The parent window of an owner-drawn button typically responds to at least three messages for the button: WM_INITDIALOG, WM_COMMAND, and WM_DRAWITEM. It is not necessary to process the WM_MEASUREITEM message for owner-drawn buttons.
When you must paint an owner-drawn button, the system sends the parent window a WM_DRAWITEM message whose lParam points to a DRAWITEMSTRUCT structure. Use this structure with all owner-drawn controls to provide the application with the information it requires to paint the control. The itemAction and itemState members of the DRAWITEMSTRUCT structure define how to paint an owner-drawn button.
The following example shows how to process WM_INITDIALOG, WM_DRAWITEM, and WM_COMMAND messages for owner-drawn buttons. This example demonstrates how to draw one of two bitmaps for a control, depending on whether the control is selected. You would typically use the wParam parameter of the WM_DRAWITEM message to identify the control; in this example, only one control is assumed.
BOOL CALLBACK OwnDrawProc(HWND hDlg, UINT message, WPARAM wParam,
LPARAM lParam)
{
HDC hdcMem;
LPDRAWITEMSTRUCT lpdis;
switch (message)
{
case WM_INITDIALOG:
// hinst, hbm1 and hbm2 are defined globally.
hbm1 = LoadBitmap((HANDLE) hinst, "OwnBit1");
hbm2 = LoadBitmap((HANDLE) hinst, "OwnBit2");
return TRUE;
case WM_DRAWITEM:
lpdis = (LPDRAWITEMSTRUCT) lParam;
hdcMem = CreateCompatibleDC(lpdis->hDC);
if (lpdis->itemState & ODS_SELECTED) // if selected
SelectObject(hdcMem, hbm2);
else
SelectObject(hdcMem, hbm1);
// Destination
StretchBlt(
lpdis->hDC, // destination DC
lpdis->rcItem.left, // x upper left
lpdis->rcItem.top, // y upper left
// The next two lines specify the width and
// height.
lpdis->rcItem.right - lpdis->rcItem.left,
lpdis->rcItem.bottom - lpdis->rcItem.top,
hdcMem, // source device context
0, 0, // x and y upper left
32, // source bitmap width
32, // source bitmap height
SRCCOPY); // raster operation
DeleteDC(hdcMem);
return TRUE;
case WM_COMMAND:
if (wParam == IDOK
|| wParam == IDCANCEL)
{
EndDialog(hDlg, TRUE);
return TRUE;
}
if (HIWORD(wParam) == BN_CLICKED)
{
switch (LOWORD(wParam))
{
case IDC_OWNERDRAW:
// application-defined processing
break;
}
}
break;
case WM_DESTROY:
DeleteObject(hbm1); // delete bitmaps
DeleteObject(hbm2);
break;
}
return FALSE;
UNREFERENCED_PARAMETER(lParam);
}