceBox final {
 public:
  typedef nscoord (TransformReferenceBox::*DimensionGetter)();

  explicit TransformReferenceBox()
      : mFrame(nullptr),
        mX(0),
        mY(0),
        mWidth(0),
        mHeight(0),
        mIsCached(false) {}

  explicit TransformReferenceBox(const nsIFrame* aFrame)
      : mFrame(aFrame), mX(0), mY(0), mWidth(0), mHeight(0), mIsCached(false) {
    MOZ_ASSERT(mFrame);
  }

  explicit TransformReferenceBox(const nsIFrame* aFrame,
                                 const nsSize& aFallbackDimensions)
      : mX(0), mY(0), mWidth(0), mHeight(0) {
    mFrame = aFrame;
    mIsCached = false;
    if (!mFrame) {
      Init(aFallbackDimensions);
    }
  }

  void Init(const nsIFrame* aFrame) {
    MOZ_ASSERT(!mFrame && !mIsCached);
    mFrame = aFrame;
  }

  void Init(const nsSize& aDimensions);

  /**
   * The offset of the reference box from the nsIFrame's TopLeft(). This
   * is non-zero only in the case of SVG content. If we can successfully
   * implement UNIFIED_CONTINUATIONS at some point in the future then it
   * may also be non-zero for non-SVG content.
   */
  nscoord X() {
    EnsureDimensionsAreCached();
    return mX;
  }
  nscoord Y() {
    EnsureDimensionsAreCached();
    return mY;
  }

  /**
   * The size of the reference box.
   */
  nscoord Width() {
    EnsureDimensionsAreCached();
    return mWidth;
  }
  nscoord Height() {
    EnsureDimensionsAreCached();
    return mHeight;
  }

  bool IsEmpty() { return !mFrame; }

 private:
  // We don't really need to prevent copying, but since none of our consumers
  // currently need to copy, preventing copying may allow us to catch some
  // cases where we use pass-by-value instead of pass-by-reference.
  TransformReferenceBox(const TransformReferenceBox&) = delete;

  void EnsureDimensionsAreCached();

  const nsIFrame* mFrame;
  nscoord mX, mY, mWidth, mHeight;
  bool mIsCached;
};

float ProcessTranslatePart(
    const mozilla::LengthPercentage& aValue, TransformReferenceBox* aRefBox,
    TransformReferenceBox::DimensionGetter aDimensionGetter = nullptr);

void ProcessInterpolateMatrix(mozilla::gfx::Matrix4x4& aMatrix,
                              const mozilla::StyleTransformOperation& aOp,
                              TransformReferenceBox& aBounds);

void ProcessAccumulateMatrix(mozilla::gfx::Matrix4x4& aMatrix,
                             const mozilla::StyleTransformOperation& aOp,
                             TransformReferenceBox& aBounds);

/**
 * Given a StyleTransform containing transform functions, returns a matrix
 * containing the value of those functions.
 *
 * @param aList the transform operation list.
 * @param aBounds The frame's bounding rectangle.
 * @param aAppUnitsPerMatrixUnit The number of app units per device pixel.
 */
mozilla::gfx::Matrix4x4 ReadTransforms(const mozilla::StyleTransform& aList,
                                       TransformReferenceBox& aBounds,
                                       float aAppUnitsPerMatrixUnit);

// Generate the gfx::Matrix for CSS Transform Module Level 2.
// https://drafts.csswg.org/css-transforms-2/#ctm
mozilla::gfx::Matrix4x4 ReadTransforms(
    const mozilla::StyleTranslate&, const mozilla::StyleRotate&,
    const mozilla::StyleScale&,
    const mozilla::Maybe<mozilla::MotionPathData>& aMotion,
    const mozilla::StyleTransform&, TransformReferenceBox& aRefBox,
    float aAppUnitsPerMatrixUnit);

/**
 * Given the x and y values, compute the 2d position with respect to the given
 * TransformReferenceBox that these values describe, in CSS pixels.
 */
mozilla::CSSPoint Convert2DPosition(const mozilla::LengthPercentage& aX,
                                    const mozilla::LengthPercentage& aY,
                                    TransformReferenceBox& aRefBox);

/**
 * Given the x and y values, compute the 2d position with respect to the given
 * TransformReferenceBox that these values describe, in device pixels.
 */
mozilla::gfx::Point Convert2DPosition(const mozilla::LengthPercentage& aX,
                                      const mozilla::LengthPercentage& aY,
                                      TransformReferenceBox& aRefBox,
                                      int32_t aAppUnitsPerDevPixel);

// Shear type for decomposition.
enum class ShearType { XY, XZ, YZ, Count };
using ShearArray = mozilla::EnumeratedArray<ShearType, ShearType::Count, float>;

/*
 * Implements the 2d transform matrix decomposition algorithm.
 */
bool Decompose2DMatrix(const mozilla::gfx::Matrix& aMatrix,
                       mozilla::gfx::Point3D& aScale, ShearArray& aShear,
                       gfxQuaternion& aRotate,
                       mozilla::gfx::Point3D& aTranslate);
/*
 * Implements the 3d transform matrix decomposition algorithm.
 */
bool Decompose3DMatrix(const mozilla::gfx::Matrix4x4& aMatrix,
                       mozilla::gfx::Point3D& aScale, ShearArray& aShear,
                       gfxQuaternion& aRotate,
                       mozilla::gfx::Point3D& aTranslate,
                       mozilla::gfx::Point4D& aPerspective);

}  // namespace nsStyleTransformMatrix

#endif