c++ MFC Window(Frame) Manipulation - c++

Question

I'm working on an Windows Application which has to show an overlaying fixed positioned window ("PopUp") in the left corner of the MainFrame which will receive some Information if a user missed some input or if certain actions have been successfully.
The "PopUp" Titlebar shall have an Icon next to the Title (e.g. ->Icon<- "Error") and the standard X - Close-Button. The ClientArea will have an descriptive text of the occurred Message.
Additionally the standard Border of the PopUp shall be set to 1px(smaller than the default windows border)
The "PopUp" is derived from CWnd and created with WS_VISLBE | WS_CLIPSIBLINGS | WS_CHILD | WS_CAPTION in the OnCreate-Method of the Applications MainFrame Window
Now I need to set/shrink the default Border of my PopUp and add the Icon to the Titlebar of the PopUp.
Can someone give me some example code of how i can solve my issues?
I'm pretty new to c++ and MFC so far my research brought me to https://msdn.microsoft.com/en-us/library/windows/desktop/bb688195(v=vs.85).aspx
but i dont know where and how to use DwmExtendFrameIntoClientArea() but so far I've read I assume Dwm is the way to go to be able to solve both problems or is there another/totally different way? Am I on the right track?

Answer 1

Finally I was able to shrinkthe default Windows Border by overriding the handling of WM_NCCALCSIZE.
I will update this answer as soon as I solved how to put my Icon in the Titlebar.
As of now I'll explain how I shrink the windows border:
Add ON_WM_NCCALCSIZE() to your MessageMap of the desired Window and Implement OnNcCalcSize() (Class Wizard will help to set this up) as followed:
void YourCWndClass::OnNcCalcSize(BOOL bCalcValidRects, NCCALCSIZE_PARAMS* lpncsp)
{
if (bCalcValidRects){
CRect rcClient, rcWind;
GetClientRect(&rcClient);
GetWindowRect(&rcWind);
int border = (rcWind.right - rcWind.left - rcClient.right) / 2 - 1;
//-1: leaves 1px of the Windows Default Border Width erase to have no border
lpncsp->rgrc->left -= border;
lpncsp->rgrc->right += border;
lpncsp->rgrc->bottom += border;
}
CWnd::OnNcCalcSize(bCalcValidRects, lpncsp);
}
The WM_NCCALCSIZE Message is sent up on the Window Creation (when you call Create()/CreateEx() ) but at this point of time GetClientRect() and GetWindowRect() will not return the proper values therefore you need to check the Bool Parameter!!!
To trigger another WM_NCCALCSIZE to be able to work with the proper Window Rectangles call SetWindowPos() right after the window creation
if (!m_MessagePopOver->Create(NULL, NULL, WS_CHILD | WS_CLIPSIBLINGS | WS_CAPTION, rect, this, NULL, NULL)){
TRACE0("failed to create MessagePopOver");
}
m_MessagePopOver->SetWindowPos(&wndTop, 0, 0, 0, 0, SWP_NOMOVE | SWP_NOSIZE);
This will result in a window like this: