How do I extend the ViewPort and use it to paint a "window" of 3D graphics on the screen - libgdx

Question

I need to create a 3D perspective camera viewport of 480x480 and display it on the bottom right corner of the screen. The rest of the screen is filled with 2D graphics.
I tried extending Viewport and using viewportX, and viewportY as well as viewportHeight and viewportWidth, but the test 3D object does not draw.
I followed this tutorial to get the basic prototype going.
https://code.google.com/p/libgdx-users/wiki/Decals
How do I properly extend the ViewPort and use it to paint a "window" of 3D graphics on the screen ?

Answer 1

The following could be used to have a Viewport with a fixed size of 480x480 which is placed on the bottom left corner. If you supply a PerspectiveCamera to it, everything will be rendered in this area.
public class CustomViewport extends Viewport {
public CustomViewport (Camera camera) {
this.camera = camera;
}
#Override
public void update (int screenWidth, int screenHeight, boolean centerCamera) {
viewportX = 0;
viewportY = 0;
viewportWidth = 480;
viewportHeight = 480;
worldWidth = 480;
worldHeight = 480;
super.update(screenWidth, screenHeight, false);
}
}
If you want to render somewhere else after that, you have to "reset" the glViewport() via Gdx.gl.glViewport(0, 0, Gdx.graphics.getWidth(), Gdx.graphics.getHeight());
Now you are free to render whereever you want, for example in the top and right areas which were left blank.
This test shows another example of how to render in those areas.