dom/smil/nsISMILType.h

   1 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* This Source Code Form is subject to the terms of the Mozilla Public
   3  * License, v. 2.0. If a copy of the MPL was not distributed with this
   4  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   5
   6 #ifndef NS_ISMILTYPE_H_
   7 #define NS_ISMILTYPE_H_
   8
   9 #include "mozilla/Attributes.h"
  10 #include "nscore.h"
  11
  12 class nsSMILValue;
  13
  14 //////////////////////////////////////////////////////////////////////////////
  15 // nsISMILType: Interface for defining the basic operations needed for animating
  16 // a particular kind of data (e.g. lengths, colors, transformation matrices).
  17 //
  18 // This interface is never used directly but always through an nsSMILValue that
  19 // bundles together a pointer to a concrete implementation of this interface and
  20 // the data upon which it should operate.
  21 //
  22 // We keep the data and type separate rather than just providing different
  23 // subclasses of nsSMILValue. This is so that sizeof(nsSMILValue) is the same
  24 // for all value types, allowing us to have a type-agnostic nsTArray of
  25 // nsSMILValue objects (actual objects, not pointers). It also allows most
  26 // nsSMILValues (except those that need to allocate extra memory for their
  27 // data) to be allocated on the stack and directly assigned to one another
  28 // provided performance benefits for the animation code.
  29 //
  30 // Note that different types have different capabilities. Roughly speaking there
  31 // are probably three main types:
  32 //
  33 // +---------------------+---------------+-------------+------------------+
  34 // | CATEGORY:           | DISCRETE      | LINEAR      | ADDITIVE         |
  35 // +---------------------+---------------+-------------+------------------+
  36 // | Example:            | strings,      | path data?  | lengths,         |
  37 // |                     | color k/words?|             | RGB color values |
  38 // |                     |               |             |                  |
  39 // | -- Assign?          |     X         |    X        |    X             |
  40 // | -- Add?             |     -         |    X?       |    X             |
  41 // | -- SandwichAdd?     |     -         |    -?       |    X             |
  42 // | -- ComputeDistance? |     -         |    -        |    X?            |
  43 // | -- Interpolate?     |     -         |    X        |    X             |
  44 // +---------------------+---------------+-------------+------------------+
  45 //
  46
  47 class nsISMILType
  48 {
  49   /**
  50    * Only give the nsSMILValue class access to this interface.
  51    */
  52   friend class nsSMILValue;
  53
  54 protected:
  55   /**
  56    * Initialises aValue and sets it to some identity value such that adding
  57    * aValue to another value of the same type has no effect.
  58    *
  59    * @pre  aValue.IsNull()
  60    * @post aValue.mType == this
  61    */
  62   virtual void Init(nsSMILValue& aValue) const = 0;
  63
  64   /**
  65    * Destroys any data associated with a value of this type.
  66    *
  67    * @pre  aValue.mType == this
  68    * @post aValue.IsNull()
  69    */
  70   virtual void Destroy(nsSMILValue& aValue) const = 0;
  71
  72   /**
  73    * Assign this object the value of another. Think of this as the assignment
  74    * operator.
  75    *
  76    * @param   aDest       The left-hand side of the assignment.
  77    * @param   aSrc        The right-hand side of the assignment.
  78    * @return  NS_OK on success, an error code on failure such as when the
  79    *          underlying type of the specified object differs.
  80    *
  81    * @pre aDest.mType == aSrc.mType == this
  82    */
  83   virtual nsresult Assign(nsSMILValue& aDest,
  84                           const nsSMILValue& aSrc) const = 0;
  85
  86   /**
  87    * Test two nsSMILValue objects (of this nsISMILType) for equality.
  88    *
  89    * A return value of true represents a guarantee that aLeft and aRight are
  90    * equal. (That is, they would behave identically if passed to the methods
  91    * Add, SandwichAdd, ComputeDistance, and Interpolate).
  92    *
  93    * A return value of false simply indicates that we make no guarantee
  94    * about equality.
  95    *
  96    * NOTE: It's perfectly legal for implementations of this method to return
  97    * false in all cases.  However, smarter implementations will make this
  98    * method more useful for optimization.
  99    *
 100    * @param   aLeft       The left-hand side of the equality check.
 101    * @param   aRight      The right-hand side of the equality check.
 102    * @return  true if we're sure the values are equal, false otherwise.
 103    *
 104    * @pre aDest.mType == aSrc.mType == this
 105    */
 106   virtual bool IsEqual(const nsSMILValue& aLeft,
 107                          const nsSMILValue& aRight) const = 0;
 108
 109   /**
 110    * Adds two values.
 111    *
 112    * The count parameter facilitates repetition.
 113    *
 114    * By equation,
 115    *
 116    *   aDest += aValueToAdd * aCount
 117    *
 118    * Therefore, if aCount == 0, aDest will be unaltered.
 119    *
 120    * This method will fail if this data type is not additive or the value was
 121    * not specified using an additive syntax.
 122    *
 123    * See SVG 1.1, section 19.2.5. In particular,
 124    *
 125    *   "If a given attribute or property can take values of keywords (which are
 126    *   not additive) or numeric values (which are additive), then additive
 127    *   animations are possible if the subsequent animation uses a numeric value
 128    *   even if the base animation uses a keyword value; however, if the
 129    *   subsequent animation uses a keyword value, additive animation is not
 130    *   possible."
 131    *
 132    * If this method fails (e.g. because the data type is not additive), aDest
 133    * will be unaltered.
 134    *
 135    * @param   aDest       The value to add to.
 136    * @param   aValueToAdd The value to add.
 137    * @param   aCount      The number of times to add aValueToAdd.
 138    * @return  NS_OK on success, an error code on failure.
 139    *
 140    * @pre aValueToAdd.mType == aDest.mType == this
 141    */
 142   virtual nsresult Add(nsSMILValue& aDest,
 143                        const nsSMILValue& aValueToAdd,
 144                        uint32_t aCount) const = 0;
 145
 146   /**
 147    * Adds aValueToAdd to the underlying value in the animation sandwich, aDest.
 148    *
 149    * For most types this operation is identical to a regular Add() but for some
 150    * types (notably <animateTransform>) the operation differs. For
 151    * <animateTransform> Add() corresponds to simply adding together the
 152    * transform parameters and is used when calculating cumulative values or
 153    * by-animation values. On the other hand SandwichAdd() is used when adding to
 154    * the underlying value and requires matrix post-multiplication. (This
 155    * distinction is most clearly indicated by the SVGT1.2 test suite. It is not
 156    * obvious within the SMIL specifications.)
 157    *
 158    * @param   aDest       The value to add to.
 159    * @param   aValueToAdd The value to add.
 160    * @return  NS_OK on success, an error code on failure.
 161    *
 162    * @pre aValueToAdd.mType == aDest.mType == this
 163    */
 164   virtual nsresult SandwichAdd(nsSMILValue& aDest,
 165                                const nsSMILValue& aValueToAdd) const
 166   {
 167     return Add(aDest, aValueToAdd, 1);
 168   }
 169
 170   /**
 171    * Calculates the 'distance' between two values. This is the distance used in
 172    * paced interpolation.
 173    *
 174    * @param   aFrom     The start of the interval for which the distance should
 175    *                    be calculated.
 176    * @param   aTo       The end of the interval for which the distance should be
 177    *                    calculated.
 178    * @param   aDistance The result of the calculation.
 179    * @return  NS_OK on success, or an appropriate error code if there is no
 180    *          notion of distance for the underlying data type or the distance
 181    *          could not be calculated.
 182    *
 183    * @pre aFrom.mType == aTo.mType == this
 184    */
 185   virtual nsresult ComputeDistance(const nsSMILValue& aFrom,
 186                                    const nsSMILValue& aTo,
 187                                    double& aDistance) const = 0;
 188
 189   /**
 190    * Calculates an interpolated value between two values using the specified
 191    * proportion.
 192    *
 193    * @param   aStartVal     The value defining the start of the interval of
 194    *                        interpolation.
 195    * @param   aEndVal       The value defining the end of the interval of
 196    *                        interpolation.
 197    * @param   aUnitDistance A number between 0.0 and 1.0 (inclusive) defining
 198    *                        the distance of the interpolated value in the
 199    *                        interval.
 200    * @param   aResult       The interpolated value.
 201    * @return  NS_OK on success, NS_ERROR_FAILURE if this data type cannot be
 202    *          interpolated or NS_ERROR_OUT_OF_MEMORY if insufficient memory was
 203    *          available for storing the result.
 204    *
 205    * @pre aStartVal.mType == aEndVal.mType == aResult.mType == this
 206    */
 207   virtual nsresult Interpolate(const nsSMILValue& aStartVal,
 208                                const nsSMILValue& aEndVal,
 209                                double aUnitDistance,
 210                                nsSMILValue& aResult) const = 0;
 211 };
 212
 213 #endif // NS_ISMILTYPE_H_