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Low Level Interfacing -- HELP!!
- To: email@example.com
- Subject: Low Level Interfacing -- HELP!!
- From: firstname.lastname@example.org (Robyn Kozierok)
- Date: 28 Sep 1994 16:26:18 GMT
- Newsgroups: comp.lang.lisp.mcl
- Organization: MIT Artificial Intelligence Lab
I am trying to do some sound processing. I have a sound handle (snd_h)
and get the offset to the sound header using the following trap:
(deftrap _GetSoundHeaderOffset ((sndhdl :handle)
(offset (:pointer :signed-long)))
(:stack-trap #xA800 :d0 (+ (ash 260 16) 36) sndhdl offset))
Then I want to access the contents of the soundheader, but I am getting
something messed up here. I need to get my hands on either the record,
or a pointer or handle to it, and I can't seem to get it right.
The definition of the soundheader is given below:
(def-mactype :soundheaderptr (find-mactype :pointer))
(samplePtr :pointer) ; if NIL then samples are in sampleArea
(length :signed-long) ; length of sound in bytes
(sampleRate :signed-long) ; sample rate for this sound
(loopStart :signed-long) ; start of looping portion
(loopEnd :signed-long) ; end of looping portion
(encode :unsigned-byte) ; header encoding
(baseFrequency :unsigned-byte); baseFrequency value
(sampleArea (:array :unsigned-byte 1))
(rlet ((n (:pointer :signed-long)))
(#_GetSoundHeaderOffset snd_h n)
(format t "offset: ~a~%" (%get-signed-long n))
;;; OK, so now I have a pointer to the signed-long offset, in n
;;; and I try to get my hands on a pointer to the soundheader
;;; by getting a pointer from the appropriate offset from snd_h
;;; only what's there is the actual soundheader, and not a pointer
;;; to it, or something, like that. but rref doesn't work either,
;;; so what I'm storing in header seems to be neither the record
;;; nor a pointer to it.
(let ((header (%hget-ptr snd_h (%get-signed-long n))))
(format t "Pointer to SoundHeader?: ~a~%" header)
(format t "sample rate is ~a~%"
(pref header soundheader.samplerate))
(format t "length is ~a~%" (pref header soundheader.length)))
Can anyone help me? What is it that is located at offset (%get-signed-long n)
from my sound handle (snd_h) and how can I use it?
Thanks very very much in advance for any help you can give me. I am stuck!