The Tor Browser: layout/style/nsIStyleRule.h@8bccb770b82d

     1 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */

     2 /* This Source Code Form is subject to the terms of the Mozilla Public

     3  * License, v. 2.0. If a copy of the MPL was not distributed with this

     4  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

     6 /*

     7  * internal abstract interface for objects providing immutable style

     8  * information

     9  */

    11 #ifndef nsIStyleRule_h___

    12 #define nsIStyleRule_h___

    14 #include <stdio.h>

    16 #include "nsISupports.h"

    18 struct nsRuleData;

    20 // IID for the nsIStyleRule interface {f75f3f70-435d-43a6-a01b-65970489ca26}

    21 #define NS_ISTYLE_RULE_IID     \

    22 { 0xf75f3f70, 0x435d, 0x43a6, \

    23  { 0xa0, 0x1b, 0x65, 0x97, 0x04, 0x89, 0xca, 0x26 } }

    25 /**

    26  * An object implementing |nsIStyleRule| (henceforth, a rule) represents

    27  * immutable stylistic information that either applies or does not apply

    28  * to a given element.  It belongs to an object or group of objects that

    29  * implement |nsIStyleSheet| and |nsIStyleRuleProcessor| (henceforth, a

    30  * sheet).

    31  *

    32  * A rule becomes relevant to the computation of style data when

    33  * |nsIStyleRuleProcessor::RulesMatching| creates a rule node that

    34  * points to the rule.  (A rule node, |nsRuleNode|, is a node in the

    35  * rule tree, which is a lexicographic tree indexed by rules.  The path

    36  * from the root of the rule tree to the |nsRuleNode| for a given

    37  * |nsStyleContext| contains exactly the rules that match the element

    38  * that the style context is for, in priority (weight, origin,

    39  * specificity) order.)

    40  *

    41  * The computation of style data uses the rule tree, which calls

    42  * |nsIStyleRule::MapRuleInfoInto| below.

    43  *

    44  * It is worth emphasizing that the data represented by a rule

    45  * implementation are immutable.  When the data need to be changed, a

    46  * new rule object must be created.  Failing to do this will lead to

    47  * bugs in the handling of dynamic style changes, since the rule tree

    48  * caches the results of |MapRuleInfoInto|.

    49  *

    50  * |nsIStyleRule| objects are owned by |nsRuleNode| objects (in addition

    51  * to typically being owned by their sheet), which are in turn garbage

    52  * collected (with the garbage collection roots being style contexts).

    53  */

    56 class nsIStyleRule : public nsISupports {

    57 public:

    58   NS_DECLARE_STATIC_IID_ACCESSOR(NS_ISTYLE_RULE_IID)

    60   /**

    61    * |nsIStyleRule::MapRuleInfoInto| is a request to copy all stylistic

    62    * data represented by the rule that:

    63    *   + are relevant for any structs in |aRuleData->mSIDs| (style

    64    *     struct ID bits)

    65    *   + are not already filled into the data struct

    66    * into the appropriate data struct in |aRuleData|.  It is important

    67    * that only empty data are filled in, since the rule tree is walked

    68    * from highest priority rule to least, so that the walk can stop if

    69    * all needed data are found.  Thus overwriting non-empty data will

    70    * break CSS cascading rules.

    71    */

    72   virtual void MapRuleInfoInto(nsRuleData* aRuleData)=0;

    74 #ifdef DEBUG

    75   virtual void List(FILE* out = stdout, int32_t aIndent = 0) const = 0;

    76 #endif

    77 };

    79 NS_DEFINE_STATIC_IID_ACCESSOR(nsIStyleRule, NS_ISTYLE_RULE_IID)

    81 #endif /* nsIStyleRule_h___ */

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