tor-browser

SVGLengthList.h (12297B)

---

/* -*- 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/. */

#ifndef DOM_SVG_SVGLENGTHLIST_H_
#define DOM_SVG_SVGLENGTHLIST_H_

#include "SVGElement.h"
#include "SVGLength.h"
#include "nsCOMPtr.h"
#include "nsDebug.h"
#include "nsIContent.h"
#include "nsINode.h"
#include "nsIWeakReferenceUtils.h"
#include "nsTArray.h"

namespace mozilla {

namespace dom {
class DOMSVGLength;
class DOMSVGLengthList;
}  // namespace dom

/**
* ATTENTION! WARNING! WATCH OUT!!
*
* Consumers that modify objects of this type absolutely MUST keep the DOM
* wrappers for those lists (if any) in sync!! That's why this class is so
* locked down.
*
* The DOM wrapper class for this class is DOMSVGLengthList.
*/
class SVGLengthList {
 friend class dom::DOMSVGLength;
 friend class dom::DOMSVGLengthList;
 friend class SVGAnimatedLengthList;

public:
 SVGLengthList() = default;
 ~SVGLengthList() = default;

 SVGLengthList& operator=(const SVGLengthList& aOther) {
   mLengths.ClearAndRetainStorage();
   // Best-effort, really.
   (void)mLengths.AppendElements(aOther.mLengths, fallible);
   return *this;
 }

 SVGLengthList(const SVGLengthList& aOther) { *this = aOther; }

 // Only methods that don't make/permit modification to this list are public.
 // Only our friend classes can access methods that may change us.

 /// This may return an incomplete string on OOM, but that's acceptable.
 void GetValueAsString(nsAString& aValue) const;

 bool IsEmpty() const { return mLengths.IsEmpty(); }

 uint32_t Length() const { return mLengths.Length(); }

 const SVGLength& operator[](uint32_t aIndex) const {
   return mLengths[aIndex];
 }

 bool operator==(const SVGLengthList& rhs) const;

 bool SetCapacity(uint32_t size) {
   return mLengths.SetCapacity(size, fallible);
 }

 void Compact() { mLengths.Compact(); }

 // Access to methods that can modify objects of this type is deliberately
 // limited. This is to reduce the chances of someone modifying objects of
 // this type without taking the necessary steps to keep DOM wrappers in sync.
 // If you need wider access to these methods, consider adding a method to
 // SVGAnimatedLengthList and having that class act as an intermediary so it
 // can take care of keeping DOM wrappers in sync.

protected:
 /**
  * This may fail on OOM if the internal capacity needs to be increased, in
  * which case the list will be left unmodified.
  */
 nsresult CopyFrom(const SVGLengthList&);
 void SwapWith(SVGLengthList& aOther) {
   mLengths.SwapElements(aOther.mLengths);
 }

 SVGLength& operator[](uint32_t aIndex) { return mLengths[aIndex]; }

 /**
  * This may fail (return false) on OOM if the internal capacity is being
  * increased, in which case the list will be left unmodified.
  */
 bool SetLength(uint32_t aNumberOfItems) {
   return mLengths.SetLength(aNumberOfItems, fallible);
 }

private:
 // Marking the following private only serves to show which methods are only
 // used by our friend classes (as opposed to our subclasses) - it doesn't
 // really provide additional safety.

 nsresult SetValueFromString(const nsAString& aValue);

 void Clear() { mLengths.Clear(); }

 bool InsertItem(uint32_t aIndex, const SVGLength& aLength) {
   if (aIndex >= mLengths.Length()) aIndex = mLengths.Length();
   return !!mLengths.InsertElementAt(aIndex, aLength, fallible);
 }

 void ReplaceItem(uint32_t aIndex, const SVGLength& aLength) {
   MOZ_ASSERT(aIndex < mLengths.Length(),
              "DOM wrapper caller should have raised INDEX_SIZE_ERR");
   mLengths[aIndex] = aLength;
 }

 void RemoveItem(uint32_t aIndex) {
   MOZ_ASSERT(aIndex < mLengths.Length(),
              "DOM wrapper caller should have raised INDEX_SIZE_ERR");
   mLengths.RemoveElementAt(aIndex);
 }

 bool AppendItem(SVGLength aLength) {
   return !!mLengths.AppendElement(aLength, fallible);
 }

protected:
 /* Rationale for using nsTArray<SVGLength> and not nsTArray<SVGLength, 1>:
  *
  * It might seem like we should use AutoTArray<SVGLength, 1> instead of
  * nsTArray<SVGLength>. That would preallocate space for one SVGLength and
  * avoid an extra memory allocation call in the common case of the 'x'
  * and 'y' attributes each containing a single length (and the 'dx' and 'dy'
  * attributes being empty). However, consider this:
  *
  * An empty nsTArray uses sizeof(Header*). An AutoTArray<class E,
  * uint32_t N> on the other hand uses sizeof(Header*) +
  * (2 * sizeof(uint32_t)) + (N * sizeof(E)), which for one SVGLength is
  * sizeof(Header*) + 16 bytes.
  *
  * Now consider that for text elements we have four length list attributes
  * (x, y, dx, dy), each of which can have a baseVal and an animVal list. If
  * we were to go the AutoTArray<SVGLength, 1> route for each of these, we'd
  * end up using at least 160 bytes for these four attributes alone, even
  * though we only need storage for two SVGLengths (16 bytes) in the common
  * case!!
  *
  * A compromise might be to template SVGLengthList to allow
  * SVGAnimatedLengthList to preallocate space for an SVGLength for the
  * baseVal lists only, and that would cut the space used by the four
  * attributes to 96 bytes. Taking that even further and templating
  * SVGAnimatedLengthList too in order to only use nsTArray for 'dx' and 'dy'
  * would reduce the storage further to 64 bytes. Having different types makes
  * things more complicated for code that needs to look at the lists though.
  * In fact it also makes things more complicated when it comes to storing the
  * lists.
  *
  * It may be worth considering using nsAttrValue for length lists instead of
  * storing them directly on the element.
  */
 FallibleTArray<SVGLength> mLengths;
};

/**
* This SVGLengthList subclass is for SVGLengthListSMILType which needs to know
* which element and attribute a length list belongs to so that it can convert
* between unit types if necessary.
*/
class SVGLengthListAndInfo : public SVGLengthList {
public:
 SVGLengthListAndInfo() : mElement(nullptr), mAxis(0), mCanZeroPadList(true) {}

 SVGLengthListAndInfo(dom::SVGElement* aElement, uint8_t aAxis,
                      bool aCanZeroPadList)
     : mElement(do_GetWeakReference(static_cast<nsINode*>(aElement))),
       mAxis(aAxis),
       mCanZeroPadList(aCanZeroPadList) {}

 void SetInfo(dom::SVGElement* aElement, uint8_t aAxis, bool aCanZeroPadList) {
   mElement = do_GetWeakReference(static_cast<nsINode*>(aElement));
   mAxis = aAxis;
   mCanZeroPadList = aCanZeroPadList;
 }

 dom::SVGElement* Element() const {
   nsCOMPtr<nsIContent> e = do_QueryReferent(mElement);
   return static_cast<dom::SVGElement*>(e.get());
 }

 /**
  * Returns true if this object is an "identity" value, from the perspective
  * of SMIL. In other words, returns true until the initial value set up in
  * SVGLengthListSMILType::InitValue() has been changed with a SetInfo() call.
  */
 bool IsIdentity() const {
   if (!mElement) {
     MOZ_ASSERT(IsEmpty(), "target element propagation failure");
     return true;
   }
   return false;
 }

 uint8_t Axis() const {
   MOZ_ASSERT(mElement, "Axis() isn't valid");
   return mAxis;
 }

 /**
  * The value returned by this function depends on which attribute this object
  * is for. If appending a list of zeros to the attribute's list would have no
  * effect on rendering (e.g. the attributes 'dx' and 'dy' on <text>), then
  * this method will return true. If appending a list of zeros to the
  * attribute's list could *change* rendering (e.g. the attributes 'x' and 'y'
  * on <text>), then this method will return false.
  *
  * The reason that this method exists is because the SMIL code needs to know
  * what to do when it's asked to animate between lists of different length.
  * If this method returns true, then it can zero pad the short list before
  * carrying out its operations. However, in the case of the 'x' and 'y'
  * attributes on <text>, zero would mean "zero in the current coordinate
  * system", whereas we would want to pad shorter lists with the coordinates
  * at which glyphs would otherwise lie, which is almost certainly not zero!
  * Animating from/to zeros in this case would produce terrible results.
  *
  * Currently SVGLengthListSMILType simply disallows (drops) animation between
  * lists of different length if it can't zero pad a list. This is to avoid
  * having some authors create content that depends on undesirable behaviour
  * (which would make it difficult for us to fix the behavior in future). At
  * some point it would be nice to implement a callback to allow this code to
  * determine padding values for lists that can't be zero padded. See
  * https://bugzilla.mozilla.org/show_bug.cgi?id=573431
  */
 bool CanZeroPadList() const {
   // NS_ASSERTION(mElement, "CanZeroPadList() isn't valid");
   return mCanZeroPadList;
 }

 // For the SMIL code. See comment in SVGLengthListSMILType::Add().
 void SetCanZeroPadList(bool aCanZeroPadList) {
   mCanZeroPadList = aCanZeroPadList;
 }

 nsresult CopyFrom(const SVGLengthListAndInfo& rhs) {
   mElement = rhs.mElement;
   mAxis = rhs.mAxis;
   mCanZeroPadList = rhs.mCanZeroPadList;
   return SVGLengthList::CopyFrom(rhs);
 }

 // Instances of this special subclass do not have DOM wrappers that we need
 // to worry about keeping in sync, so it's safe to expose any hidden base
 // class methods required by the SMIL code, as we do below.

 /**
  * Exposed so that SVGLengthList baseVals can be copied to
  * SVGLengthListAndInfo objects. Note that callers should also call
  * SetInfo() when using this method!
  */
 nsresult CopyFrom(const SVGLengthList& rhs) {
   return SVGLengthList::CopyFrom(rhs);
 }
 const SVGLength& operator[](uint32_t aIndex) const {
   return SVGLengthList::operator[](aIndex);
 }
 SVGLength& operator[](uint32_t aIndex) {
   return SVGLengthList::operator[](aIndex);
 }
 bool SetLength(uint32_t aNumberOfItems) {
   return SVGLengthList::SetLength(aNumberOfItems);
 }

private:
 // We must keep a weak reference to our element because we may belong to a
 // cached baseVal SMILValue. See the comments starting at:
 // https://bugzilla.mozilla.org/show_bug.cgi?id=515116#c15
 // See also https://bugzilla.mozilla.org/show_bug.cgi?id=653497
 nsWeakPtr mElement;
 uint8_t mAxis;
 bool mCanZeroPadList;
};

/**
* This class wraps SVGLengthList objects to allow frame consumers to process
* SVGLengthList objects as if they were simply a list of float values in user
* units. When consumers request the value at a given index, this class
* dynamically converts the corresponding SVGLength from its actual unit and
* returns its value in user units.
*
* Consumers should check that the user unit values returned are finite. Even
* if the consumer can guarantee the list's element has a valid viewport
* ancestor to resolve percentage units against, and a valid presContext and
* ComputedStyle to resolve absolute and em/ex units against, unit conversions
* could still overflow. In that case the value returned will be
* numeric_limits<float>::quiet_NaN().
*/
class MOZ_STACK_CLASS SVGUserUnitList {
public:
 SVGUserUnitList() : mList(nullptr), mElement(nullptr), mAxis(0) {}

 void Init(const SVGLengthList* aList, const dom::SVGElement* aElement,
           uint8_t aAxis) {
   mList = aList;
   mElement = aElement;
   mAxis = aAxis;
 }

 bool IsEmpty() const { return mList->IsEmpty(); }

 uint32_t Length() const { return mList->Length(); }

 /// This may return a non-finite value
 float operator[](uint32_t aIndex) const {
   return (*mList)[aIndex].GetValueInPixelsWithZoom(mElement, mAxis);
 }

 bool HasPercentageValueAt(uint32_t aIndex) const {
   return (*mList)[aIndex].IsPercentage();
 }

private:
 const SVGLengthList* mList;
 const dom::SVGElement* mElement;
 uint8_t mAxis;
};

}  // namespace mozilla

#endif  // DOM_SVG_SVGLENGTHLIST_H_