diff -r 51a74ef9ed63 -r ae94777fff8f Symbian3/SDK/Source/GUID-4957E6BB-C41D-52F1-94CD-68CF6D61C271.dita --- a/Symbian3/SDK/Source/GUID-4957E6BB-C41D-52F1-94CD-68CF6D61C271.dita Wed Mar 31 11:11:55 2010 +0100 +++ b/Symbian3/SDK/Source/GUID-4957E6BB-C41D-52F1-94CD-68CF6D61C271.dita Fri Jun 11 12:39:03 2010 +0100 @@ -1,48 +1,48 @@ - - - - - -Format -layering -

The Symbian platform uses the principle of format layering -in which new formatting is added as a layer onto the previous layer of formatting. -The following diagram shows a less efficient technique for applying format -layering to text. The inefficiency arises because each format layer stores -not only the new attribute which it introduces, but also every attribute which -it inherits from the preceding format layer.

- - - -

The Symbian platform avoids this inefficiency by using the system of based-on -links. Here, each new layer adds attributes in a natural way without -restating all attributes previously set. A based-on link is a pointer to the -format layer whose attributes are inherited by another layer. For example, -when the italic attribute is applied to a region of bold text, the new layer -stores only the italic attribute and a pointer to the previous attribute layer. -Chains of format layers can thus be formed, with each layer based on the previous -one. In order to determine a character or paragraph’s effective format, -a chain of format layers must typically be examined. The final layer in the -chain of based on links is the one whose based on link is NULL and is not -therefore based upon any other layer.

-

This method is demonstrated in the following two diagrams, in which each -arrow represents a based-on link.

- -Format layering - - -

The following diagram demonstrates the system of based-on links when attributes -are applied to different parts of text rather than added on top of existing -attribute layers.

- - - -

In this case, several format layers are required, all of which are based -on the normal layer.

+ + + + + +Format +layering +

The Symbian platform uses the principle of format layering +in which new formatting is added as a layer onto the previous layer of formatting. +The following diagram shows a less efficient technique for applying format +layering to text. The inefficiency arises because each format layer stores +not only the new attribute which it introduces, but also every attribute which +it inherits from the preceding format layer.

+ + + +

The Symbian platform avoids this inefficiency by using the system of based-on +links. Here, each new layer adds attributes in a natural way without +restating all attributes previously set. A based-on link is a pointer to the +format layer whose attributes are inherited by another layer. For example, +when the italic attribute is applied to a region of bold text, the new layer +stores only the italic attribute and a pointer to the previous attribute layer. +Chains of format layers can thus be formed, with each layer based on the previous +one. In order to determine a character or paragraph’s effective format, +a chain of format layers must typically be examined. The final layer in the +chain of based on links is the one whose based on link is NULL and is not +therefore based upon any other layer.

+

This method is demonstrated in the following two diagrams, in which each +arrow represents a based-on link.

+ +Format layering + + +

The following diagram demonstrates the system of based-on links when attributes +are applied to different parts of text rather than added on top of existing +attribute layers.

+ + + +

In this case, several format layers are required, all of which are based +on the normal layer.

\ No newline at end of file