expose shaping args

fontland/fontland/font.rkt

@@ -73,14 +73,19 @@ https://github.com/mbutterick/fontkit/blob/master/src/TTFFont.js
 ;; (though this is good news, as it avoids massive disk caches hanging around)
 ;; ram cache in pitfall suffices
 
-;; todo: preserve semantics of user-features argument from pitfall, which is
-;; #f = no features, null = default features, list = explicit features
-(define (layout font str [features #f] [script #f] [language #f])
+(define (layout font str
+                [features null]
+                [script 'HB_SCRIPT_LATIN]
+                [lang #"en"]
+                [direction 'HB_DIRECTION_LTR])
   (define buf (hb-buf font))
   (hb_buffer_reset buf)
+  (hb_buffer_set_script buf script)
+  (hb_buffer_set_language buf (hb_language_from_string lang))
+  (hb_buffer_set_direction buf direction)
   (define codepoints (for/list ([c (in-string str)]) (char->integer c)))
   (hb_buffer_add_codepoints buf codepoints)
-  (hb_shape (hb-font font) buf (map tag->hb-feature (or features null)))
+  (hb_shape (hb-font font) buf (map tag->hb-feature features))
   (define gis (hb_buffer_get_glyph_infos buf))
   (define hb-gids (map hb_glyph_info_t-codepoint gis))
   (define hb-clusters (break-at codepoints (map hb_glyph_info_t-cluster gis)))