Author: David

Some thoughts about game AI

Some thoughts about game AI

Posted on by David
Military
Image by Dimitris Vetsikas from Pixabay

When I say AI, I mean control logic for computer played units in a game, not Ai as in Machine Learning or Artificial Intelligence. For instance in the Empire type game, that I started (On the Games source link) which has ships and units fighting on land and sea, capturing cities and building new units.

An AI for an Empire type game has a lot of logic to be implemented. I thought about this quite a bit and came up with a task based Ai system. A neutral city is spotted by an exploring ship. If its a transport with armour on infantry then it just attacks the city and hopefully captures it.

If not a task is created. This comprises a number of steps.

  1. Locate units nearest to the city that aren’t allocated to the task.
  2. If the units are on the same continent then just send them to attack the city.
  3. If not Locate the nearest transport and send it to rendezvous with the units at the nearest point to them. Load the units.
  4. If there aren’t any units free then locate the nearest friendly city that’s not tasked with anything and task it to build the units.
  5. If there’s no transport, have the city build a transport after building the armour/infantry units.

That’s just one for task but what if a friendly city is threatened and the tasked units are the nearest. Care has to be taken so that units aren’t flip flopped, getting orders one turn then being pulled away three turns later to a different task.

Each task should be given a time-to-live (say 30 turns), long enough to acquire the resources (units it needs) to do the job and reach the target. The rule then is no diverting units on a task unless a dire emergency (like threatening one of its cities) and those are the nearest.

There’s nothing worse than allocating units to a task then seeing enemy units sail right past unopposed. Writing code to deal with different situations and priorities is not an easy task

 

An amazing repository of articles on Chess programming

An amazing repository of articles on Chess programming

Posted on by David
Chess pieces
Image by Steve Buissinne from Pixabay

When I went to University, I stayed in the halls of residence and there was a final year student there who was into chess programming- heady stuff for a first year student. It’s always held a bit of a fascination for me – I’ve been playing chess since the age of 11 though never particularly well. I’ve found most chess programs could beat me unless I take a great deal of care and spend a long time thinking.

The Chess Programming Wiki has almost 4,000 articles on all aspects of chess programming across 7500 pages. If you are interested in chess programming and unfamiliar with this then you are missing out.  This uses the mediawiki software (same as Wikipedia) so can be a little opaque. I’ve found if you click the Special pages link on the left then All pages that it gives a much wider overview.

A bit of searching found the programming languages page and disappointingly there is no entry for C although there is a page on C in the Wiki!  This links to CFish, a C port of the Stockfish open source chess engine which is mostly C++. If you can write a program to beat beat Stockfish then you are indeed an awesome programmer!

Of course, AlphaZero has recently dominated play in chess, Go and Shogi. What makes this different is that its mostly self taught using an AI technique called reinforcement learning. You just tell it the rules of chess. This contrasts with “traditional” chess programming where moves are determined ahead and evaluation routines called.

 

 

Pacman in C99 that runs in the browser

Pacman in C99 that runs in the browser

Posted on by David

PacmanSuch a simple game yet still incredibly popular. Pacman is now 40 years old. I must confess, its not one that I was great at (that would be Battle Zone- the 3D wireframe tanks on the moon game- I could play that for an hour for just 10p),

This cross-platform implementation by German programmer Andre Weissflog (aka Flooh) looks spot on and plays it as well. Most of the game has been implemented in one C source file and its definitely worth reading the comments at the top of that file to see how things are done.

For instance “audio output works through an actual Namco WSG emulator which generates sound samples for 3 hardware voices from a 20-bit frequency counter,  4-bit volume and 3-bit wave type (for 8 wavetables made of 32 sample values each stored in a ROM dump)”.

The game uses the author’s Sokol libraries which are Simple STB-style cross-platform libraries for C and C++, written in C. It’s the first time I'[d come across these and they’re worthy of a separate look at. STB is a another library that I’ll also look at in the future. I’ve added a link to this Pacman to the C Code library. Happy Christmas!

PS. Also included in the GitHub download is The Pac-man dossier by Jamey Pittman, which is a 48 page PDF and tells you everything about playing Pacman. Stuff like the logic of gameplay, mechanics, easter eggs and the hardware specs of the original game boards not to mention the infamous level 255 overflow.

Interestingly the original hardware was a 3MHZ Z80A with 2 KB of RAM and 16KB of ROM on a 224 x 288 16 colour screen .

 

I added an if and switch tutorial

I added an if and switch tutorial

Posted on by David
Teachjer and blackboard
Image by mohamed Hassan from Pixabay

The next tutorial is Simple control flow in C. This demonstrates how to do if, if else and then switch statements. These are pretty siomple concepts but they are fundamentals so you do need to know them.

One thing I didin’t show in the switch tutorial is that you can mix in labels for that real write-only code experience. It’s not a technique I recvommend which is why its NOT in the tutorial but if you promise never to use this except in the rarest of circumstances, here’s what I mean.

#include <stdio.h>

int main() {
	int a = 10;
	switch (a) {
	case 1:
	case 2:
	case 3:
	case 4:
	{
		printf("a<5\n");
		break;
	};
	case 5:
fred:
	case 6:
		printf("a ==5 or a ==6\n");
		break;
	case 7:
	case 8:
	case 9:
		printf("a <9\n");
	case 10:
	{
		printf("a=10\n");
		goto fred;
	}
	default:
		printf("a not in range 1-10\n");
		break;
	}
}

The label is the line fred: and you can see in case 10 that after printing “a=10\n”, it jumps to fred which is just after the 5 case. That does nothing and falls through to the 6 case where it prints out “a ==5 or a ==6\n”. It’s not recommended but at least now if you ever see a jump to a label in a switch statement you can be sure that the programmer was not really at the top of his or her game.

I like web games

I like web games

Posted on by David

IllyriadNot the Flash type games you get on sites like Kongregate but strategy games like Illyriad, (Pictured) Though you can waste an awful lot of time playing them. The web is an excellent platform for certain of multiplayer games. Heck you can even play games like Quake III which was a desktop game but redone using WebAssembly.

I used to play a strategy game Inselkampf (German for Island war) where you start off with one island and improve it then you can start building ships and invading other islands. I remember getting to the point where I was managing an empire of 80 islands and the only way I could do track all the details was with an Excel spreadsheet. But it was a big time hog, taking up over and hour and a half each day (just mad!) and I stopped playing.

It seems to have closed down a few years ago which is a shame as it was very popular in the mid 2000s. The UK website inselkampf.co.uk just has a start Game Over message on it! Searching about I even found a copy of the Inselkampf rules online.

Given my postal games background (I created three Play by Mail games back in the late 80s, two of which are still run today on kjcgames.com. ) I still have an inkling to create a big web or mobile playable game. I’m not saying I’ll make a £million like torn.com.  I’m not a great fan of web development (well the JavaScript part of it) but I’m currently studying a Udemy course on Blazor which is Microsoft’s take on C# and WebAssembly.  This lets you create websites in C# running in the browser. And C# I am most definitely a fan of.

 

The L game by Edward de Bono

The L game by Edward de Bono

Posted on by David
The L Game
Image from Wikipedia

I bought a book The Five Day course in Thinking by the author Edward de Bono when I was at University. It included a seemingly very simple two player strategy game called The L Game.  If you’ve heard of the phrase Lateral Thinking that was invented by him back in 1967.

On a 4 x 4 board there are two L shapes and two neutral single pieces. To win you just have to move your L shape and (optionally) one of the neutral pieces so that your opponent can’t move his L shape.

I’ve had a cursory search for C source versions of this game and there are bound to be more than the one I found which was written for an Arduino WifiBoy Pro. There’s a downloadable zip file which contains a file wbpro_chess_L.ino. Despite the extension, it is a C source code text file.

If you are looking for an interesting programming problem then create a computer opponent for a game. The good thing about this is, its so simple graphics wise that you could draw the board in a console with B = Blue, R = red and 1 and 2 the two neutral pieces like this.

1RR.
.BR.
.BR.
.BB2

 

New tutorial on installing SDL on Linux

New tutorial on installing SDL on Linux

Posted on by David

SDl Demo programWell you might say, “Don’t many Linux distros have SDL installed so people can play games?” and the answer is yes but not the development files and headers, and that’s what this shows you how to do along with a simple program to test that you can compile and run.

You’ll also need clang or gcc installed but as you can do that with a simple sudo apt install clang, it’s hardly worth a tutorial on its own.

However you also need to install VS Code and the C/C++ extension. Go to the VS Code website, download the Linux x64 version and double click on it to install it. After that from a terminal type code and it’ll appear. You then need to select extensions (5th icon down the left hand side) and pick the Microsoft C/C++ extension and install it.

I’ve added a new tutorial on the Tutorials page How to Install SDL on Linux. That includes a link to a demo file (its just above the screenshot) containing all three source code files and four VS Code configuration files for VS Code.

This program is almost identical to the asteroids_ch25 file (it draws lots of random size and colour rectangles on screen) but has been upgraded for Clang 10 and also what looks like a bug with search paths. There’s an extra line in Tasks.json to include the path to the SDL2 header files or you’ll get a can’t find a particular SDL header error when you compile.

Building code with VS Code is easy to understand once you “get” how the Folder works. I always keep the .vscode folder in there with the four C/C++ JSON configuration files and all source for that whatever it is you are compiling.  In the screenshot below (from WinSCP), you can see the path is /home/david/Projects/Examples and it contains the .vscode folder the three source files and demo which is the compiled code.  In VS Code I opened Examples as the Folder.

VS Code Folder

 

The .vscode folder is greyed out because the . means it’s normally hidden.

Coding a text adventure in C

Coding a text adventure in C

Posted on by David

Text AdventuresText adventures have been around since the likes of Colossal Cave which I first played in 1980. They were quite popular on the early home computers like ZX 81 which were quite limited in RAM and capability. With the capacity of modern computers there are Interactive fiction (the modern name for adventure games) games with over a million words of text.

I suspect I’d probably want to code them in another language because C isn’t the best language when it comes to text. Nevertheless other have gone ahead and there’s an almost complete (20 out of 23 lessons) on how to program a text adventure in C on GitHub.

It’s a fine piece of work and some of the 20 articles like 20. Combat are quite long with lots of annotated code. At the bottom of each page you can download the source code on that page as a zip file or run the sources on repl.it. If you are learning C the line-by-line annotations really help explain why something was done.

The C template library

The C template library

Posted on by David

Texture templateC of course doesn’t have generics or templates like C++ does, but I came across Gustav Lou’s C Template library this morning. It provides C equivalents to the following C++ template libraries. Each is done as a header file that you include.

deq.h -> std::deque
lst.h -> std::list
pqu.h -> std::priority_queue
que.h -> std::queue
set.h -> std::set
stk.h -> std::stack
str.h -> std::string
vec.h -> std::vector

The page on GitHub shows how to use libraries with an example of vector. The string equivalent library str.h would be an interesting one to see just how much of C++ string is supported.  C would still never be my language of choice for anything text heavy but if this is better than strcpy, strcat etc. I’ll happily use it.  Likewise list and vector. From memory C++ std::array is just a wrapper around the C standard array!