From 6f50064fa0690ec591da9b91d156d0a4d377c172 Mon Sep 17 00:00:00 2001
From: Masaya Tojo <masaya@tojo.tokyo>
Date: Sun, 4 Aug 2024 02:11:09 +0900
Subject: Support writing plain PNM formats

---
 pnm/write.scm | 108 ++++++++++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 93 insertions(+), 15 deletions(-)

(limited to 'pnm/write.scm')

diff --git a/pnm/write.scm b/pnm/write.scm
index 75cd433..849e3de 100644
--- a/pnm/write.scm
+++ b/pnm/write.scm
@@ -19,27 +19,105 @@
 (define-library (pnm write)
   (export image-write)
   (import (scheme base)
+          (scheme case-lambda)
           (pnm image))
   (begin
-    (define (image-write image out)
-      (define (write-string-u8 str)
-        (string-for-each (lambda (c) (write-u8 (char->integer c) out))
-                         str))
+    (define image-write
+      (case-lambda
+        ((image out)
+         (case (image-type image)
+           ((ppm)
+            (write-string-u8 "P6\n" out))
+           ((pgm)
+            (write-string-u8 "P5\n" out))
+           ((pbm)
+            (write-string-u8 "P4\n" out))
+           (else
+            (error "(pnm write) image-write: Not supported type" (image-type image))))
+         (write-string-u8 (number->string (image-width image)) out)
+         (write-string-u8 " " out)
+         (write-string-u8 (number->string (image-height image)) out)
+         (write-string-u8 "\n" out)
+         (case (image-type image)
+           ((pgm ppm)
+            (write-string-u8 (number->string (image-maxval image)) out)
+            (write-string-u8 "\n" out)))
+         (write-bytevector (image-data image) out))
+        ((image out plain?)
+         (if plain?
+             (image-write/plan image out)
+             (image-write image out)))))
+
+    (define (image-write/plan image out)
       (case (image-type image)
         ((ppm)
-         (write-string-u8 "P6\n"))
+         (write-string-u8 "P3\n" out))
         ((pgm)
-         (write-string-u8 "P5\n"))
+         (write-string-u8 "P2\n" out))
         ((pbm)
-         (write-string-u8 "P4\n"))
+         (write-string-u8 "P1\n" out))
         (else
-         (error "(pnm write) pnm-write: Not supported type" (image-type image))))
-      (write-string-u8 (number->string (image-width image)))
-      (write-string-u8 "\n")
-      (write-string-u8 (number->string (image-height image)))
-      (write-string-u8 "\n")
+         (error "(pnm write) image-write: Not supported type" (image-type image))))
+      (write-string-u8 (number->string (image-width image)) out)
+      (write-string-u8 " " out)
+      (write-string-u8 (number->string (image-height image)) out)
+      (write-string-u8 "\n" out)
       (case (image-type image)
         ((pgm ppm)
-         (write-string-u8 (number->string (image-maxval image)))
-         (write-string-u8 "\n")))
-      (write-bytevector (image-data image) out))))
+         (write-string-u8 (number->string (image-maxval image)) out)
+         (write-string-u8 "\n" out)))
+      (let-values (((write-token write-newline)
+                    (limit-line-length-writer 70 out)))
+        (let ((width (image-width image))
+              (height (image-height image)))
+          (define (write-raster write-pixel)
+            (do ((y 0 (+ y 1)))
+                ((= y height))
+              (write-pixel 0 y)
+              (do ((x 1 (+ x 1)))
+                  ((= x width))
+                (write-pixel x y))
+              (write-newline)))
+          (case (image-type image)
+            ((ppm)
+             (write-raster
+              (lambda (x y)
+                (let-values (((r g b) (image-ref image x y)))
+                  (write-token (number->string r))
+                  (write-token (number->string g))
+                  (write-token (number->string b))))))
+            ((pgm)
+             (write-raster
+              (lambda (x y)
+                (let ((v (image-ref image x y)))
+                  (write-token (number->string v))))))
+            ((pbm)
+             (write-raster
+              (lambda (x y)
+                (let ((b (image-ref image x y)))
+                  (write-token (if b "1" "0"))))))))))
+
+    (define (write-string-u8 str out)
+      (string-for-each (lambda (c) (write-u8 (char->integer c) out))
+                       str))
+
+    (define (limit-line-length-writer limit out)
+      (let ((current-length 0))
+        (define (write-token str)
+          (let ((str-len (string-length str)))
+            (cond ((zero? current-length)
+                   (write-string-u8 str out)
+                   (set! current-length str-len))
+                  ((<= (+ current-length str-len 1) limit)
+                   (write-string-u8 " " out)
+                   (write-string-u8 str out)
+                   (set! current-length (+ current-length 1 str-len)))
+                  (else
+                   (write-string-u8 "\n" out)
+                   (write-string-u8 str out)
+                   (set! current-length str-len)))))
+        (define (write-newline)
+          (write-string-u8 "\n" out)
+          (set! current-length 0))
+        (values write-token
+                write-newline)))))
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