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;;; R7RS-PNM --- Library for reading and writing PNM (Portable Any Map) files for R7RS
;;; Copyright © 2024 Masaya Tojo <masaya@tojo.tokyo>
;;;
;;; This file is part of R7RS-PNM.
;;;
;;; R7RS-PNM is free software: you can redistribute it and/or modify it
;;; under the terms of the GNU Lesser General Public License as published
;;; by the Free Software Foundation, either version 3 of the License, or
;;; (at your option) any later version.
;;;
;;; R7RS-PNM is distributed in the hope that it will be useful, but
;;; WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
;;; GNU Lesser General Public License for more details.
;;;
;;; You should have received a copy of the GNU Lesser General Public License
;;; along with R7RS-PNM. If not, see <https://www.gnu.org/licenses/>.
(define-library (pnm pgm)
(export make-pgm-image
%make-pgm-image)
(import (scheme base)
(scheme case-lambda)
(pnm image))
(begin
(define make-pgm-image
(case-lambda
((width height)
(make-pgm-image width height 255))
((width height maxval)
(when (or (< maxval 0)
(< 65536 maxval))
(error "(pnm pgm) make-pgm: maxval is out of range"))
(let* ((byte-count (* width height
(if (< maxval 256)
1
2)))
(data (make-bytevector byte-count 0)))
(%make-pgm-image width height maxval data)))))
(define (%make-pgm-image width height maxval data)
(when (or (< maxval 0)
(< 65536 maxval))
(error "(pnm pgm) make-pgm: maxval is out of range"))
(if (< maxval 256)
(let ((byte-count (* width height)))
(define (xy->idx x y) (+ x (* y width)))
(define (pixel-reader x y)
(let ((idx (xy->idx x y)))
(bytevector-u8-ref data idx)))
(define (pixel-writer x y v)
(let ((idx (xy->idx x y)))
(bytevector-u8-set! data idx v)))
(unless (= byte-count (bytevector-length data))
(error (string-append "(pnm pbm) make-pbm-image: Invalid bytevector length" byte-count)))
(make-image 'pgm width height maxval data pixel-reader pixel-writer))
(let ((byte-count (* width height 2)))
(define (xy->idx x y) (+ x (* y width)))
(define (pixel-reader x y)
(let ((idx (xy->idx x y)))
(combine-values (bytevector-u8-ref data idx)
(bytevector-u8-ref data (+ idx 1)))))
(define (pixel-writer x y v)
(let ((idx (xy->idx x y)))
(let-values (((v1 v2) (split-value v)))
(bytevector-u8-set! data idx v1)
(bytevector-u8-set! data (+ idx 1) v2))))
(unless (= byte-count (bytevector-length data))
(error (string-append "(pnm pbm) make-pbm-image: Invalid bytevector length" byte-count)))
(make-image 'pgm width height maxval data pixel-reader pixel-writer))))
(define (split-value v)
(values (modulo (quotient v 256) 256)
(modulo v 256)))
(define (combine-values l r)
(+ (* 256 l) r))))
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