CODEWITHSUNDEEP
c++winapi
napco
napco

Reputation: 63

Create a child window inside another application

I'm trying to write a bot in C++ for a PC game using the windows API. I've managed to find the process HANDLE, its ID and finally its HWNDwith EnumWindows. I've managed also to send messages to its window (using SendMessage) in order to simulate keystrokes. Since the game runs full screen I'd like to create a child window inside it with custom controls to switch on/off the bot easily but i'm having problems with it. I've tried to register a window class and create a window with the game's HWND as a parent but I can't see anything. This is the code I've used to create the child window (not working):

// ... Window class registering etc...

HWND hChild = CreateWindowEx(0, 
                             "MyWindowClass", 
                             "Title", 
                             WS_CHILD | WS_VISIBLE, 
                             0, 0, 100, 100, 
                             hParent, 
                             NULL, 
                             AHInstance, 
                             NULL); // Parent is a valid window handle from another process

Honestly I'm not a skilled windows API programmer, this whole thing is new to me. I'm not even sure if this is the right way to do such thing.

[Edit.] When i minimize/maximize the game my window shows correctly for a second or two. It seems that the game's rendering is happening after the rendering of my window. Any idea? And what about messages? Should i manage them or not? Is the game going to forward messages to my window?

Upvotes: 1

Views: 4219

Answers (2)

Eric Brown
Eric Brown

Reputation: 13942

Windows have thread affinity. This means that the thread that creates the window will be processing the messages for that window. Furthermore, all windows in a parent-child chain should be processed by the same thread. Otherwise, bad things happen.

So - how is your code being run? If it's a separate executable, you're going to be much better off leaving your window as a top-level window, and simply monitoring the target window for move events (using UI Automation, for example) and having your window move appropriately.

Otherwise, you're going to need to inject your code into the game executable, and have it create the windows on the appropriate thread. I wouldn't recommend that.

Upvotes: 1

David Heffernan
David Heffernan

Reputation: 613451

You are not going to have much success by running the code from a different process. Cross process parent/child relationships seldom work. Especially if the other process is not expecting it. This is not something you take on lightly. The capability only exists as a compatibility sop to 16 bit Windows. No place for that technique today.

It seems plausible to me that you don't need to parent the window in this way. If you don't need it to be a child of a window in the other process, don't do that.

If you do need it to be a child of the other process then you might be in trouble. Perhaps you could inject a DLL into the other process and create the window there. Also not without difficulties.

Upvotes: 1

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