Step 2. Declare the Filter Class

Step 2. Declare the Filter Class

This is step 2 of the tutorial Writing Transform Filters.

Start by declaring a C++ class that inherits the base class:

class CRleFilter : public CTransformFilter
{
    /* Declarations will go here. */
};

Each of the filter classes has associated pin classes. Depending on the specific needs of your filter, you might need to override the pin classes. In the case of CTransformFilter, the pins delegate most of their work to the filter, so you probably don't need to override the pins. 

You must generate a unique CLSID for the filter. You can use the Guidgen or Uuidgen utility; never copy an existing GUID. There are several ways to declare a CLSID. The following example uses the DEFINE_GUID macro:

[RleFilt.h]
// {1915C5C7-02AA-415f-890F-76D94C85AAF1}
DEFINE_GUID(CLSID_RLEFilter, 
0x1915c5c7, 0x2aa, 0x415f, 0x89, 0xf, 0x76, 0xd9, 0x4c, 0x85, 0xaa, 0xf1);

[RleFilt.cpp]
#include <initguid.h>
#include "RleFilt.h"

Next, write a constructor method for the filter:

CRleFilter::CRleFilter()
  : CTransformFilter(NAME("My RLE Encoder"), 0, CLSID_RLEFilter)
{ 
   /* Initialize any private variables here. */
}

Notice that one of the parameters to the CTransformFilter constructor is the CLSID defined earlier.

Next: Step 3. Support Media Type Negotiation.

See Also

• Writing DirectShow Filters