gecko-dev/layout/style/nsStyleTransformMatrix.h

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

#ifndef nsStyleTransformMatrix_h_
#define nsStyleTransformMatrix_h_

#include "nsCSSValue.h"
#include "gfxMatrix.h"
#include "nsRect.h"

/**
 * A class representing a style transformation matrix.  The class actually
 * wraps three different matrices, a constant matrix and two matrices
 * whose values are scaled by the width and the height of the bounding
 * rectangle for the object to transform.  Thus, given a frame rectangle
 * of dimensions (width, height) and a point (x, y) to transform, the matrix
 * corresponds to the transform operation
 *
 * | a c e |   |0 0 dX1|           |0 0 dY1|           | x |
 *(| b d f | + |0 0 dX2| (width) + |0 0 dY2| (height)) | y |
 * | 0 0 1 |   |0 0   0|           |0 0   0|           | 1 |
 *
 * Note that unlike the Thebes gfxMatrix, vectors are column vectors and
 * consequently the multiplication of a matrix A and a vector x is Ax, not xA.
 */
class nsStyleContext;
class nsPresContext;
class nsStyleTransformMatrix
{
 public:
  /**
   * Constructor sets the matrix to the identity.
   */
  nsStyleTransformMatrix();

  /**
   * Given a frame's bounding rectangle, returns a gfxMatrix
   * corresponding to the transformation represented by this
   * matrix.  The transformation takes points in the frame's
   * local space and converts them to points in the frame's
   * transformed space.
   *
   * @param aBounds The frame's bounding rectangle.
   * @param aFactor The number of app units per device pixel.
   * @return A Thebes matrix corresponding to the transform.
   */
  gfxMatrix GetThebesMatrix(const nsRect& aBounds, float aFactor) const;

  /**
   * Multiplies this matrix by another matrix, in that order.  If A'
   * is the value of A after A *= B, then for any vector x, the
   * equivalence A'(x) == A(B(x)) holds.
   *
   * @param aOther The matrix to multiply this matrix by.
   * @return A reference to this matrix.
   */
  nsStyleTransformMatrix& operator *= (const nsStyleTransformMatrix &aOther);

  /**
   * Returns a new nsStyleTransformMatrix that is equal to one matrix
   * multiplied by another matrix, in that order.  If C is the result of
   * A * B, then for any vector x, the equivalence C(x) = A(B(x)).
   *
   * @param aOther The matrix to multiply this matrix by.
   * @return A new nsStyleTransformMatrix equal to this matrix multiplied
   *         by the other matrix.
   */
  const nsStyleTransformMatrix
    operator * (const nsStyleTransformMatrix &aOther) const;

  /**
   * Given an nsCSSValue::Array* containing a -moz-transform function,
   * updates this matrix to hold the value of that function.
   *
   * @param aData The nsCSSValue::Array* containing the transform function.
   * @param aContext The style context, used for unit conversion.
   * @param aPresContext The presentation context, used for unit conversion.
   * @param aInherited Set to true if the result cannot be cached in the rule
   *                   tree, otherwise untouched.
   */
  void SetToTransformFunction(const nsCSSValue::Array* aData,
                              nsStyleContext* aContext,
                              nsPresContext* aPresContext,
                              PRBool& aInherited);

  /**
   * Sets this matrix to be the identity matrix.
   */
  void SetToIdentity();

  /**
   * Returns the value of the entry at the 2x2 submatrix of the
   * transform matrix that defines the non-affine linear transform.
   * The order is given as
   * |elem[0]  elem[2]|
   * |elem[1]  elem[3]|
   *
   * @param aIndex The element index.
   * @return The value of the element at that index.
   */
  float GetMainMatrixEntry(PRInt32 aIndex) const
  {
    NS_PRECONDITION(aIndex >= 0 && aIndex < 4, "Index out of bounds!");
    return mMain[aIndex];
  }

  /**
   * Returns the value of the X or Y translation component of the matrix,
   * given the specified bounds.
   *
   * @param aBounds The bounds of the element.
   * @return The value of the X or Ytranslation component.
   */
  nscoord GetXTranslation(const nsRect& aBounds) const;
  nscoord GetYTranslation(const nsRect& aBounds) const;

  /**
   * Returns whether the two matrices are equal or not.
   *
   * @param aOther The matrix to compare to.
   * @return Whether the two matrices are equal.
   */
  PRBool operator== (const nsStyleTransformMatrix& aOther) const;
  PRBool operator!= (const nsStyleTransformMatrix& aOther) const
  {
    return !(*this == aOther);
  }

 private:
  /* The three matrices look like this:
   * |mMain[0] mMain[2] mDelta[0]|
   * |mMain[1] mMain[3] mDelta[1]| <-- Constant matrix
   * |       0        0         1|
   *
   * |       0        0     mX[0]|
   * |       0        0     mX[1]| <-- Scaled by width of element
   * |       0        0         1|
   *
   * |       0        0     mY[0]|
   * |       0        0     mY[1]| <-- Scaled by height of element
   * |       0        0         1|
   */
  float mMain[4];
  nscoord mDelta[2];
  float mX[2];
  float mY[2];
};

#endif