在早期版本的android蜂窝中，OpenGL ES对象形状没有正确绘制

Question

Im drawing a circle and even if i draw a basic shape (eg.square, diamond) using java opengl ES in android.

If I run the application in honeycomb the shape is coming fine but if I run it in gingerbread with the shape few more unnecessary points where getting drawn(it getting scattered) and if I keep on executing it rarely it comes without those points.

My Renderer class,

public void onDrawFrame(GL10 gl) {
     gl.glClear(GL10.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT);
     gl.glMatrixMode(GL10.GL_MODELVIEW);
gl.glLoadIdentity();
gl.glTranslatef(0, 0, -5.0f);
gl.glRotatef(-100, 1.0f, 0.0f, 0.0f);
gl.glRotatef(40, 1.0f, 0.0f, 0.0f);

mCircle= new Circle();
     Circle.setCirclePoints(1.5f,4, 1, 360);
Circle.draw(gl);

}

public void onSurfaceChanged(GL10 gl, int width, int height) {
gl.glViewport(0, 0, width, height);         
     float ratio = (float) width / height;
gl.glMatrixMode(GL10.GL_PROJECTION);
gl.glLoadIdentity();
gl.glOrthof(-6.5f, +6.5f, -6.5f, 6.5f, 6.5f, -6.5f);

  }
          public void onSurfaceCreated(GL10 gl, EGLConfig config) {
       gl.glHint(GL10.GL_PERSPECTIVE_CORRECTION_HINT, GL10.GL_NICEST);
gl.glClearColor(0,0,0,0);
gl.glEnable(GL10.GL_CULL_FACE);
gl.glShadeModel(GL10.GL_SMOOTH);
gl.glEnable(GL10.GL_DEPTH_TEST);
    }   

In my Circle Class

public void setCirclePoints(float radius, int slices, int stacks,
        float angle)
    ByteBuffer vbb = ByteBuffer.allocateDirect(((slices+2)* 3 * 4));
    vbb.order(ByteOrder.nativeOrder());
    mSliceVertexBuffer = vbb.asFloatBuffer();

    mSliceVertexBuffer.put(0.0f);
    mSliceVertexBuffer.put(0.0f);
    mSliceVertexBuffer.put(nsign * radius);

    for (int j = 0; j <= slices; j++) {
        theta = j * dtheta;
        x = (float) 1.25f * (float) (Math.cos(theta + dupTheta));
        y = (float) Math.sin(theta + dupTheta);
        z = nsign;
        mSliceVertexBuffer.put(x * radius);
        mSliceVertexBuffer.put(y * radius);
        mSliceVertexBuffer.put(z * radius);
        } 

              }
public void draw(GL10 gl){
     gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);
     gl.glVertexPointer(3, GL10.GL_FLOAT, 0, mSliceVertexBuffer);
     gl.glColor4f(212,21,54,34);
    gl.glDrawArrays(GL10.GL_TRIANGLE_FAN, 0,sliceCount);
     gl.glDisableClientState(GL10.GL_VERTEX_ARRAY);
}

Im really clue less.. I dont know why its not drawing properly in android version <3.0.

edit: I tried to solve it, I found that when I'm trying to plot the points, few vertex are going out of the viewport(may be infinity, I dont know) in android 2.3.3, but for the same points in android 3.0 it drawing the proper shape.

Help me out.

Answer 1

 x = (float) 1.25f * (float) (Math.cos(theta + dupTheta)); 

What's that factor 1.25 supposed to mean? If your circle is coming out as an ellipse, then that's because your projection matrix doesn't take into account window aspect.

Answer 2

I made a blunder mistake The issue was in

    gl.glDrawArrays(GL10.GL_TRIANGLE_FAN, 0,sliceCount);

where the sliceCount is total number of points x,y,z. I divided that one by 3.

       gl.glDrawArrays(GL10.GL_TRIANGLE_FAN, 0,sliceCount/3);