JOGL glArrayElement point providing 0,0,0

Question

I have a JOGL opengl problem, I'm trying to use Vertex Arrays, but whenever I use glArrayElement (Note: glDrawElements doesn't work either.), it gives the point 0,0,0. Important code. I'm assuming a window is initialized and a reshape function is specified.

...
public void display(GLDrawable glDrawable) {
 final GL gl = glDrawable.getGL();
 gl.glClear(GL.GL_COLOR_BUFFER_BIT | GL.GL_DEPTH_BUFFER_BIT);
 gl.glLoadIdentity();
 gl.glTranslatef(0, 0, -6);
 gl.glBegin(GL.GL_TRIANGLES);
  gl.glColor3f(1.0f, 0.0f, 0.0f);
  gl.glArrayElement(4);
  /*gl.glArrayElement(5); // These are what I'm trying to use, but they seem to return the point 0,0,0.
  gl.glArrayElement(6);
  gl.glArrayElement(5);
  gl.glArrayElement(6);
  gl.glArrayElement(7);*/
  //gl.glVertex3f(1, 1, -1); // Replaced with uncommented glArrayElement above.
  gl.glColor3f(0.0f, 1.0f, 0.0f);
  gl.glVertex3f(-1, 1, -1);
  gl.glVertex3f(1, -1, -1);
  gl.glColor3f(0.0f, 0.0f, 1.0f);
  gl.glVertex3f(-1, 1, -1);
  gl.glVertex3f(1, -1, -1);
  gl.glVertex3f(-1, -1, -1);
 gl.glEnd();
}
...
protected final static float[] mesh = {1,1,1, -1,1,1, 1,-1,1, -1,-1,1, 

1,1,-1, -1,1,-1, 1,-1,-1, -1,-1,-1};
protected static ByteBuffer stdMesh;
...
public void init(GLDrawable glDrawable) {
 final GL gl = glDrawable.getGL();
 gl.glShadeModel(GL.GL_SMOOTH);
 gl.glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
 gl.glClearDepth(1.0f);
 gl.glEnable(GL.GL_DEPTH_TEST);
 gl.glDepthFunc(GL.GL_LEQUAL);
 gl.glHint(GL.GL_PERSPECTIVE_CORRECTION_HINT, GL.GL_NICEST);
 gl.glEnableClientState(GL.GL_VERTEX_ARRAY);
 stdMesh = ByteBuffer.allocateDirect(mesh.length * 4);
 stdMesh.asFloatBuffer().put(mesh);
 gl.glVertexPointer(3, GL.GL_FLOAT, 0, stdMesh);
}
...

Are there other initalization functions/draw functions I also need to call, or is it another problem? Any help is appreciated.

brian_d · Answer 1 · 2011-01-24T08:20:29.347

You need to properly populate your buffer with your array values. The way you are doing it returns a new FloatBuffer but you are discarding the result instead of storing it.

Instead of

...
protected static ByteBuffer stdMesh;
...
 stdMesh = ByteBuffer.allocateDirect(mesh.length * 4);
 stdMesh.asFloatBuffer().put(mesh);
...

Do

...
protected static FloatBuffer stdMesh;
...
stdMesh = BufferUtil.newFloatBuffer(mesh.length * 3);
for (int i = 0; i < mesh.length; i++){
    stdMesh.put(mesh[i]);
}
stdMesh.flip();
...

Make sure to call flip() on the buffer before using it.

JOGL glArrayElement point providing 0,0,0

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