OpenGL ES: A Gentle Introduction - Beginning Android Games - page 331

Now let's assume we are instantiating 100 Bob instances, like this:
Bob[] bobs = new Bob[100];
for( int i = 0; i < 100; i++) {
bobs[i] = new Bob();
}
To render each of these Bob instances, we'd do something like this (assuming we've already
cleared the screen, set the projection matrix, and bound the texture):
gl.glMatrixMode(GL10.GL_MODELVIEW);
for( int i = 0; i < 100; i++) {
bob.update(deltaTime);
gl.glLoadIdentity();
gl.glTranslatef(bobs[i].x, bobs[i].y, 0);
bobModel.render(GL10.GL_TRIANGLES, 0, 6);
}
That is pretty sweet, isn't it? For each Bob instance, we call its update() method, which will
advance its position and make sure it stays within the bounds of our little world. Next, we
load an identity matrix into the model-view matrix of OpenGL ES so we have a clean slate. We
then use the current Bob instance's x and y coordinates in a call to glTranslatef() . When we
render the Bob model in the next call, all the vertices will be offset by the current Bob instance's
position—exactly what we wanted.
Putting It Together
Let's make this a full-blown example. Listing 7-13 shows the code with comments interpersed.
Listing 7-13. BobTest.java; 100 Moving Bobs!
package com.badlogic.androidgames.glbasics;
import javax.microedition.khronos.opengles.GL10;
import com.badlogic.androidgames.framework.Game;
import com.badlogic.androidgames.framework.Screen;
import com.badlogic.androidgames.framework.gl.FPSCounter;
import com.badlogic.androidgames.framework.gl.Texture;
import com.badlogic.androidgames.framework.gl.Vertices;
import com.badlogic.androidgames.framework.impl.GLGame;
import com.badlogic.androidgames.framework.impl.GLGraphics;
public class BobTest extends GLGame {
public Screen getStartScreen() {
return new BobScreen( this );
}
class BobScreen extends Screen {
static final int NUM_BOBS = 100;
GLGraphics glGraphics;