Why is my child window unresponsive to mouse events?

Question

I have created a customized static window which displays a bitmap image, this window is the child window of some other window. Now I want to capture mouse events for this window, so that I can provide functionality to crop the image.

But the problem is Mouse events are not passed to this child window.... following is a code snippet of the WndProc of child window ..

WNDPROC origStatProc;
    // Variable which stores the handle of BITMAP image
HBITMAP hBitmap=NULL;
LRESULT CALLBACK dispWndProc(HWND hwnd,UINT msg, WPARAM wParam, LPARAM lParam)
{
    static HDC hdc;
    static PAINTSTRUCT paintSt;
    static RECT aRect;

    switch(msg)
    {
        case WM_PAINT:
        {
            hdc = BeginPaint(hwnd,&paintSt);
            GetClientRect(hwnd,&aRect);
            if(hBitmap!=NULL)
            {               
                HDC memDC = CreateCompatibleDC(hdc);
                if(memDC!=NULL)
                {
                    BITMAP bmp;
                    GetObject(hBitmap,sizeof(bmp),&bmp);
                    SelectObject(memDC,hBitmap);
                    SetStretchBltMode(hdc,HALFTONE);
                    StretchBlt(hdc,0,0,aRect.right,aRect.bottom,
                    memDC,0,0,bmp.bmWidth,bmp.bmHeight,
                    SRCCOPY);
                    DeleteObject(&bmp);
                    ReleaseDC(hwnd,memDC);
                }
            }           
            // the code for painting 
            EndPaint(hwnd,&paintSt);
        }
        break;
        case STM_SETIMAGE:
        {           
            InvalidateRect(hwnd,&aRect,true);           
        }
            break;  
        case WM_LBUTTONDOWN:
            {
                int xPos = GET_X_LPARAM(lParam);
                int yPos = GET_Y_LPARAM(lParam);
                char xstr[10];
                _itoa(xPos,xstr,10);
                MessageBox(NULL,xstr,"X Value ",MB_OK);
            }
            break;

        default:
            return origStatProc(hwnd,msg,wParam,lParam);

    }
    return 0;
}

Can anyone tell me what else I need to capture mouse events inside this Child window...

Answer 1

The window class that you use for the window will determine certain default behaviors for the window. The Static window class is particularly difficult to work with, because Windows makes assumptions that the window will never change its contents, and won't interact with the user in any way. You'll probably find that the WM_LBUTTONDOWN is being passed to the parent window.

Answer 2

If I remember correctly: static windows declare themselves to be 'invisible' to mouse clicks by returning HTTRANSPARENT in response to WM_NCHITTEST. Because of this, windows passes the mouse click on to the parent. If you want to process the mouse clicks in the statics, you'll need to also override this behavior to return HTCLIENT instead.