Android 2.2 3D – cube with a shadow

1: Intro

In this article/tutorial I ll present how to create *cough* simple *cough* – well simple after you make it, cube with shadow effect. The idea is to make our android based device to display cube that will rotate around it own and – well that happened without my intention – around light source.  Problems I meet ware mostly based on me being not familiar with GL API.. but.. one step at time.. in next post I ll present how to add bitmap on the surface of cube..

2: Cube class

```package mobile.napier;

import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.IntBuffer;

import javax.microedition.khronos.opengles.GL10;

/**
* A vertex shaded cube.
*/
class Cube
{
public Cube()
{
int one = 0x10000;
int vertices[] = {
-one, -one, -one,
one, -one, -one,
one,  one, -one,
-one,  one, -one,
-one, -one,  one,
one, -one,  one,
one,  one,  one,
-one,  one,  one,
};

int colors[] = {
0,    0,    0,  one,
one,    0,    0,  one,
one,  one,    0,  one,
0,  one,    0,  one,
0,    0,  one,  one,
one,    0,  one,  one,
one,  one,  one,  one,
0,  one,  one,  one,
};

byte indices[] = {
0, 4, 5,    0, 5, 1,
1, 5, 6,    1, 6, 2,
2, 6, 7,    2, 7, 3,
3, 7, 4,    3, 4, 0,
4, 7, 6,    4, 6, 5,
3, 0, 1,    3, 1, 2
};

//Buffers

ByteBuffer vbb = ByteBuffer.allocateDirect(vertices.length*4);
vbb.order(ByteOrder.nativeOrder());
mVertexBuffer = vbb.asIntBuffer();
mVertexBuffer.put(vertices);
mVertexBuffer.position(0);

ByteBuffer cbb = ByteBuffer.allocateDirect(colors.length*4);
cbb.order(ByteOrder.nativeOrder());
mColorBuffer = cbb.asIntBuffer();
mColorBuffer.put(colors);
mColorBuffer.position(0);

mIndexBuffer = ByteBuffer.allocateDirect(indices.length);
mIndexBuffer.put(indices);
mIndexBuffer.position(0);
}

public void draw(GL10 gl)
{
gl.glFrontFace(gl.GL_CW);
gl.glVertexPointer(3, gl.GL_FIXED, 0, mVertexBuffer);
gl.glColorPointer(4, gl.GL_FIXED, 0, mColorBuffer);
gl.glDrawElements(gl.GL_TRIANGLES, 36, gl.GL_UNSIGNED_BYTE, mIndexBuffer);
}

private IntBuffer   mVertexBuffer;
private IntBuffer   mColorBuffer;
private ByteBuffer  mIndexBuffer;
}
```

I have found this class online but not sure where so there will be no link.. if the owner wants.. drop me an email. 🙂

3: Below Renderer for Cube class

```package mobile.napier;

import javax.microedition.khronos.egl.EGL10;
import javax.microedition.khronos.egl.EGLConfig;
import javax.microedition.khronos.opengles.GL10;

import android.opengl.GLSurfaceView.Renderer;

public class CubeRenderer implements Renderer {

public CubeRenderer(boolean useTranslucentBackground) {
mTranslucentBackground = useTranslucentBackground;
mCube = new Cube();
}

@Override
public void onDrawFrame(GL10 gl) {
// TODO Auto-generated method stub
/*
* Usually, the first thing one might want to do is to clear
* the screen. The most efficient way of doing this is to use
* glClear().
*/

gl.glClear(GL10.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT);

/*
* Now we're ready to draw some 3D object
*/

gl.glMatrixMode(GL10.GL_MODELVIEW);
gl.glLoadIdentity();
gl.glTranslatef(0, 0, -3.0f);
gl.glRotatef(mAngle,        0, 1, 0);
gl.glRotatef(mAngle*0.25f,  1, 0, 0);

gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);
gl.glEnableClientState(GL10.GL_COLOR_ARRAY);

mCube.draw(gl);

mAngle += 1.2f;
}

public void onSurfaceChanged(GL10 gl, int width, int height) {
gl.glViewport(0, 0, width, height);

/*
* Set our projection matrix. This doesn't have to be done
* each time we draw, but usually a new projection needs to
* be set when the viewport is resized.
*/

float ratio = (float) width / height;
gl.glMatrixMode(GL10.GL_PROJECTION);
gl.glLoadIdentity();
gl.glFrustumf(-ratio, ratio, -1, 1, 1, 10);
}

public void onSurfaceCreated(GL10 gl, EGLConfig config) {
/*
* By default, OpenGL enables features that improve quality
* but reduce performance. One might want to tweak that
* especially on software renderer.
*/
gl.glDisable(GL10.GL_DITHER);

/*
* Some one-time OpenGL initialization can be made here
* probably based on features of this particular context
*/
gl.glHint(GL10.GL_PERSPECTIVE_CORRECTION_HINT,
GL10.GL_FASTEST);

//lights on!
gl.glEnable(GL10.GL_LIGHTING);
gl.glEnable(GL10.GL_LIGHT0);

float lightAmbient[] = new float[] { 0.2f, 0.3f, 0.6f, 1.0f };
gl.glLightfv(GL10.GL_LIGHT0, GL10.GL_AMBIENT, lightAmbient, 0);

// position
float[] light0Position = new float[] { 0, 0, 3, 1 };
gl.glLightfv(GL10.GL_LIGHT0, GL10.GL_POSITION, light0Position, 0);

gl.glLightfv(GL10.GL_LIGHT0, GL10.GL_AMBIENT, lightAmbient,     0);
gl.glLightfv(GL10.GL_LIGHT0, GL10.GL_POSITION, light0Position, 0);
gl.glEnable(GL10.GL_DEPTH_TEST);
gl.glDepthFunc(GL10.GL_LEQUAL);

gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);

gl.glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
gl.glClearDepthf(1.0f);

gl.glEnable(GL10.GL_CULL_FACE);
gl.glShadeModel(GL10.GL_SMOOTH);

gl.glClearStencil(0);

gl.glClearStencil(0);
}
private boolean mTranslucentBackground;
private Cube mCube;
private float mAngle;
}
```

4: Notes

I had a problem with this lines:

```float lightAmbient[] = new float[] { 0.2f, 0.3f, 0.6f, 1.0f };
gl.glLightfv(GL10.GL_LIGHT0, GL10.GL_AMBIENT, lightAmbient, 0);
// position
float[] light0Position = new float[] { 0, 0, 3, 1 };
gl.glLightfv(GL10.GL_LIGHT0, GL10.GL_POSITION, light0Position, 0);
```

In many tutorials they were using GLfloat and for some reason my eclipse was throwing out some weird errors that I cannot use it.. need to find a reason why that is happening.. anyway.. easy fix.. use floats!

now one global variable

```private GLSurfaceView  mGLSurfaceView;
```

5: Main Class

and one small change for main class

```@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);

mGLSurfaceView = new GLSurfaceView(this);
mGLSurfaceView.setRenderer(new CubeRenderer(false));
setContentView(mGLSurfaceView);

}
```

to use GLSurfaceView instead of standard.

I hope it will help someone to save a couple hours of struggling with code,

Published by

Luke Iwanski

Senior Graphics Programmer @ CD Projekt RED