Tagcross platform

Getting started with the Universal Tween Engine

This is a guest post by Alexander Fröhlich. Alexander is a freelance developer and is supporting ANDLABS at its libgdx-based development. 

If you are not familiar with libgdx yet, please check out the first part of this series, the Getting started with libgdx-guide.

 

1 Tweening?

“Tweening” in games is the process of creating intermediate states and thus frames between two or more given states.

Example (Sprite Translation):
The most simple example would be moving a sprite or image from one x1, y1 position to another x2, y2 position on the screen.

Yet, as you might already suspect, this “Universal Tween Engine” is capable of manipulating not only x, y coordinates for sprite objects…. no, this cross-platform-engine written entirely in java language lets you tween every property of any object given that it has its getter/setter methods attached.

In this tutorial I will show you how this comes in handy for game developers when building ingame hints or tutorials for their game.

The following sample code illustrates basic use and setup of the universal tween engine in a libgdx code project.

2 Ingame Tutorial Tweening

First of all, declare your tweenManager instance. The tweenManager lets you keep track and manage all your tweens (i.e. tweening, tween actions and so on)

public class MyGame implements ApplicationListener {

    // Only one manager is needed, like a 
    // libgdx Spritebatch (MyGame.java)

    private static TweenManager tweenManager;

}

Instantiate the manager inside create() of your libgdx lifecycle:

Register an accessor class, which is the key binding between the manager and the object to be tweened. Here this will be the TutorMessage class. (see below).
So after calling registerAccessor every single object of class TutorMessage we create can be tweened by the TweenManager.

@Override
public void create() {
    setTweenManager(new TweenManager());
    Tween.setCombinedAttributesLimit(4);// default is 3, yet
                                        // for rgba color setting          
                                        //we need to raise to 4! 
    Tween.registerAccessor(TutorMessage.class, new 
                             TutorMessageAccessor()); 

}

The TutorMessage’s are the internal game objects for this sample which hold the position, scale and color message attributes.

public class TutorMessage {

    private String message; // string objects can not be tweened
    private float x;
    private float y;
    private Color color;
    private float scale;

}

To tween these message properties and make them accessible by the manager we have to declare how getting and setting every single attribute works.

Getter/Setter
So we define 3 sections (POS_XY, SCALE, COLOR) that process the current float[] values, handled over by the manager during runtime when tweening is active.

Of course same applies for the setters.

public class TutorMessageAccessor implements TweenAccessor<TutorMessage> {

    public static final int POS_XY = 1;
    public static final int SCALE = 2
    public static final int COLOR = 3;

    @Override
    public int getValues(TutorMessage target, int tweenType, 
                           float[] returnValues) {
        switch (tweenType) {
            case POS_XY:
                returnValues[0] = target.getX();
                returnValues[1] = target.getY();
                return 2;

            case SCALE:
                returnValues[0] = target.getScale();
                return 1;

            case COLOR:
                returnValues[0] = target.getColor().r;
                returnValues[1] = target.getColor().g;
                returnValues[2] = target.getColor().b;
                returnValues[3] = target.getColor().a;
                return 4;

            default: 
                assert false; 
                return -1;
        }
    }

    @Override
    public void setValues(TutorMessage target, int tweenType, 
                            float[] newValues) {
        switch (tweenType) {
            case POS_XY: 
                target.setPosition(newValues[0], newValues[1]); 
                break;

            case SCALE: 
                target.setScale(newValues[0]); 
                break;

            case COLOR:
                Color c = target.getColor();
                c.set(newValues[0], newValues[1], newValues[2], 
                        newValues[3]);
                target.setColor(c);
                break;

            default: 
                assert false;
        }
    }
}

Having bind our TutorMessage class to the TweenManager we can now integrate it into the game.
Remember? We want to provide a kind of ingame tutorial system. So every time our user should see an animated on-screen help, we call the now defined method. The tweenHelpingHand method takes the parameter targetX, targetY that indicate the position where the helping hand (sprite) and its bound message (bitmapfont) should move to.

Then we say Tween
  .to (
      – TutorMessage currentTm ( the message to be moved )
      – int TutorMessageAccessor.POS_XY (constant to select which property should be tweened)
      – float 3f (total tweening duration)
  )
  .target (
    – targetX, targetY ( the final screen position of our tweened message )
  )
  .ease (
    – TweenEquations.easeOutCirc ( one possible interpolation pattern – i.e. moving pattern here)
  )
  .start (
    – MyGame.getTweenManager()  ( binds this tween to the manager )
  )

private void tweenHelpingHand(int targetX, int targetY) {

    // kill current tween - or pre-existing
    MyGame.getTweenManager().killTarget(currentTm);

    // move
    Tween.to(currentTm, TutorMessageAccessor.POS_XY, 3f)
         .target(targetX, targetY)
         .ease(TweenEquations.easeOutCirc)
         .start(MyGame.getTweenManager());

    // colorize
    Tween.to(currentTm, TutorMessageAccessor.COLOR, 3f)
         .target(1f, 1f, 1f, 1f)
         .ease(TweenEquations.easeOutCirc)
         .start(MyGame.getTweenManager());

}

Finally we have to call update inside the libgdx render() method to have the started Tween be updated constantly.

MyGame.getTweenManager().update(delta);

Here you go!
Enjoy this very powerful any easy to use tweening library.

Combining Scene2d animations and Tweening is also possible. You just have to write the ActorAccessor binding class and provide access (getter/setter) to its properties.
Like with Scene2d actions, the universal tween engine also allows sequencing of multiple tweens!

 

If you have any questions or suggestions, please leave a comment.

Getting started with libgdx

This is a guest post by Alexander Fröhlich. Alexander is a freelance developer and is supporting ANDLABS at its libgdx-based development. 

 

libgdx is an open source, Open GL based, cross platform game development framework. It’s supporting Web, Desktop, Android and iOS. This step by step introduction will teach you how to get started with the initial setup and your very first hello world in libgdx.


1 Prerequisites


2 Setup a new libgdx project

  • Choose “CREATE” in order to create a new project and enter the following setup screen
  • ConfigurationTab lets you set names for projekt/package/mainGameClass and the destination folder
  • Library Selection lets you download all required libraries (libgdx as the core libs are always required)
  • Overview gives you an outlook on which projects will be created
  • Generation checks for a valid setup (green colored) and when read you can open the generation screen (launch window coming up)
  • Launch displays the log output while creating the project. Here just click “Launch” to finalize your setup and create all chosen libgdx projects

3 Import libgdx projects into eclipse

Now we need to import these project into eclipse (other IDE provide similar options -> wiki)
NOTE: iOS projects have to be imported with XCode only (apple-mac) -> wiki

 

4 Project launch configurations

You now should see four projects… YourGameName, YourGameName-Android, YourGameName-Desktop and YourGameName-html within eclipse’s package explorer. The first one being the core source project holding all your game logic and the latter being launcher projects holding only one starter class.


DESKTOP
Go to your newly imported desktop project and launch its Main.java (run as java application)
This should bring up this demo screen. As you can see libgdx already provides you with a small hello world application.

 

ANDROID
Your eclipse android project should have been marked with a red x (eclipse way of telling you something is wrong with your setup).
Go to project properties (ALT-ENTER) and select your available Android-SDK-version..
NOTE: on versions prior to 4.0 you might have to remove the line

android:configChanges=”keyboard|keyboardHidden|orientation|screenSize”>

from your AndroidManifest.xml as this option being unsupported

After this, refresh both your core source project and your android project and rebuild both projects.
Now right-click on your Android project and choose “Run as Android Application”.

A dialogue will come up showing all connected devices and you may either want to push it on one of these or use the emulator (which will automatically start without any registered devices).
Make a choice and the game will be transfered on started on your device.

HTML5
A red cross over your project might mean that you have to install GWT.
After having GWT set up correctly, right-click on your HTML5-project and choose “Run as Web Application”.
Double click on the provided link ( e.g. http://127.0.0.1:8888/index.html?gwt.codesvr=127.0.0.1:9997)
A browser window will show up maybe requiring to install a GWT Developer Plugin
(Development Mode requires the Google Web Toolkit Developer Plugin).
If so, do restart the browser and you should see the libgdx logo screen.

Now you are up and ready to start building your own libgdx-based game. If you have any questions, please post them in the comments.
 

Update [2013-09-13], important links:

Starter Tutorial:
http://bitowl.de/day1/

Libgdx Wiki
https://code.google.com/p/libgdx-users/wiki/AAATopPaaage

Forum: (most problems have been solved already.. just learn to query it wisely like the web :-)
http://www.badlogicgames.com/forum/

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