There are three phases to most games: the initialization phase, the game loop, and the shutdown phase. The core of any game is the game loop.

The game loop is a sequence of processes that run continuously as long as the game is running. The three main processes that occur in the game loop are input, update, and render.

The input process is how the player controls the game. This could be any combination of keyboard, mouse, or control pad. Newer technologies allow the game to be controlled via a sensing device that detects gestures, while mobile devices detect touch, acceleration, and even GPS.

The update process encompasses all of the tasks required to update the game: calculating where characters and game objects have moved, determining whether items in the game have collided, and applying physics and other forces in the game.

Once the preceding calculations have been completed, then it is time to draw results. This is known as the render process. OpenGL is the library of code that handles the rendering for your game.

Let's take a closer look at each stage of the game so that we can get a better idea of how OpenGL fits in.

Now that we created our RoboRacer2D project in Visual Studio project, let's learn how to modify this code to create our game structure. Start Visual Studio and open the project we just created.

You should now see a window with code in it. The name of the code file should be RoboRacer2D.cpp. If you don't see this code window, then find Solution Explorer, navigate to RoboRacer2D.cpp, and open it up.

I'll be the first person to admit that the Windows C++ code is both ugly and intimidating! There is a lot of code created from you by Visual Studio when you choose the Windows desktop template to create your project. In fact, you can run this code right now by clicking DEBUG from the menu bar and then choosing Start Debugging. You can also press the F5 key.

Go ahead and do it!

You will see a window telling you that the project is out of date. This simply means that Visual Studio needs to process your code and turn it into an executable—a process called building the project. For the computer science majors out there, this is where your code is compiled, linked, and then executed by the operating system.

Click Yes to continue.

Congratulations! You have now created and run your first program in Visual Studio. It may not look like much, but there is a lot going on here:

Keep in mind that you haven't written a single line of code yet!

Now that you see it, feel free to use the close button to close the window and return to Visual Studio.

But wait, this doesn't look like a game!

If you are thinking the RoboRacer2D program doesn't look much like a game, you are correct! In fact, to make a game we typically strip away about everything that you now see! However, for this demonstration, we are going to keep the window just like it is, and worry more about the code than the appearance.

int APIENTRY wWinMain

// Main message loop:
while (GetMessage(&msg, nullptr, 0, 0))
{
  if (!TranslateAccelerator(msg.hwnd, hAccelTable, &msg))
  {
    TranslateMessage(&msg);
    DispatchMessage(&msg);
  }
}

StartGame();
//Game Loop
bool done = false;
while (!done)
{
  if (PeekMessage(&msg, NULL, 0, 0, PM_REMOVE))
  {
    if (msg.message == WM_QUIT)
    {
      done = true;
    }
    else
    {
      TranslateMessage(&msg);
      DispatchMessage(&msg);
    }
  }
  else
  {
    GameLoop();
  }
}
EndGame();

void StartGame()
{
}

void GameLoop()
{
}

void EndGame()
{
}

OpenGL makes it possible to render sophisticated 2D and 3D graphics on your computer screen. In fact, OpenGL is also the technology behind most mobile devices and tablet devices.

OpenGL works in conjunction with your device's graphics device to draw graphics on the screen. Most modern computing devices have two processors: the Central Processing Unit (CPU) and the Graphics Processing Unit (GPU).

Drawing modern 2D and 3D graphics is a very processor intensive task. In order to free the computer's main processor (the CPU) to do its job, the GPU takes on the task of rendering to the screen. OpenGL is a language that tells the GPU what to do and how to do it.

By the way, you have probably heard of the "other" graphics engine—Microsoft's DirectX. Similar to OpenGL, DirectX allows programmers to talk to the GPU. A lot of people want to know the differences between OpenGL and DirectX, and which is the best choice.

Although there are certainly going to be fans and defenders of both technologies, the only real difference between DirectX and OpenGL is the specific way that you code them. Both technologies are about the same when it comes to features and abilities.

There is one advantage that OpenGL has over DirectX. DirectX only works on Microsoft technologies, while OpenGL works on Microsoft technologies and many others, including most modern cell phones, and the Apple Mac line of computers.

I remember when I was first learning OpenGL. I searched in vain, looking for the link to download the OpenGL SDK. It turns out that you don't have to download the OpenGL SDK because it is already installed when you install Visual Studio.

You do want to make sure that you have the latest OpenGL driver for your video card. To do that, go to http://www.opengl.org/wiki/Getting_started#Downloading_OpenGL and follow the appropriate link.

In order to use OpenGL in our program, we will need to add some code. Open the RoboRacer2D project that we have been working on, and let's do this!

Linking to the OpenGL library

Everything that you need to use OpenGL is found in the OpenGL32.dll lib file. It's up to you to tell Visual Studio that you want to use the OpenGL library in your project.

Right-click on Project | RoboRacer2D properties.

Tip

By the way, Visual Studio first creates a solution, and then puts a project in the solution. The solution is the top entry in the Solution Explorer hierarchy, and the project is the first child. In this case, make sure you right-click on the project, not the solution.

1. For the Configuration drop-down box, make sure you select All Configurations.
2. Open the Configuration Properties branch, then the Linker branch.
3. Select the Input option.
4. Click the dropdown for Additional Dependencies and choose <Edit…>.
5. Enter OpenGL32.lib into the dialog window and click OK.
   
6. Close the Property Pages window.

Even if you are writing a 64 bit application, you will use the OpenGL 32 bit library.

Next, we need to tell Visual Studio that you want to include the OpenGL headers in your program. If you take a look at the top of your code, you will see several headers already being loaded:

#include "stdafx.h"
#include "RoboRacer2D.h"

Just below these lines, add the following:

#include <Windows.h>
#include <gl\GL.h>
#include <gl\GLU.h>

Tip

GL.h is the main header for the OpenGL library. GLU.h stands for GL Utility and is an additional library of features that make OpenGL a little easier to use. These headers correspond to the OpenGL32.lib and Glu32.lib libraries that we added to the project.

Congratulations! You have set up the development environment to use OpenGL and you are now ready to program your first game.