There is something I would like to understand in my custom control. I handle WM_NCCALCSIZE to set the client area to the entire window, in other terms there is no nonclient area. I was expecting to not receive WM_NCPAINT but I still receive it each time the window size changes. Here is my WndProc code:
if (m.Msg == Win32Calls.WM_NCPAINT)
{
// I don't know why WM_NCPAINT is sent when WM_NCCALCSIZE has stated that there is no client area, so here is my workaround to stop processing here
if (Bounds.Size == ClientSize)
return;
// Draw borders if any
if (handled)
return;
}
else if (m.Msg == Win32Calls.WM_NCCALCSIZE)
{
if (m.WParam != IntPtr.Zero)
{
Win32Calls.NCCALCSIZE_PARAMS csp;
csp = (Win32Calls.NCCALCSIZE_PARAMS)Marshal.PtrToStructure(m.LParam, typeof(Win32Calls.NCCALCSIZE_PARAMS));
Rectangle rect = new Rectangle(csp.rgrc0.Left, csp.rgrc0.Top,
csp.rgrc0.Right - csp.rgrc0.Left, csp.rgrc0.Bottom - csp.rgrc0.Top);
_drawManager.NcCalcSize(ref rect);
csp.rgrc0.Left = rect.X;
csp.rgrc0.Right = rect.X + rect.Width;
csp.rgrc0.Top = rect.Y;
csp.rgrc0.Bottom = rect.Y + rect.Height;
Marshal.StructureToPtr(csp, m.LParam, false);
}
}
So, when a resize occurs, I checked and WM_NCCALCSIZE is correctly received, _drawManager.NcCalcSize does not modify "rect", then WM_NCPAINT is received and I'm obliged to compare the bounds and client rect to check if any non client painting should occur. Is this normal?