Hello, OLC!

It's time to write your first program using olc::PixelGameEngine. how can we break the tradition, we will start by writing a simple Hello, World program.

Setting up the Project

• Begin by making a directory to store your Code. I'll name it Space Warrior that will be the name of the game we are going to create
• Add Header file olcPixelGameEngine.h to our current directory which you can download here.
• Create a new .cpp file, name it main.cpp in the current direcotry.

Hello, World!

Add following contents to the main.cpp file. We begin by including the header olcPixelGameEngine

#define OLC_PGE_APPLICATION
#include "olcPixelGameEngine.h"

Now let us create a new class for our Game, Game it will inherit olc::PixelGameEngine

  class Game : public olc::PixelGameEngine
  {
    public:
	Game()
	{
		sAppName = "Space Warrior";
	}

	bool OnUserCreate() override
	{
		// Called once at the start, so create things here
		return true;
	}

	bool OnUserUpdate(float fElapsedTime) override
	{
	  Clear(olc::BLACK);
	  DrawString(5,5, "Hello, World");	
	  return true;
	}
};

Any class that inherits from olc::PixeGameEngine should override two functions, OnUserCreate and OnUserUpdate. Don't worry we will get into details later.

Now lets write our main function, main function would be very neat

int main()
{
	Game game;
	if (game.Construct(256, 240, 4, 4))
		game.Start();

	return 0;
}

Compilation and Running the Program

If you have everything setup as mentioned in the chapter Write your First Game in C++, you should be able to issue following commands in the terminal/command prompt.

For Linux

You should move on to the current directory first.

Compiling

$ g++ -o main main.cpp -lX11 -lGL -lpthread -lpng -lstdc++fs -std=c++17

Running

$ ./main

For Windows

You should move on to the current working directory first.

Compiling

$ g++ -o main.exe main.cpp -luser32 -lgdi32 -lopengl32 -lgdiplus -lShlwapi -ldwmapi -lstdc++fs -static -std=c++17

Running

$ main.exe

That's it now if you run this program, you should see a window with string "Hello, World" being displayed like this:

Getting into Details

As mentioned earlier we inherited our class from olc::PixelGameEngine and then we override two functions,

OnUserCreate()

The function OnUserCreate is called only once by the engine at the start. Let us look at the definition again,

bool OnUserCreate() override
 {
     // Called once at the start, so create things here
     return true;
 }

This function returns a bool value, since the function is called only once, we can use this for the initialization stuff. However at the moment we have nothing to initialize, so we will just return true from the method.

OnUserUpdate()

This function is called repeatedly by the engine per frame. For smooth transition of the game, we need to keep updating the frame and whenever the frame is updated this function is called. Let us check out the code of OnUserUpdate method again,

bool OnUserUpdate(float fElapsedTime) override
 {
   Clear(olc::BLACK);
   DrawString(5,5, "Hello, World");	
   return true;
 }

Let us look at the function signature first, it returns a bool value, recieves a float as a parameter. We call the Clear function inside the function, Clear function clears contents of the previous frame We then called DrawString function and passed in the x, y coordinates where the string would be displayed, and then the third parameter, Hello, World is the string to be displayed in the screen. We exit the function by returning true.

The main function

int main()
{
    Game game;
    if (game.Construct(256, 240, 4, 4))
        game.Start();

    return 0;
}

In the main Function, we first created an object game, of type Game. We then need to tell the engine about the size of window we want to create we do so by using theConstruct method. The Construct method returns true if the construction was successfull and then we call the start method which starts our game engine.

Next up we will look at some useful functions to draw basic shapes using the game engine.