drawing to offscreen bitmap bombs

[mcdougal@cs.uchicago.edu (Tom McDougal)]

This very short piece of code crashes MCL 2.0p2.  Would you mind taking a
quick look at it and helping me understand what I am doing wrong?   I have
some similar code that seems to work fine.

Thanks very much.

For what it is worth, Macsbug says the error is:

Bus Error at 01643FD2 01234567+1B52
while writing long word (data = BC1DBC16) to BD43813E in User data space

This is on a MacIIfx with all extensions turned off.

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;;; Create a bitmap and draw something to it.

(require :quickdraw)

(defvar *bitmap-1* (make-bitmap 0 0 200 200))

(rlet ((port :grafport))
  (unwind-protect
    (without-interrupts
     (#_openPort port)
     (with-port port
       (#_setPortBits *bitmap-1*)
       (#_moveTo 20 20)
       (#_lineTo 70 30)))
    (#_closePort port)))


-----------------------------------------------------------
Tom McDougal   mcdougal@cs.uchicago.edu   +1 (312) 702-9923
     University of Chicago Artificial Intelligence