From 4cd69f71db120b3cb113623647ce864a0b402fb2 Mon Sep 17 00:00:00 2001
From: Matthew Butterick <mb@mbtype.com>
Date: Wed, 15 Jan 2020 14:30:05 -0800
Subject: [PATCH] allow percentage for font-tracking

---
 quad/quadwriter/attrs.rkt  | 11 ++++++-----
 quad/quadwriter/font.rkt   | 12 +++++++++++-
 quad/quadwriter/render.rkt |  1 +
 3 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/quad/quadwriter/attrs.rkt b/quad/quadwriter/attrs.rkt
index cba53402..26a1db36 100644
--- a/quad/quadwriter/attrs.rkt
+++ b/quad/quadwriter/attrs.rkt
@@ -16,16 +16,17 @@
 (define (parse-dimension x)
   (match x
     [#false #false]
-    [(? number?) x]
-    [(? string? x)
-     (match (cdr (regexp-match #px"^(-?[0-9\\.]+)\\s*([a-z]+)$"  (string-downcase x)))
-       [(list num-string unit)
+    [(? number? num) num]
+    [(? string? str)
+     (match (regexp-match #px"^(-?[0-9\\.]+)\\s*([a-z]+)$"  (string-downcase str))
+       [#false str] ; a string other than a dimension string, so leave it
+       [(list _ num-string unit)
         ((match unit
            [(regexp #rx"(pt|point)(s)?$") values]
            [(regexp #rx"in(ch(es)?)?$") in->pts]
            [(regexp #rx"cm$") (compose1 in->pts cm->in)]
            [(regexp #rx"mm$") (compose1 in->pts cm->in mm->cm)]
-           [_ (raise-argument-error 'parse-dimension "dimension string" x)]) (string->number num-string))])]))
+           [_ (raise-argument-error 'parse-dimension "dimension string" str)]) (string->number num-string))])]))
 
 (define (copy-block-attrs source-hash dest-hash)
   (define new-hash (make-hasheq))
diff --git a/quad/quadwriter/font.rkt b/quad/quadwriter/font.rkt
index 60d19da7..8f1adaba 100644
--- a/quad/quadwriter/font.rkt
+++ b/quad/quadwriter/font.rkt
@@ -76,7 +76,10 @@
     (hash-set! attrs :font-path (font-attrs->path this-font-family this-bold this-italic))))
 
 (define (parse-percentage pstr)
-  (/ (string->number (string-trim pstr "%")) 100.0))
+  (and
+   (string? pstr)
+   (string-suffix? pstr "%")
+   (/ (string->number (string-trim pstr "%")) 100.0)))
 
 (define (adjuster-base attrs key adjustment-key default-value)
   (define this-val (hash-ref! attrs key default-value))
@@ -91,3 +94,10 @@
 
 (define (resolve-line-height! attrs)
   (adjuster-base attrs :line-height :line-height-adjust default-line-height))
+
+(define (resolve-font-tracking! attrs)
+  ;; if it's a percentage, we need to look at the font size.
+  ;; if it's anything else, we're done.
+  (match (parse-percentage (hash-ref attrs :font-tracking #false))
+    [#false (void)]
+    [pct (hash-set! attrs :font-tracking (* pct (hash-ref attrs :font-size)))]))
\ No newline at end of file
diff --git a/quad/quadwriter/render.rkt b/quad/quadwriter/render.rkt
index c2d08f51..ed0786d5 100644
--- a/quad/quadwriter/render.rkt
+++ b/quad/quadwriter/render.rkt
@@ -112,6 +112,7 @@
                              complete-every-path!
                              resolve-font-path!
                              resolve-font-size!
+                             resolve-font-tracking!
                              resolve-line-height!
                              parse-font-features!))])
        (proc attrs)))