how do I feed hwnd to screencapture?

Void CaptureScreen()
{
    int nScreenWidth = GetSystemMetrics(SM_CXSCREEN);
    int nScreenHeight = GetSystemMetrics(SM_CYSCREEN);
    HWND hDesktopWnd = GetDesktopWindow();
    HDC hDesktopDC = GetDC(hDesktopWnd);
    HDC hCaptureDC = CreateCompatibleDC(hDesktopDC);
    HBITMAP hCaptureBitmap =CreateCompatibleBitmap(hDesktopDC,
                            nScreenWidth, nScreenHeight);
    SelectObject(hCaptureDC,hCaptureBitmap);

    //  I run this to prepare to capture screen, and after this I can run


    // I run this to capture. but I can't make it out the part to pass it to the getpixel function

    BitBlt(hCaptureDC,0,0,nScreenWidth,nScreenHeight,
           hDesktopDC,0,0,SRCCOPY|CAPTUREBLT);



    SaveCapturedBitmap(hCaptureBitmap);
    //Place holder - Put your code
    //here to save the captured image to disk

    // what does this do?



    ReleaseDC(hDesktopWnd,hDesktopDC);
    DeleteDC(hCaptureDC);
    DeleteObject(hCaptureBitmap);
   
    // I run these 3 only when I am done capturing right?
}

in your code example,

return hBitmap



is this what I feed to getpixel?

a problem, I don't get your code is doing.


    BitBlt(hCaptureDC,0,0,nScreenWidth,nScreenHeight,
           hDesktopDC,0,0,SRCCOPY|CAPTUREBLT);



where is the equivalent of this one?

void CaptureWindow(HWND hWnd)             //     maybe I need to split this into 3 functions
                                          //     see below
{
     RECT rect;
     if  (!GetWindowRect(hWnd, &rect))
          return NULL;
     HDC hWindowDC = ::GetDC(hWnd);
     if (!hWindowDC)
          return NULL;
     HDC hCaptureDC = CreateCompatibleDC(hWindowDC);
     if (!hCaptureDC)
          return NULL;
     HBITMAP hBitmap = CreateCompatibleBitmap(hWindowDC, rect.right-rect.left+1, rect.top-rect.bottom+1));
     if (!hBitmap) {
          DeleteDC(hCaptureDC);
          return NULL;
     }


     HBITMAP oldBmp = (HBITMAP)SelectObject(hCaptureDC, hBitmap);
     int result = PrintWindow(hWnd, hCaptureDC, 0);
 
   
     //     does it help speed to keep the same DC and then reuse it by capturing onto it?
     //     if it helps, i would do
     //    
     //     //  a function to create a empty DC, return it
     //     //  capture onto this DC,            return it
     //     //  finishe with the DC,             run below
     //     //  to use this DC, see bottom


     // cleaning tasks before returning
     SelectObject(hCaptureDC, oldBmp);
     DeleteDC(hCaptureDC);
     DeleteObject(hBitmap);
 }








// you can use getpixel right here, passing hCaptureDC
//I need to access a lot of points with a function like this
//so I need to return hCaptureDC from above function somehow


getpixel ( ?type,   hCaptureDC,  x, y)
{
  //  place holder
  return color;
}






does this make sense?

yeah that's one i planned to use.


would it help it to run faster if I keep the same dc?

how about doing this in 3 functions?

1st to return dc with capture on it
2nd given dc return getpixel
3rd  release dc.

i am, not sure how to do it, you mean


HDC hWindowDC = ::GetDC(hWnd);

byte bytecolor = getpixel ( hWindowDC, x, y );


?

that't ALL I need ?

HDC hWindowDC = ::GetDC(hWnd);
(?)          COLORREF GetPixel(   HDC hWindowDC, int x, int y );



I have problem with the (?) part.

I didn't get the type of variable I need to store the values

also, how do I convert those values into

int red
int green
int blue

?

oh party begins with that :p

https://www.experts-exchange.com/questions/22983831/how-do-I-save-a-screen-shot.html


please take a look of this.