In this tutorial series you will learn how to make a simple single-player Pong-like game for the Sega Mega Drive using SGDK! If you just want to see the full source code, you can get it from Github.

Megapong 1 - Hello Mega Drive World!

Posted August 31, 2019

Update: May 4th 2020: The first two parts of this tutorial have been rewritten to make things easier and more stable for newcomers!

Welcome to my new tutorial series on Mega Drive development! In it we will be creating a Mega Drive game from scratch using SGDK, the Sega Genesis Development Kit. This awesome piece of software allows you to program games for the Mega Drive in C instead of ASM, which makes things a whole lot easier. I will show you how to set up your development environment, how to import graphics, how to put things on the screen, how to control them and have them collide…

And this is what we will be making:

images/screenshotmegapong.png

I call it Megapong. It is a very simple single-player Ponglike where the goal is to keep the ball in play for as long as possible. Each time you hit it you’ll receive points and when you’ve hit the ball a certain number of times, it’ll get faster. The game is over when the ball leaves the screen at the bottom. No it’s not gonna knock any blue hedgehogs off the shelf, but it’s a very good game to learn the basics of Mega Drive programming. And that’s the whole point!

This tutorial will lead you through every step of making this game, from setting up your environment to the collision code. While I will try to make everything as simple and accessible as possible, don’t forget that coding for retro platforms is tricky. If you run into any issues, don’t hesitate to post them in the comments below!

And one last thing before we start: If you like what I’m doing, please consider supporting me on Patreon. I’d love to do more of these tutorials on a regular basis, also expanding to other genres like platformers. Becoming a patron lets me make more time for these, and it gets you some cool perks too!

Become a Patron!

Alright, without further ado: Let’s get this show on the road!

Setting up SGDK

First we have to install and set up SGDK. You can download the latest version here. Please note that out of the box, SGDK only works on Windows. Linux users can give the Gendev Project a try, of which there also exists a Mac OS version here. Keep in mind that I have used neither of these and thus can’t really help with setting them up. The actual coding will work the same across all platforms, since all environments use SGDK, but the stuff around it (setting up folders, toolchains etc.) will most likely be different.

Note: SGDK requires Java, so you will have to install that as well if you haven’t already. The latest version of SGDK uses Java to compile resources, which lets it do some pretty powerful and cool stuff.

Once you’ve downloaded SGDK, unzip the archive anywhere you want. I put mine in C:\sgdk so that I have paths like C:\sgdk\bin.

Next we’ll have to define two environment variables and add sgdk to our PATH. This site shows you how to access those settings on different versions of Windows. I recommend adding them to the user variables, not the system ones. That way, the changes only apply to your account, not to the whole computer. Here is what you need to do:

  1. Add an environment variable called GDK pointing to the installation directory in unix path format. In my case this would be C:/sgdk.
  2. Add an environment variable called GDK_WIN pointing to the installation directory in windows path format. The only difference here is that you use backslashes instead of regular slashes. So in my case, I’d add the path C:\sgdk.
  3. Finally, look for the variable called Path and click on edit. Add the path to the bin directory of your SGDK installation to the list that appears. I would add C:\sgdk\bin.

Alright, now for the last step: Compiling the library. Open a command prompt and type in the following line:

%GDK_WIN%\bin\make -f %GDK_WIN%\makelib.gen

If you get an error message complaining that %GDK_WIN% could not be found or something like that, restart your computer and try again. Sometimes new environment variables aren’t set right away.

If you’re still having trouble, try hardcoding your installation path instead of using the variable. So if you installed SGDK in C:\sgdk like I did, you would type:

C:\sgdk\bin\make -f C:\sgdk\makelib.gen

SGDK will do its thing and if everything goes well, you will end up with a file called libmd.a inside the lib folder of your SGDK installation! You don’t have to do anything with it, SGDK just needs it to work.

Alright, that’s the first step taken care of! Time to make a project.

Setting up a project

A project in SGDK is just a folder with some stuff in it. The easiest way to set up a new one is to copy an empty template project. I’ve prepared one for you, so just download it below:

Click here to download the empty project file

Unzip it anywhere you want, then rename the extracted folder to helloworld. In the root of the folder you should now find the following things:

out
res
src
compile.bat

This is the structure of a basic SGDK project. The out folder will contain our rom file once we have created one. res will hold the resources (graphics, audio…) for our project. The src folder contains our source code files. Inside you will find the main.c file, which is where we will add all of our code. Finally, compile.bat is a script I wrote that we’ll use in a second. But first, we need to do a final bit of setup.

Emulators

In order to test our games, we’ll need an emulator to load the roms we create. If you already have a favorite one, feel free to use it! Any reasonably up-to-date emulator should work. However, if you only want to use an emulator for Mega Drive development, you might want to use Gens KMod. It’s based on the famous Gens emulator codebase but adds a few debugging tools that are very useful for developers. Just download the archive and unpack it anywhere you want; it makes sense to keep it close to the SGDK folder, but it doesn’t really matter as long as you remember where it is.

Compiling and running Hello World

Now that we have finally set everything up, let’s see if we can actually get things running! We’ll do that by creating the old programmer standby, the Hello World program. Open up your project folder and open main.c (it’s within src, remember?) in your text editor of choice. You’ll see that there is already some code in there, but it doesn’t really do much. So add the following line of code at the beginning of the main() function:

VDP_drawText("Hello Mega Drive World!", 8, 12);

For reference, your main.c file should now look like this:

#include <genesis.h>

int main()
{
    VDP_drawText("Hello Mega Drive World!", 8, 12);
    while(1)
    {
        VDP_waitVSync();
    }
    return (0);
}

I’ll explain what these lines do in a second, but first let’s try to compile and run our program! This is very simple: Simply double-click on the compile.bat file I’ve included in the project folder. A command prompt should open up, do some stuff, then close again. And if you now check in the out folder of your project, you should see a bunch of files, including one called rom.bin. That is your rom file! So load it up in your emulator and you should see the following:

images/hellomdworld.png

Success! You’ve made your first Mega Drive program. Give yourself a pat on the back! It may not look like much yet, but it is a big step on a brand new road. I mean, you just made a Mega Drive program. You wouldn’t have been able to do that yesterday!

But Wait, What Did I Just Write?

But now for a quick explanation of what you’ve actually typed. Most lines are simple boilerplate stuff that you’ll need for the program to even run. But two lines are of special interest for now. Let’s take a look:

VDP_drawText("Hello Mega Drive World!", 8, 12);

As you can probably tell, this function draws text on the screen. To be more precise, in this case, it draws the text “Hello Mega Drive World!” on the screen, at the coordinates (8,12). We’ll learn about coordinates later, but feel free to change these numbers around and see what happens!

By the way: This function uses the VDP of the Mega Drive, or the Video Display Processor, which explains the VDP_ prefix. Basically every function starting with VDP_ in SGDK does something visual, in this case drawing text on the screen.

The next interesting line also uses the VDP:

VDP_waitVSync();

This is a very important function. Basically, everything you put into the while(1){ ... } loop is executed as quickly as possible, which might or might not sync up with your display. In order to avoid display issues, you have to tell your Mega Drive to wait until the screen display has been fully updated before it starts processing more stuff. And that’s what VDP_waitVSync() does!

If that sounds confusing to you, don’t worry - you don’t really need to know the details for now. Just remember to always put VDP_waitVSync(); at the end of your game loop and things should be fine!

Wrapping Up

That was a lot of stuff at once, but you’ve made it through and ended up with a working rom. Congratulations! Here’s what we will be taking a look at next:

It might not sound exciting, but it will make everything a lot easier and more pleasant. And once you’ve set everything up you can use it for any future Mega Drive project you might try your hands on.

Thank you for reading! Until next time and be excellent to each other!

If you have any questions, comments or criticism, post them in the comments below or reach out to me on Twitter @ohsat_games! Special thanks to Stephane Dallongeville for creating SGDK and everyone in the SGDK Discord for their help and keeping the dream alive!

Download the source code

All patrons on Patreon get the complete source code for this tutorial, as well as other perks such as early access! Become a Patron!
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Check out the rest of this tutorial series!

  • Megapong 1 - Hello Mega Drive World!
  • Megapong 2 - Setting Up The Environment
  • Megapong 3 - Importing Resources
  • Megapong 4 - Palettes
  • Megapong 5 - Sprites
  • Megapong 6 - Input and Paddles
  • Megapong 7 - Collisions
  • Megapong 8 - Score and HUD
  • Megapong 9 - Game Over
  • Megapong BONUS - Flashing!
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