; xModels Tutorial 4:  Complex Objects

; The real power of xModels (what there is of it) comes from
; fact that it is a "hierarchical" modeling language.  You
; can combine several objects into one complex object,
; which can then be treated as a unit.  Transformations
; applied to a complex object apply to the object as a
; whole.  A complex object can even include other complex
; objects.  It is also possible to define a name to 
; represent a complex object.  Then the name can be
; used in the scene, just as if it were one of the
; predefined objects such as "square" and "cone".

animate 60  ; This will be a 60-frame animation

[       ; A complex object begins with a "[" and ends with "]".

   square scale 4  ; Transformations can be applied to the
                   ; objects inside a complex object.   

   [   ; Complex objects can be nested inside other objects.
      circle translate 5
      circle translate -5
   ] rotate 45:-45  ; The rotation command applies to the
                    ; entire complex object, consisting of
                    ; two circles.
   
   red ; A complex object can contain color commands
       ; in addition to objects

   line scale 8 rotate 90 xtranslate -4:4
   
] scale 0.5:1.2  ; The entire complex object grows from
                 ; half of its basic size to 1.2 times
                 ; that size.
                 
; Note: At this point, the drawing color is black.
;       The color change INSIDE the object has no
;       effect outside.  (On the other hand, a color
;       change made BEFORE the object does "leak into"
;       a complex object.


define wheel [  ; Begin the defintino of an object named "wheel".
   circle
   line              ; A wheel contains a circle and three
   line rotate 60    ; lines, which act as spokes.
   line rotate -60
]   ; The end of the definition

; "Wheel" has been defined, but no wheel has been put into
; the scene.  Now we add two wheels with different
; colors, sizes, and rotation speeds to the scene:

wheel scale 2 rotate 0:360 xtranslate -8  ; This one is black.

green

wheel scale 4 rotate 0:-180 xtranslate 8


; A defined object can be used inside the definition
; of another object.


define wagon [
   red
   square scale 4 2
   blue
   wheel scale 2 rotate 0:-720 translate -2 -1
   wheel scale 2 rotate 0:-720 translate 2 -1
]

wagon ytranslate -8        ; A wagon across the bottom of
      xtranslate -10:10    ;    the screen