API Hooking question

[olinn]

I want to hook some APIs. I has some questions when reading the article on codeproject website http://www.codeproject.com/dll/apihijack.asp[^] The sample in that article is to hook DirectDrawCreate function in DDRAW.dll, and change it with his own function in his own dll. I am just wondering why he set a global WH_CBT hook but with a callback function doing nothing (just do CallNextHookEx). When I made some mouse hook or keyborad hook, I always did my work in the callback function, so I am confused that why we changed when do API hooking. Thanks in advance!