void RedrawBGStrip(int start, int num)
{
var s = _screenStartStrip + start;
for (var i = 0; i < num; i++)
Gdi.SetGfxUsageBit(s + i, Gdi.UsageBitDirty);
Gdi.DrawBitmap(roomData.Image, _mainVirtScreen, s, 0,
roomData.Header.Width, _mainVirtScreen.Height, s, num, roomData.Header.Width, 0);
}