Learn C Games Programming

Fixing an unbootable Raspberry Pi

Posted on May 19, 2020May 7, 2020 by David

Well to be fair, it was me that made it unbootable. I’d been reading this Wiki page on configuring the Pi. I’d told it to give the GPU almost a GB of RAM. The Pi is a 4 GB Pi 4B. I did it last night and so this morning, I found it not working at all well.

My first thoughts were I’d messed up the Operating system and so I took the SD card put it in a holder and booted up my old laptop which has Ubuntu 18.04 LTS on it. This page on switchdoc suggested I could do a repair with these commands.

First lsblk to view attached devices. There was a /dev/sdc2 . There was also a /dev/sdc1

Then

sudo fsck -fy /dev/sdc1

That gave information about the drive but not the disk. That took

sudo fsck -fy /dev/sdc2

That took a few seconds and listed information, but still my drive wouldn’t boot back in the Pi.

Then I remembered I’d changed the boot config.txt and it was back with the SD card in the laptop and rebooted that. It showed two devices on the desktop (no need to mount anything) and clicking boot gave me a directory listing of /boot. I edited config.txt and changed the GPU Mem value to 256MB.

That fixed it and my PI is now booting quite happily again. I am now going to make a backup copy! It wouldn’t the end of the world if I had made it permanently unbootable, I’d just burn the OS again. It’s just the time wasted and minor hassles copying files, downloading and reinstalling software. Best avoided if possible!

Code::Blocks revisited

Posted on May 18, 2020May 6, 2020 by David

So after yesterday’s post I also installed Code::Blocks on Ubuntu 20.04 LTS, the recent six monthly Ubuntu release. Guess what, it’s a much newer version of Code::Blocks that looks slightly different and does include SDL2. Although the demo program it creates is C++ not C (That coloured bar picture is the demo). I haven’t used it enough to see what’s different between this and version 16.01.

The version of Code::Blocks on the 18.04LTS Ubuntu was 16.01 and on Ubuntu 20.04 LTS it’s Code::Blocks 20.03. I keep my Ubuntus up to date but the 18.04 LTS hasn’t switched to the newer Code::Blocks which surprised me. I’m guessing that the maintainers of the 18.04 LTS Ubuntu repositories just haven’t updated their copy of Code::Blocks.

One thing I hadn’t explored in Code::Blocks is the debugging and this seems a lot more powerful than what you get in Visual Studio Code. This screenshot below from version 20 shows it is more akin to Visual Studio debugging rather than Visual Studio Code debugging what with CPU registers, stack, memory dump and threads.

So I thought I’d try Code::Blocks

Posted on May 17, 2020May 5, 2020 by David

Code::Blocks is an alternative cross-platform open source IDE for C/C++ (and Fortran!). It doesn’t include a compiler but can work with most of them. It’s also written in C++ (you’d never guess from the name!) and so is fast.

Installing is just a

sudo apt install codeblocks

When you install it, it looks for installed compilers and gives you the choice of which is the default.

When you create a project there are a few types and one that got me excited was SDL. It creates a skeletal project and it was only when compiling that I realised it was for SDL1, not 2. It’s the nature of open source that things take time to remedy. So don’t bother with it.

Anyway I copied in my source files and clang objected because it couldn’t find the SDL2 files. The fix isn’t too difficult. In Code::Blocks, navigate to Project Build Options then in Compiler settings > Other compiler options add these lines

-lSDL2

-lSDL2_image

-lSDL2_mixer

and in the Linker settings > Other linker options

-lSDL2

-lSDL2_image

-lSDL2_mixer

Note those are -l () not i or 1.

After that it compiled and linked ok. The compiled code is in the bin/Debug folder. However to get Asteroids to run you need to copy in the images, sounds, and masks folders and the highscore.txt file. After that it runs fine, but note when you compile it seems to delete everything in the folder.

So overall it wasn’t a difficult thing to do and I’m going to install it on a Raspberry Pi and see how that goes. I’ve already got Visual Studio Code installed on it and working but having a second IDE (both using the same compiler) is no bad thing.

A page of tips

Posted on May 16, 2020May 4, 2020 by David

I’ve done 70 odd blog posts so far since I started this in March 2020 and there’s a fair number of gems and nuggets in there. Finding them though is probably a bit of hassle, so to let you see them easily, I’ve created a page of tips, accessible from Tips in the menu above.

I’ll keep this updated as this blog progresses.

Success with gamepad mappings

Posted on May 15, 2020May 17, 2020 by David

SNES Gamepad — Image by Marco Sberveglieri from Pixabay

My ploy with running gamepad-tool on the Linux laptop worked and I was able to get the correct mappings to use in my game. Though weirdly it seems to have X and Y buttons mixed up as well as A and B.

In the end I hard-coded the mapping string and set it up with this code:

	if (SDL_GameControllerAddMapping("030000001008000001e5000010010000,NEXT SNES Controller2,platform:Linux,a:b2,b:b1,x:b3,y:b0,back:b8,start:b9,leftshoulder:b4,rightshoulder:b5,dpup:-a1,dpdown:+a1,dpleft:-a0,dpright:+a0")==-1){
		LogError("Unable to load gamepad mappings from gamepad.txt");
	}

Then in my ProcessEvents() function which handles I/O events, I added this code:

			case SDL_CONTROLLERBUTTONDOWN:
			if (event.cbutton.state== SDL_PRESSED){
				switch(event.cbutton.button){
					case SDL_CONTROLLER_BUTTON_A:
					    fireFlag =1;
					    break;
					case SDL_CONTROLLER_BUTTON_B:						
					    jumpFlag =1;
					    break;
					case SDL_CONTROLLER_BUTTON_X:
					    shieldFlag =1;
					    break;
					case SDL_CONTROLLER_BUTTON_Y:						
					    thrustFlag =1;
					    break;						
					case SDL_CONTROLLER_BUTTON_LEFTSHOULDER:
					    rotateFlag = 1;
					    break;
					case SDL_CONTROLLER_BUTTON_RIGHTSHOULDER:
					    rotateFlag= 2;				
					    break;
					}
				}

There’s similar code for the SDL_CONTROLLERBUTTONUP except it checks for the state = SDL_RELEASED and in the switch statement it sets each flag to 0. So inspite of the code, it’s the Y button that does shields and the X button does thrust, B button fires and A button does the hyper space jump.

More on Raspberry Pi Gamepad

Posted on May 14, 2020May 3, 2020 by David

Unfortunately there’s no gamepad-tool for the PI, but there is a program called jstest and in particular a visual one called jstest-gtk. That’s it on the left. You install it on any Linux system, including Raspbian on the Pi with the command

sudo apt install jstest-gtk

Then run it with a jstest-gtk command from a terminal.

It then detects your game pad and responds to button presses and joystick movements.

The weird thing is although my gamepad identifies it as a NEXT SNES but so far attempts to load that have not been successful in the Asteroids game. It loads but doesn’t seem to work and its not recognising the right shoulder button and has A and B buttons muddled up. Yet in jstest, it is clearly able to identify them.

Time I think to create a mapping under Linux with gamepadtool. Unfortunately it doesn’t work on the Hyper-V Ubuntu so it’s time to fetch my Linux laptop and try it on that.

Fun with game pads

Posted on May 13, 2020May 2, 2020 by David

I’ve never dealt with a game pad (joypad etc.) before. It seems that there is no absolute mapping, it’s more like TV remote controls. There’s lots of them and they’re all different. So although SDL2 has a set of enum values for the buttons, I found that my game pad wasn’t responding to what I thought were the game keys.

But SDL2 to the rescue. The SDL_GameController has a flexible scheme where the game pad can be setup by a text string. There’s a database of schemes available on Github. That includes a couple of tools for discerning what the setup for your game pad is. That’s one of them shown. That program from General Arcade is free and cross-platform. I downloaded and ran it on Windows with my game pad attached.

So, my controller is a NEXT SNES Controller (no surprises there) and the setup string for it is 030000001008000001e5000000000000,NEXT SNES Controller,a:b2,b:b1,back:b8,dpdown:+a1,dpleft:-a0,dpright:+a0,dpup:-a1,leftshoulder:b4,rightshoulder:b6,start:b9,x:b3,y:b0,platform:Windows.

There’s a database of these on Github and it currently has 780 odd strings. You can view it here though it’s not that great a read!

So I think the idea is, you can include that file in your application and any game that uses game pads can get the GUID from the game pad via one of the SDL calls- see this list of SDL GameController functions and load the file into memory et voila, your application can now use the game pad.

My Orange Pi – self resurrected

Posted on May 12, 2020April 30, 2020 by David

Back in November 2018, I was in Nottingham and passed a stand at the Winter Fayre. It was offering a console with 18,000 games on it for about £70. I bought one and what I got was an Orange PI with a 16 GB SD Card (all but full) and two USB joypads.

The game software used the Retro-Pie software, but the games were a massively illegal collection of games (for about ten different consoles including CBM-64, SNES, ZX Spectrum) put together by the company that supplied these “consoles”. Amazingly I found four games on there that I had written back in the 80s in this collection.

It was a bit of an odd PI. Instead of powering up through the power slot, it came with a USB to 5V connector. Looking about on the web I found it is this model in a nice acrylic case. Anyway, after three months it stopped working and it was pushed in to a drawer where it remained until today. I tried it today and it came back to life, I suspect the mains-to-USB adaptor is broken but as I’ve a drawer full of them it’s not a problem.

The reason for mentioning this is not the Orange Pi, nor the games but the joypads. I had a look on the libSDL website and I hadn’t realised that there was quite extensive support built in to SDL. So my next task is to add game controller support for the asteroids game.

1566 Compile errors with just two characters!

Posted on May 11, 2020April 29, 2020 by David

When programmers have to explain why it took longer to get something working,you don’t often here reasons like this. A simple syntax error error took me an hour to find and fix. Yet it does happen and it happened to me today.

Oh sure you feel silly afterwards and it was only a 131 lines of C code. The very last of the 1566 compile errors was unexpected end-of-file found on line 132. That was a red herring of sorts. The error actually occurred right at the start of the program.

Here’s the first 10 lines. It should be quite easy to spot but when you are looking through 130 lines with a hint that it’s messed up the end of the file, it’s not so obvious.

// tictactoe.c
#include <stdio.h>
#include <stdlib.h>
#include <string>
#include <time.h>

int playerIsX, computerFirst, x, y, danger, turn;
char board[3][3];  // holds X, O and space
char playerPiece, computerPiece;

In case you haven’t spotted it, it’s the missing .h; it should be string.h not string in that 3rd #include. An obvious-in-hindsight clue is the error listing. The files that are mentioned don’t have .h on them. (cctype, cstdint etc. Those are C++ files and string is a C++ header file. Also mention of namespace in the error message is also a big hint.

Still I think that sets a record for the most errors generated in a C compile! The compiler btw was Visual Studio 2019’s C/C++ compiler.

Developing for Raspberry Pi without one

Posted on May 10, 2020April 29, 2020 by David

Yes it is possible, as the screenshot shows. You can download a copy of Raspbian from Raspberry-pi. You can either download the .iso directly or save them a bit of bandwidth and do it via a file Torrent. It then takes about 15 minutes or so to install it. When you first run it, it will do an update.

It looks exactly like Raspbian on a PI but there are one or two little things to bear in mind. It’s 32-bit, the clipboard doesn’t seem to work and SSH by default is disabled. It’s real easy to enable it, just find Raspberry Pi Configuration. Click the Raspberry in a circle menu button at the top, then click Preferences and there it is on the menu that pops up. In the Interfaces tab, tick the Enabled checkbox for SSH.

I use the excellent WinSCP to connect to it. Conveniently the Pi will show you its ip address (or from a terminal run ifconfig and it will show you the ip address of eth0) and just put that in with username pi and your pi’s password which you should have changed when you set up Raspbian.

Finally you have to install Visual Studio Code and as usual, it’s not quite so easy. Most Linux distros these days are 64-bit and the official VS Code is only available for Debian in 64-bit and Raspbian is of course 32-bit. But there are community builds and it’s the same place that I got the ARM version from.

And here’s the result. A slightly sluggish (well it is under Hyper-V). I had to comment out the code that initialises the audio. Line 580 ish.

/*	int success=Mix_OpenAudio(22050, AUDIO_S16LSB, 2, 8192);
	if (success==-1 ) {
		LogError("InitSetup failed to init audio");
	}
	LoadSoundFiles();
*/

And here’s the results.