IDirectSoundBuffer::Lock

The IDirectSoundBuffer::Lock method obtains a valid write pointer to the sound buffer's audio data.

HRESULT Lock(
  DWORD dwWriteCursor,    
  DWORD dwWriteBytes,     
  LPVOID lplpvAudioPtr1,  
  LPDWORD lpdwAudioBytes1,  
  LPVOID lplpvAudioPtr2,  
  LPDWORD lpdwAudioBytes2,  
  DWORD dwFlags           
);

Parameters

dwWriteCursor

Offset, in bytes, from the start of the buffer to where the lock begins. This parameter is ignored if DSBLOCK_FROMWRITECURSOR is specified in the dwFlags parameter.

dwWriteBytes

Size, in bytes, of the portion of the buffer to lock. Note that the sound buffer is conceptually circular.

lplpvAudioPtr1

Address of a pointer to contain the first block of the sound buffer to be locked.

lpdwAudioBytes1

Address of a variable to contain the number of bytes pointed to by the lplpvAudioPtr1 parameter. If this value is less than the dwWriteBytes parameter, lplpvAudioPtr2 will point to a second block of sound data.

lplpvAudioPtr2

Address of a pointer to contain the second block of the sound buffer to be locked. If the value of this parameter is NULL, the lplpvAudioPtr1 parameter points to the entire locked portion of the sound buffer.

lpdwAudioBytes2

Address of a variable to contain the number of bytes pointed to by the lplpvAudioPtr2 parameter. If lplpvAudioPtr2 is NULL, this value will be 0.

dwFlags

Flags modifying the lock event. The following flags are defined:

DSBLOCK_FROMWRITECURSOR

Locks from the current write position, making a call to IDirectSoundBuffer::GetCurrentPosition unnecessary. If this flag is specified, the dwWriteCursor parameter is ignored.

DSBLOCK_ENTIREBUFFER

Locks the entire buffer. The dwWriteBytes parameter is ignored.

Return Values

If the method succeeds, the return value is DS_OK.

If the method fails, the return value may be one of the following error values:

Remarks

This method accepts an offset and a byte count, and returns two write pointers and their associated sizes. Two pointers are required because sound buffers are circular. If the locked bytes do not wrap around the end of the buffer, the second pointer, lplpvAudioBytes2, will be NULL. However, if the bytes do wrap around, then the second pointer will point to the beginning of the buffer.

If the application passes NULL for the lplpvAudioPtr2 and lpdwAudioBytes2 parameters, DirectSound will not lock the wrap-around portion of the buffer.

The application should write data to the pointers returned by the IDirectSoundBuffer::Lock method, and then call the IDirectSoundBuffer::Unlock method to release the buffer back to DirectSound. The sound buffer should not be locked for long periods of time; if it is, the play cursor will reach the locked bytes and configuration-dependent audio problems, possibly random noise, will result.

Warning  This method returns a write pointer only. The application should not try to read sound data from this pointer; the data might not be valid even though the DirectSoundBuffer object contains valid sound data. For example, if the buffer is located in on-board memory, the pointer might be an address to a temporary buffer in main system memory. When IDirectSoundBuffer::Unlock is called, this temporary buffer will be transferred to the on-board memory.

Requirements

  Windows NT/2000: Requires Windows NT 4.0 SP3 or later.
  Windows 95/98: Requires Windows 95 or later. Available as a redistributable for Windows 95.
  Header: Declared in dsound.h.
  Import Library: Use dsound.lib.

See Also

IDirectSoundBuffer, IDirectSoundBuffer::GetCurrentPosition, IDirectSoundBuffer::Unlock