layout/style/nsIStyleRule.h

   1 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* ***** BEGIN LICENSE BLOCK *****
   3  * Version: MPL 1.1/GPL 2.0/LGPL 2.1
   4  *
   5  * The contents of this file are subject to the Mozilla Public License Version
   6  * 1.1 (the "License"); you may not use this file except in compliance with
   7  * the License. You may obtain a copy of the License at
   8  * http://www.mozilla.org/MPL/
   9  *
  10  * Software distributed under the License is distributed on an "AS IS" basis,
  11  * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
  12  * for the specific language governing rights and limitations under the
  13  * License.
  14  *
  15  * The Original Code is mozilla.org code.
  16  *
  17  * The Initial Developer of the Original Code is
  18  * Netscape Communications Corporation.
  19  * Portions created by the Initial Developer are Copyright (C) 1998
  20  * the Initial Developer. All Rights Reserved.
  21  *
  22  * Contributor(s):
  23  *
  24  * Alternatively, the contents of this file may be used under the terms of
  25  * either of the GNU General Public License Version 2 or later (the "GPL"),
  26  * or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
  27  * in which case the provisions of the GPL or the LGPL are applicable instead
  28  * of those above. If you wish to allow use of your version of this file only
  29  * under the terms of either the GPL or the LGPL, and not to allow others to
  30  * use your version of this file under the terms of the MPL, indicate your
  31  * decision by deleting the provisions above and replace them with the notice
  32  * and other provisions required by the GPL or the LGPL. If you do not delete
  33  * the provisions above, a recipient may use your version of this file under
  34  * the terms of any one of the MPL, the GPL or the LGPL.
  35  *
  36  * ***** END LICENSE BLOCK ***** */
  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 nsIContent;
  52 struct nsRuleData;
  53
  54 // IID for the nsIStyleRule interface {f75f3f70-435d-43a6-a01b-65970489ca26}
  55 #define NS_ISTYLE_RULE_IID     \
  56 { 0xf75f3f70, 0x435d, 0x43a6, \
  57  { 0xa0, 0x1b, 0x65, 0x97, 0x04, 0x89, 0xca, 0x26 } }
  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   virtual void MapRuleInfoInto(nsRuleData* aRuleData)=0;
 107
 108   virtual nsIStyleRule* GetImportantRule(void) { return nsnull; }
 109
 110 #ifdef DEBUG
 111   virtual void List(FILE* out = stdout, PRInt32 aIndent = 0) const = 0;
 112 #endif
 113 };
 114
 115 NS_DEFINE_STATIC_IID_ACCESSOR(nsIStyleRule, NS_ISTYLE_RULE_IID)
 116
 117 #endif /* nsIStyleRule_h___ */