Simple Game Engine

Presentation

For educational purposes

A project I made a while ago. It's a 2D game engine that uses SDL2 as a base. As it's name implies, it's a very simple game engine designed for quick prototype building.

The engine's design is heavily inspired from Unity. Everything is an Object that is updated at every frame. The game creator can add Components to enrich objects and create his own ScriptComponents where their write the logical behaviour of each object.

Some of the engine's features include:

• 📦 Dynamic object-component system: Safely instanciate or destroy objects at any time while playing. Attach or detach components and scripts freely from any object.
• 📝 Scripts: Write scripts that can be attached to objects with easy-access to various sub-systems like Input, Camera, Object, Audio, etc.
• 🎧 Audio: Play music and sounds easily from anywhere. You can choose to use playSound() or playSoundFast() to load the file in memory or not.
• 👾 Texture: Draw your object on screen with TextureComponent. The engine handles texture caching so you can have multiple objects with the same texture.
• 🚶‍♂️ Animated Texture: Animate objects with the AnimatedTextureComponent. It requires an *.sganim file that describes where animations start and end on a spritesheet. Once initialized, animating an object is just a matter of calling playAnimation().
• 💿 Object deserialization: Construct objects from a *.sgo file. Within an SGO file you can specify default data for an object as well as which components it holds when instanciated and their default data. You can also specify children for the object.
• 🌍 World deserialization: Similarly to object serialization, you can create *.sgworld files which contain data to instanciate and destroy multiple objects quickly.
• 🗺 Generate level from a Tiled JSON file: Generate a level from JSON data and a tileset contained in an image file. You can also create an optional *.sgmap file which associates SGO file to a tile index in the JSON. This allows you to place game objects like player or enemy spawns, checkpoints, pick-ups, etc. directly in Tiled

Dependencies

This engine uses SDL2, SDL_image, SDL_ttf and SDL_mixer

How to build

This git repository contains both the engine's source as well as a project's basic structure.

Building the engine

Before building the engine you must copy SDL2 headers under SimpleGameEngine/dependencies/SDL/include don't forget to put other SDL2 libraries headers like SDL2_image, SDL2_ttf and SDL2_mixer.

the SimpleGameEngine folder contains the engine's source and a makefile to build a static library At the root of this repository you'll find a shell script named update-engine-deps.sh. This shell script simply builds the engine and copies all .h files and the generated .a file to the Game folder.

This is useful if you want to work on the engine and immediatly test your changes in a project.

Making a game

Pre-requisites

If you just want to build a game you are most likely not interested in fiddling with the engine's source. The pre-requisites are the following:

• Under Game/SGE place the engine's static library in the lib folder and the engine's headers in the include folder. This GitHub repository has a release which includes the built engine, it's sources and the include files.
• Under dependencies/SDL place SDL2 headers, SDL2_image headers, SDL2_ttf headers and SDL2_mixer headers in the include folder and SDL2 shared libraries under lib

Adding assets

Any of your game's assets should be placed under the resources folder. The engine's API is designed so that whenever you have to specify a filepath, it should always be a relative path from the inside of resources.

Adding scripts

Create a new folder within the scripts folder with the name of your script. Place your .cpp and .h files inside that folder

If you want to make use of the deserialization feature with your scripts, you must populate the std::map inside ScriptParsing.cpp which is used to associate a script name as a string to a function that adds the script to a target object.

{"scriptName", SCRIPT_LAMBDA_SIGNATURE{ target->addScript<ScriptName>(); }}

Building the game

Run the python script within the Build folder to automatically generate an executable inside GameOut (Currently only on MacOS) Alternativly:

• Running the Makefile inside the Game folder produces a shared library
• Running the Makefile inside the Buildfolder produces an executable. You might need to manually create the GameOut folder and place your dylib in it

Missing documentation

This project was made long ago and lacks documentation.

TODO

• Add a config file to change the Game's name
• Make the building process cross-platform (only MacOS for now)
• Support Visual Studio .sln format

Known issues

• When making a .app folder, the game doesn't find the dylib despite rpath being set
• Improve SDL2 linking to make applications portable

Conclusion

There is a lot to improve and fix on this engine but it fulfills it's main purpose. You can create simple 2D prototypes without having to worry about anything else but your game.

I would not recommend this engine to anyone who wants to make a polished, content-rich and optimized game. There are lots of very powerful free engines with an active community and a documentation, namely Unity, Unreal Engine, Godot