Android OpenGL ES Polygon Tutorial Assistance

Question

I have followed some Android tutorials and have this Triangle program that works and runs and creates a filled Triangle successfully.

I am now trying to follow several different Polygon tutorials but none seem to help translating my code to a polygon. I have scoured stack and everywhere else, so I know this may seem repetitive.

I want to be able to enter the number of sides and have the program generate the polygon with that many sides. I can sort of hard code in vertices in order to generate a polygon but cannot make this a polygon of n sides.

Would anyone be able to guide me in the right direction or provide some examples? I am lost.

Triangle.java

import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.FloatBuffer;

import javax.microedition.khronos.opengles.GL10;

public class Triangle{

private FloatBuffer vertexBuffer;
private int vSize = 7;

public Triangle(){
    float vertices[] = {
            -.5f, -.433f, 0, 1, 0, 0, 1,
            .5f, -.433f, 0, 0, 1, 0, 1,
            0, .433f, 0, 0, 0, 1, 1
    };
    ByteBuffer byteBuffer = ByteBuffer.allocateDirect(vertices.length*4);
    byteBuffer.order(ByteOrder.nativeOrder());
    vertexBuffer = byteBuffer.asFloatBuffer();
    vertexBuffer.put(vertices);

}
public void onDrawFrame(GL10 gl) {
    vertexBuffer.position(0);
    gl.glVertexPointer(3, GL10.GL_FLOAT, vSize*4, vertexBuffer);
    vertexBuffer.position(3);
    gl.glColorPointer(4, GL10.GL_FLOAT, vSize*4, vertexBuffer);
    gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);
    gl.glEnableClientState(GL10.GL_COLOR_ARRAY);
    gl.glDrawArrays(GL10.GL_TRIANGLES, 0, 3);    // GL_TRAINGLEFAN for polygon?
    gl.glDisableClientState(GL10.GL_VERTEX_ARRAY);
    gl.glDisableClientState(GL10.GL_COLOR_ARRAY);

}

}

MyRenderer.java

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

import android.opengl.GLSurfaceView.Renderer;

public class MyRenderer implements Renderer {
private Triangle triangle;

@Override
public void onDrawFrame(GL10 gl) {
    gl.glClear(GL10.GL_COLOR_BUFFER_BIT|GL10.GL_DEPTH_BUFFER_BIT);
    triangle.onDrawFrame(gl);

}

@Override
public void onSurfaceChanged(GL10 gl, int width, int height) {
    if(width<height){
        gl.glViewport(0, 0, width, width);
    }else{
        gl.glViewport(0, 0, height, height);
    }
    gl.glMatrixMode(GL10.GL_PROJECTION); //to work with the projection matrix
    //to do: set up ortho projection
    gl.glLoadIdentity();
    gl.glOrthof(-1.0f, 1.0f, -1.0f, 1.0f, -0.1f, 0.1f);
    gl.glMatrixMode(GL10.GL_MODELVIEW);//methods should restore model view matrix mode
}

@Override
public void onSurfaceCreated(GL10 gl, EGLConfig arg1) {
    gl.glClearColor(0.8f, 0.8f, 0.8f, 1);
    triangle = new Triangle();
}

}

MainActivity.java

import android.opengl.GLSurfaceView;
import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;

public class MainActivity extends Activity {

private GLSurfaceView  view;
private MyRenderer renderer;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    //setContentView(R.layout.activity_main);
    view = new GLSurfaceView(this);
    renderer = new MyRenderer();
    view.setRenderer(renderer);
    setContentView(view);
}

@Override
protected void onPause() {
    view.onPause();
    super.onPause();
}

@Override
protected void onResume() {
    view.onResume();
    super.onResume();
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

}

Answer 1

Sample a circle every (2 * pi) / n radians:

void glPolygon( unsigned int sides )
{
    glBegin( GL_TRIANGLE_FAN );
    glVertex2f( 0, 0 );
    for( unsigned int i = 0; i <= sides; i++ )
    {
        const float u = ( i / (float)sides );
        const float a = ( 2 * 3.14159 ) * u;
        glVertex2f( cos( a ), sin( a ) );
    }
    glEnd();
}