From eeb23310033d08863f523cb2087553f8f2d3c754 Mon Sep 17 00:00:00 2001
From: Matthew Butterick <mb@mbtype.com>
Date: Tue, 27 Nov 2018 13:10:18 -0800
Subject: [PATCH] cachier

---
 fontland/fontland/font.rkt     | 18 ++++++++++++++++--
 fontland/fontland/glyphrun.rkt | 13 ++++++++++++-
 2 files changed, 28 insertions(+), 3 deletions(-)

diff --git a/fontland/fontland/font.rkt b/fontland/fontland/font.rkt
index 30fd23c0..2355e112 100644
--- a/fontland/fontland/font.rkt
+++ b/fontland/fontland/font.rkt
@@ -233,14 +233,28 @@ https://github.com/mbutterick/fontkit/blob/master/src/TTFFont.js
                    CFFGlyph
                    TTFGlyph) glyph characters this))
 
+(define current-layout-caching (make-parameter #false))
+(define layout-cache (make-hash))
 
 ;; Returns a GlyphRun object, which includes an array of Glyphs and GlyphPositions for the given string.
 (define/contract (layout this string [userFeatures #f] [script #f] [language #f])
   ((string?) ((option/c (listof symbol?)) (option/c symbol?) (option/c symbol?)) . ->*m . GlyphRun?)
   (unless (· this _layoutEngine)
     (set-field! _layoutEngine this (+LayoutEngine this)))
-  #;(report*/file 'in-layout (· this _layoutEngine))
-  (send (· this _layoutEngine) layout string userFeatures script language))
+  (define (get-layout string)
+    (define key (list string (and userFeatures (sort userFeatures symbol<?)) script language))
+    (hash-ref! layout-cache key (λ () (send (· this _layoutEngine) layout . key))))
+  ;; work on substrs to reuse cached pieces
+  ;; caveat: no shaping / positioning that involve word spaces
+  (cond
+    ;; todo: why does caching produce slightly different results in test files
+    ;; theory: because word space is not included in shaping
+    [(current-layout-caching)
+     (define substrs (for/list ([substr (in-list (regexp-match* " " string #:gap-select? #t))]
+                                #:when (positive? (string-length substr)))
+                               substr))
+     (apply append-glyphruns (map get-layout substrs))]
+    [else (get-layout string)]))
 
 
 ;; Returns an array of Glyph objects for the given string.
diff --git a/fontland/fontland/glyphrun.rkt b/fontland/fontland/glyphrun.rkt
index 14e9e777..ed137cf6 100644
--- a/fontland/fontland/glyphrun.rkt
+++ b/fontland/fontland/glyphrun.rkt
@@ -18,4 +18,15 @@ https://github.com/mbutterick/fontkit/blob/master/src/layout/GlyphRun.js
 
   (define/public (advanceWidth)
     (for/sum ([pos (in-list positions)])
-             (· pos xAdvance))))
\ No newline at end of file
+             (· pos xAdvance))))
+
+
+(define (append-glyphruns . grs)
+  (for/fold ([glyphss null]
+             [positionss null]
+             #:result (make-object GlyphRun
+                        (apply append (reverse glyphss))
+                        (apply append (reverse positionss))))
+            ([gr (in-list grs)])
+    (values (cons (get-field glyphs gr) glyphss)
+            (cons (get-field positions gr) positionss))))