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(define-module (starlet colours)
#:use-module (oop goops)
#:use-module (ice-9 exceptions)
#:export (<colour>
colour?
make-colour-cmy
make-colour-rgb
colour-as-cmy
interpolate-colour
white))
(define-class <colour> (<object>)
(type
#:init-form (error "Colour type must be specified")
#:init-keyword #:type
#:getter colour-type)
(value
#:init-form (error "Colour value must be specified")
#:init-keyword #:value
#:getter colour-value))
(define (colour? c)
(is-a? c <colour>))
(define cyan car)
(define magenta cadr)
(define yellow caddr)
(define red car)
(define green cadr)
(define blue caddr)
(define-method (display (col <colour>) port)
(format port "#<<colour> ~a ~a>"
(colour-type col)
(colour-value col)))
(define-method (write (col <colour>) port)
(let ((cmy (colour-as-cmy col)))
(format port "(make-colour-cmy ~a ~a ~a)"
(cyan cmy)
(magenta cmy)
(yellow cmy))))
(define (make-colour-cmy c m y)
(make <colour>
#:type 'cmy
#:value (list c m y)))
(define (make-colour-rgb r g b)
(make <colour>
#:type 'rgb
#:value (list r g b)))
(define white
(make-colour-cmy 0 0 0))
(define (colour-as-cmy col)
(let ((val (colour-value col)))
(case (colour-type col)
((cmy)
val)
((rgb)
(list (- 100 (red val))
(- 100 (green val))
(- 100 (blue val))))
(else
(raise-exception (make-exception
(make-exception-with-message "Unrecognised colour type")
(make-exception-with-irritants (colour-type col))))))))
(define (interpolate-cmy a b frac)
(let ((cmy1 (colour-as-cmy a))
(cmy2 (colour-as-cmy b)))
(make-colour-cmy
(+ (cyan cmy1) (* frac (- (cyan cmy2) (cyan cmy1))))
(+ (magenta cmy1) (* frac (- (magenta cmy2) (magenta cmy1))))
(+ (yellow cmy1) (* frac (- (yellow cmy2) (yellow cmy1)))))))
(define* (interpolate-colour a b frac #:key (interpolation-type 'linear-cmy))
(case interpolation-type
((linear-cmy)
(interpolate-cmy a b frac))
(else
(raise-exception (make-exception
(make-exception-with-message
"Unrecognised colour interpolation type")
(make-exception-with-irritants interpolation-type))))))
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