Technical Note TE24

TextEdit Record Size Limitations Revisited

CONTENTS Introduction Check All Constraints References Downloadables

This Technical Note describes another limit on the length of a TextEdit record that was previously undocumented. [Jun 01 1989]

Introduction

The TextEdit chapters in Inside Macintosh document the 32K character limit on a TextEdit record length. They do not, however, discuss the more subtle constraint on the size of the destRect. By definition, the destRect uses integer values for the top-left and bottom-right boundary points. It is possible to have values too large for the destRect without reaching the teLength limit.

The nLines field gives the number of lines in the edit record, and the lineHeight field specifies the vertical distance from the ascent line from one line of text to the ascent line of the next line. In styled TextEdit, the lineHeight may vary for each line depending on the font and font size. These values are entries in the lineHeight table.

Figure 1. LineHeight

The product of the lineHeight (or the largest lineHeight value in styled TextEdit) and nLines gives a good approximation, in pixels, of the vertical dimension of the destRect of the TERec used. If this value is greater than 32,768, then unpredictable and erratic behavior may result.

For example:

2,400 lines of Chicago 12 point yields nLines = 2,400 and lineHeight = 16.

nLines * lineHeight = 2400 * 16 = 38,400. This is above the 32K limit.

1,200 lines of Times 24 point yields nLines = 1,200 and lineHeight = 30.

nLines * lineHeight = 1200 * 30 = 36,000. This is above the 32K limit.

In both of the examples above, the number of characters in the edit record was less than 32,768.

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Check All Constraints

Both TELength and the size of the destRect must be under the 32K limit. You can compute an approximate vertical height of the destRect by finding the product of nLines and lineHeight (or the largest lineHeight value in styled TextEdit).

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References

Inside Macintosh, Volumes I-371 & V-259, TextEdit

M.OV.ManagerAbuse

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Downloadables