OpenGL

OpenGL was developed by Silicon Graphics in 1992
Android implements a subset of OpenGL call OpenGL for Embedded Systems OpenGL ES
This standard was developed by the Khronos Group which had as members Intel, AMD, Nvidia, Nokia, Samsung, and Sony.
OpenGL is also available on iPhone.
Each language has its own binding to OpenGL. Java's binding were defined in JSR239

An OpenGL Project

Let's create a new project OpenGL test.

To start we create a new Activity:

package org.pollett;

import javax.microedition.khronos.egl.EGL10;
import javax.microedition.khronos.egl.EGL11;
import javax.microedition.khronos.egl.EGLConfig;
import javax.microedition.khronos.egl.EGLContext;
import javax.microedition.khronos.egl.EGLDisplay;
import javax.microedition.khronos.egl.EGLSurface;
import javax.microedition.khronos.opengles.GL10;

import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import android.view.SurfaceHolder;
import android.view.SurfaceView;

public class OpenGLTest extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(new GLView(this));
    }
}

More OpenGL Project rest of Activity File

Here's a first pass at what else is in the file:

class GLView extends SurfaceView implements SurfaceHolder.Callback 
{
   GLView(Context context)
   {
      super(context);
      getHolder().addCallback(this); // we will be called if surface 
         // created or destroyed
      
      // set up hardware acceleration if possible
      getHolder().setType(SurfaceHolder.SURFACE_TYPE_GPU);
      
   }
   
   public void surfaceCreated(SurfaceHolder holder)
   {

   }
 
   public void surfaceDestroyed(SurfaceHolder holder)
   {

   }

   public void surfaceChanged(SurfaceHolder holder, int format, int w, int h)
   {
     // should implement to handle window resizing 
   }

SurfaceView's are special kinds of views for 3D graphics
A Surface is a place for drawing like a canvas (only exists while your activity is running in the foreground).
SurfaceHolder stays around even if surface goes away.
SurfaceHolder.Callback is an interface that with two methods to allow you to handle creation, destruction, resizing of Surfaces.

Threads in OpenGL

In the simple graphics we did on Monday, we saw that the onDraw method of the View is used whenever the view needs to redraw a section of the screen.
In OpenGL you create a thread which is dedicated to drawing the display.

We put the code to manage this thread in our surfaceCreated and surfaceDestroyed methods:

private GLThread glThread;
public void surfaceCreated(SurfaceHolder holder)
{
   glThread = new GLThread(this);
   glThread.start();
}
 
public void surfaceDestroyed(SurfaceHolder holder)
{
   glThread.requestExitAndWait();
   glThread = null;
}

The GLThread class

We next need to actually define the GLThread class...

class GLThread extends Thread
{
   private final GLView view;
   private boolean done = false;
	
   GLThread(GLView view) 
   {
      this.view = view;
   }
    
   @Override
   public void run() 
   {
      while(!done)
      {
         //draw a frame
      }
	
    }
		
   public void requestExitAndWait()
   {
      //called when surface is destroyed
      //Tell the thread to quit
      done = true;
		
      try
      {
         join();
      }
      catch(InterruptedException ex)
      {
      }
   }
}

Drawing a Frame

We next need to fill in how to draw a frame by adding code to the run() method...

@Override
public void run() 
{
   // Init OpenGL
   EGL10 egl = (EGL10)EGLContext.getEGL();

   // create and initialize a display handle
   EGLDisplay display = egl.eglGetDisplay(EGL10.EGL_DEFAULT_DISPLAY);	   
   int[] version = new int[2];
   egl.eglInitialize(display, version);

   //set up that we want 16 bits of color and how they are split into rgb	   
   EGLConfig[] configs = new EGLConfig[1];
   int[] configSpec = { EGL10.EGL_RED_SIZE, 5,
      EGL10.EGL_GREEN_SIZE, 6, EGL10.EGL_BLUE_SIZE, 5,
      EGL10.EGL_DEPTH_SIZE, 16, EGL10.EGL_NONE};
	   
   int[] numConfig = new int[1];
   egl.eglChooseConfig(display, configSpec, configs, 1, numConfig);
	   
   EGLConfig config = configs[0];

   //using the config stuff we create a context and a surface	   
   EGLContext glc = egl.eglCreateContext(display, 
      config, EGL10.EGL_NO_CONTEXT, null);
	   
   EGLSurface surface = egl.eglCreateWindowSurface(display, config, view.getHolder(), null);
      egl.eglMakeCurrent(display, surface, surface, glc);
   
   //create an interface into openGL
   GL10 gl = (GL10)(glc.getGL());
	   
   init(gl); //will describe in a bit

   //loop until asked to quit	     
   while(!done)
   {
      //draw a frame (describe in a minute)
      drawFrame(gl);
      egl.eglSwapBuffers(display, surface);
		   
      //Error Handling
      if(egl.eglGetError() == EGL11.EGL_CONTEXT_LOST)
      {
         Context c = view.getContext();
         if(c instanceof Activity)
         {
            ((Activity) c).finish();
         }
      }
   }

   //Free OpenGL resources
   egl.eglMakeCurrent(display, EGL10.EGL_NO_SURFACE, EGL10.EGL_NO_SURFACE, 
      EGL10.EGL_NO_CONTEXT);
   egl.eglDestroySurface(display, surface);
   egl.eglDestroyContext(display, glc);
   egl.eglTerminate(display);
	
}

Initializing OpenGL options

We next give the code for init(gl) we had on the last slide.

private void init(GL10 gl)
{
   //define the view frustrum
   gl.glViewport(0, 0, view.getWidth(), view.getHeight());
   gl.glMatrixMode(GL10.GL_PROJECTION);
   gl.glLoadIdentity();
   float ratio = (float) view.getWidth() / view.getHeight();
		
   //set viewing angle of view frustrum. ratio of its width to
   // height, near and far clipping planes
   GLU.gluPerspective(gl, 45.0f, ratio, 1, 100);
		
   //pixels farther than those already drawn ignored
   gl.glEnable(GL10.GL_DEPTH_TEST);
   gl.glDepthFunc(GL10.GL_LEQUAL);
   gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);
		
}

The code above sets up the viewport and the viewing frustrum as illustrated by this picture:

Draw a Frame

Finally, we actually draw a frame...

private void drawFrame(GL10 gl)
{
   //clear screen to black
   gl.glClear(GL10.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT);
		
   //Position model so can see
   gl.glMatrixMode(GL10.GL_MODELVIEW);
   gl.glLoadIdentity();
   gl.glTranslatef(0, 0, -3.0f);
		
}

A Cube Example

We now are going to work towards drawing a spinning cube. For today we will only draw a stationary one.
To draw a cube we will use triangle strips, which are a sequence of points (in our case we will use 3D points), the first three representing a starting triangle, each additional point allows use to add one more triangle.
A pair of triangle is a strip can be used to make a square, and six squares can be put together to make a cube.
In order, to light such a strip correctly, we need to specify a normal vector to the triangles we are drawing.

Code for GLCube Class

class GLCube 
{
   private final IntBuffer mVertexBuffer;
	
   GLCube()
   {
      int one = 65536;
      int half = one/2;
		
      int vertices[] = 
      {
         //Front
         -half, -half, half, half, -half, half,
         -half, half, half, half, half, half,
         //Back
         -half, -half, -half, -half, half, -half,
         half, -half, -half, half, half, -half,
         //Left
         -half, -half, half, -half, half, half,
         -half, -half, -half, -half, half, -half,
         //Right
         half, -half, -half, half, half, -half,
         half, -half, half, half, half, half,
         //Top
         -half, half, half, half, half, half,
         -half, half, -half, half, half, -half,
         //Bottom
         -half, -half, half, -half, -half, -half,
         half, -half, half, half, -half, -half
      };
		
      ByteBuffer vbb = ByteBuffer.allocateDirect(vertices.length*4);
      vbb.order(ByteOrder.nativeOrder());
      mVertexBuffer = vbb.asIntBuffer();
      mVertexBuffer.put(vertices);
      mVertexBuffer.position(0);
  }

   void draw(GL10 gl)
   {
      gl.glVertexPointer(3, GL10.GL_FIXED, 0, mVertexBuffer);
		
      gl.glColor4f(1, 1, 1, 1);
      gl.glNormal3f(0, 0, 1);
      gl.glDrawArrays(GL10.GL_TRIANGLE_STRIP, 0, 4);
      gl.glNormal3f(0, 0, -1);
      gl.glDrawArrays(GL10.GL_TRIANGLE_STRIP, 4, 4);
		
      gl.glColor4f(1, 1, 1, 1);
      gl.glNormal3f(-1, 0, 0);
      gl.glDrawArrays(GL10.GL_TRIANGLE_STRIP, 8, 4);
      gl.glNormal3f(1, 0, 0);
      gl.glDrawArrays(GL10.GL_TRIANGLE_STRIP, 12, 4);
      
      gl.glColor4f(1, 1, 1, 1);
      gl.glNormal3f(0, 1, 0);
      gl.glDrawArrays(GL10.GL_TRIANGLE_STRIP, 16, 4);
      gl.glNormal3f(0, -1, 0);
      gl.glDrawArrays(GL10.GL_TRIANGLE_STRIP, 20, 4);

   }
}

Putting it together with the previous code

To add the cube to our previous example, we add the field:
```
   private final GLCube cube = new GLCube();
```
to our GLThreadclass.

Then we modify drawFrame to:

private void drawFrame(GL10 gl)
{
   //clear screen to black
   gl.glClear(GL10.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT);
		
   //Position model so can see
   gl.glMatrixMode(GL10.GL_MODELVIEW);
   gl.glLoadIdentity();
   gl.glTranslatef(0, 0, -3.0f);
		
   cube.draw(gl);

}

OpenGL Android

Outline