add font-features attributes (closes #28)

quad/qtest/test-ot-features.rkt

@@ -0,0 +1,23 @@
+#lang quadwriter
+
+'(q ((font-features "liga 0")) "No ligs: fifle")
+
+'(q ((break "para")))
+
+'(q ((font-features "liga 1")) "Ligs: fifle")
+
+'(q ((break "para")))
+
+'(q ((font-features "liga 1")) (q ((font-features "liga 0")) "No ligs: fifle"))
+
+'(q ((break "para")))
+
+'(q ((font-features "liga 1")) (q ((font-features-adjust "liga 0")) "No ligs: fifle"))
+
+'(q ((break "para")))
+
+'(q ((font-features "zero 1")) (q ((font-features "liga 0")) "No ligs, no slashed zero: fifle0"))
+
+'(q ((break "para")))
+
+'(q ((font-features "zero 1")) (q ((font-features-adjust "liga 0")) "No ligs, slashed zero: fifle0"))

quad/quad/scribblings/quad.scrbl

@@ -584,6 +584,14 @@ Whether the quad has bold styling applied. Activated only when value is @racket[
 Whether the quad has italic styling applied. Activated only when value is @racket["true"]. 
 }
 
+@deftogether[(@defthing[#:kind "attribute" font-features symbol?]
+              @defthing[#:kind "attribute" font-features-adjust symbol?])]{
+Two ways of setting OpenType layout features. @racket[font-features] takes a @deftech{feature string}, which is an alternating list of OT feature tags and values, separated by white space. For instance, @racket{liga 0 smcp 1} would deactivate the ligature feature and activate the small-cap feature. @racket[font-features-adjust] works the same way, but rather than replacing the current feature settings, it amends them.
+
+@margin-note{Fonts with OpenType layout features may be configured so that certain features, like ligatures, are activated by default. Your font will display these layout features even though there is no @racket[font-features] attribute in your Q-expression. You can, however, still turn them off with @racket[font-features].}
+}
+ 
+
 @defthing[#:kind "attribute" font-tracking symbol?]{
 Spacing between characters. Value is given as a @tech{dimension string}.
 }

quad/quadwriter/attrs.rkt

@@ -63,10 +63,12 @@ Naming guidelines
 |#
 
 (define-attrs (font-family
+               font-path
                font-size
                font-size-adjust
                font-color
                font-features
+               font-features-adjust
                font-italic
                font-bold
                font-tracking

quad/quadwriter/font.rkt

@@ -2,7 +2,8 @@
 (require racket/runtime-path
          racket/string
          racket/path
-         racket/match)
+         racket/match
+         "attrs.rkt")
 (provide (all-defined-out))
 
 (define-runtime-path quadwriter-fonts-dir "fonts")
@@ -64,20 +65,20 @@
     [(hash-ref font-paths regular-key #false)]
     [else default-font-face]))
 
-(define (resolve-font-path attrs)
-  (define this-font-family (hash-ref! attrs 'font-family default-font-family))
+(define (resolve-font-path! attrs)
+  (define this-font-family (hash-ref! attrs :font-family default-font-family))
   (unless (complete-path? this-font-family)
-    (define this-bold (hash-ref! attrs 'font-bold #false))
-    (define this-italic (hash-ref! attrs 'font-italic #false))
-    (hash-set! attrs 'font-path (font-attrs->path this-font-family this-bold this-italic))))
+    (define this-bold (hash-ref! attrs :font-bold #false))
+    (define this-italic (hash-ref! attrs :font-italic #false))
+    (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))
 
-(define (resolve-font-size attrs)
-  (define this-font-size (hash-ref! attrs 'font-size default-font-size))
-  (define this-font-size-adjust (parse-percentage (hash-ref! attrs 'font-size-adjust "100%")))
+(define (resolve-font-size! attrs)
+  (define this-font-size (hash-ref! attrs :font-size default-font-size))
+  (define this-font-size-adjust (parse-percentage (hash-ref! attrs :font-size-adjust "100%")))
   ;; we bake the adjustment into the font size...
-  (hash-set! attrs 'font-size (* this-font-size this-font-size-adjust))
+  (hash-set! attrs :font-size (* this-font-size this-font-size-adjust))
   ;; and then set the adjustment back to 100% (since it's now accounted for)
-  (hash-set! attrs 'font-size-adjust "100%"))
+  (hash-set! attrs :font-size-adjust "100%"))

quad/quadwriter/render.rkt

@@ -4,6 +4,9 @@
          txexpr/base
          racket/contract
          racket/file
+         racket/string
+         racket/sequence
+         racket/list
          pitfall
          quad
          hyphenate
@@ -63,9 +66,31 @@
                                        (struct-copy quad q [elems (list substr)]))]
                      [_ (list q)]))))
 
+
+(define (string->feature-list str)
+  (for/list ([kv (in-slice 2 (string-split str))])
+            (cons (string->bytes/utf-8 (first kv)) (string->number (second kv)))))
+
+(define (parse-font-features! attrs)
+  (cond
+    [(match (hash-ref attrs :font-features-adjust #f)
+       [(? string? str)
+        ;; override any existing features
+        (define parsed-features (string->feature-list str))
+        (hash-update! attrs :font-features (λ (fs) (remove-duplicates (append parsed-features fs) equal? #:key car)))
+        ;; adjustment is incorporated, so delete it
+        (hash-set! attrs :font-features-adjust #false)]
+       [_ #false])]
+    [else (match (hash-ref attrs :font-features #f)
+            [(? string? str)
+             (define parsed-features (string->feature-list str))
+             (hash-set! attrs :font-features parsed-features)]
+            [_ #false])]))
+
 (define (handle-cascading-attrs attrs)
-  (resolve-font-path attrs)
-  (resolve-font-size attrs))
+  (resolve-font-path! attrs)
+  (resolve-font-size! attrs)
+  (parse-font-features! attrs))
 
 (define default-line-height-multiplier 1.42)
 (define (setup-qs qx-arg pdf-path)
@@ -83,7 +108,7 @@
                                #:fallback "fallback"
                                #:emoji "fallback-emoji"
                                #:math "fallback-math"
-                               #:font-path-resolver resolve-font-path))]
+                               #:font-path-resolver resolve-font-path!))]
   [define hyphenated-qs (time-log hyphenate (handle-hyphenate atomized-qs))]
   [define typed-quads (map generic->typed-quad hyphenated-qs)]
   [define indented-qs (insert-first-line-indents typed-quads)]