// ====================================================================
// Add the following pure virtual function to Object3D and define it
// in each of its subclasses.  The paint routine is responsible for
// making the OpenGL calls to draw the object to the screen.
// ====================================================================

#include <GL/gl.h>

  virtual void paint(void) = 0;

// ====================================================================
// Below are some OpenGL commands that will be essential for 
// implementing the paint routines.
//
// Use the glPushMatrix() and glPopMatrix() commands to save the
// current transformation to the stack or restore a transformation
// matrix from the top of the stack.
// ====================================================================

  glPushMatrix();
  glPopMatrix();

// ====================================================================
// These routines are used to translate, rotate, or scale an object
// The indicated transformation will modify the current matrix, and 
// will thus affect all subsequent OpenGL calls.
//
// glTranslate translates by (x,y,z)
// glRotate rotates by 'angle' degrees about axis (x,y,z)
// glScale scales by (x,y,z)
//
// Data type can be either float or double, depending on whether
// the f or d is used in the function name
// ====================================================================

  glTranslate{fd}(x, y, z);
  glRotate{fd}(angle, x, y, z)
  glScale{fd}(x, y, z);

// ====================================================================
// The parameters to glVertex can be either a listing or an array
// of floats or doubles, depending on how the routine is called
// ====================================================================

  glVertex3f(float x, float y, float z);     // List of floats
  glVertex3d(double x, double y, double z);  // List of doubles
  glVertex3fv(float *arr);                   // Array of floats
  glVertex3dv(double *arr);                  // Array of doubles

// ====================================================================
// glMultMatrix{fd} can be used to multiply the current matrix by
// an arbitrary matrix.  We've added a glGet() routine to the Matrix
// class to construct a matrix with the appropriate structure.
//
// OpenGL matrices created with this routine should be deleted
// when they are no longer needed.
// ====================================================================

  GLfloat *glMatrix = matrix.glGet();
  glMultMatrixf(glMatrix);
  delete[] glMatrix;

// ====================================================================
// Geometry is constructed with a series of calls to glVertex,
// sandwiched between glBegin() and glEnd() statements.
// ====================================================================

  glBegin(GL_TRIANGLES);
    glVertex3f(x0, y0, z0);
    glVertex3f(x1, y1, z1);
    glVertex3f(x2, y2, z2);
  glEnd();

// ====================================================================
// The parameter passed to the glBegin() command changes how the
// following vertices are interpreted.
//
// GL_POINTS: Each vertex will be drawn as a single pixel
// GL_TRIANGLES: Each set of three vertices will be drawn as a triangle
// GL_QUADS: Each set of four vertices will be drawn as a quadrilateral
// GL_LINES: Each pair of vertices will be drawn as a line segment
//
// To change the normal vector, use glNormal3{fd}[v]().  This routine
// can take a variety of different parameters, just like glVertex().
// ====================================================================

  glNormal3f(float x, float y, float z);     // List of floats
  glNormal3d(double x, double y, double z);  // List of doubles
  glNormal3fv(float *arr);                   // Array of floats
  glNormal3dv(double *arr);                  // Array of doubles

// ====================================================================
// Note that some statements, like glVertex() and glNormal() should
// always appear between glBegin() and glEnd() statements.  Other
// commands, like glPushMatrix() or glTranslate(), should not appear
// between glBegin() and glEnd().
// ====================================================================