glPushMatrix,	glPopMatrix - push and pop the current matrix

	  void glPushMatrix( void )

	  void glPopMatrix( void )

	  There	is a stack of matrices for each	of the matrix modes.
	  In GL_MODELVIEW mode,	the stack depth	is at least 32.	 In
	  the other two	modes, GL_PROJECTION and GL_TEXTURE, the depth
	  is at	least 2.  The current matrix in	any mode is the	matrix
	  on the top of	the stack for that mode.

	  glPushMatrix pushes the current matrix stack down by one,
	  duplicating the current matrix.  That	is, after a
	  glPushMatrix call, the matrix	on top of the stack is
	  identical to the one below it.

	  glPopMatrix pops the current matrix stack, replacing the
	  current matrix with the one below it on the stack.

	  Initially, each of the stacks	contains one matrix, an
	  identity matrix.

	  It is	an error to push a full	matrix stack, or to pop	a
	  matrix stack that contains only a single matrix.  In either
	  case,	the error flag is set and no other change is made to
	  GL state.

	  GL_STACK_OVERFLOW is generated if glPushMatrix is called
	  while	the current matrix stack is full.

	  GL_STACK_UNDERFLOW is	generated if glPopMatrix is called
	  while	the current matrix stack contains only a single

	  GL_INVALID_OPERATION is generated if glPushMatrix or
	  glPopMatrix is executed between the execution	of glBegin and
	  the corresponding execution of glEnd.

	  glGet	with argument GL_MATRIX_MODE
	  glGet	with argument GL_MODELVIEW_MATRIX
	  glGet	with argument GL_PROJECTION_MATRIX
	  glGet	with argument GL_TEXTURE_MATRIX
	  glGet	with argument GL_MODELVIEW_STACK_DEPTH
	  glGet	with argument GL_PROJECTION_STACK_DEPTH
	  glGet	with argument GL_TEXTURE_STACK_DEPTH
	  glGet	with argument GL_MAX_MODELVIEW_STACK_DEPTH
	  glGet	with argument GL_MAX_PROJECTION_STACK_DEPTH
	  glGet	with argument GL_MAX_TEXTURE_STACK_DEPTH

	  glFrustum, glLoadIdentity, glLoadMatrix, glMatrixMode,
	  glMultMatrix,	glOrtho, glRotate, glScale, glTranslate,