Category: Ebook

Thrusting in different directions

Thrusting in different directions

Image by dognamedseven from Pixabay

When you press the control key, the player’s ship will accelerate in whatever direction (0-23) it is facing. To make this possible, I pre-populated a couple of float arrays with values x and y for thrust in any of the 24 directions.

This function populate the two arrays. These are declared as

float thrustx[24];
float thrusty[24];

void InitThrustAngles() {
    const float pi = 3.14159265f;
    const float degreeToRad = pi / 180.0f;
    float degree = 0.0f;
    for (int i = 0; i<24; i++) {
        float radianValue = degree * degreeToRad;
        thrustx[i] = (float)sin(radianValue);
        thrusty[i] = (float)-cos(radianValue);
        degree += 15;

It uses trigonometry to calculate the horizontal and vertical amounts for any of the angles 0,15,30..345 degrees. As sin and cos functions work in radians rather than degrees, the variable radianValue is calculated from the degree angle by multiplying by the value degreesToRad. If you remember your school trigonometry, one radian = 180/pi degrees. So the code divides by this value (or multiplies by its inverse in this case).

Then when you press the control key, it just adds the appropriate thrustx and thrusty value to the vx and vy variables. Simple and fast.


Free Programming Books

Free Programming Books

Guide to Scintifc Computing in C++The publisher Springer has made a whole raft of their books available as free downloads and this should last until the end of July. This includes a Guide to Scientific Programming in C++  and Systems Programming in Unix/Linux.

There’s also books on networking, cryptography and more.

Alternatively, if you fancy learning x86-64 Assembly Language Programming with Ubuntu then knock yourself out.  I used to write a lot of assembler (6502 and z80) a very long time ago. It’s a lot easier these days with debuggers.


SDL. Surfaces or textures?

SDL. Surfaces or textures?

Screenshot from DominionsWhen I first started on the asteroids game, I did it as a set of tutorials on That was around 2011/2012 and back then I used SDL 1 which was all about surfaces not textures. When I picked up SDL coding again in 2018, it had progressed to SDL2 which uses textures.

As I understand it, a surface is a structure in RAM while a texture is a structure in VRAM ( the memory in the GPU(. That makes it much faster copying pixels from VRAM to VRAM than from RAM to VRAM.

But I found it much easier to read pixels from a surface than from a texture. Chapter 38 in my e-book has a mask utility. It loads the images from disk into a surface then reads the pixels and creates the masks from that. Masks are used in collision detection. I had previously thought you couldn’t read from a texture.

However after reading this article, which writes directly to the pixels in a texture, it makes me think that reading from them should be possible. I will give it a go just because I’ve not seen it done anywhere.

Picture is from the game Dominions, created with SDL.

C++ Asteroids is progressing

C++ Asteroids is progressing

C++ AsteroidsThis is a screenshot of it as it stands and yes those asteroids are moving! It looks identical to the C version; the only difference is the code, not the appearance.

What makes it interesting is the structure. The Player and Asteroids classes both inherit from a Common base class that has all the position and move data.

It took a bit of time to get the overall architecture right. There’s a Game class which manages everything; the Player, Asteroid and Lib classes.  But Asteroids and Player classes also use the Lib class so  it took a bit of faffing around to make them all play happily together.

This is the biggest difference between C++ and C; the classes and how they all fit together. My biggest source of frustration has been arm wrestling with the C++ compiler; it sometimes seems as if never get easier! Sometimes a wrongly placed semicolon can generate hundreds of compile errors…

It took half a day to get it right and bullets should fit in much easier. Mind you I’ve had to incorporate two static variables in the Common class. One is a copy of the SDL renderer; this is needed to draw things on screen. The other is a pointer to the Game class so that I can access the DebugFlag state.  This is used to show debug information but I may be able to move the flag itself into the Common base class and change it through a call on a Player method. So long as it is static then changing it for the Player also changes it for the Asteroids and Bullets.


I’ve started on the C++ Windows eBook

I’ve started on the C++ Windows eBook

C++ Code listing photoI made the mistake of starting by trying to convert the final version of Asteroid; all 2,200 lines of C into C++.

It got very messy because I was trying to have all the moving objects (Player ship, asteroids, bullets, aliens ship) all based on a common ancestor class but then was trying to manipulate those instances of the ancestor class and downcast back from the ancestor instances and I don’t think you can in C++. Compiler errors galore!

It was the wrong approach and I wasn’t using virtual functions. So instead I’m doing it step by step, adding on new features. Much like the original C development in 13 different steps.

Here’s the slightly shorter asteroids.cpp:

// Asteroids C++ 2020 Chapter 27
#include "game.h"

int main(int argc,char * args[])
	Game g;
    return 0;

There are other classes used from Game. I haven’t put everything in one “God” class!

How I write my ebooks

How I write my ebooks

Screenshot of JutohMy secret: is I use a piece of software called Jutoh from a Scottish software house. It costs £35 and if you are writing a book or e-book I highly recommend it.

Note I have no connection with them except as a very satisfied customer.  

It’s all the little things, inserting pictures, tables, handling source code that make it particularly good for non-fiction books.

It also includes formatting for various programming languages and is cross-platform with versions for Linux, Mac and Windows.

The current version of the Linux e-book has 55144 words, (307407 characters). It takes about 10 seconds to compile that into a .mobi (Amazon) or .epub file with all sorts of warnings.

Originally I started writing the first e-book in a text editor then imported it to MS-Word. But Word is not exactly great software for publishing non-fiction as it’s not desktop publishing. Actually you don’t need desktop publishing per se because Kindle reflows the text, but having pictures, source code and tables makes it more complicated.

I looked about, found Jutoh and consider myself very fortunate; it makes life much easier. I’ve also had excellent support from Jutoh’s creator Dr. Julian Smart who is also well known as a creator of wxWidgets.

Writing an e-book is a multi-pass project that takes me roughly 3-4 months part-time.

  • Pass 1. Develop the software and e-book structure i.e. chapters.
  • Pass 2. Write the chapters.
  • Pass 3. Look for typos. For now this is just me, but eventually I hope to be able to afford a technical editor.
  • Pass 4. Tidy up the layout. This is probably the slowest phase. Because of the images, tables and shortish code listings, it might look neat and tidy at one size, but if you change the viewing font size, it looks er not quite so neat! I can’t see any way round that.

A friend drew the original book cover but I’ve decided to pay for the cover for the Linux version.

Made it to the end of the Linux EBook

Made it to the end of the Linux EBook

Tux with books
Image by OpenClipart-Vectors from Pixabay

That is, I have completed every one of the 13 stages in the game’s development and each is up and running on Ubuntu. It turned out easier than I thought though I still need to fix one or two things.

Because Clang doesn’t support the MSVC fopen_s, I did a quick fix and removed the error checking and when it first ran, it did another segmentation fault because the high score table file didn’t exist. D’oh!

That’s fixed now. Crashing because a file is missing is a very bad practice! Also for some reason last night, Windows and Ubuntu fell out and copy/paste between them wasn’t working. It is working today. I’ve noticed this can be a little bit sensitive at times and I think it was the Windows side that fell over.

However I’ve also been playing with Ubuntu 19.10 and Copy/Paste appears to be disabled on that. That kind of thing I find extremely irritating. I have Guest services ticked, so why does nothing I do enable it? 18.04 LTS apart from last night’s glitch is perfectly happy. And 20.04 Focal Fossa (I know!) is due out on April 23rd.  It’s not quite ready but you can try it an early version if you like. I will be upgrading.


Just a picture post!

Just a picture post!

Lots of collisions here with explosions turned offIn the chapter 42 of both e-books when the first collision detection is introduced, I added a SHOWOVERLAP #define. If this is uncommented, instead of things blowing up, it shows every pixel where two objects pixel’s overlap in bright green.

In the picture above you can see the player ship in the centre and all those green bits where things overlap. You don’t normally see this and it is so intensive that it drops the frame rate from the usual 60 fps to about 3 or 4. But I think it’s quite cool!


SSSnakes – a game for the next Ebook

SSSnakes – a game for the next Ebook

Screenshot of snake gameI’ve done a snake game in the past for About. That’s the picture and today I’ve uploaded it complete with source to Github. The thing with snake is, everyone knows it, its old hat and not particularly exciting.

Back in the early 80s the same was true about Breakout games. It was a common trope for game programming, bouncing a ball off a bat to break through a wall.

But then in 1987 along came the Arkanoid game which could be best described as Breakout re-imagined.  More balls, special bricks when when hit gave different features. It made Breakout games cool again for a few years.

So Ssnakes, is my name for a re-imagined snake game.  We’ll throw away losing your life when the snake hits a wall or itself. Only if your snake runs out of space is it dead, or if it is killed by an enemy. And as it travels around it picks up food which gives it energy. You can burn this energy is making it longer, moving faster or .. spawn off a new snake! Also you can attack enemy snakes – spitting venom directly ahead or sinking fangs into an enemy body if  your snake’s head is next to it.

Having 2, 3 or 4 snakes on the go will make it a bit more stressful to control. You only lose a life when you only have one snake left in play and you lose it.

Plus instead of a plain empty arena there will be a few static objects in it.