David | Learn C Games Programming Blog

Author: David

Browsing the source code of old and commercial games

Posted on June 17, 2020June 12, 2020 by David

Archive photos — Image by Pexels from Pixabay

This page on a website called WikiZero has a long and very extensive list of games whose source code is available. That doesn’t always mean you can build the game. Many games are very old and in BASIC or assembly (.g. Elite is available in various forms).

It might have been created for a different platform or more likely the source code is available but the graphics and sound assets aren’t, unless you have bought the game, perhaps from sites like gog.com and so have them.

One thing to be aware of, many of the links on WikiZero go to the excellent wayback machine which is part of archive.org. This is under threat by some commercial publishers because they have lent ebooks during the Covid lockdown period without any limitation. So if you are interested in anything I suggest you check it out sooner rather than later, just in case.

For instance here is the C source code for a TRS-80 game from 1979 called Paravia. It looks like a much expanded version of the Classic Computer game Hammurabi. Note the wayback machine can take a few seconds to retrieve a webpage. They have a very large chunk of the web’s websites in there…

Goto is considered bad programming in C but

Posted on June 16, 2020June 11, 2020 by David

There is one case for using goto when you have nested loops and you’d like to jump all the way out. The goto statement was very popular in BASIC but often resulted in programs being like spaghetti with gotos all over the place.

Here’s a contrived example where I have used a goto.

#include <stdio.h> 

int array[10][10][10];
int main() {
    // Populate array
    for (int y=0;y<10;y++)
      for (int x=0;x<10;x++) 
        for (int z=0;z<10;z++) {
          if (array[x][y][z]==0)
            goto exit;
    }
exit:;
}

In my C programs, for-loops are the most popular followed by while-loops, do-while loops and gotos are hardly ever used at all.

My trial by Windows Defender is over

Posted on June 15, 2020June 10, 2020 by David

EXpression opf irritation! — Image by prettysleepy1 from Pixabay

There’s nothing wrong with this short C program, which is in my ebook and which I was compiling to test it.

#include <stdio.h>

int main() {

	int a = 10;
	for (int i = 0; i < 5; i++) {
		a--;
		printf("i = %d\n", i);
		if (a == 8) break;
	}
}

Nothing wrong, except Windows Defender went ape-shit every time I compiled it! Talk about annoying. This was in Visual Studio. I’m fairly scrupulous about keeping nasties off my PC but if you believed Defender I had some weird Trojan.

I did a search and found an unanswered question on StackOverflow from someone with the same reported trojan. So I answered it!

Thankfully there was an update from Windows Defender last night and they have quashed this false positive. If the worst came to the worst, I’d hop on to Hyper-V and compile it in Ubuntu or Raspberry Pi OS with clang. But still a bit irritating!

Another Visual Studio Code source – VSCodium

Posted on June 14, 2020June 8, 2020 by David

VSCodium As they say “This is not a fork. This is a repository of scripts to automatically build Microsoft’s vscode repository into freely-licensed binaries with a community-driven default configuration.”

Microsoft’s code includes telemetry and tracking code. The code built here is the same as Microsoft’s but with that telemetry and tracking code removed. Also it includes builds for both ARM (32 and 64-bit) which you don’t get from Microsoft.

The Docs page provides info on how to copy JSON bindings from Visual Studio Code to VSCodium. I shall be giving this a try. Much as I like the code.headmelted.com Visual Studio Code, it doesn’t appear to be updated very often whereas VSCodium seems to be built every night.

My raspberry Pi touchscreen arrived but it wasn’t smooth going

Posted on June 13, 2020June 7, 2020 by David

I bought the Longruner (no, not a typo!) 7″ touch screen and it turned up after a few days. It’s nicely made and similar to this, though it looks slightly different. That hand must be a dolls hand!

It doesn’t have any documentation but there was a DVD with three MS Word documents which I opened on my Windows PC (It comes in useful sometimes!). One of them the “7inch HDMI Display user Manual(En).docx” has a photo of the three ports.

There’s a full size HDMI socket and a USB to Android (Micro USB-B I believe) cable is included that plugs into a USB port and either of the Android type ports. You can either have power and touch screen with the port nearest the HDMI as I did or just power alone, if you want to use it as a monitor. The two green squares show the USB and touch/power cables.

When I switched it on, it just sat there saying no HDMI signal. That MS Word document included instructions to edit the config.txt in \boot. Of course I had no display but the Pi was plugged into the network and I ran WinSCP which logged in and let me view files. I don’t think you can edit files as root with WinSCP, and that config.txt file needs root access to edit it.

However I am a long time user of Putty. (You can also get putty from putty.org but I don’t know if that is also an official one). After that I could ssh into the pi, do a sudo -s command to switch in root and then nano /boot/config.txt to edit config.txt.

Here’s a photo of my fat finger moving the cursor round the screen. It works surprisingly well, and the display is lovely though my photos probably do not do it justice.

These are the lines you paste into the end of the config.txt, save it out and reboot.

max_usb_curren=1
hdmi_force_hotplug=1
config_hdmi_boost=7
hdmi_group=2
hdmi_mode=87
hdmi_drive=1
display_rotate=0
hdmi_cvt 1024 600 60 6 0 0 0

Now I just have to figure out how to use it in my games. The display is 1024 x 600 btw.

Plugging in a second monitor worked fine as this photo shows. The blacks are darker on the touchscreen but that’s just because the gammas don’t match and I was too lazy to change them!

Playing with 64-bit Raspberry Pi OS

Posted on June 12, 2020June 3, 2020 by David

So after deciding I was going to wait until the 64-bit Pi OS was tested and ready for use, I changed my mind and downloaded the beta and installed it.

It ran ok, though as with any Beta there are bound to be little glitches. There’s a survey where they are interested in what the PI is being used for and it showed UNDEFINED for my Pi’s serial number, though

cat /proc/cpuinfo

worked fine and displayed it.

The display utility let me change my display to 75 HZ at 1920 x 1080 and then promptly crashed. After reboot though it was at 75 HZ.

My main reason for trying it out though, I was curious about development tools, particularly IDES. I had forgotten that code.headmelted.com, the alternative source for Visual Studio Code (my favourite) supported arm64 which is what the 64-bit runs. I was able to install VS Code from there without any problems.

64-bit vs 32-bit

32-bit has the memory limitation of 3 GB (in both Windows and Linux) whereas 64-bit offers any amount of RAM up to what’s available. It’s not that big thing with a 4 GB PI but with 8 GB it can make a big difference. This article (Sorry that the link is to an article on Medium.com which offers a few free articles then paid) suggests that 64-bit Debian (which Raspberry Pi OS is) is quite a bit faster than 32-bit. My impression is that it feels a bit snappier but that could be wishful thinking n my part!

I’ll put Asteroids on and see what fps I can get though that may not be a great way to compare them as the GPU plays a big part and I can’t see it making any difference, but I could be completely wrong on that. More as I investigate further.

C Amalgamation – for SQLite

Posted on June 11, 2020June 3, 2020 by David

Image by CopyrightFreePictures from Pixabay

If I were to use a database in a game, it’s likely that it would be SQLite. It’s an open source SQL database that is 102 different C files and 32 others. Of those 102, 75% are C and the remainder header files.

Unlike many other SQL databases (for example MySQL, SQL Server, PostgreSQL) it doesn’t need to run as a separate server. It compiles directly into your application, adding a whopping 400 KB! (I’ve seen bigger picture files…) It’s fast and very well tested. For every line of code there are 644 lines of test code! Details of testing here.

You wouldn’t use SQLite in an arcade game as it would be a bit of an overkill just to hold a high-score table, but in something like a Rogue or Mud game, I could easily see it being used to store rooms, corridors, treasures etc. SQLite is also very easy to use.

The word amalgamation means that all the 102 source files have been combined (amalgamated) into one file called SQLite3.c. So building it is a single command.

SQLite is probably the worlds most popular database. It’s found in most operating systems and is used in every smartphone.

Raspbian vs Raspberry Pi OS

Posted on June 10, 2020June 2, 2020 by David

I’ve always referred to the version of Debian running on a Raspberry Pi as Raspbian and so it was until the recent 8 GB RAM Raspberry Pi was launched. But it turns out that Raspbian was an independent version of Debian created by people at raspbian.org. As they say “Note: Raspbian is not affiliated with the Raspberry Pi Foundation. Raspbian was created by a small, dedicated team of developers that are fans of the Raspberry Pi hardware, the educational goals of the Raspberry Pi Foundation and, of course, the Debian Project.”

From now on, it seems the correct name is Raspberry Pi OS and no longer Raspbian. The change was announced at the bottom of this Raspberry Pi Foundation blog post. This has something to do with the fact that Raspbian is mainly 32-bit while the Raspberry Pi OS is both 32-bit and 64-bit though the latter is still at beta. You can read more about the recent changes to Raspberry Pi OS on this blog entry.

A very small sort in C

Posted on June 9, 2020June 1, 2020 by David

I came across this article on efforts to make the smallest sort function in C. Being cynical I did wonder if it would compile and run. I mean 56 bytes is kind of short!

To get it to compile in VS 2019 I had to add a couple of changes, mainly ints and the void. This is it wrapped in a program. The screenshot shows it running and the output at the bottom. Very clever!

The sort function is that void s(… at the top.

#include <stdio.h>

void s(int *a, int n) { n-- > 1 ? s(a, n), s(a + 1, n), 
     n = *a, * a = a[1], a[n > * a] = n : 0; }

int arr[10] = { 9,1,2,6,8,11,45,-1,6,4 };
int main() {
	s(arr, 10);
	for (int i = 0; i < 10; i++) {
		printf("%d ", arr[i]);
	}
	printf("\n");
	return 0;
}

What I didn’t show you is the number of times Windows defender went ape and declared it a trojan, every time it compiled! My PC is kept pretty bug free and this is a false positive…

Looking at Intrinsics in C

Posted on June 8, 2020May 31, 2020 by David

AVX Registers — From WikiMedia. https://commons.wikimedia.org/wiki/File:AVX_registers.svg

This post probably has the most mystifying title yet. Here’s a little background. Modern CPUs have some hardware that can speed up operations like addition or multiplication by doing them in parallel. The words SIMD (short for Single Instruction Multiple Data) and vectorization apply.

These are very processor specific. Even something like x86-64 CPUS have a whole raft of alphabet soup. SSE, MMX, AVX. Intel even have a website so you can see what instructions are supported with examples in C.

My i5930K CPU supports AVX so if you tick the AVX box on the left hand side of the Intel intrinsics guide, you can see can there are something like 12,000+ instructions and variants listed. If you tick one of the categories, it filters out the instructions to those applicable to that category.

Click one of the instructions on the right and you’ll see a rough equivalent in C to what it does. Also the header that it is found in, typically

#include <immintrin.h>

which Visual C++ is happy to compile. An intrinsic is a special C instruction that gives you access to these low level vectorization instructions without you having to drop into assembler.

On a Raspberry Pi, the ARM processor supports a similar type of scheme but it’s called NEON.

If you are interested in finding out more, take a look at Microsoft’s intrinsics documentation which covers both Intel and ARM.