From: Charles Turner <vze26m98@...>
Date: 2008-08-21T13:11:38+09:00
Subject: Ruby/DL: How to create and use a buffer?

Hi all-

I'm trying to hookup Erik de Castro Lopo's libsndfile with Ruby via 
Ruby/DL: my first encounter with it. I've had some success with DL, but 
am stuck at creating a multibyte buffer that can be passed by reference 
into the libsndfile library.

libsndfile: <http://www.mega-nerd.com/libsndfile/>

me: Darwin spinoza.local 9.4.0 Darwin Kernel Version 9.4.0: Mon Jun  9 
19:30:53 PDT 2008; root:xnu-1228.5.20~1/RELEASE_I386 i386

Ruby 1.9: ruby 1.9.0 (2007-12-25 revision 14709) [i686-darwin9.4.0]

My code is included below.

As you can see, I can malloc a DL::CPtr (buffer) and pass it into the 
sf_readf_short() function. But I'm unclear what to do with it 
afterwards.

I've been able to reference data by treating buffer like an array, like 
so: buffer[2], but I'm not sure I'm getting valid data. It doesn't look 
right, but I haven't compared it the audio file I'm using.

Any thoughts greatly appreciated!

Best, Charles Turner

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. . . . .

require 'dl'
require 'dl/import'

module SndFile
  extend ::DL::Importer

  dlload "libsndfile.dylib"

  SF_INFO = struct [
        "long long frames",
        "int samplerate",
	"int channels",
	"int format",
	"int sections",
	"int seekable",
                   ]

# Modes for opening files.
  SFM_READ	= 0x10
  SFM_WRITE	= 0x20
  SFM_RDWR	= 0x30

# Major formats.
  SF_FORMAT_WAV = 0x010000    # Microsoft WAV format
  SF_FORMAT_AIFF = 0x020000   # Apple/SGI AIFF format

# Minor formats
  SF_FORMAT_PCM_S8 = 0x0001   # Signed 8 bit data
  SF_FORMAT_PCM_16 = 0x0002   # Signed 16 bit data
  SF_FORMAT_PCM_24 = 0x0003   # Signed 24 bit data
  SF_FORMAT_PCM_32 = 0x0004   # Signed 32 bit data

  SF_FORMAT_PCM_U8 = 0x0005   # Unsigned 8 bit data

  SF_FORMAT_FLOAT = 0x0006    # 32 bit float data
  SF_FORMAT_DOUBLE = 0x0007   # 64 bit float data


  extern "int sf_format_check(SF_INFO*)"
  extern "SNDFILE* sf_open(char*, int, SF_INFO*)"
  extern "long long sf_readf_short(SNDFILE*, short*, long long)"
  extern "int sf_close(SNDFILE*)"

end


sfinfo = SndFile::SF_INFO.malloc()

sndfile = SndFile.sf_open("foo32.wav", SndFile::SFM_READ, sfinfo)

sfinfo.frames   # => 53248
sfinfo.samplerate   # => 44100
sfinfo.channels   # => 1
sfinfo.format.to_s(16)   # => "10004"
sfinfo.sections   # => 1
sfinfo.seekable   # => 1

buffer = DL::CPtr.malloc(40)

frames = SndFile.sf_readf_short( sndfile, buffer, 10 )
frames   # => 10

result = SndFile.sf_close( sndfile )
result   # => 0