jMonkeyEngine 3 Tutorial (1) - Hello SimpleApplication

Previous: Installing JME3, Next: Hello Node

Prerequisites: This tutorial assumes that you have .

In this tutorial series, we assume that you use the jMonkeyEngine SDK. As an intermediate or advanced Java developer, you will quickly see that, in general, you can develop jMonkeyEngine code in any integrated development environment (NetBeans IDE, Eclipse, IntelliJ) or even from the command line.

OK, let's get ready to create our first jMonkeyEngine3 application.

In the jMonkeyEngine SDK:

1. Choose File???New Project??? from the main menu.
2. In the New Project wizard, select the template JME3???Basic Game. Click Next.
   1. Specify a project name, e.g. "HelloWorldTutorial"
   2. Specify a path where to store your new project, e.g. a jMonkeyProjects directory in your home directory.
3. Click Finish.

If you have questions, read more about Project Creation here.

For this tutorial, you want to create a jme3test.helloworld package in your project, and create a file HelloJME3.java in it.

In the jMonkeyEngine SDK:

1. Right-click the Source Packages node of your project.
2. Choose New??????Java Class to create a new file.
3. Enter the class name: HelloJME3
4. Enter the package name: jme3test.helloworld.
5. Click Finish.

The SDK creates the file HelloJME3.java for you.

Replace the contents of the HelloJME3.java file with the following code:

package jme3test.helloworld;
 
import com.jme3.app.SimpleApplication;
import com.jme3.material.Material;
import com.jme3.math.Vector3f;
import com.jme3.scene.Geometry;
import com.jme3.scene.shape.Box;
import com.jme3.math.ColorRGBA;
 
/** Sample 1 - how to get started with the most simple JME 3 application.
 * Display a blue 3D cube and view from all sides by
 * moving the mouse and pressing the WASD keys. */
public class HelloJME3 extends SimpleApplication {
 
    public static void main(String[] args){
        HelloJME3 app = new HelloJME3();
        app.start(); // start the game
    }
 
    @Override
    public void simpleInitApp() {
        Box b = new Box(Vector3f.ZERO, 1, 1, 1); // create cube shape at the origin
        Geometry geom = new Geometry("Box", b);  // create cube geometry from the shape
        Material mat = new Material(assetManager,
          "Common/MatDefs/Misc/Unshaded.j3md");  // create a simple material
        mat.setColor("Color", ColorRGBA.Blue);   // set color of material to blue
        geom.setMaterial(mat);                   // set the cube's material
        rootNode.attachChild(geom);              // make the cube appear in the scene
    }
}

Right-click the HelloJME3 class and choose Run. If a jME3 settings dialog pops up, confirm the default settings.

1. You should see a simple window displaying a 3D cube.
2. Press the WASD keys and move the mouse to navigate around.
3. Look at the FPS text and object count information in the bottom left. You will use this information during development, and you will remove it for the release. (To read the numbers correctly, consider that the 14 lines of text counts as 14 objects with 914 vertices.)
4. Press Escape to close the application.

Congratulations! Now let's find out how it works!

The code above has initialized the scene, and started the application.

Look at the first line. The HelloJME3.java class extends com.jme3.app.SimpleApplication.

public class HelloJME3 extends SimpleApplication {
  // your code...
}

Every JME3 game is an instance of com.jme3.app.SimpleApplication. The SimpleApplication class manages your 3D scene graph and automatically draws it to the screen ??? that is, in short, what a game engine does for you!

You start every JME3 game from the main() method, as every standard Java application:

1. Instantiate your SimpleApplication-based class
2. Call the application's start() method to start the game engine.

    public static void main(String[] args){
        HelloJME3 app = new HelloJME3(); // instantiate the game
        app.start();                     // start the game!
    }

This code opens your application window. Let's learn how you put something into the window next.

If you are unfamiliar with the vocabulary, read more about the Scene Graph here.

Look at rest of the code sample. The simpleInitApp() method is automatically called once at the beginning when the application starts. Every JME3 game must have this method. In the simpleInitApp() method, you load game objects before the game starts.

    public void simpleInitApp() {
       // your initialization code...
    }

The initialization code of a blue cube looks as follows:

    public void simpleInitApp() {
        Box b = new Box(Vector3f.ZERO, 1, 1, 1); // create a 1x1x1 box shape at the origin
        Geometry geom = new Geometry("Box", b);  // create a cube geometry from the box shape
        Material mat = new Material(assetManager,
          "Common/MatDefs/Misc/Unshaded.j3md");  // create a simple material
        mat.setColor("Color", ColorRGBA.Blue);   // set color of material to blue
        geom.setMaterial(mat);                   // set the cube geometry 's material
        rootNode.attachChild(geom);              // make the cube geometry appear in the scene
    }

A typical JME3 game has the following initialization process:

1. You initialize game objects:
   • You create or load objects and position them.
   • You make objects appear in the scene by attaching them to the rootNode.
   • Examples: Load player, terrain, sky, enemies, obstacles, ???, and place them in their start positions.
2. You initialize variables
   • You create variables to track the game state.
   • You set variables to their start values.
   • Examples: Set the score to 0, set health to 100%, ???
3. You initialize keys and mouse actions.
   • The following input bindings are pre-configured:
     • W,A,S,D keys ??? Move around in the scene
     • Mouse movement and arrow keys ??? Turn the camera
     • Escape key ??? Quit the game
   • Define your own additional keys and mouse click actions.
   • Examples: Click to shoot, press Space to jump, ???

You have learned that a SimpleApplication is a good starting point because it provides you with:

• A simpleInitApp() method where you create objects.
• A rootNode where you attach objects to make them appear in the scene.
• Useful default input settings that you can use for navigation in the scene.

When developing a game application, you want to:

1. Initialize the game scene
2. Trigger game actions
3. Respond to user input.

The now following tutorials teach how you accomplish these tasks with the jMonkeyEngine 3.

Continue with the Hello Node tutorial, where you learn more details about how to initialize the game world, also known as the scene graph.

See also:

• SimpleApplication From the Commandline
• Create a JME3 project.