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

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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

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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:

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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

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private GLSurfaceView  mGLSurfaceView;

5: Main Class

and one small change for main class

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@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,

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