In this article by Nikhil Malankar, author of Learning Android Game Development, We have almost learnt everything about the basics that we need to create various components in Android and so we can now move on to do some more exciting stuff. Now at this point we will start working on a proper 2D game. It will be a small 2D side scroller game like Mario. But before we do that, lets first talk about games as a development concept. In order to understand more about games, you will need to understand a bit of Game Theory. So before we proceed with creating images and backgrounds on screen lets dive into some game theory. Here are a list of topics we will be covering in this article:

Game Theory
Working with colors
Creating images on screen
Making a continuous scrolling background

(For more resources related to this topic, see here.)

Lets start with the first one.

Game Theory

If you observe a game carefully in its source code level, you will observe that a game is just a set of illusions to create certain effects and display them on screen. Perhaps, the best example of this can be the game that we are about to develop itself. In order to make your character move ahead you can do either of the two things:

Make the character move ahead
Make the background move behind

Illusions

Either of the two things mentioned above will give you an illusion that the character is moving in a certain direction. Also, if you remember Mario properly then you will notice that the clouds and grasses are one and the same. Only their colors were changed. This was because of the memory limitations of the console platform at the time:

Image Source: http://hub.packtpub.com/wp-content/uploads/2017/06/mario-clouds-is-grass.jpg

Game developers use many such cheats in order to get their game running. Of course, in today's times we don't have to worry much about memory limitations because our mobile device today has the capability of the Apollo 11 rocket which landed on the Moon. Now, keep in mind the above two scenarios, we are going to use one of them in our game to make our character move.

We also have to understand that every game is a loop of activities. Unlike an app, you need to draw your game resources every frame per second which will give you the illusion of moving or any effect on screen. This concept is called as Frames Per Second(FPS). Its almost similar to that of the concept of old films where a huge film used to be projected on screen by rolling per frame. Take a look at the following image to understand this concept better:

Sprite Sheet of a game character

As you can see above, a sprite sheet is simply an image consisting of multiple images within themselves in order to create an animation and thereby a sprite is simply an image. If we want to make our character run we will simply read the file Run_000 and play it all the way sequentially through to Run_009 which will make it appear as though the character is running.

Majority of the things that you will be working with when making a game would be based on manipulating your movements. And so, you will need to be clear about your coordinates system because it will come in handy. Be it for firing a bullet out of a gun, character movement or simply turning around to look here and there. All of it is based on the simple component of movement.

Game Loop

In its core, every game is basically just a loop of events. It is a set up to give calls to various functions and code blocks to execute in order to have draw calls on your screen and thereby making the game playable. Mostly, your game loop comprises of 3 parts:

Initialize
Update
Draw

Initializing the game means to set an entry point to your game through which the other two parts can be called.

Once your game is initialized you need to start giving calls to your events which can be managed through your update function.

The draw function is responsible for drawing all your image data on screen. Everything you see on the screen including your backgrounds, images or even your GUI is the responsibility of the draw method.

To say the least, your game loop is the heart of your game. This is just a basic overview of the game loop and there is much more complexity you can add to it. But for now, this much information is sufficient for you to get started.

The following image perfectly illustrates what a game loop is:

Image Source: https://gamedevelopment.tutsplus.com/articles/gamedev-glossary-what-is-the-game-loop--gamedev-2469

Game Design Document

Also, before starting a game it is very essential to create a Game Design Document(GDD). This document serves as a groundwork for the game you will be making. 99% of times when we start making a game we lose track of the features planned for it and deviate from the core game experience. So, it is always recommended to have a GDD in place in order to keep focus. A GDD consists of the following things:

Game play mechanics
Story (if any)
Level design
Sound and music
UI planning and game controls

You can read more about the Game Design Document by going to the following link:

https://en.wikipedia.org/wiki/Game_design_document

Prototyping

When making a game we need to test it simultaneously. A game is one of the most complex pieces of software and if we mess up on one part there is a chance that it might break the entire game as a whole. This process can be called as Prototyping. Making a prototype of your game is one of THE most important aspects of a game because this is where you test out the basic mechanics of your game. A prototype should be a simple working model of your game with basic functionality. It can also be termed as a stripped down version of your game.