gecko-dev/layout/style/nsStyleContext.h

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 *   David Hyatt <hyatt@netscape.com>
 *   Pierre Phaneuf <pp@ludusdesign.com>
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/* the interface (to internal code) for retrieving computed style data */

#ifndef _nsStyleContext_h_
#define _nsStyleContext_h_

#include "nsRuleNode.h"
#include "nsIAtom.h"

class nsPresContext;

/**
 * An nsStyleContext represents the computed style data for an element.
 * The computed style data are stored in a set of structs (see
 * nsStyleStruct.h) that are cached either on the style context or in
 * the rule tree (see nsRuleNode.h for a description of this caching and
 * how the cached structs are shared).
 *
 * Since the data in |nsIStyleRule|s and |nsRuleNode|s are immutable
 * (with a few exceptions, like system color changes), the data in an
 * nsStyleContext are also immutable (with the additional exception of
 * GetUniqueStyleData).  When style data change,
 * nsFrameManager::ReResolveStyleContext creates a new style context.
 *
 * Style contexts are reference counted.  References are generally held
 * by:
 *  1. the |nsIFrame|s that are using the style context and
 *  2. any *child* style contexts (this might be the reverse of
 *     expectation, but it makes sense in this case)
 * Style contexts participate in the mark phase of rule node garbage
 * collection.
 */

class nsStyleContext
{
public:
  nsStyleContext(nsStyleContext* aParent, nsIAtom* aPseudoTag, 
                 nsRuleNode* aRuleNode, nsPresContext* aPresContext) NS_HIDDEN;
  ~nsStyleContext() NS_HIDDEN;

  NS_HIDDEN_(void*) operator new(size_t sz, nsPresContext* aPresContext) CPP_THROW_NEW;
  NS_HIDDEN_(void) Destroy();

  nsrefcnt AddRef() {
    if (mRefCnt == PR_UINT32_MAX) {
      NS_WARNING("refcount overflow, leaking object");
      return mRefCnt;
    }
    ++mRefCnt;
    NS_LOG_ADDREF(this, mRefCnt, "nsStyleContext", sizeof(nsStyleContext));
    return mRefCnt;
  }

  nsrefcnt Release() {
    if (mRefCnt == PR_UINT32_MAX) {
      NS_WARNING("refcount overflow, leaking object");
      return mRefCnt;
    }
    --mRefCnt;
    NS_LOG_RELEASE(this, mRefCnt, "nsStyleContext");
    if (mRefCnt == 0) {
      Destroy();
      return 0;
    }
    return mRefCnt;
  }

  nsPresContext* PresContext() const { return mRuleNode->GetPresContext(); }

  nsStyleContext* GetParent() const { return mParent; }

  nsIAtom* GetPseudoType() const { return mPseudoTag; }

  NS_HIDDEN_(already_AddRefed<nsStyleContext>)
  FindChildWithRules(const nsIAtom* aPseudoTag, nsRuleNode* aRules);

  PRBool    HasTextDecorations() { return !!(mBits & NS_STYLE_HAS_TEXT_DECORATIONS); }

  NS_HIDDEN_(void) SetStyle(nsStyleStructID aSID, void* aStruct);

  nsRuleNode* GetRuleNode() { return mRuleNode; }
  void AddStyleBit(const PRUint32& aBit) { mBits |= aBit; }

  /*
   * Mark this style context's rule node (and its ancestors) to prevent
   * it from being garbage collected.
   */
  NS_HIDDEN_(void) Mark();

  /*
   * Get the style data for a style struct.  This is the most important
   * member function of nsIStyleContext.  It fills in a const pointer
   * to a style data struct that is appropriate for the style context's
   * frame.  This struct may be shared with other contexts (either in
   * the rule tree or the style context tree), so it should not be
   * modified.
   *
   * This function will NOT return null (even when out of memory) when
   * given a valid style struct ID, so the result does not need to be
   * null-checked.
   *
   * The typesafe functions below are preferred to the use of this
   * function.
   */
  NS_HIDDEN_(const void*) NS_FASTCALL GetStyleData(nsStyleStructID aSID);

  /**
   * Define typesafe getter functions for each style struct by
   * preprocessing the list of style structs.  These functions are the
   * preferred way to get style data.  The macro creates functions like:
   *   const nsStyleBorder* GetStyleBorder();
   *   const nsStyleColor* GetStyleColor();
   */

  #define STYLE_STRUCT(name_, checkdata_cb_, ctor_args_)                      \
    NS_HIDDEN_(const nsStyle##name_ *) NS_FASTCALL GetStyle##name_();
  #include "nsStyleStructList.h"
  #undef STYLE_STRUCT


  NS_HIDDEN_(const void*) PeekStyleData(nsStyleStructID aSID);

  NS_HIDDEN_(void*) GetUniqueStyleData(const nsStyleStructID& aSID);

  NS_HIDDEN_(nsChangeHint) CalcStyleDifference(nsStyleContext* aOther);

#ifdef DEBUG
  NS_HIDDEN_(void) List(FILE* out, PRInt32 aIndent);
#endif

protected:
  NS_HIDDEN_(void) AddChild(nsStyleContext* aChild);
  NS_HIDDEN_(void) RemoveChild(nsStyleContext* aChild);

  NS_HIDDEN_(void) ApplyStyleFixups(nsPresContext* aPresContext);

  nsStyleContext* const mParent;

  // Children are kept in two circularly-linked lists.  The list anchor
  // is not part of the list (null for empty), and we point to the first
  // child.
  // mEmptyChild for children whose rule node is the root rule node, and
  // mChild for other children.  The order of children is not
  // meaningful.
  nsStyleContext* mChild;
  nsStyleContext* mEmptyChild;
  nsStyleContext* mPrevSibling;
  nsStyleContext* mNextSibling;

  // If this style context is for a pseudo-element, the pseudo-element
  // atom.  Otherwise, null.
  nsCOMPtr<nsIAtom> mPseudoTag;

  // The rule node is the node in the lexicographic tree of rule nodes
  // (the "rule tree") that indicates which style rules are used to
  // compute the style data, and in what cascading order.  The least
  // specific rule matched is the one whose rule node is a child of the
  // root of the rule tree, and the most specific rule matched is the
  // |mRule| member of |mRuleNode|.
  nsRuleNode* const       mRuleNode;

  // |mCachedStyleData| points to both structs that are owned by this
  // style context and structs that are owned by one of this style
  // context's ancestors (which are indirectly owned since this style
  // context owns a reference to its parent).  If the bit in |mBits| is
  // set for a struct, that means that the pointer for that struct is
  // owned by an ancestor rather than by this style context.
  nsCachedStyleData       mCachedStyleData; // Our cached style data.
  PRUint32                mBits; // Which structs are inherited from the
                                 // parent context.
  PRUint32                mRefCnt;
};

NS_HIDDEN_(already_AddRefed<nsStyleContext>)
NS_NewStyleContext(nsStyleContext* aParentContext,
                   nsIAtom* aPseudoTag,
                   nsRuleNode* aRuleNode,
                   nsPresContext* aPresContext);
#endif