midiplayer.cs

中文名：Windows Forms 程序设计 英文名：Windows Forms Programming in c# 作者： Chris Sells 翻译： 荣耀 蒋贤哲 出版社：人民

// MidiPlayer.cs
// A simple wrapper around the DirectX 7 MIDI-playback service
// NOTE: I'm using DX7 instead of DX8 because DX7 works on DX8 machines, but not vice versa.
using System;
using System.ComponentModel;
using System.Runtime.InteropServices;
using DxVBLib;

namespace EmbeddingUnmanagedResourcesSample {
  class MidiPlayer : Component {
    public MidiPlayer() {
      // A loader object is what parses the data from a file
      // on the hard drive to the area in memory.
      loader = dx.DirectMusicLoaderCreate();

      // A performance controls the music. It looks after
      // sending data to the music port, setting options
      // converting time sigs. etc...
      // A performance is what organises the events
      // think of it as a conductor - syncronising things
      // setting things up; looking after the individual pieces
      // of music.
      perf = dx.DirectMusicPerformanceCreate();

      // Set it's options - these options should be standard
      // across most projects.
      perf.Init(null, 0);
      perf.SetPort(-1, 80);
      perf.SetMasterAutoDownload(true);

      Volume = 75;
    }

    public int Volume {
      // TODO: get

      set {
        // The value can be any number between 0 (mute) and 100 (max).
        // The formula just uses this number to create a volume DM can understand.
        if( value < 0 || value > 100 ) throw new ApplicationException("Volume must be between 0 and 100");
        perf.SetMasterVolume(value * 42 - 3000);
      }
    }

    public void LoadFromFile(string fileName) {
      // A segment is where the actual data is stored;
      // like a buffer or a surface in other DirectX objects
      // Use the loader object to create us a music buffer
      // NOTE: Needs to be of type "DMSEG"
      seg = loader.LoadSegment(fileName);

      // Set the format of the segment to be a MIDI
      seg.SetStandardMidiFile();
    }

    // TODO: Need to support numberic IDs, too
    // (i.e. using a managed implementation of MAKEINTRESOURCE);
    public void LoadFromResource(string fileName, string id) {
      // NOTE: If this fails, try passing in the ID as upper case
      seg = loader.LoadSegmentFromResource(fileName, id);
      seg.SetStandardMidiFile();
    }

    public void Start() {
      if( seg == null ) throw new ApplicationException("Must load a MIDI resource before starting");

      // Make sure we're stopped before starting
      Stop();

      // This variable lets us know what the music is
      // doing. At the simplest level this is "am I playing?"
      // "am i stopped?" etc.
      // This is all it takes to start playing.
      // The last variable states where to start playing from;
      // in this case "0", which means the beginning.
      segstate = perf.PlaySegment(seg, 0, 0);
    }

    public void Stop() {
      if( perf != null ) {
        perf.Stop(seg, segstate, 0, 0);
        if( segstate != null ) {
          Marshal.ReleaseComObject(segstate);
          segstate = null;
        }
      }
    }

    protected override void Dispose(bool isManagedDispose) {
      // Otherwise, it's the finalizer firing and all
      // of our managed references will be handled for us
      if( isManagedDispose ) {
        Stop();

        if( perf != null ) {
          perf.CloseDown();

          if( seg != null ) {
            Marshal.ReleaseComObject(seg);
            seg = null;
          }

          Marshal.ReleaseComObject(perf);
          perf = null;
        }
      }

      // Let the base class have a chance, too
      base.Dispose(isManagedDispose);
    }

    // DirectX 7
    DirectX7 dx = new DirectX7Class();
    DirectMusicLoader loader;
    DirectMusicPerformance perf;
    DirectMusicSegment seg;
    DirectMusicSegmentState segstate;

    /*
     * DirectX 8
     * DirectX8 dx = new DirectX8Class();
     * DirectMusicLoader8 dml = dx.DirectMusicLoaderCreate();
     * DirectMusicPerformance8 dmp = dx.DirectMusicPerformanceCreate();
     * DMUS_AUDIOPARAMS    dmA = new DMUS_AUDIOPARAMS();
     * DirectSound8        ds = null;
     * dmp.InitAudio(Handle.ToInt32(), CONST_DMUS_AUDIO.DMUS_AUDIOF_ALL, ref dmA, ref ds, CONST_DMUSIC_STANDARD_AUDIO_PATH.DMUS_APATH_SHARED_STEREOPLUSREVERB, 64);
     * DirectMusicSegment8 seg = dml.LoadSegment(@"C:\temp\MIDIDemo\sample4.mid");
     * seg.Download(dmp.GetDefaultAudioPath());
     * dmp.PlaySegmentEx(seg, 0, 0, null, null);
     */
  }
}