From a80bc303b630dfc012952978b0ff79a35b8fe817 Mon Sep 17 00:00:00 2001 From: Matthew Butterick Date: Sun, 21 May 2017 21:55:54 -1000 Subject: [PATCH] refac --- pitfall/pitfall/png-reader.rkt | 18 ++++++++++-------- 1 file changed, 10 insertions(+), 8 deletions(-) diff --git a/pitfall/pitfall/png-reader.rkt b/pitfall/pitfall/png-reader.rkt index 398bcea8..af9d85be 100644 --- a/pitfall/pitfall/png-reader.rkt +++ b/pitfall/pitfall/png-reader.rkt @@ -79,7 +79,6 @@ Grab key chunks from PNG. Doesn't require heavy lifting from libpng. (bytes? number? number? number? . -> . any/c) (define pixelBytes (/ pixelBitLength 8)) (define scanlineLength (* pixelBytes width)) - (define pixels (make-bytes (* scanlineLength height))) (define (left-byte i c) (if (< i pixelBytes) @@ -97,8 +96,9 @@ Grab key chunks from PNG. Doesn't require heavy lifting from libpng. (define (get-col i) ((i . - . (modulo i pixelBytes)) . / . pixelBytes)) (parameterize ([current-input-port (open-input-bytes (inflate imgData))]) - (for/fold ([c 0]) ([row (in-naturals)] - #:break (eof-object? (peek-byte))) + (for/fold ([c 0]) + ([row (in-naturals)] + #:break (eof-object? (peek-byte))) (case (read-byte) [(0) ; none (for/fold ([c c]) @@ -143,13 +143,15 @@ Grab key chunks from PNG. Doesn't require heavy lifting from libpng. (list upper upperLeft)])) (define left (left-byte i c)) - (define p (+ left upper (- upperLeft))) + (match-define (list pa pb pc) - (map (λ (x) (abs (- p x))) (list left upper upperLeft))) - + (for/list ([x (in-list (list left upper upperLeft))]) + (define p (+ left upper (- upperLeft))) + (abs (- p x)))) + (define paeth (cond - [((pa . <= . pb) . and . (pa . <= . pc)) left] - [(pb . <= . pc) upper] + [(and (<= pa pb) (<= pa pc)) left] + [(<= pb pc) upper] [else upperLeft])) (bytes-set! pixels c (modulo (+ byte paeth) 256))