layout/style/nsIStyleRule.h

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  37
  38 /*
  39  * internal abstract interface for objects providing immutable style
  40  * information
  41  */
  42
  43 #ifndef nsIStyleRule_h___
  44 #define nsIStyleRule_h___
  45
  46 #include <stdio.h>
  47
  48 #include "nsISupports.h"
  49
  50 class nsIStyleSheet;
  51 class nsPresContext;
  52 class nsIContent;
  53 struct nsRuleData;
  54
  55 // IID for the nsIStyleRule interface {40ae5c90-ad6a-11d1-8031-006008159b5a}
  56 #define NS_ISTYLE_RULE_IID     \
  57 {0x40ae5c90, 0xad6a, 0x11d1, {0x80, 0x31, 0x00, 0x60, 0x08, 0x15, 0x9b, 0x5a}}
  58
  59 /**
  60  * An object implementing |nsIStyleRule| (henceforth, a rule) represents
  61  * immutable stylistic information that either applies or does not apply
  62  * to a given element.  It belongs to an object or group of objects that
  63  * implement |nsIStyleSheet| and |nsIStyleRuleProcessor| (henceforth, a
  64  * sheet).
  65  *
  66  * A rule becomes relevant to the computation of style data when
  67  * |nsIStyleRuleProcessor::RulesMatching| creates a rule node that
  68  * points to the rule.  (A rule node, |nsRuleNode|, is a node in the
  69  * rule tree, which is a lexicographic tree indexed by rules.  The path
  70  * from the root of the rule tree to the |nsRuleNode| for a given
  71  * |nsStyleContext| contains exactly the rules that match the element
  72  * that the style context is for, in priority (weight, origin,
  73  * specificity) order.)
  74  *
  75  * The computation of style data uses the rule tree, which calls
  76  * |nsIStyleRule::MapRuleInfoInto| below.
  77  *
  78  * It is worth emphasizing that the data represented by a rule
  79  * implementation are immutable.  When the data need to be changed, a
  80  * new rule object must be created.  Failing to do this will lead to
  81  * bugs in the handling of dynamic style changes, since the rule tree
  82  * caches the results of |MapRuleInfoInto|.
  83  *
  84  * |nsIStyleRule| objects are owned by |nsRuleNode| objects (in addition
  85  * to typically being owned by their sheet), which are in turn garbage
  86  * collected (with the garbage collection roots being style contexts).
  87  */
  88
  89
  90 class nsIStyleRule : public nsISupports {
  91 public:
  92   NS_DECLARE_STATIC_IID_ACCESSOR(NS_ISTYLE_RULE_IID)
  93
  94   /**
  95    * |nsIStyleRule::MapRuleInfoInto| is a request to copy all stylistic
  96    * data represented by the rule that:
  97    *   + are relevant for any structs in |aRuleData->mSIDs| (style
  98    *     struct ID bits)
  99    *   + are not already filled into the data struct
 100    * into the appropriate data struct in |aRuleData|.  It is important
 101    * that only empty data are filled in, since the rule tree is walked
 102    * from highest priority rule to least, so that the walk can stop if
 103    * all needed data are found.  Thus overwriting non-empty data will
 104    * break CSS cascading rules.
 105    */
 106   NS_IMETHOD MapRuleInfoInto(nsRuleData* aRuleData)=0;
 107
 108 #ifdef DEBUG
 109   NS_IMETHOD List(FILE* out = stdout, PRInt32 aIndent = 0) const = 0;
 110 #endif
 111 };
 112
 113 NS_DEFINE_STATIC_IID_ACCESSOR(nsIStyleRule, NS_ISTYLE_RULE_IID)
 114
 115 #endif /* nsIStyleRule_h___ */