Expose a directshow filter property example with program AND filter sourcecode

Question

I'm trying to find an example where a parameter that could be controlled through the filter property page has an exposed getter/setter so that, without loading the property page, the filter property can be changed by the parent program that generated the graph.

Ezrgb24 from the windows sdk has a working property page, but I don't see how to expose the functions used in the property page so that my program can access them directly without initalizing the property page itself. I looked through the Programming Microsoft Directshow book and saw that it goes through the YUVGray example filter and mentions that the colors used could be exposed so that the parent program of the graph could change them, but does not give an example how.

Meanwhile, samples from directshow.net, like the windows sdk samples, appear to include only the filter or only the program source, and I didn't see any example filter that has such properties directly exposed. But examples like the BitmapMixer call IVMRMixerBitmap9.SetAlphaBitmap, an interface for VMR9. I'd like a sample that gives me the code for a similar interface and the filter so I can see how they are related, and the program so I can see how my environment should be set up to utilize the interface.

I'm guessing this is a basic exercise in utilizing COM, but I really would like a complete example with all of the source so I can fully understand how everything is connected. Even if the exposed property is trivially used it would be enough of a skeleton to go on. Is there such an example somewhere that I missed? I'm in C# for the program but have been using directshow.net and can get any graph set up and running, so a C++ program would be fine.

Toboe Toboe · Accepted Answer · 2011-08-01T22:08:28

Alright here we go:

We'll be using the ezrgb24 filter example that comes out of the samples that ship with the windows sdk because it's free and open source. It also already has the interface on this side defined. See the iez.h file for the interface, specifically we'll note two things from this file:

1) Our GUID is fd5010a3-8ebe-11ce-8183-00aa00577da1 - we'll need that for the code in the C# side 2) we're exposing the get_IPEffect and put_IPEffect functions which are defined in the ezrgb24.cpp file

So all the work on that side has already been done for us, and it gives us a good idea of how to make our own functions to expose.

Now in our C# program, we're going to make an interface that adapts to this:

using System;
using System.Runtime.InteropServices;

...

[ComImport, 
  System.Security.SuppressUnmanagedCodeSecurity,
  Guid("fd5010a3-8ebe-11ce-8183-00aa00577da1"),
  InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
public interface IIPEffect
{
    [PreserveSig]
    void get_IPEffect([Out] out int effectNum, [Out] out double StartTime, [Out] out double Length);

    [PreserveSig]
    void put_IPEffect([In] int effectNum, [In] double StartTime, [In] double Length);
}

Notice that the Guid is the same and our exposed functions match what is defined inside the filter's code (you can just use [Out] when the C++ function asks for a pointer, in this specific case remember that REFTIME in ezrgb24 is just another name for the double class).

That is all you need to start using the interface.

For example, say I create a graph with directshow.net and make an instance of the ezrgb24 filter (quick and dirty - after registering my compiled dll of ezrgb24 with regsvr32.exe, I just looked up the moniker in GraphEdit and added it that way). I called the instance of the ezrgb24 filter that I was using in my graph IEfilter.

I add it to my graph and connect the pins as usual. Then I can use the interface class I defined as follows at any point to change the properties of the filter, without any need to restart the graph or bring up the property page:

IIPEffect myIIPEffect = IEfilter as IIPEffect;
int myInt;
double myDouble1, myDouble2;
if (myIIPEffect != null) //the cast will break if you didn't use the right GUID in your interface
{
    myIIPEffect.put_IPEffect(1002, 6, 7); //for this filter, look at resource.h for what the int should be, in this case 1002 is the emboss effect
    myIIPEffect.get_IPEffect(out myInt, out myDouble1, out myDouble2);
}

And that's it. I hope this helps anyone looking for a complete picture of exposing and accessing filter properties!

Expose a directshow filter property example with program AND filter sourcecode

1 Answers