Game Window Cursor Clipping
Contents
Summary
This implementation allows you to clip the cursor to the game window such as in DOOM and DOOM Eternal (id Tech 6 - 7), also brings some fixes to various bugs on VGUI.

Requirements
- Knowledge of C++
- Knowledge of Source Engine
- Source SDK Base 2013 - Currently tested on Source SDK Base 2013 Multiplayer.
Getting the Implementation/Code
First of all, you'll need the following files from the following GitHub repository:
Which you will copy to src/game/client/. You can also create a subfolder if you wish to, and copy these files there.
Implementation
Now head over to cdll_client_int.cpp' and include
#include "CCursorClipManagement.h"
Anywhere before
// memdbgon must be the last include file in a .cpp file!!!
#include "tier0/memdbgon.h"

In the same cpp, find CHLClient::PostInit() and add this to the end:
CCursorClipManagement::Init();
Lastly, find void OnRenderEnd() and add this to the end:
g_pCursorClipManager->Think();
Conclusion
You're all set! Compile your client project and check if it works.
Notes
If you start the game/mod with one of the following parameters:
- -tools
- -dev
- -developer
- -nocursorclipping
Or if you're compiling into a different platform, else than WIN32, the cursor clipping will be disabled and won't work by default.
This behavior can be changed by modifying CCursorClipManagement::Think().
You can also add a ConVar to enable or disable this dynamically in-game, all you'll need to do is adding one more check on CCursorClipManagement::Think().