michael@0: /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
michael@0: /* This Source Code Form is subject to the terms of the Mozilla Public
michael@0:  * License, v. 2.0. If a copy of the MPL was not distributed with this
michael@0:  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0: 
michael@0: /*
michael@0:  * internal abstract interface for objects providing immutable style
michael@0:  * information
michael@0:  */
michael@0: 
michael@0: #ifndef nsIStyleRule_h___
michael@0: #define nsIStyleRule_h___
michael@0: 
michael@0: #include <stdio.h>
michael@0: 
michael@0: #include "nsISupports.h"
michael@0: 
michael@0: struct nsRuleData;
michael@0: 
michael@0: // IID for the nsIStyleRule interface {f75f3f70-435d-43a6-a01b-65970489ca26}
michael@0: #define NS_ISTYLE_RULE_IID     \
michael@0: { 0xf75f3f70, 0x435d, 0x43a6, \
michael@0:  { 0xa0, 0x1b, 0x65, 0x97, 0x04, 0x89, 0xca, 0x26 } }
michael@0: 
michael@0: /**
michael@0:  * An object implementing |nsIStyleRule| (henceforth, a rule) represents
michael@0:  * immutable stylistic information that either applies or does not apply
michael@0:  * to a given element.  It belongs to an object or group of objects that
michael@0:  * implement |nsIStyleSheet| and |nsIStyleRuleProcessor| (henceforth, a
michael@0:  * sheet).
michael@0:  *
michael@0:  * A rule becomes relevant to the computation of style data when
michael@0:  * |nsIStyleRuleProcessor::RulesMatching| creates a rule node that
michael@0:  * points to the rule.  (A rule node, |nsRuleNode|, is a node in the
michael@0:  * rule tree, which is a lexicographic tree indexed by rules.  The path
michael@0:  * from the root of the rule tree to the |nsRuleNode| for a given
michael@0:  * |nsStyleContext| contains exactly the rules that match the element
michael@0:  * that the style context is for, in priority (weight, origin,
michael@0:  * specificity) order.)
michael@0:  *
michael@0:  * The computation of style data uses the rule tree, which calls
michael@0:  * |nsIStyleRule::MapRuleInfoInto| below.
michael@0:  *
michael@0:  * It is worth emphasizing that the data represented by a rule
michael@0:  * implementation are immutable.  When the data need to be changed, a
michael@0:  * new rule object must be created.  Failing to do this will lead to
michael@0:  * bugs in the handling of dynamic style changes, since the rule tree
michael@0:  * caches the results of |MapRuleInfoInto|.
michael@0:  *
michael@0:  * |nsIStyleRule| objects are owned by |nsRuleNode| objects (in addition
michael@0:  * to typically being owned by their sheet), which are in turn garbage
michael@0:  * collected (with the garbage collection roots being style contexts).
michael@0:  */
michael@0: 
michael@0: 
michael@0: class nsIStyleRule : public nsISupports {
michael@0: public:
michael@0:   NS_DECLARE_STATIC_IID_ACCESSOR(NS_ISTYLE_RULE_IID)
michael@0: 
michael@0:   /**
michael@0:    * |nsIStyleRule::MapRuleInfoInto| is a request to copy all stylistic
michael@0:    * data represented by the rule that:
michael@0:    *   + are relevant for any structs in |aRuleData->mSIDs| (style
michael@0:    *     struct ID bits)
michael@0:    *   + are not already filled into the data struct
michael@0:    * into the appropriate data struct in |aRuleData|.  It is important
michael@0:    * that only empty data are filled in, since the rule tree is walked
michael@0:    * from highest priority rule to least, so that the walk can stop if
michael@0:    * all needed data are found.  Thus overwriting non-empty data will
michael@0:    * break CSS cascading rules.
michael@0:    */
michael@0:   virtual void MapRuleInfoInto(nsRuleData* aRuleData)=0;
michael@0: 
michael@0: #ifdef DEBUG
michael@0:   virtual void List(FILE* out = stdout, int32_t aIndent = 0) const = 0;
michael@0: #endif
michael@0: };
michael@0: 
michael@0: NS_DEFINE_STATIC_IID_ACCESSOR(nsIStyleRule, NS_ISTYLE_RULE_IID)
michael@0: 
michael@0: #endif /* nsIStyleRule_h___ */