Processing the WM_RENDERFORMAT and WM_RENDERALLFORMATS Messages

If a window passes a NULL handle to the SetClipboardData function, it must process the WM_RENDERFORMAT and WM_RENDERALLFORMATS messages to render data upon request.

If the WM_RENDERFORMAT message delayed rendering a specific format and an application requested data in that format, the message is sent to the clipboard owner. If the WM_RENDERFORMAT message has delayed rendering one or more formats, the message is sent to the clipboard owner before it is destroyed.

To render a clipboard format, the window procedure must place a data handle on the clipboard by using the SetClipboardData function. It must not open the clipboard before calling SetClipboardData.

The Label application processes the WM_RENDERFORMAT and WM_RENDERALLFORMATS messages as follows.

case WM_RENDERFORMAT: 
    RenderFormat((UINT) wParam); 
    break; 
 
case WM_RENDERALLFORMATS: 
    RenderFormat(uLabelFormat); 
    RenderFormat(CF_TEXT); 
    break; 

In both cases, the window procedure calls the application-defined RenderFormat function, defined as follows.

void WINAPI RenderFormat(UINT uFormat) 
{ 
    HGLOBAL hglb; 
    PLABELBOX pbox; 
    LPTSTR  lptstr; 
    int cch; 
 
    if (pboxLocalClip == NULL) 
        return; 
 
    if (uFormat == CF_TEXT) 
    { 
        // Allocate a buffer for the text. 
 
        cch = pboxLocalClip->cchLabel; 
        hglb = GlobalAlloc(GMEM_MOVEABLE, 
            (cch + 1) * sizeof(TCHAR)); 
        if (hglb == NULL) 
            return; 
 
        // Copy the text from pboxLocalClip. 
 
        lptstr = GlobalLock(hglb); 
        memcpy(lptstr, pboxLocalClip->atchLabel, 
            cch * sizeof(TCHAR)); 
        lptstr[cch] = (TCHAR) 0; 
        GlobalUnlock(hglb); 
 
        // Place the handle on the clipboard. 
 
        SetClipboardData(CF_TEXT, hglb); 
    } 
    else if (uFormat == uLabelFormat) 
    { 
        hglb = GlobalAlloc(GMEM_MOVEABLE, sizeof(LABELBOX)); 
        if (hglb == NULL) 
            return; 
        pbox = GlobalLock(hglb); 
        memcpy(pbox, pboxLocalClip, sizeof(LABELBOX)); 
        GlobalUnlock(hglb); 
 
        SetClipboardData(uLabelFormat, hglb); 
    } 
}