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Category: C

Doing 3D Math(s) in C

Posted on January 16, 2021January 15, 2021 by David

If you’re interested in seeing how 3D math(s) are done, this article by ex Googler Andy Sloane is about a program he wrote called donut.c. The name is doubly appropriate as not only is the source code shaped like a Donut (doughnut for us Brits), when run on Linux, it outputs an animated 3D donut. This was an attempt at obfuscated C back in 2006.

Now 15 years later he’s updated it to work without using the math library. Interesting is the explanation of how he did all the mathematics without using sin and cos directly. Also it includes a version that uses 10 bit integer arithmetic; no floats at all. If you’re interested in understanding how Donuts.c works, read this post from 2011.

I like articles like this- they’re a bit different and add to programming knowledge. and you can never get enough of that

New Tutorial – Implementing the Windows game Slay

Posted on January 14, 2021January 14, 2021 by David

One of my favourite casual games is Slay by Sean O’Connor. I bought the full game which sells for $10 and it’s still selling well via his site or Steam. His game is only for Windows so my reimagining (great word!) will be for Linux only including Raspberry Pi.

His game comes with several hundred islands, in four sizes from very small, small, Large and very large. You play against 6 computer players with intelligence ranging from very stupid, stupid, clever to very clever. In addition there are a bunch of predefined maps like Britain or even the world.

Troops exist in four sizes with each size three times bigger than the one below. Your territory must be big enough to support the troops there and if it isn’t they all starve. Splitting an enemies’ territory to starve his troops is a valid tactic.

Add in with trees which can spread and waste land which spreads even faster and its a cute addictive game.

My game will be called Onslaught and use its own graphics. Islands will be computer generated and hopefully the AI will play a decent game. The first tutorial which just explains the game and the scope of what I intend to do is now available.

Atoms tutorial three- finishing the game off

Posted on January 13, 2021January 10, 2021 by David

I fixed the bug in the Atoms game and the third tutorial finishes it off. The source code (in this case atoms3.c) has been placed on GitHub and the final version is about 300 lines long.

As well as the bug fix, I added a line to show the number of cells owned by the player and the computer. You can see it after the player move (Player : 41 Computer 16) and after the Computer move.

This whole atoms game was an experiment to see if I can introduce C programming without having to go overboard explaining every statement etc as I’ve done in the past. I think I’ll get back to programming games!

Tronus Project 1945 – Coursework

Posted on January 12, 2021January 10, 2021 by David

A university student by the pen name of Tronus has put a project from his 3rd year in his degree course on GitHub. The screenshot shows the game running on my PC. The build folder includes a release folder with game exe plus all dlls and game assets in a resources folder below that so you can run it immediately on Windows. ,

I vaguely remember playing a similar game (a vertical scroller) in arcades back in the 1980s. That game was 1942.

The 1945 game has been programmed in C and uses SDL2. As always I took a walk through the source just to compare how it was done say compared to my own efforts. One thing I noticed is that he uses a fixed delay of 11 milliseconds each frame in the game loop by calling SDL_delay(11) rather than setting up the video to sync to the fly back. Is this better or worse? I’m not sure.

I think I prefer my method in case something takes a bit longer. Having a fixed delay means that you could risk overrunning the 16.666 milliseconds allowed per frame. That could never happen with my asteroids game as syncing to the fly back means my game can take as long as 16.66 milliseconds per frame and still not overrun.

Answer to simple C Question

Posted on January 11, 2021January 9, 2021 by David

Answer sign — Image by Gerd Altmann from Pixabay

Hopefully you got choice 2. 62. Here’s the question again.

#include <stdio.h>
int main() {
	float* p = (float*)50;
	p = p + 3;
	printf("%u\n", p);
}

The first line in main() creates a “pointer to a float” p with the initial value 50. This 50 is the value of p i.e. the address that p is pointing to, NOT the value at that address P is pointed to.

Adding 3 to p moves the pointer by 3 x the size of a float. As it’s unspecified, this size of a float is typically 32-bits or 4 bytes. So this line adds 12 to p. It now has the value 62.

You can try this out and step through it on the Python Tutor. Despite its name, it will let you run run programs in Python, C, C++, Java, JavaScript, TypeScript and Ruby. It compiles C with GCC 4.8 and uses a Valgrind Memcheck plugin. There are a few restrictions its quite a nice way to show off execution of simple programs.

Simple C question

Posted on January 10, 2021January 9, 2021 by David

question marks — Image by Gerd Altmann from Pixabay

I saw this this morning and got the correct answer. I also tried it just to be sure in Visual Studio and apart from a warning, it compiled ok and ran and gave the correct answer.

#include <stdio.h>
int main() {
	float* p = (float*)50;
	p = p + 3;
	printf("%u\n", p);
}

If you want to avoid the warning, change the last line to

	printf("%u\n", (unsigned int)p);

So the question is what does this output?

Answer and explanation tomorrow.

Next atoms tutorial added

Posted on January 9, 2021January 6, 2021 by David

The first version of the program was 90 lines long but now it has grown to 275. This includes code to let the computer play and checking code plus I’ve refactored it a bit, simplifying the code. I haven’t extensively tested it and at least one bug has crept in. Occasionally the computer seems to claim ownership of a player cell. This stops you adding one to that cell so its not good.

You are welcome to have a look at the code and fix it. I will in a few days. The code is on GitHub and is a single file atoms2.c. As before its been compiled with Visual Studio 2019 Community edition though it should compile more or less unchanged with gcc, clang etc. It runs in a terminal/command line. You can see the computer playing in the screenshot.

I’ve also added the tutorial for this.

Program a NES game in C

Posted on January 7, 2021January 4, 2021 by David

Back in the mid 80s I was busy writing games for ZX Spectrum, MSX and CBM-64 and also porting games between 6502 and Z80. That was also when the original NES appeared. That had a 6502 CPU but a lot less RAM than the CBM-64.

In those days the NES was programmed in assembly language. C was still too new for most things but now, it’s possible to program a NES game in C. Developer Douglas Fraker has produced a series of tutorials on how to create NES games in C using cc65, a C compiler/assembler that takes C code and outputs 6502 assembly language.

His tutorials cover the whole range of things including sprites, how palettes work, music, sound effects, even how to use the Zapper (a stand alone gun-like accessory) with all source code on GitHub. You can run games on an emulator such as the one that comes with RetroPie.

Reading the page on 6502 ASM Basics brought it all back to me even though it’s 31 years since I last wrote 6502 code.

Interesting notes on C

Posted on January 5, 2021January 2, 2021 by David

If you are learning C there are a number of points that may not be mentioned and possibly aren’t obvious. For instance with multidimension arrays. “The array size can be derived from its initialization but that’s applicable for first dimension only. For example, ‘int arr[][2] = {1,2,3,4}’ is valid but ‘int arr[2][] = {1,2,3,4}’ is not valid.” and “Unlike ‘long long int’, there’s nothing like ‘long long double’ in C. Besides, real data types (i.e. float, double, long double) can’t be unsigned.”

These and a whole lot more notes can be found here. It’s definitely worth a read. The only thought I had that was worthwhile is to do with the order of execution in a for statement.

The definition is in this order: for (initialisation, end test, alter loop variable ) statement; but the actual order of execution is initialisation; statement; alter loop variable; end test.

Wizznic – a cross platform game in C

Posted on January 3, 2021January 1, 2021 by David

Wizznic screenshot Wizznic is a sliding blocks puzzle game. The game is written in C and used SDL and SDL Gfx. The developer a Danish programmer called Jimmy Christensen has made it freely available on GitHub so you can modify it, do what you want with it. It’s distributed under the GNU GPL (General Public Licence).

The game itself is multi level and there are other levels (DLC – free) available, just get the code on the content page. The game includes an editor which is why I guess there are so many downloads available.

The game itself is for gp2x, Windows and Linux and also includes make files for Pandora and PSP (PlayStation Portable). I’m always curious about the source code and the main game comes in 36 .c files and 37 .h with the biggest file being the 2000 lines of code menu.c.

If you are learning C or just want to see how a game is done, it’s an excellent way to study, especially because it’s cross platform. I suspect it’s SDL 1.25 because it uses surfaces rather than textures as in SDL 2.