No sound. Uses Ruby and winmm through RubyDL

Question

Expected behavior: middle C played on one midi instrunment, then another. Actual behavior: a DL deprecation warning and no sound. Running Windows 7.

The code:

require "dl/import"

class LiveMIDI
    ON = 0x90
    OFF =0x80
    PC = 0xc0

    def initialize
        open
    end

    def note_on(channel, note, velocity=64)
        message(ON | channel, note, velocity)
    end

    def note_off(channel, note, velocity=64)
        message(OFF | channel, note, velocity)
    end

    def program_change(channel, preset) 
        message(PC | channel, preset)
    end

    module C
        extend DL::Importer
        dlload "winmm"

        extern "int midiOutOpen(HMIDIOUT*, int, int, int, int)"
        extern "int midiOutClose(int)"
        extern "int midiOutShortMsg(int, int)"
    end

    def open
        @device = DL.malloc(DL::Importer.sizeof("int"))
        C.midiOutOpen(@device, -1, 0, 0, 0)
    end

    def close
        C.midiOutClose(@device.ptr.to_i)
    end

    def message(one, two=0, three=0)
        message = one + (two << 8) + (three << 16)
        C.midiOutShortMsg(DL::CPtr.to_ptr(@device).to_i, message)
    end
end

midi = LiveMIDI.new
midi.note_on(0, 60, 100)
sleep(1)
midi.note_off(0, 60)
midi.program_change(1, 40)
midi.note_on(1, 60, 100)
sleep(1)
midi.note_off(1, 60)

Taken from the book Practical Ruby Projects. By the numbers on the page, 11-15, in chapter 2. The code is slightly modified to handle changes to the Ruby DL in Ruby 1.9.

Answer 1

You have to write

DL::CPtr.malloc(DL::Importer.sizeof("int")

instead of

DL.malloc(DL::Importer.sizeof("int"))

to create a pointer object (DL::CPtr) and not just get an address as integer.

Also

DL::CPtr.to_ptr(@device).to_i

has to be

@device.ptr.to_i

or maybe even

@device.ptr

---

Here's an fixed version of your code using DL's replacement Fiddle:

require 'fiddle/import'
require 'fiddle/types'

class LiveMIDI
  ON = 0x90
  OFF = 0x80
  PC = 0xc0

  def initialize
    open
  end

  def note_on(channel, note, velocity = 64)
    message(ON | channel, note, velocity)
  end

  def note_off(channel, note, velocity = 64)
    message(OFF | channel, note, velocity)
  end

  def program_change(channel, preset)
    message(PC | channel, preset)
  end

  module C
    extend Fiddle::Importer
    dlload 'winmm'
    # defines a few Windows-specific types such as DWORD or UINT
    include Fiddle::Win32Types
    # some other types not defined by the previous line
    typealias 'HMIDIOUT', 'void*'
    typealias 'LPHMIDIOUT', 'HMIDIOUT*'
    typealias 'DWORD_PTR', 'uintptr_t'
    typealias 'MMRESULT', 'UINT'

    extern 'MMRESULT midiOutOpen(LPHMIDIOUT, UINT, DWORD_PTR, DWORD_PTR, DWORD)'
    extern 'MMRESULT midiOutClose(HMIDIOUT)'
    extern 'MMRESULT midiOutShortMsg(HMIDIOUT, DWORD)'
  end

  def open
    @device = Fiddle::Pointer.malloc(Fiddle::SIZEOF_VOIDP)
    C.midiOutOpen(@device, -1, 0, 0, 0)
  end

  def close
    C.midiOutClose(@device.ptr)
  end

  def message(one, two = 0, three = 0)
    message = one + (two << 8) + (three << 16)
    C.midiOutShortMsg(@device.ptr, message)
  end
end

It's more or less the same except for the type stuff which I've added or corrected according to the documentation on MSDN. Wrong types may lead to non-obvious issues.