Producing a Dialog Box for Selecting a Filter

An application can allow users to select an arbitrary filter operation and apply it to waveform-audio data. In the following example, the application allocates a buffer to hold the filter and then uses the acmFilterChoose function to select the filter. The functions in this example must be called with the appropriate filter or filter tag.

MMRESULT        mmr; 
PWAVEFILTER     pwfltr; 
DWORD           cbwfltr; 
// Determine the maximum size required for any valid filter 
// for which the ACM has a driver installed and enabled. 
mmr = acmMetrics(NULL, ACM_METRIC_MAX_SIZE_FILTER, &cbwfltr); 
if (MMSYSERR_NOERROR != mmr) { 
    // The ACM probably has no drivers installed and 
    // enabled for filter operations. 
    return (mmr); 
// Dynamically allocate a structure large enough to hold the 
// maximum sized filter enabled in the system. 
pwfltr = (PWAVEFILTER)LocalAlloc(LPTR, (UINT)cbwfltr); 
if (NULL == pwfltr) { 
    return (MMSYSERR_NOMEM); 
// Initialize the ACMFILTERCHOOSE members. 
memset(&afc, 0, sizeof(afc)); 
afc.cbStruct    = sizeof(afc); 
afc.fdwStyle    = 0L;               // no special style flags 
afc.hwndOwner   = hwnd;             // hwnd of parent window 
afc.pwfltr      = pwfltr;           // wfltr to receive selection 
afc.cbwfltr     = cbwfltr;          // size of wfltr buffer 
afc.pszTitle    = TEXT("Any Filter Selection"); 
// Call the ACM to bring up the filter-selection dialog box. 
mmr = acmFilterChoose(&afc); 
if (MMSYSERR_NOERROR == mmr) { 
    // The user selected a valid filter. The pwfltr buffer, 
    // allocated above, contains the complete filter description. 
// Clean up and exit. 
return (mmr);