Moiré Patterns: Square and Hexagon

Overlaid hexagon grids with moderate rotational offset

A square grid with a slight rotational offset gives a square or diamond zig-zag grid:

With smaller squares, the checkerboard pattern is more interesting:

Hexagonal grids give an interesting variety of overlap patterns in one image:

The new code is below:

;; Copyright 2021 Christopher Howard

;; Licensed under the Apache License, Version 2.0 (the "License");
;; you may not use this file except in compliance with the License.
;; You may obtain a copy of the License at

;;     http://www.apache.org/licenses/LICENSE-2.0

;; Unless required by applicable law or agreed to in writing, software
;; distributed under the License is distributed on an "AS IS" BASIS,
;; WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
;; See the License for the specific language governing permissions and
;; limitations under the License.

(define* (draw-square-block r orig-x orig-y base-l
                         #:key (rotr 0))
  (let* ((lrot (if (zero? rotr) (lambda (x) x)
                   (lambda (c) (rot rotr c))))
         (ccomp (lambda (c) (cex (lrot c)))))
    (render-draw-lines
     r
     (map ccomp (list (list orig-x orig-y)
                      (list (+ orig-x base-l) orig-y)
                      (list (+ orig-x base-l) (+ orig-y base-l)))))))

(define* (draw-square-pattern r offset-x offset-y #:key (rotr 0))
  (let* ((base-l 10))
    (do ((j 0 (1+ j)))
        ((> j 80))
        (do ((i 0 (1+ i)))
            ((> i 80))
          (draw-square-block
           r
           (+ (* i base-l) offset-x)
           (+ (* j base-l) offset-y)
           base-l
           #:rotr rotr)))))

(define* (draw-hexagon-block r orig-x orig-y base-l
                         #:key (rotr 0))
  (let* ((base-hl (* 0.5 base-l))
         (base-h (* (* base-l (sqrt 3)) 0.5))
         (lrot (if (zero? rotr) (lambda (x) x)
                   (lambda (c) (rot rotr c))))
         (ccomp (lambda (c) (cex (lrot c)))))
    (render-draw-lines
     r
     (map ccomp (list (list orig-x orig-y)
                      (list (- orig-x base-hl)
                            (+ orig-y base-h))
                      (list orig-x
                            (+ orig-y (* 2 base-h)))
                      (list (+ orig-x base-l)
                            (+ orig-y (* 2 base-h)))
                      (list (+ orig-x base-l base-hl)
                            (+ orig-y base-h))
                      (list (+ orig-x base-l)
                            orig-y))))
    (render-draw-lines
     r
     (map ccomp (list (list (- orig-x base-hl)
                            (+ orig-y base-h))
                      (list (- orig-x base-hl base-l)
                            (+ orig-y base-h)))))))

(define* (draw-hexagon-pattern r offset-x offset-y #:key (rotr 0))
  (let* ((base-l 20)
         (base-h (* (* base-l (sqrt 3)) 0.5))
         (base-hl (* 0.5 base-l)))
    (do ((j 0 (1+ j)))
        ((> j 40))
        (do ((i 0 (1+ i)))
            ((> i 40))
          (draw-hexagon-block
           r
           (+ offset-x
              (* i 3 base-l))
           (+ offset-y (* j 2 base-h))
           base-l
           #:rotr rotr)))))