dom/svg/SVGLengthList.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #ifndef DOM_SVG_SVGLENGTHLIST_H_
   8 #define DOM_SVG_SVGLENGTHLIST_H_
   9
  10 #include "nsCOMPtr.h"
  11 #include "nsDebug.h"
  12 #include "nsIContent.h"
  13 #include "nsINode.h"
  14 #include "nsIWeakReferenceUtils.h"
  15 #include "SVGElement.h"
  16 #include "nsTArray.h"
  17 #include "SVGLength.h"
  18
  19 namespace mozilla {
  20
  21 namespace dom {
  22 class DOMSVGLength;
  23 class DOMSVGLengthList;
  24 }  // namespace dom
  25
  26 /**
  27  * ATTENTION! WARNING! WATCH OUT!!
  28  *
  29  * Consumers that modify objects of this type absolutely MUST keep the DOM
  30  * wrappers for those lists (if any) in sync!! That's why this class is so
  31  * locked down.
  32  *
  33  * The DOM wrapper class for this class is DOMSVGLengthList.
  34  */
  35 class SVGLengthList {
  36   friend class dom::DOMSVGLength;
  37   friend class dom::DOMSVGLengthList;
  38   friend class SVGAnimatedLengthList;
  39
  40  public:
  41   SVGLengthList() = default;
  42   ~SVGLengthList() = default;
  43
  44   SVGLengthList& operator=(const SVGLengthList& aOther) {
  45     mLengths.ClearAndRetainStorage();
  46     // Best-effort, really.
  47     Unused << mLengths.AppendElements(aOther.mLengths, fallible);
  48     return *this;
  49   }
  50
  51   SVGLengthList(const SVGLengthList& aOther) { *this = aOther; }
  52
  53   // Only methods that don't make/permit modification to this list are public.
  54   // Only our friend classes can access methods that may change us.
  55
  56   /// This may return an incomplete string on OOM, but that's acceptable.
  57   void GetValueAsString(nsAString& aValue) const;
  58
  59   bool IsEmpty() const { return mLengths.IsEmpty(); }
  60
  61   uint32_t Length() const { return mLengths.Length(); }
  62
  63   const SVGLength& operator[](uint32_t aIndex) const {
  64     return mLengths[aIndex];
  65   }
  66
  67   bool operator==(const SVGLengthList& rhs) const;
  68
  69   bool SetCapacity(uint32_t size) {
  70     return mLengths.SetCapacity(size, fallible);
  71   }
  72
  73   void Compact() { mLengths.Compact(); }
  74
  75   // Access to methods that can modify objects of this type is deliberately
  76   // limited. This is to reduce the chances of someone modifying objects of
  77   // this type without taking the necessary steps to keep DOM wrappers in sync.
  78   // If you need wider access to these methods, consider adding a method to
  79   // SVGAnimatedLengthList and having that class act as an intermediary so it
  80   // can take care of keeping DOM wrappers in sync.
  81
  82  protected:
  83   /**
  84    * This may fail on OOM if the internal capacity needs to be increased, in
  85    * which case the list will be left unmodified.
  86    */
  87   nsresult CopyFrom(const SVGLengthList&);
  88   void SwapWith(SVGLengthList& aOther) {
  89     mLengths.SwapElements(aOther.mLengths);
  90   }
  91
  92   SVGLength& operator[](uint32_t aIndex) { return mLengths[aIndex]; }
  93
  94   /**
  95    * This may fail (return false) on OOM if the internal capacity is being
  96    * increased, in which case the list will be left unmodified.
  97    */
  98   bool SetLength(uint32_t aNumberOfItems) {
  99     return mLengths.SetLength(aNumberOfItems, fallible);
 100   }
 101
 102  private:
 103   // Marking the following private only serves to show which methods are only
 104   // used by our friend classes (as opposed to our subclasses) - it doesn't
 105   // really provide additional safety.
 106
 107   nsresult SetValueFromString(const nsAString& aValue);
 108
 109   void Clear() { mLengths.Clear(); }
 110
 111   bool InsertItem(uint32_t aIndex, const SVGLength& aLength) {
 112     if (aIndex >= mLengths.Length()) aIndex = mLengths.Length();
 113     return !!mLengths.InsertElementAt(aIndex, aLength, fallible);
 114   }
 115
 116   void ReplaceItem(uint32_t aIndex, const SVGLength& aLength) {
 117     MOZ_ASSERT(aIndex < mLengths.Length(),
 118                "DOM wrapper caller should have raised INDEX_SIZE_ERR");
 119     mLengths[aIndex] = aLength;
 120   }
 121
 122   void RemoveItem(uint32_t aIndex) {
 123     MOZ_ASSERT(aIndex < mLengths.Length(),
 124                "DOM wrapper caller should have raised INDEX_SIZE_ERR");
 125     mLengths.RemoveElementAt(aIndex);
 126   }
 127
 128   bool AppendItem(SVGLength aLength) {
 129     return !!mLengths.AppendElement(aLength, fallible);
 130   }
 131
 132  protected:
 133   /* Rationale for using nsTArray<SVGLength> and not nsTArray<SVGLength, 1>:
 134    *
 135    * It might seem like we should use AutoTArray<SVGLength, 1> instead of
 136    * nsTArray<SVGLength>. That would preallocate space for one SVGLength and
 137    * avoid an extra memory allocation call in the common case of the 'x'
 138    * and 'y' attributes each containing a single length (and the 'dx' and 'dy'
 139    * attributes being empty). However, consider this:
 140    *
 141    * An empty nsTArray uses sizeof(Header*). An AutoTArray<class E,
 142    * uint32_t N> on the other hand uses sizeof(Header*) +
 143    * (2 * sizeof(uint32_t)) + (N * sizeof(E)), which for one SVGLength is
 144    * sizeof(Header*) + 16 bytes.
 145    *
 146    * Now consider that for text elements we have four length list attributes
 147    * (x, y, dx, dy), each of which can have a baseVal and an animVal list. If
 148    * we were to go the AutoTArray<SVGLength, 1> route for each of these, we'd
 149    * end up using at least 160 bytes for these four attributes alone, even
 150    * though we only need storage for two SVGLengths (16 bytes) in the common
 151    * case!!
 152    *
 153    * A compromise might be to template SVGLengthList to allow
 154    * SVGAnimatedLengthList to preallocate space for an SVGLength for the
 155    * baseVal lists only, and that would cut the space used by the four
 156    * attributes to 96 bytes. Taking that even further and templating
 157    * SVGAnimatedLengthList too in order to only use nsTArray for 'dx' and 'dy'
 158    * would reduce the storage further to 64 bytes. Having different types makes
 159    * things more complicated for code that needs to look at the lists though.
 160    * In fact it also makes things more complicated when it comes to storing the
 161    * lists.
 162    *
 163    * It may be worth considering using nsAttrValue for length lists instead of
 164    * storing them directly on the element.
 165    */
 166   FallibleTArray<SVGLength> mLengths;
 167 };
 168
 169 /**
 170  * This SVGLengthList subclass is for SVGLengthListSMILType which needs to know
 171  * which element and attribute a length list belongs to so that it can convert
 172  * between unit types if necessary.
 173  */
 174 class SVGLengthListAndInfo : public SVGLengthList {
 175  public:
 176   SVGLengthListAndInfo() : mElement(nullptr), mAxis(0), mCanZeroPadList(true) {}
 177
 178   SVGLengthListAndInfo(dom::SVGElement* aElement, uint8_t aAxis,
 179                        bool aCanZeroPadList)
 180       : mElement(do_GetWeakReference(static_cast<nsINode*>(aElement))),
 181         mAxis(aAxis),
 182         mCanZeroPadList(aCanZeroPadList) {}
 183
 184   void SetInfo(dom::SVGElement* aElement, uint8_t aAxis, bool aCanZeroPadList) {
 185     mElement = do_GetWeakReference(static_cast<nsINode*>(aElement));
 186     mAxis = aAxis;
 187     mCanZeroPadList = aCanZeroPadList;
 188   }
 189
 190   dom::SVGElement* Element() const {
 191     nsCOMPtr<nsIContent> e = do_QueryReferent(mElement);
 192     return static_cast<dom::SVGElement*>(e.get());
 193   }
 194
 195   /**
 196    * Returns true if this object is an "identity" value, from the perspective
 197    * of SMIL. In other words, returns true until the initial value set up in
 198    * SVGLengthListSMILType::Init() has been changed with a SetInfo() call.
 199    */
 200   bool IsIdentity() const {
 201     if (!mElement) {
 202       MOZ_ASSERT(IsEmpty(), "target element propagation failure");
 203       return true;
 204     }
 205     return false;
 206   }
 207
 208   uint8_t Axis() const {
 209     MOZ_ASSERT(mElement, "Axis() isn't valid");
 210     return mAxis;
 211   }
 212
 213   /**
 214    * The value returned by this function depends on which attribute this object
 215    * is for. If appending a list of zeros to the attribute's list would have no
 216    * effect on rendering (e.g. the attributes 'dx' and 'dy' on <text>), then
 217    * this method will return true. If appending a list of zeros to the
 218    * attribute's list could *change* rendering (e.g. the attributes 'x' and 'y'
 219    * on <text>), then this method will return false.
 220    *
 221    * The reason that this method exists is because the SMIL code needs to know
 222    * what to do when it's asked to animate between lists of different length.
 223    * If this method returns true, then it can zero pad the short list before
 224    * carrying out its operations. However, in the case of the 'x' and 'y'
 225    * attributes on <text>, zero would mean "zero in the current coordinate
 226    * system", whereas we would want to pad shorter lists with the coordinates
 227    * at which glyphs would otherwise lie, which is almost certainly not zero!
 228    * Animating from/to zeros in this case would produce terrible results.
 229    *
 230    * Currently SVGLengthListSMILType simply disallows (drops) animation between
 231    * lists of different length if it can't zero pad a list. This is to avoid
 232    * having some authors create content that depends on undesirable behaviour
 233    * (which would make it difficult for us to fix the behavior in future). At
 234    * some point it would be nice to implement a callback to allow this code to
 235    * determine padding values for lists that can't be zero padded. See
 236    * https://bugzilla.mozilla.org/show_bug.cgi?id=573431
 237    */
 238   bool CanZeroPadList() const {
 239     // NS_ASSERTION(mElement, "CanZeroPadList() isn't valid");
 240     return mCanZeroPadList;
 241   }
 242
 243   // For the SMIL code. See comment in SVGLengthListSMILType::Add().
 244   void SetCanZeroPadList(bool aCanZeroPadList) {
 245     mCanZeroPadList = aCanZeroPadList;
 246   }
 247
 248   nsresult CopyFrom(const SVGLengthListAndInfo& rhs) {
 249     mElement = rhs.mElement;
 250     mAxis = rhs.mAxis;
 251     mCanZeroPadList = rhs.mCanZeroPadList;
 252     return SVGLengthList::CopyFrom(rhs);
 253   }
 254
 255   // Instances of this special subclass do not have DOM wrappers that we need
 256   // to worry about keeping in sync, so it's safe to expose any hidden base
 257   // class methods required by the SMIL code, as we do below.
 258
 259   /**
 260    * Exposed so that SVGLengthList baseVals can be copied to
 261    * SVGLengthListAndInfo objects. Note that callers should also call
 262    * SetInfo() when using this method!
 263    */
 264   nsresult CopyFrom(const SVGLengthList& rhs) {
 265     return SVGLengthList::CopyFrom(rhs);
 266   }
 267   const SVGLength& operator[](uint32_t aIndex) const {
 268     return SVGLengthList::operator[](aIndex);
 269   }
 270   SVGLength& operator[](uint32_t aIndex) {
 271     return SVGLengthList::operator[](aIndex);
 272   }
 273   bool SetLength(uint32_t aNumberOfItems) {
 274     return SVGLengthList::SetLength(aNumberOfItems);
 275   }
 276
 277  private:
 278   // We must keep a weak reference to our element because we may belong to a
 279   // cached baseVal SMILValue. See the comments starting at:
 280   // https://bugzilla.mozilla.org/show_bug.cgi?id=515116#c15
 281   // See also https://bugzilla.mozilla.org/show_bug.cgi?id=653497
 282   nsWeakPtr mElement;
 283   uint8_t mAxis;
 284   bool mCanZeroPadList;
 285 };
 286
 287 /**
 288  * This class wraps SVGLengthList objects to allow frame consumers to process
 289  * SVGLengthList objects as if they were simply a list of float values in user
 290  * units. When consumers request the value at a given index, this class
 291  * dynamically converts the corresponding SVGLength from its actual unit and
 292  * returns its value in user units.
 293  *
 294  * Consumers should check that the user unit values returned are finite. Even
 295  * if the consumer can guarantee the list's element has a valid viewport
 296  * ancestor to resolve percentage units against, and a valid presContext and
 297  * ComputedStyle to resolve absolute and em/ex units against, unit conversions
 298  * could still overflow. In that case the value returned will be
 299  * numeric_limits<float>::quiet_NaN().
 300  */
 301 class MOZ_STACK_CLASS SVGUserUnitList {
 302  public:
 303   SVGUserUnitList() : mList(nullptr), mElement(nullptr), mAxis(0) {}
 304
 305   void Init(const SVGLengthList* aList, const dom::SVGElement* aElement,
 306             uint8_t aAxis) {
 307     mList = aList;
 308     mElement = aElement;
 309     mAxis = aAxis;
 310   }
 311
 312   bool IsEmpty() const { return mList->IsEmpty(); }
 313
 314   uint32_t Length() const { return mList->Length(); }
 315
 316   /// This may return a non-finite value
 317   float operator[](uint32_t aIndex) const {
 318     return (*mList)[aIndex].GetValueInPixelsWithZoom(mElement, mAxis);
 319   }
 320
 321   bool HasPercentageValueAt(uint32_t aIndex) const {
 322     return (*mList)[aIndex].IsPercentage();
 323   }
 324
 325  private:
 326   const SVGLengthList* mList;
 327   const dom::SVGElement* mElement;
 328   uint8_t mAxis;
 329 };
 330
 331 }  // namespace mozilla
 332
 333 #endif  // DOM_SVG_SVGLENGTHLIST_H_