Scheme Extensions

 

 

Technical Article
Scheme is a public domain programming language, based on the LISP language, that uses an interpreter to run commands. ACIS provides extensions (written in C++) to the native Scheme language that can be used by an application to interact with ACIS through its Scheme Interpreter. The C++ source files for ACIS Scheme extensions are provided with the product. Spatial's Scheme based demonstration application, Scheme ACIS Interface Driver Extension (Scheme AIDE), also uses these Scheme extensions and the Scheme Interpreter.

entity:bend

Action
Modifies an entity or list of entities by bending it around an axis.

Filename
scm/scmext/warp/bend_scm.cpp

APIs
api_bend_entity, api_part_note_state, api_pm_start_state

Syntax
(entity:bend ent-list neutral-root bending-axis
    bending-direction bend-radius
    [bend-angle [bend-width
    [center-bend-flag [bend-position*]]]])

Arg Types
ent-list entity | (entity ...)
neutral-root position
bending-axis gvector
bending-direction gvector
bend-radius real
bend-angle real
bend-width real
center-bend-flag boolean
bend-position* position

Returns
entity | (entity ...)

Description
Neutral-root, bending-axis, and bending-direction define a neutral plane for the bending operation. A neutral plane is the location where the material is not stretched or compressed during bending. The material above the neutral plane (along bending direction) is compressed and the material below the neutral plane is stretched. The location of a neutral plane varies with the type of material to be bent.

Arguments
neutral-root is a position that defines the location of neutral plane.
 
bending-axis is a gvector that defines the rotational axis of bending action.
 
bending-direction is auxiliary gvector that is used to define a bending plane.
 
The bending axis, denoted by bending-axis, and the bending direction, denoted by bending-direction, define a bending plane with normal vector bending-axis x bending-direction. The bending axis and bending direction should be perpendicular to each other. The cross product of these two vectors defines the positive and negative sides of the entity to be bent.
 
bend-radius is a real number that specifies the radius to the neutral plane.
 
bend-angle (optional) is the angle in degrees that specifies the amount to bend.
 
bend-width (optional) is the width of bend region. The bend-radius, bend-angle, and bend-width are used to determine the region to be bent. Because only two parameters are independent, bend-width can be optional. Assigning zero or negative values to any of the three parameters implies that the parameter is skipped. It is always desirable to use just two of the three parameters. However, if only the bend-radius is given, the entire entity is bent. These parameters are related by: bend-width=bend-radius*bend-angle*PI/180
 
center-bend-flag (optional) is a Boolean type to specify final orientation, i.e., center bend or fix end bend. The center-bend-flag is used to control the final orientation of the bend entity. If center-bend-flag is set to #t, material at both sides of the bending plane are equally bend by half of the bend-angle. If the center-bend-flag is not set or set to #f, the negative side is fixed, i.e., only the positive side is bent by bend-angle. This mode is called fixed end bending.
 
bend-position* (optional) specifies the portions of the entity to bend. The asterisk (*) means one or more positions can be defined. The positions must be within the components to be bent or on their faces. Several bend positions can be specified to localize bending operation. The specified bend positions are tested to determine if they are within the bending region. If all bend positions are outside of the bending region or outside the entity and its faces, no bending is performed.
; entity:bend
; Create a block
(define block1 (solid:block (position -30 -10 0)
    (position 30 10 1)))
;; block1
; OUTPUT Original
; Bend the block
(entity:bend block1 (position 0 0 0)
    (gvector 0 1 0) (gvector 0 0 1) 10 30)
; 0.930000 = api_time
; 0.000000 = updating
;; #[entity 2 1]
; OUTPUT Example

Figure. entity:bend - Example 1

;Additional Example 2
; Create several objects for bending
(part:clear)
;; #t
; Create a block
(define a-part (solid:block (position -24 -8 -0.25)
    (position 40.5 8 0.25)))
;; a-part
; Create another block
(define b2 (solid:block (position -8 -24 -.25)
    (position 8 24 .25)))
;; b2
; Unite the blocks
(define a-part (bool:unite a-part b2))
;; a-part
; Create another small block
(define a-block (solid:block
    (position -2 -22 -1) (position 2 -2 1)))
;; a-block
; Subtract a-block from a-part
(define a-part (bool:subtract a-part a-block))
;; a-part
; Create another small block
(define b-block (solid:block
    (position 20 -22 -.25) (position 24 -2 0.25)))
;; b-block
; Unite the blocks
(define a-part (bool:unite a-part b-block))
;; a-part
; Visualize positions for local bending
; by creating spots
(define a-spot (solid:sphere
    (position 6 -8.25 0.25) 0.25))
;; a-spot
; Change the spot's color
(entity:set-color a-spot 1)
;; ()
(define b-spot (solid:sphere
    (position -6 -8.25 0.25) 0.25))
;; b-spot
; Change the spot's color
(entity:set-color b-spot 3)
;; ()
(define c-spot (solid:sphere
    (position 22 -8.25 0.25) 0.25))
;; c-spot
; Change the spot's color
(entity:set-color c-spot 6)
;; ()
; OUTPUT Original
; Only radius is given, space warp whole part.
(define bend (entity:bend a-part (position 0 -8. 0)
    (gvector 1 0 0) (gvector 0 0 1) 20))
;; bend
; OUTPUT Example

Figure. entity:bend - Example 2

; Additional Example 3
; Create several objects for bending
; Create a block
(part:clear)
;; #t
(define a-part (solid:block (position -24 -8 -0.25)
    (position 40.5 8 0.25)))
;; a-part
; Create another block
(define b2 (solid:block (position -8 -24 -.25)
    (position 8 24 .25)))
;; b2
; Unite the blocks
(define a-part (bool:unite a-part b2))
;; a-part
; Create another small block
(define a-block (solid:block
    (position -2 -22 -1) (position 2 -2 1)))
;; a-block
; Subtract a-block from a-part
(define a-part (bool:subtract a-part a-block))
;; a-part
; Create another small block
(define b-block (solid:block
    (position 20 -22 -.25) (position 24 -2 0.25)))
;; b-block
; Unite the blocks
(define a-part (bool:unite a-part b-block))
;; a-part
; Visualize positions for local bending
; by creating spots
(define a-spot (solid:sphere
    (position 6 -8.25 0.25) 0.25))
;; a-spot
; Change the spot's color
(entity:set-color a-spot 1)
;; ()
(define b-spot (solid:sphere
    (position -6 -8.25 0.25) 0.25))
;; b-spot
; Change the spot's color
(entity:set-color b-spot 3)
;; ()
(define c-spot (solid:sphere
    (position 22 -8.25 0.25) 0.25))
;; c-spot
; Change the spot's color
(entity:set-color c-spot 6)
;; ()
; OUTPUT Original
(define bend (entity:bend a-part (position 0 -8. 0)
    (gvector 1 0 0) (gvector 0 0 1) 0.5 90 ))
;; bend
; OUTPUT Example

Figure. entity:bend - Example 3

; Additional Example 4
; Create several objects for bending
; Create a block
(part:clear)
;; #t
(define a-part (solid:block (position -24 -8 -0.25)
    (position 40.5 8 0.25)))
;; a-part
; Create another block
(define b2 (solid:block (position -8 -24 -.25)
    (position 8 24 .25)))
;; b2
; Unite the blocks
(define a-part (bool:unite a-part b2))
;; a-part
; Create another small block
(define a-block (solid:block
    (position -2 -22 -1) (position 2 -2 1)))
;; a-block
; Subtract a-block from a-part
(define a-part (bool:subtract a-part a-block))
;; a-part
; Create another small block
(define b-block (solid:block
    (position 20 -22 -.25) (position 24 -2 0.25)))
;; b-block
; Unite the blocks
(define a-part (bool:unite a-part b-block))
;; a-part
; Visualize positions for local bending
; by creating spots
(define a-spot (solid:sphere
    (position 6 -8.25 0.25) 0.25))
;; a-spot
; Change the spot's color
(entity:set-color a-spot 1)
;; ()
(define b-spot (solid:sphere
    (position -6 -8.25 0.25) 0.25))
;; b-spot
; Change the spot's color
(entity:set-color b-spot 3)
;; ()
(define c-spot (solid:sphere
    (position 22 -8.25 0.25) 0.25))
;; c-spot
; Change the spot's color
(entity:set-color c-spot 6)
;; ()
; OUTPUT Original
; Bend area given is not complete, but
; command intelligence completes the bend
; automatically
(define bend (entity:bend a-part (position 0 -8. 0)
    (gvector 1 0 0) (gvector 0 0 1) 0.5 90 0 #f
    (position 6 -8.25 0.25)))
;; bend
; OUTPUT Example

Figure. entity:bend - Example 4

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entity:bend-to-curve

Action
Modifies an entity by bending it to a curve.

Filename
scm/scmext/warp/bend_to_curve_scm.cpp

APIs
api_part_note_state, api_pm_start_state, api_bend_to_curve_entity

Syntax
(entity:bend-to-curve body start end initial-rail
    edge final-rail)

Arg Types
body entity
start position
end position
initial-rail gvector
edge edge
final-rail law

Returns
entity
Arguments
body is one of the entity of a Scheme Component.
 
start gives the start position for bending the curve.
 
end gives the end position for bending the curve.
 
initial-rail is a gvector.
 
edge is an edge of the entity.
 
final-rail is a law.
; entity:bend-to-curve
; Define geometry to demonstrate command.
(option:set "match_paren" #f)
;; #t
(cond ( ( = 0 (length (part:views))) (view:dl)))
;; #f
(define color (view:set-bg-color 7))
;; color
(part:clear)
;; #t
; Make a spring edge
(define handiness #t)
;; handiness
(define pitch1 10)
;; pitch1
(define pitch_degrees1 1440)
;; pitch_degrees1
(define axis_point (position 0 0 0)))
;; axis_point
(define axis_vector (gvector 0 1 0))
;; axis_vector
(define start_position (position 0 0 6))
;; start_position
(define spring
    (edge:spring axis_point axis_vector
    start_position handiness pitch1 pitch_degrees1))
;; spring
; Create the part to warp.
(define height 40)
;; height
(define hneg (- 0 height))
;; hneg
(define width 1)
;; width
(define wneg (- 0 width))
;; wneg
(define ent (solid:block (position wneg 5 wneg)
     (position width (- height 5) width)))
;; ent
(define move (entity:move ent -10 0 0))
;; move
(define zoom (zoom-all))
;; zoom
; OUTPUT Original
(render:rebuild)
;; ()
(define start (position 0 0 0))
;; start
(define end (position 0 height 0))
;; end
(define e1 (edge:linear start end ))
;; e1
(define w1 (wire-body e1))
;; w1
(define rail (gvector 0 0 1))
;; rail
(define final_rail (law "norm (cross
    (law1, dcur (edge2,1)))" axis_vector spring))
;; final_rail
(define final_rail_simple (law "law1"
    (gvector 0 0 1)))
;; final_rail_simple
(define bend (entity:bend-to-curve ent start end
    rail spring))
; 6.329000 = api_time
; 0.020000 = redrawing
;; bend
; Color the bend for better illustration.
(define color (entity:set-color bend 3))
;; color
; Zoom in better.
(define zoom (zoom-all))
;; zoom
; OUTPUT Result
; Render the object.
(render)
;; ()
; OUTPUT Rendered Result

Figure. entity:bend-to-curve

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entity:simplify

Action
Simplifies the faces and edges of a body or the face and edges of a face.

Filename
scm/scmext/warp/warp_scm.cpp

APIs
api_simplify_entity

Syntax
(entity:simplify ent-list [acis-opts])

Arg Types
ent-list entity | (entity ...)
acis-opts acis-options

Returns
entity | (entity ...)

Description
The face(s) and edges of an entity (body or face) are replaced with analytic surfaces and curves, if possible. Otherwise, they are replaced with their B-spline approximations.

Arguments
ent-list gives the list of entities that can be either body or face.
 
acis-opts contains versioning and journaling information.
; entity:simplify
; Create the geometry to illustrate command.
(option:set "match_paren" #f)
;; #t
(cond (( = 0 (length (part:views))) (view:gl)))
;; #f
(define view (view:edges #t))
;; view
(define color (view:set-bg-color 7))
;; color
(part:clear)
;; #t
(define profile (edge:ellipse
    (position 0 0 0) (gvector 0 0 1)10))
;; profile
(define opts (sweep:options "draft_law" "sin(x)"))
;; opts
(define sweep (sweep:law profile
    (gvector 0 0 10) opts))
;; sweep
(define zoom (zoom-all))
;; zoom
(face:types)
; entity:(entity 3 1)
;      face:(entity 4 1) face_type:sweepsur-spline
;      face:(entity 5 1) face_type:Plane
;      face:(entity 6 1) face_type:Plane
;; #t
; simplify the entity
(define simplify (entity:simplify sweep))
;; simplify
; show that the faces have been simplified.
(face:types)
; entity:(entity 3 1)
;      face:(entity 4 1) face_type:exactsur-spline
;      face:(entity 5 1) face_type:Plane
;      face:(entity 6 1) face_type:Plane
;; #t

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entity:stretch

Action
Creates a stretch for a given region of a body along the given axis.

Filename
scm/scmext/warp/stretch_scm.cpp

APIs
api_part_note_state, api_pm_start_state, api_stretch_entity

Syntax
(entity:stretch body position1 position2 distance1 distance2 continuity)

Arg Types
body entity | (entity . . .)
position1 position
position2 position
distance1 real
distance2 real
continuity integer

Returns
entity

Description
Entity stretching is a specialized space warping operation. The position1 and position2 arguments represent endpoints of the axis along which stretching is to be performed, and can be either inside or outside the body. The region within which stretching is to occur is bounded by the two planes through position1 and position2, and normal to this axis.

The distance1 and distance2 parameters are real numbers that specify the translations of the non-stretched portions of the body. Typically, distance1 is chosen to be 0, indicating that the portion of the body below the stretch's starting region retains its position. If a nonzero value for distance1 is specified, on the other hand, the entire body is translated along the stretch axis by the given distance before the stretch is performed.

Let heightA be the distance between position1 and position2.

Let heightB be heightA + (distance2 - distance1).

Let heightR be heightB/heightA.

Then heightR represents the amount of scaling to apply to the stretch region of the body, along the stretch axis. (If heightR=1, therefore, no stretching or scaling need be applied.)

The continuity value can be 0 or 1, and refers to G0 and G1 continuity between the stretched and unstretched sections. The interpolation function uses a linear polynomial to obtain G0 continuity. To obtain G1 continuity, it uses a piece of a sine function. (The advantage of the sine function over a degree-3 polynomial is that its inverse is well-defined.)

Arguments
body specifies the body to be stretched.
 
position1 and position2 represent the endpoints of an axis along which stretching is to be performed and can be either inside or outside the body.
 
distance1 and distance2 are real parameters that specify the offset distances at the start and end of the stretch axis, respectively.
 
continuity specifies the continuity (G0 and G1) required of the stretch.
; entity:stretch
; Create an entity
(define ent (solid:cone
    (position 0 0 -40)
    (position 0 0 40) 30 5))
;; ent
(define e1 (edge:linear
    (position 35 0 -40) (position 10 0 40) ))
;; e1
(define w1(wire-body e1))
;; w1
(define e2 (edge:linear
    (position -35 0 -40)
    (position -10 0 40) ))
;; e2
(define w2(wire-body e2))
;; w2
(define unite (bool:unite ent w1 w2))
;; unite
(define continuity 0)
;; continuity
; OUTPUT Original
(define stretch (entity:stretch ent
    (position 0 0 -20)
    (position 0 0 20) 0 -30 continuity))
;; stretch
; OUTPUT Result
; Render for a better view.
(render)
;; ()
; OUTPUT Rendered Result

Figure. entity:stretch

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entity:twist

Action
Creates a twist for a given region of a body about an axis by the specified amount.

Filename
scm/scmext/warp/twist_scm.cpp

APIs
api_part_note_state, api_pm_start_state, api_twist_entity

Syntax
(entity:twist body position1 position2 theta1 theta2 continuity)

Arg Types
body entity
position1 position
position2 position
theta1 real
theta2 real
continuity integer

Returns
entity

Description
Entity twisting is a specialized space warping operation. The position1 and position2 are of type position. They represent endpoints of an axis about which twisting is to be performed and can be either inside or outside the body. Two planes are formed at the position1 and position2 positions which are normal to the axis. They specify the region of the body where twisting is to occur.

The theta1 and theta2 parameters are real numbers that specify in degrees the orientation of the non-twisted portions of the body. Typically, theta1 is 0, meaning that the portion of the body below the twist's starting region retains its orientation to the coordinate system. If a nonzero value for theta1 is specified, the entire body is transformed about the axis by the given amount before performing the twist.

The difference between theta1 and theta2 represents the amount in degrees that the twist region is warped around the axis. Both theta1 and theta2 can be greater than or multiples of +/- 360 degrees to provide more turns in the twisting region.

The continuity value can be 0, 1, or 2 and refer to G0, G1, and G2 continuity. The interpolation function uses a linear, cubic, or quintic polynomial to obtain G0, G1, or G2 continuity between twisted and untwisted sections.

Arguments
body gives the entity of a Scheme Component.
 
position1 and position2 represent endpoints of an axis about which twisting is to be performed and can be either inside or outside the body.
 
theta1 and theta2 are real numbers that specify in degrees the orientation of the non-twisted portions of the body.
 
continuity value can be 0, 1, or 2 and refer to G0, G1, and G2 continuity.
; entity:twist
; Create some geometry to twoist.
(define block1 (solid:block
    (position 10 20 30) (position 0 0 -30)))
;; block1
; OUTPUT Original
; Twist the blank.
(define pos1 (position 5 10 20))
;; pos1
(define pos2 (position 5 10 -20))
;; pos2
(define theta2 (law:eval "2*360"))
;; theta2
(define twist1
    (entity:twist block1 pos1 pos2 0 theta2 2))
;; twist1
(render)
;; ()
; OUTPUT Example

Figure. entity:twist - Example 1

; Additional Example 2
; Create some geometry to twoist.
(define c1 (solid:cylinder
    (position 0 0 0) (position 0 0 40) 5))
;; c1
(define c2 (solid:cylinder
    (position 0 -5 0) (position 0 -5 40) 3))
;; c2
(define c3 (solid:cylinder
    (position 0 5 0) (position 0 5 40) 3))
;; c3
(define blank (solid:subtract c1 c2))
;; blank
(define blank (solid:subtract c1 c3))
;; blank
; OUTPUT Original
; Twist the blank.
(define screw (entity:twist blank (position 0 0 0)
    (position 0 0 40) 0 (law:eval "2*360") 0))
;; screw
(render)
;; ()
; OUTPUT Example

Figure. entity:twist - Example 2

; Additional Example 3
; Create some geometry to twoist.
(define c1 (solid:cylinder
    (position 0 0 0) (position 0 0 40) 5))
;; c1
(define c2 (solid:cylinder
    (position 0 -5 0) (position 0 -5 40) 3))
;; c2
(define c3 (solid:cylinder
    (position 0 5 0) (position 0 5 40) 3))
;; c3
(define blank (solid:subtract c1 c2))
;; blank
(define blank (solid:subtract c1 c3))
;; blank
; OUTPUT Original
; Twist the blank.
(define screw (entity:twist blank (position 0 -10 5)
    (position 0 10 35) 0 (law:eval "0.25*360") 0))
;; screw
(render)
;; ()
; OUTPUT Example

Figure. entity:twist - Example 3

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law:warp

Action
Modifies an entity or list of entities according to a given input law.

Filename
scm/scmext/warp/warp_scm.cpp

APIs
api_space_warp

Syntax
(law:warp ent-list law)

Arg Types
ent-list entity | (entity ...)
law law | string

Returns
entity | (entity ...)
Arguments
ent-list gives the list of entities of a Scheme Component.
 
law is an input law that specifies how the entity should be modified.
; law:warp
; Create a block for warping.
(define block1
    (solid:block (position -20 -10 -15)
    (position 20 10 15)))
;; block1
; Set the color of the block
(entity:set-color block1 3)
;; ()
(define cyl1
    (solid:cylinder (position 0 -15 0)
    (position 0 15 0) 10))
;; cyl1
; Set the color of the cylinder
(entity:set-color cyl1 6)
;; ()
; OUTPUT Original
(define subtract (solid:subtract block1 cyl1))
;; subtract
(define law (law:warp block1 "vec
    (x,y+3* (sin (x*.5)),z)"))
;; law
; OUTPUT Result

Figure. law:warp

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