How can a program control another program?

Question

Bots, how do they work? Do they tell the video game a key was pressed or the mouse was clicked?

If not is there a way to have your program tell another program a key was pressed? I would like to make a program to beat some game. So any resources or examples are appreciated.

Update: So one way is to emulate keystrokes, so what are some methods to do this (in any language)?

Answer 1

I've written a bunch of bots at one time or another (from Pogo games to Yohoho Puzzle Pirates). For windows, you're usually going to either be sending Win32 events to simulate mouse movements, or spoof the actually low-level messages sent between windows when the mouse is actually clicked. A lot of it really depends on how the program reacts (by accepting the message with the coordinates, or, in Java's case, immediately reading the mouse coordinates). The "automation" part usually involves reading the screen and writing heuristics or algorithms for determining the state, but can also be as nice as packet sniffing (a lot of information there in poor poker implementations) or as hacky as reading memory locations directly. Pretty big "field", and poorly documented as it's pretty profitable and not hard to get into.

Sending Input

C/C++ (in Windows)

For keys, try CodeProject:

http://www.codeproject.com/KB/cpp/sendkeys_cpp_Article.aspx

And messages:

http://www.codeproject.com/KB/threads/sendmsg.aspx

Your best bet is to learn to send messages using the Win32 API, then use something like Spy++ or its derivatives to "reverse engineer" how KeyPresses and mouse movements are sent to the window.

Java

Java has an amazingly portable Robot class that is able to:

1. Read Pixels from the screen.
2. Control the mouse.
3. Send keys.

I'd give that a shot if you're looking for quick and easy.

Basic Logic

This is described elsewhere on the internet in depth, but most bots follow a simple state-machine program flow. You read the screen (or packets, or memory), find out what "state" you're in based on your readings and past data, do calculations, and send the result back out to the program.

Reading the screen can be difficult, but can be made easier if you consider that a lot of times, there are a few "lucky" pixels relative to the window that will give you an idea of what state the program is in. The process of finding these pixels can be automated.

Answer 2

There are a couple of kinds of bots. From what I remember when I used to play CS (a long, long time ago)

Some bots use the libraries of the application itself to inspect the environment (the map, where players are etc...) The bots also use the library to control movement. I doubt there are many bot implementations that invoke mouse messages to tell the game how to move etc...

Some bots emulate the application level protocol (if it's multi-player). So in other words, the game doesn't even need to run. A bot can run in a virtual game.

I'm going to run counter to what one other poster has suggested: writing a game bot is probably a more valuable exercise than actually playing the game, and being curious about how they work is a good sign. :)

Answer 3

Some programs (such as ones that grind for you in an MMORPG) are simply emulating keystrokes. A tool to do this is AutoIt.

As for bots that actually play the games themselves, I've not really done anything with them, but I'm assuming they would use some sort of predefined set of actions, maybe a heuristic, but not likely.