How to draw on an unfilled box on a video stream using the mouse

I am using dshownet(first time) and C#. I have got a sample to take the web cam input and display it on a form. I now need to draw a rectangle on top of the video stream using the mouse. (the intent is to track what is inside the box from there onwards).

I heard that there is something called VMR. So I went to the dshownet samples and went through them. I didnt find any samples that use the mouse to overlay a shape on the video stream. Someone on here suggested to use colorkey. Another person said to use GDI+ and mouse handling. I tried to compile the DXLogo sample but got this error :

Error 1 Cannot create an instance of the abstract class or interface 'System.Drawing.Image' C:\Documents and Settings\TLNA\Desktop\Final Year Project\Libraries\DirectShow library 2\DirectShowSamples-2010-February\Samples\Capture\DxLogo\Capture.cs 128 32 DxLogo-2008

for the code section:

   if (fileName.Length > 0)
           {
               m_Bitmap = new Image(fileName); // error happened here

               Rectangle r = new Rectangle(0, 0, m_Bitmap.Width, m_Bitmap.Height);
               m_bmdLogo = m_Bitmap.LockBits(r, ImageLockMode.ReadOnly, PixelFormat.For开发者_高级运维mat24bppRgb);
           }

I know that I must go through the Bitmap9 Interface. But I really dont know where to start. Should I read the Directshow API docs.

btw I also have the book Programming Microsoft Directshow for digital video and television. I started reading that book and stopped after a few pages since the code is mainly in C++. Should I continue to read this is book ? How can I accomplish the certain mentioned tasks in C# ?

Any suggestions as how to draw on the video. Some useful links(tutorials) would be helpful.

Many Thanks Tlna

I'm not sure why the DirectShow sample doesn't compile, but you may be able to change the problem line:

m_Bitmap = new Image(fileName);

to this:

m_Bitmap = new Bitmap(fileName);

and get it to work.

You're actually facing a pretty difficult problem here. DirectShow renders a video by drawing a series of still frames to a device context (like a PictureBox or a Form, or even the screen) many times a second (depending on whatever the frame rate is). You (as a programmer) can also (easily) render graphics directly to this same device context.

However, in order to make your drawn box appear over top of a running video, your code needs to draw the rectangle immediately after DirectShow draws each frame of the video; otherwise, the next frame will obliterate your rectangle. DirectShow objects probably have some sort of frame rendering event that you can handle, and then inside the event handler you just re-draw your box (based on the initial and current mouse coordinates, which you can get from the MouseDown and MouseMove events of whatever control you're drawing on).

Update: I just took a look at my code from when I was playing around with DirectShow.NET, and it looks like there is an event (DsEvCode.Repaint) that you could hook into and use to draw your box.

I haven't looked at the code sample you're working with, but do a search and see if you can find an OnGraphNotify() method in your code, you should be able to add something like this:

if (code == DsEvCode.Repaint)
{
    // draw the box here
}

Presumably, this event is fired after each frame of the video is rendered, so if you redraw your box here every time it will appear as if the box is persisting.