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TextWidthHook

TextEdit Width Hooks

TextEdit's width hooks are called each the time the width of various

components of a line is calculated. This section describes two new hooks,

nWIDTHHook and TextWidthHook, and their relationships with the

original WIDTHHook hook. The new hook nWIDTHHook allows you access to

TextEdit's measuring routine for non-Roman script systems and provides a

way for you to replace this routine with your own script- compatible

measuring routine. TextWidthHook provides a way for you to replace the new

calls to the TextWidth function in TextEdit with your own measuring

routine.

Note: To test for the availability of the new width-measuring hooks, you

can call the Gestalt function with the gestaltTextEditVersion selector. A

result of gestaltTE2 or greater returned in the response parameter

indicates that the new width measurement hook nWIDTHHook is available.

A result of gestaltTE5 or greater returned in the response parameter

indicates that the new text width measurement hook TextWidthHook is

available. (For details, see

Determining the Version of TextEdit.)

TextWidthHook is available for version 6.0.7 (or higher) systems with

non-Roman script systems installed. However, there is no Gestalt constant

that indicates this availability.

The original WIDTHHook hook is available to provide backward

compatibility for your applications. TextEdit still uses WIDTHHook;

however, it now performs additional checks to determine whether to use

WIDTHHook or nWIDTHHook. TextEdit first determines whether a

non-Roman script system is installed. If it is, TextEdit uses the new

nWIDTHHook routine even if an application has overridden WIDTHHook

with a different measuring routine. If TextEdit finds that only the Roman

Script System is installed, it checks to see if WIDTHHook contains the

address of TextEdit's default routine for measuring. If it does, TextEdit uses

the nWIDTHHook routine. Otherwise, an application has provided a different

measuring routine to be used for system software with only the Roman Script

System installed, so TextEdit uses this routine instead of its own default

routine.

It is possible for you to provide alternate routines for both of these hooks to

guarantee that your routine is always used. However, unless the routine

measures correctly for non-Roman scripts, you should only replace

WIDTHHook and TextWidthHook.

The appropriate font, face, and size characteristics have already been set into

the current port by the time any of these routines is called.

The default action for WIDTHHook is to call the QuickDraw function

TextWidth and return.

The default action for nWIDTHHook is to call the Script Manager's

Char2Pixel function or TextWidth to measure accurately for non-Roman

scripts. For more information on Char2Pixel, see

Worldwide Software Overview. For comprehensive details, refer to

Macintosh Worldwide Development: Guide to System Software.

For a discussion of the slop value, see Worldwide Software Overview

description.

TextEdit also includes the new TextWidthHook routine that provides a way

for you to replace the new TextWidth calls in TextEdit with your own

measuring routine. You must use TextWidthHook in addition to WIDTHHook

and nWIDTHHook to replace TextEdit's measuring routines completely.

Note: There is a TextWidth call in the TextBox procedure that does not

use this hook because no edit record is allocated.

The default action for TextWidthHook is to always call the QuickDraw

TextWidth function (the same default action as for the original

WIDTHHook routine).

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