pattern:alternating-keep
List of: Scheme Extensions
Subjects: Patterns
Contents: Kernel

Action: Creates a new pattern by applying an alternating keep filter to an existing pattern.

Filename: kern/kern_scm/pattern_scm.cxx

APIs: api_alternating_keep_pattern

Syntax: (pattern:alternating-keep pat keep1 keep2


which-dim [merge=#t])

Arg Types: pat pattern

keep1 real

keep2 real

which-dim integer

merge boolean

Returns: pattern

Description: Applies an alternating keep filter to an existing pattern, merging with any existing filter or, optionally (with merge=#f), replacing it.


pat specifies a pattern.


keep1 and keep2 are successive Boolean keep values.


which-dim specifies the dimension in which the filter is applied.


If merge is false (#f), the existing pattern is replaced.

Example: ; pattern:alternating-keep

; make a prism

(define height 1)

;; height

(define maj_rad 1)

;; maj_rad

(define min_rad 0.5)

;; min_rad

(define num_sides 3)

;; num_sides

(define prism (solid:prism height


maj_rad min_rad num_sides))

;; prism

; position the prism

(define origin (position 1 2 3))

;; origin

(define transform (entity:transform prism


(transform:axes origin


(gvector 1 0 0) (gvector 0 1 0))))

;; transform

; make a pattern

(define x-vec (gvector 4 0 0))

;; x-vec

(define num_x 8)

;; num_x

(define y-vec (gvector 0 2 0))

;; y-vec

(define num_y 10)

;; num_y

(define pat (pattern:linear x-vec num_x y-vec num_y))

;; pat

; modify the pattern

(define keep1 #f)

;; keep1

(define keep2 #t)

;; keep2

(define dim 1)

;; dim

(set! pat (pattern:alternating-keep pat


keep1 keep2 dim))

;; #[pattern

;; trans-vec: "DOMAIN(X*VEC(4,0,0)+X2*VEC

;; (0,2,0),0,7,0,9)"

;; x-vec:
"null_law"

;; y-vec:
"null_law"

;; z-vec:
"null_law"

;; scale:
"null_law"

;; keep:
"null_law"

;; no list]

; apply the pattern to the prism

(define body (entity:pattern prism pat))

;; body
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