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4.3 3D transformations

This corresponds to, before performing the transformations  and describing the object, to declare the start and end of operations in some way.

•      SUBROUTINE PUSH
  

  indicates the  start of an occurrence of an object (it stacks a unit matrix).

•      SUBROUTINE PREPAR
  

  must imperatively terminate the  sequence describing the transformations and precede the sequence describing the object (it evaluates the transformation matrix).

•      SUBROUTINE PULL
  

  must imperatively follow the  sequence describing an object (returns to the called object's space). A correct calling sequence for an object must therefore have the following form:

       CALL PUSH
          DEFINITION OF THE TRANSFORMATIONS
       CALL PREPAR
          SEQUENCE DESCRIBING THE OBJECT CALLED
       CALL PULL
  

  The PUSHes and PULLs can be nested up to 8 levels in the following manner:

       CALL PUSH
          .....
       CALL PREPAR
          .....
          CALL PUSH
            .....
          CALL PREPAR
            .....
          CALL PULL
          .....
       CALL PULL
  

•      SUBROUTINE RAZPSK
  

  is used to set the transformation stack pointer to 0   (done automatically in DEVICE).