layout/style/nsStyleTransformMatrix.h

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  21  *   Keith Schwarz <kschwarz@mozilla.com> (original author)
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  36
  37 /*
  38  * A class representing three matrices that can be used for style transforms.
  39  */
  40
  41 #ifndef nsStyleTransformMatrix_h_
  42 #define nsStyleTransformMatrix_h_
  43
  44 #include "nsCSSValue.h"
  45 #include "gfxMatrix.h"
  46 #include "nsRect.h"
  47
  48 /**
  49  * A class representing a style transformation matrix.  The class actually
  50  * wraps three different matrices, a constant matrix and two matrices
  51  * whose values are scaled by the width and the height of the bounding
  52  * rectangle for the object to transform.  Thus, given a frame rectangle
  53  * of dimensions (width, height) and a point (x, y) to transform, the matrix
  54  * corresponds to the transform operation
  55  *
  56  * | a c e |   |0 0 dX1|           |0 0 dY1|           | x |
  57  *(| b d f | + |0 0 dX2| (width) + |0 0 dY2| (height)) | y |
  58  * | 0 0 1 |   |0 0   0|           |0 0   0|           | 1 |
  59  *
  60  * Note that unlike the Thebes gfxMatrix, vectors are column vectors and
  61  * consequently the multiplication of a matrix A and a vector x is Ax, not xA.
  62  */
  63 class nsStyleContext;
  64 class nsPresContext;
  65 class nsStyleTransformMatrix
  66 {
  67  public:
  68   /**
  69    * Constructor sets the matrix to the identity.
  70    */
  71   nsStyleTransformMatrix();
  72
  73   /**
  74    * Given a frame's bounding rectangle, returns a gfxMatrix
  75    * corresponding to the transformation represented by this
  76    * matrix.  The transformation takes points in the frame's
  77    * local space and converts them to points in the frame's
  78    * transformed space.
  79    *
  80    * @param aBounds The frame's bounding rectangle.
  81    * @param aFactor The number of app units per device pixel.
  82    * @return A Thebes matrix corresponding to the transform.
  83    */
  84   gfxMatrix GetThebesMatrix(const nsRect& aBounds, float aFactor) const;
  85
  86   /**
  87    * Multiplies this matrix by another matrix, in that order.  If A'
  88    * is the value of A after A *= B, then for any vector x, the
  89    * equivalence A'(x) == A(B(x)) holds.
  90    *
  91    * @param aOther The matrix to multiply this matrix by.
  92    * @return A reference to this matrix.
  93    */
  94   nsStyleTransformMatrix& operator *= (const nsStyleTransformMatrix &aOther);
  95
  96   /**
  97    * Returns a new nsStyleTransformMatrix that is equal to one matrix
  98    * multiplied by another matrix, in that order.  If C is the result of
  99    * A * B, then for any vector x, the equivalence C(x) = A(B(x)).
 100    *
 101    * @param aOther The matrix to multiply this matrix by.
 102    * @return A new nsStyleTransformMatrix equal to this matrix multiplied
 103    *         by the other matrix.
 104    */
 105   const nsStyleTransformMatrix
 106     operator * (const nsStyleTransformMatrix &aOther) const;
 107
 108   /**
 109    * Given an nsCSSValue::Array* containing a -moz-transform function,
 110    * updates this matrix to hold the value of that function.
 111    *
 112    * @param aData The nsCSSValue::Array* containing the transform function.
 113    * @param aContext The style context, used for unit conversion.
 114    * @param aPresContext The presentation context, used for unit conversion.
 115    * @param aInherited Set to true if the result cannot be cached in the rule
 116    *                   tree, otherwise untouched.
 117    */
 118   void SetToTransformFunction(const nsCSSValue::Array* aData,
 119                               nsStyleContext* aContext,
 120                               nsPresContext* aPresContext,
 121                               PRBool& aInherited);
 122
 123   /**
 124    * Sets this matrix to be the identity matrix.
 125    */
 126   void SetToIdentity();
 127
 128   /**
 129    * Returns the value of the entry at the 2x2 submatrix of the
 130    * transform matrix that defines the non-affine linear transform.
 131    * The order is given as
 132    * |elem[0]  elem[2]|
 133    * |elem[1]  elem[3]|
 134    *
 135    * @param aIndex The element index.
 136    * @return The value of the element at that index.
 137    */
 138   float GetMainMatrixEntry(PRInt32 aIndex) const
 139   {
 140     NS_PRECONDITION(aIndex >= 0 && aIndex < 4, "Index out of bounds!");
 141     return mMain[aIndex];
 142   }
 143
 144   /**
 145    * Returns the value of the X or Y translation component of the matrix,
 146    * given the specified bounds.
 147    *
 148    * @param aBounds The bounds of the element.
 149    * @return The value of the X or Ytranslation component.
 150    */
 151   nscoord GetXTranslation(const nsRect& aBounds) const;
 152   nscoord GetYTranslation(const nsRect& aBounds) const;
 153
 154   /**
 155    * Returns whether the two matrices are equal or not.
 156    *
 157    * @param aOther The matrix to compare to.
 158    * @return Whether the two matrices are equal.
 159    */
 160   PRBool operator== (const nsStyleTransformMatrix& aOther) const;
 161   PRBool operator!= (const nsStyleTransformMatrix& aOther) const
 162   {
 163     return !(*this == aOther);
 164   }
 165
 166  private:
 167   /* The three matrices look like this:
 168    * |mMain[0] mMain[2] mDelta[0]|
 169    * |mMain[1] mMain[3] mDelta[1]| <-- Constant matrix
 170    * |       0        0         1|
 171    *
 172    * |       0        0     mX[0]|
 173    * |       0        0     mX[1]| <-- Scaled by width of element
 174    * |       0        0         1|
 175    *
 176    * |       0        0     mY[0]|
 177    * |       0        0     mY[1]| <-- Scaled by height of element
 178    * |       0        0         1|
 179    */
 180   float mMain[4];
 181   nscoord mDelta[2];
 182   float mX[2];
 183   float mY[2];
 184 };
 185
 186 #endif