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This Technical Note explains why custom window definition functions may not
respond to a wDraw message from the system (if you follow the
documentation in Inside Macintosh).
[Feb 01 1991]
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Problem & Solution
Inside Macintosh, Volume I-299, documents the declaration of the window
definition function (WDEF) as follows:
FUNCTION MyWindow(varCode: INTEGER; theWindow: WindowPtr; message:
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On the first examination of the parameters, one may assume param
always contains a long value; however, when the system is calling the WDEF with
message = wDraw, it only stores a short value in param
without clearing the high-order word of param. If the high-order word
contains any value other than zero, the content of param is different
from what the WDEF expects.
For the custom WDEF to work correctly, it should use only the low-order word of
param when message = wDraw.
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Note:
This problem exists in all systems up to and including System
Software 7.0. The suggested fix is valid for all of these systems.
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Acrobat version of this Note (40K).
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