AWTGLCanvas & ModelViewMatrix

[nbs]

Hi!

I started developing an Visualisation Application with LWJGL using AWTGLCanvas. At first I wanted to set up my Projection an coordinate system but get stuck pretty early. Somehow I seem to miss the essence of the Canvas.

First of all I added an MouseWheelListener to the Canvas:

public void mouseWheelMoved(MouseWheelEvent wheelEvent) {
   zTransform += wheelEvent.getUnitsToScroll();
   wheelEvent.consume();
   paintGL();
}


And overwrote the initGL and paintGL methods (I used some static import, all from GL11.*):


@Override
protected void initGL() {
   glClearColor(0f, 0f, 0f, 1f);
   glEnable(GL_DEPTH_TEST);
   glDepthFunc(GL_LEQUAL);
   glShadeModel(GL_SMOOTH);
}
   
@Override
protected void paintGL() {
   try {
      synchronized (GL_LOCK) {
         makeCurrent();
         glClear(GL11.GL_COLOR_BUFFER_BIT | GL11.GL_DEPTH_BUFFER_BIT);
         glMatrixMode(GL11.GL_MODELVIEW);
         glLoadIdentity();
            
         GL11.glTranslatef(0, 0, zTransform);
         FloatBuffer buffer = ByteBuffer.allocateDirect(16*Double.SIZE/8).asFloatBuffer();
         buffer.rewind();
         GL11.glGetFloat(GL11.GL_MODELVIEW_MATRIX, buffer);
         System.out.println("ModelView Matrix: ");
         System.out.println(getMatrixAsString(buffer));
            
         buffer.rewind();
         GL11.glGetFloat(GL11.GL_PROJECTION_MATRIX, buffer);
         System.out.println("Projection Matrix: ");
         System.out.println(getMatrixAsString(buffer));
         
         drawRectBox(20, 20, 20); // Contains one glBegin..glEnd block drawing some quads
         swapBuffers();
      }
   } catch (LWJGLException e) {
      e.printStackTrace();
   }
      

}
   
private String getMatrixAsString(FloatBuffer matrix) {
   String s = "";
   s += String.format("| %f %f %f %f \n", matrix.get(0), matrix.get(4), matrix.get(8), matrix.get(12));
   s += String.format("| %f %f %f %f \n", matrix.get(1), matrix.get(5), matrix.get(9), matrix.get(13));
   s += String.format("| %f %f %f %f \n", matrix.get(2), matrix.get(6), matrix.get(10), matrix.get(14));
   s += String.format("| %f %f %f %f \n", matrix.get(3), matrix.get(7), matrix.get(11), matrix.get(15));
   
   return s;
}


While zTransform always contains correct int values, both the ModelView and the Projection matrix are echoed all 0. What do I do wrong?

Furthermore, what exactly does swapBuffers? I understand that makeCurrent sets the current Canvas GL Context as global context. Where does swapBuffers come into play?

Thanks in advance,
Nico

[Matthias]

You allocate your FloatBuffer wrong. The easiest way is to just use BufferUtils from LWJGL:

BufferUtils.createFloatBuffer(16);

Also in Java the size of all data types is fixed in the language spec - a float is always 4 bytes.

[nbs]

Hi, thanks, works like charm. Actually my way of allocation wasnt overall wrong. If you look what the BufferUtil does:

ByteBuffer.allocateDirect(size << 2).order(ByteOrder.nativeOrder()).asFloatBuffer();

It would be nice if glGet* would check the order of the buffer if it depends on the native order.