Box2DLights in libGDX - Bad quality of the light gradient on Android

Question

I am facing a problem while porting one of my libGDX project from desktop to Android : My game uses Box2DLights. While the light effect look very fancy on the desktop version of the game, it looks really ugly on the Android version. The light gradient is not smooth at all. Take a look at the comparative screenshot below :

To use Box2DLights in my game, I use this code in my GameScreen :

 rayHandler = new RayHandler(world); 
 rayHandler.resizeFBO(Gdx.graphics.getWidth()/5, Gdx.graphics.getHeight()/5); 
 rayHandler.setBlur(true);   
 RayHandler.useDiffuseLight(true); 
 rayHandler.setAmbientLight(new Color(0.15f, 0.15f, 0.15f, 0.1f)); 

Of course, I tried to play with different parameters, such as :

RayHandler.useDiffuseLight(fasle);

Or

rayHandler.diffuseBlendFunc.set(GL20.GL_DST_COLOR, GL20.GL_SRC_COLOR);

Or

rayHandler.shadowBlendFunc.set(GL20.GL_DST_COLOR, GL20.GL_SRC_COLOR);

Everything I tried so fare gave the same ugly light gradient. I already played games that uses Box2DLights that rendered very well on my tablet, thus, I don't think it's due to a limitation of Android.

Does anybody know what's the trick to overcome this problem ?

Thanks !

Answer 1

I suspect what's going on to cause that rainbow coloured banding is that the textures or render targets involved are of a low bit-depth on Android (maybe 5-6-5 instead of 8-8-8). There could also be some texture compression involved somewhere, as 5-6-5 usually only gives green and grey banding, because the green channel has an extra bit.

A quick search suggests that enabling dithering using Gdx.gl.glEnable(GL10.GL_DITHER); should help.

Alternatively, you could try changing the background to give it a bit of texture.

Answer 2

Here is the solution :

As Adam said in his answer, the problem was linked to a low bit depth on Android. If you look to the code of AndroidApplicationConfiguration.java, you'll notice at lines 30 and 31 this code :

/** number of bits per color channel **/
public int r = 5, g = 6, b = 5, a = 0;

Thus, Android applications with libGDX render, by default, low bit images. This can be easily modified in the AndroidLauncher.java of your application.

The default AndroidLauncher.java of your app looks like this :

public class AndroidLauncher extends AndroidApplication {
    @Override
    protected void onCreate (Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        AndroidApplicationConfiguration config = new AndroidApplicationConfiguration();
        initialize(new MyGdxGame(), config);
    }
}

All you have to do, to have a render format of RGBA8888 for your Android app is :

public class AndroidLauncher extends AndroidApplication {
    @Override
    protected void onCreate (Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        AndroidApplicationConfiguration config = new AndroidApplicationConfiguration();
        config.r = 8;
        config.g = 8;
        config.b = 8;
        config.a = 8;
        initialize(new MyGdxGame(), config);
    }
}

Et voilà ! Here is a comparative screenshot of Android RGB565 VS Android RGBA8888 VS Desktop :

You can see that the Android RGBA8888 is very close to the desktop version.