How to hook api calls in another application

I am trying to hook the ExtTextOut and DrawTextExt GDI method calls of another application.

I know that I need to Use GetProcAddress to find the address of those methods in gdi32.dll, and overwrite the address in the process I want to hook with the address of my function. Then in my function I do what I need, then call the original function.

I want to make this hook functionality available to .net applications, and apparently this is do-able by creating an 'intermediate' unmanaged dll that does the hooking, and is capable of firing a event on the .net s开发者_如何学JAVAide, so that the new function can bet written in the managed environment. I'm just not sure how to implement this. Does anyone have any code samples or links to information?

I would recommend Microsoft's Detours (C++ x86 only) or EasyHook (C++ & C#, x86/x64).

http://easyhook.codeplex.com/

I've used it before, works pretty well. You have to pass a function or address and where you want it redirected to, and you can have all calls (for all processes or a specific one) sent into your function. The tutorials cover most of the basics, but I can edit code into this answer if you'd like.

A bit of trivia is that it also works the other way. Pass a pointer to your function and you can redirect calls into external code. Makes for some interesting integration with old apps or closed-source ones.

You can use Deviare API Hook, use DeviareCSharpConsole that is a tool that is in the package that let you hook any API and see parameter values in a treeview-like control. The only trick that it needs in Windows7 is to be load as admin, I reported.

How I Built a Working Poker Bot has samples of injecting code and hooking gdi events.