OpenGL ES: Going 3D - Beginning Android Games - page 514

Figure 10-15. The crate system

The HierarchicalObject Class
Let's define a simple class that can encode a generic solar system object with the following
properties:

ï?® A position relative to its parent's center

ï?® A rotation angle around the parent

ï?® A rotation angle around its own y axis

ï?® A scale

ï?® A list of children

Vertices3 instance to be rendered
Our HierarchicalObject instance should update its rotation angles and its children, and render
itself and all its children. This is a recursive process since each child will render its own children.
We will use glPushMatrix() and glPopMatrix() to save a parent's transformations so that
children will move along with the parent. Listing 10-7 shows the code.

ï?® A reference to a

Listing 10-7. HierarchicalObject.java, Representing an Object in the Crate System

package com.badlogic.androidgames.gl3d;

import java.util.ArrayList;
import java.util.List;

import javax.microedition.khronos.opengles.GL10;

import com.badlogic.androidgames.framework.gl.Vertices3;

public class HierarchicalObject {
public float x, y, z;
public float scale = 1;
public float rotationY, rotationParent;