Text Edit record Types

The TERec structure itself has not changed, but several fields have new

meaning, in an upwardly-compatible sort of way:

• When the txSize field is set to -1, the changes have been implemented and

the record is "style-aware".

• When lineHeight and fontAscent are -1, TextEdit performs automatic

line-height calculations. The height of each line is stored in an array of type

LHTable. You may override the "floating" height of any line by setting the

high bit of its LHElement structure.

• The 4 bytes starting at txFont (offset 74) contain a handle to a TEStyleRec

structure containing all the style-related information (or handles leading

the the various sub structures).

Thus, when you get a TEHandle, just examine the txSize field to see if the

record is "style aware" and take appropriate action.

The Style Record

The TEStyleRec structure is the starting point for all the structures

associated with styles. See that structure for details, but in general, the

system works like this: Each unique set of attributes has an STElement

structure and there is an array of these elements, called the style table.

TextEdit maintains a linear array identifying style runs; a run is defined

by a starting point (an offset into the data at TERec.hText), and an index into

the style table. As text is inserted or deleted, these style runs are updated to

reflect the changes. When a style is applied to text, the resulting combination

is compared to other elements of the style table and if it doesn't exist, a new

style is added to the style table. Then style runs are updated to reflect the

changes.

To keep track of the now-variable height of lines, TextEdit maintains a

linear array of line-height information (see LHTable). This array parallels

the elements of the TERec.lineStarts array (the variable-length array found at

the end of the edit record). For instance, TERec.lineStarts[n ] is the offset of

the first character of line n and LHTable[n ] contains the height of that line.

The line heights are calculated automatically but you may force a recalculation

The Style Scrap

The StScrpRec structure is a variable-length structure defining runs of

styles that apply to any unformatted text. When you use TECut, TECopy, or

GetStylScrap, TextEdit builds up one of these structures. Unlike the style

table and indexing scheme used for edit text, this data is not space-efficient;

each style run gets defined by a full 22 bytes of information. However, this

makes it portable between applications and is the format of a 'styl' resource,

which you might come across in the desk scrap.

applies the formatting of an StScrpRec to some text. On the older TEInsert

function and the TEKey function, TextEdit applies the style of the character

to the left of the insertion point (or the first character of the selection range)

to the inserted text. TextEdit also maintains a null style scrap, consisting

mainly of a single ScrpSTElement. This style is used as the default for cases

where there is no obvious style to use.