plugin panel with qt GUI turns white while moving panel on windows

I remember we used to have this problem and I had to look up how we handled it. In a nutshell, you need to fill in a missing message propagation by drawing the widget yourself.

Qt isn't processing WM_PRINT or WM_PRINTCLIENT properly (though if its AI's fault for not passing along the message or Qt's fault I don't actually know). We attached a Windows Message proc to the result of AIPanelSuite::GetPlatformWindow() (invoked on the panel), and inside you need something that handles those messages like this:

LRESULT CALLBACK WindowMessageProc(HWND window, UINT message, WPARAM wParam, LPARAM lParam)

{

     switch (message) {

          // .. other messages to handle

          case WM_PRINTCLIENT:

               if (!(PRF_CLIENT & lParam)) {

                    break;

               }

          case WM_PRINT:

               {

                    // I wrote this off the top of my head, so you will need to fill in some bits, most notably widget_inside_panel

                    // We put this inside a class that we attached to the widget and made sure it contained a QWidget* that pointed to the widget inside the panel

                    // Also note that this code is doing zero error checking; you should really be checking the results of GetObject(), SelectDCObject(), etc.

                    QPixmap widgetPixmap = QPixmap::grabWidget(widget_inside_panel);

                    HBITMAP bitmap = widgetPixmap.toWinHTBITMAP();

                    HDC dc = 0;

                    HGDIOBJ oldObject = 0;

                    CreateDC(dc);

                    SelectDCObject(dc, bitmap, oldObject);

                    DIBSECTION dibSection;

                    GetObjectW(widgetBitmap, sizeof(dibSection), &dibSection);

                    BitBlt(reinterpret_cast<HDC>(wParam, 0, 0, dibSection.dsBmih.biWidget, dibSection.dsBmih.biHeight, dc, 0, 0, SRCCOPY);

                    if (oldObject) {

                         SelectObject(oldObject);

                    }

                    DeleteDC(dc);

                    DeleteObject(widgetBitmap);

               }

               break;

     }
}

This is useful method to have to work around other bugs, like if you have trouble with mouse wheel (we had several problems with that) or focus bugs.