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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 pbm)
(export make-pbm-image)
(import (scheme base)
(scheme case-lambda)
(pnm image))
(cond-expand
((library (scheme bitwise))
(import (only (scheme bitwise) bit-set? copy-bit)))
((library (srfi 60))
(import (only (srfi 60) bit-set? copy-bit))))
(begin
(define make-pbm-image
(case-lambda
((width height)
(let* ((byte-width (ceiling (/ width 8)))
(byte-count (* byte-width height))
(data (make-bytevector byte-count 0)))
(make-pbm-image width height data)))
((width height data)
(let* ((byte-width (ceiling (/ width 8))))
(define (xy->byte-idx+bit-idx x y)
(let-values (((byte-x bit-x) (floor/ x 8)))
(values (+ (* y byte-width)
byte-x)
bit-x)))
(define (pixel-getter x y)
(let-values (((byte-idx bit-idx) (xy->byte-idx+bit-idx x y)))
(let ((byte (bytevector-u8-ref data byte-idx)))
(bit-set? (- 7 bit-idx) byte))))
(define (pixel-setter x y b)
(let-values (((byte-idx bit-idx) (xy->byte-idx+bit-idx x y)))
(let ((byte (bytevector-u8-ref data byte-idx)))
(bytevector-u8-set! data byte-idx
(copy-bit (- 7 bit-idx) byte b)))))
(make-image 'pbm width height 1 data pixel-getter pixel-setter)))))))
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