Problem with settgin a callback under directshow

abachler · 06-23-2009, 09:32 PM

1>..\Include\CDirectShowCamera.cpp(224) : error C3867: 'CDirectShowCamera::BufferCB': function call missing argument list; use '&CDirectShowCamera::BufferCB' to create a pointer to member

Code:

this->pGrabber->SetCallback(this->BufferCB , 1);

keep returning errors, here is the callback function, which is implimented as a member function

Code:

HRESULT CDirectShowCamera::BufferCB(double SampleTime , BYTE* pImage , long BufferLen){ 
 // snip irrelevant guts
   return S_OK;
 }

except if I add the ampersand it gives this error

Code:

 this->pGrabber->SetCallback(&CDirectShowCamera::BufferCB , 1);

1>..\Include\CDirectShowCamera.cpp(224) : error C2664: 'ISampleGrabber::SetCallback' : cannot convert parameter 1 from 'HRESULT (__thiscall CDirectShowCamera::* )(double,BYTE *,long)' to 'ISampleGrabberCB *'

which makes even less sense. Obviously I need to be able to call this callback function, but I need it to know what instance of CDIrectShowCamera it is handling, so that it can add the sampels to the appropriate buffer. There will be more than one instance of the class operating simultaneously. I know im probably missing somethign realyl obvious.

Cactus_Hugger · 06-23-2009, 09:44 PM

Never worked with these, but: "You can't convert a member-function pointer to a ISampleGrabberCB *" -- is what that error says... where are you getting lost?

Seems to me you should derive from ISampleGrabberCB, and implement that interface, instantiate it, and pass the instance. The derived class could hold whatever data you needed it to, such as a pointer to your CDIrectShowCamera. No different than predicates to C++'s standard functions, such as sort(), really.

Sebastiani · 06-23-2009, 10:10 PM

Right, assuming you've derived the class from ISampleGrabberCB and overloaded the BufferCB or SampleCB functions, you'll just need to pass a pointer to the object itself, ie:

Code:

this->pGrabber->SetCallback(this, 1);

abachler · 06-23-2009, 10:24 PM

I tried making a derived class but the compiler pukes because there is no appropriate constructor type in the base class, and when I tried overloading the constructor it puked again saying constructors are not allowed a return type, which didnt make sense since the constructor had no return type. I think im starting to see why pointers to member functions are not used very often.

I'm rethinking my strategy to possibly avoid pointers to member functions. It late and I think im messing up on implimenting the ISampleGrabberCB interface, so ill get soem sleep adn try again tomorrow.

Sebastiani · 06-23-2009, 10:38 PM

>> I tried making a derived class but the compiler pukes because there is no appropriate constructor type in the base class, and when I tried overloading the constructor it puked again

Well, you can't override a constructor. Can you post a compilable example?

**laserlight** · 06-24-2009, 05:22 AM

Quote:

Originally Posted by abachler

I tried making a derived class but the compiler pukes because there is no appropriate constructor type in the base class

If I understand this particular hurdle correctly, you could invoke the appropriate base class constructor in the derived class constructor's initialisation list.

abachler · 06-24-2009, 11:32 AM

Quote:

Originally Posted by Sebastiani

>> I tried making a derived class but the compiler pukes because there is no appropriate constructor type in the base class, and when I tried overloading the constructor it puked again

Well, you can't override a constructor. Can you post a compilable example?

The last compilable example I have doesnt have any of this code in it. It's using the GetCurrentBuffer() method, which I want to improve so that I get every image, with no duplicates. All im trying to do is add the callback so I can buffer each sample and then ill rewrite the CDirectShowCamera::GetCurrentImage() member function to retrieve images from the buffer instead of from GetCurrentBuffer(). This is the relevant code from the constructor function in the last compilable version,

Code:

  this->pGrabber->SetCallback(NULL , 1);
  this->pGrabber->SetBufferSamples(TRUE);

  this->Stage = 17;
  hr = this->pControl->Run();
  if(FAILED(hr)) return;

  this->Stage = 0xffffffff;
  this->Initialized = TRUE;
  return;

I cant post the whole class as its quite lengthy, this is actually the last thing it does before running the graph

06-23-2009, 09:32 PM	#1
abachler Rampaging 35 Stone Welsh Join Date: Apr 2007 Posts: 2,924	Problem with settgin a callback under directshow 1>..\Include\CDirectShowCamera.cpp(224) : error C3867: 'CDirectShowCamera::BufferCB': function call missing argument list; use '&CDirectShowCamera::BufferCB' to create a pointer to member Code: this->pGrabber->SetCallback(this->BufferCB , 1); keep returning errors, here is the callback function, which is implimented as a member function Code: HRESULT CDirectShowCamera::BufferCB(double SampleTime , BYTE* pImage , long BufferLen){ // snip irrelevant guts return S_OK; } except if I add the ampersand it gives this error Code: this->pGrabber->SetCallback(&CDirectShowCamera::BufferCB , 1); 1>..\Include\CDirectShowCamera.cpp(224) : error C2664: 'ISampleGrabber::SetCallback' : cannot convert parameter 1 from 'HRESULT (__thiscall CDirectShowCamera::* )(double,BYTE ,long)' to 'ISampleGrabberCB ' which makes even less sense. Obviously I need to be able to call this callback function, but I need it to know what instance of CDIrectShowCamera it is handling, so that it can add the sampels to the appropriate buffer. There will be more than one instance of the class operating simultaneously. I know im probably missing somethign realyl obvious. __________________ He is free, you say. Ah! That is his misfortune… These men… [have] the most terrible, the most imperious of masters, that is, need. … They must therefore find someone to hire them, or die of hunger. Is that to be free? - Simon Linguet
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06-23-2009, 09:44 PM	#2
Cactus_Hugger int x = ((int ) NULL); Join Date: Jul 2003 Location: Banks of the River Styx Posts: 891	Never worked with these, but: "You can't convert a member-function pointer to a ISampleGrabberCB " -- is what that error says... where are you getting lost? Seems to me you should derive from ISampleGrabberCB, and implement that interface, instantiate it, and pass the instance. The derived class could hold whatever data you needed it to, such as a pointer to your CDIrectShowCamera. No different than predicates to C++'s standard functions, such as sort(), really. __________________ long time; / know C? */ Unprecedented performance: Nothing ever ran this slow before. Any sufficiently advanced bug is indistinguishable from a feature. Real Programmers confuse Halloween and Christmas, because dec 25 == oct 31. The best way to accelerate an IBM is at 9.8 m/s/s. recursion (re - cur' - zhun) n. 1. (see recursion)
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06-23-2009, 10:10 PM	#3
Sebastiani Guest Join Date: Aug 2001 Posts: 4,922	Right, assuming you've derived the class from ISampleGrabberCB and overloaded the BufferCB or SampleCB functions, you'll just need to pass a pointer to the object itself, ie: Code: this->pGrabber->SetCallback(this, 1);
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06-23-2009, 10:24 PM	#4
abachler Rampaging 35 Stone Welsh Join Date: Apr 2007 Posts: 2,924	I tried making a derived class but the compiler pukes because there is no appropriate constructor type in the base class, and when I tried overloading the constructor it puked again saying constructors are not allowed a return type, which didnt make sense since the constructor had no return type. I think im starting to see why pointers to member functions are not used very often. I'm rethinking my strategy to possibly avoid pointers to member functions. It late and I think im messing up on implimenting the ISampleGrabberCB interface, so ill get soem sleep adn try again tomorrow. __________________ He is free, you say. Ah! That is his misfortune… These men… [have] the most terrible, the most imperious of masters, that is, need. … They must therefore find someone to hire them, or die of hunger. Is that to be free? - Simon Linguet
abachler is online now

06-23-2009, 10:38 PM	#5
Sebastiani Guest Join Date: Aug 2001 Posts: 4,922	>> I tried making a derived class but the compiler pukes because there is no appropriate constructor type in the base class, and when I tried overloading the constructor it puked again Well, you can't override a constructor. Can you post a compilable example? Last edited by Sebastiani; 06-23-2009 at 10:40 PM.
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