Add kerning

data/DrivingCodeWithData.cakedata

@@ -206,4 +206,6 @@ is hard.
 
 That doesn't mean it shouldn't be done, but does
 mean it should be done carefully.")
+  (slide-data :heading "In conclusion"
+              :body "Using data to drive code is generally useful.")
   (slide-data :heading "Questions?"))

src/FontAtlas.cake

@@ -1,3 +1,5 @@
+;; FontAtlas.cake: Cache FreeType-rendered fonts into a font atlas and kerning table
+;; TODO: Support UTF-8 by using non char-sized keys
 (import
  ;; GameLib
  "FreeType.cake" "Dictionary.cake")
@@ -13,10 +15,17 @@
   height uint16_t
   to-origin-left int16_t
   to-origin-top int16_t
-  advance-x uint16_t)
+  advance-x int16_t)
+
+(defstruct kerning-entry
+  key uint16_t ;; first character << 8, second character
+  x int16_t
+  ;; Unused
+  y int16_t)
 
 (defstruct font-atlas
   glyph-lookup-table (* glyph-entry) ;; dictionary
+  kerning-lookup-table (* kerning-entry) ;; dictionary
   pixel-buffer (* (unsigned char)) ;; malloc'd
   width uint16_t
   height uint16_t
@@ -28,6 +37,11 @@
   (dict-free (path font-atlas-to-free > glyph-lookup-table))
   (free (path font-atlas-to-free > pixel-buffer)))
 
+(defun font-atlas-make-character-pair (character-a char
+                                       character-b char
+                                       &return uint16_t)
+  (return (bit-or (bit-<< character-a 8) character-b)))
+
 ;; Returns 0 for success or anything else for failure
 (defun build-font-atlas (font-face (* (const (unsigned char)))
                          font-face-size (unsigned int)
@@ -161,4 +175,38 @@
       ;; Wrapping happens after we know what the next glyph's dimensions are
       (set atlas-write-x (+ atlas-write-x num-columns))))
 
+  ;; Build kerning lookup table
+  (each-in-array ranges-to-render range-index-a
+    (var range-a (* ascii-glyph-range) (addr (at range-index-a ranges-to-render)))
+    (each-in-range (- (+ 1 (path range-a > end-character-inclusive)) (path range-a > start-character))
+        character-offset-from-start
+      (var character-a char (+ character-offset-from-start (path range-a > start-character)))
+      (var glyph-index-a int (FT_Get_Char_Index typeface character-a))
+      (unless glyph-index-a
+        (continue))
+
+      (each-in-array ranges-to-render range-index-b
+        (var range-b (* ascii-glyph-range) (addr (at range-index-b ranges-to-render)))
+        (each-in-range (- (+ 1 (path range-b > end-character-inclusive)) (path range-b > start-character))
+            character-offset-from-start
+          (var character-b char (+ character-offset-from-start (path range-b > start-character)))
+          ;; If this is slow, it might make sense to cache it in the outer loop
+          (var glyph-index-b int (FT_Get_Char_Index typeface character-b))
+          (unless glyph-index-b
+            (continue))
+
+          (var kerning FT_Vector)
+          (set result (FT_Get_Kerning typeface glyph-index-a glyph-index-b
+                                      FT_KERNING_DEFAULT (addr kerning)))
+          (freetype-check-result-or-return result "Getting kerning value")
+          (when (or (field kerning x) (field kerning y))
+            (var new-kerning-entry kerning-entry (array 0))
+            (var character-pair uint16_t (font-atlas-make-character-pair
+                                          character-a character-b))
+            (set (field new-kerning-entry key) character-pair)
+            (set (field new-kerning-entry x) (bit->> (field kerning x) 6))
+            (set (field new-kerning-entry y) (bit->> (field kerning y) 6))
+            (dict-set-struct (path font-atlas-out > kerning-lookup-table)
+                             new-kerning-entry))))))
+
   (return 0))

src/Presentation.cake

@@ -13,6 +13,8 @@
           &with-decls "<stdint.h>")
 
 (var s-draw-atlases bool false)
+(var s-enable-kerning bool true) ;; F2
+(var s-enable-debug-overlay bool false) ;; F1
 
 (bundle-file s-start-ubuntu-regular-font s-end-ubuntu-regular-font
              (unsigned char) "data/Fonts/Ubuntu-R.ttf")
@@ -31,6 +33,9 @@
   (array SDL_SCANCODE_BACKSPACE)
   (array SDL_SCANCODE_PAGEUP))
 
+(define-keybind s-toggle-kerning-keybind (array SDL_SCANCODE_F2))
+(define-keybind s-toggle-debug-overlay-keybind (array SDL_SCANCODE_F1))
+
 (var s-key-states sdl-key-states (array 0))
 
 (defmacro preslog (format string &optional &rest arguments any)
@@ -187,7 +192,15 @@
        (path glyph > height)))
     (SDL_RenderCopy renderer font-texture
                     (addr source-rectangle) (addr destination-rectangle))
-    (set write-x (+ write-x (path glyph > advance-x)))))
+    (set write-x (+ write-x (path glyph > advance-x)))
+
+    (when (and s-enable-kerning (+ 1 current-char))
+      (var character-pair uint16_t (font-atlas-make-character-pair
+                                    (deref current-char) (at 1 current-char)))
+      (var kerning (* kerning-entry)
+        (dict-ptr-at (path font > kerning-lookup-table) character-pair))
+      (when kerning
+        (set write-x (+ write-x (path kerning > x)))))))
 
 (defun-local make-font-atlas-and-texture (renderer (* SDL_Renderer)
                                           font-atlas-out (* font-atlas) font-texture-out (* (* SDL_Texture))
@@ -375,6 +388,11 @@
       (when (< current-slide-index 0)
         (set current-slide-index 0)))
 
+    (when (keybind-tapped (addr s-toggle-kerning-keybind) (addr s-key-states))
+      (set s-enable-kerning (not s-enable-kerning)))
+    (when (keybind-tapped (addr s-toggle-debug-overlay-keybind) (addr s-key-states))
+      (set s-enable-debug-overlay (not s-enable-debug-overlay)))
+
     (SDL_SetRenderDrawColor renderer 17 17 17 255)
 	(SDL_RenderClear renderer)
 
@@ -427,7 +445,7 @@
          (+ text-x (/ window-width 7)) (/ window-height 4)
          (path slide > body)))
 
-    (scope
+    (when s-enable-debug-overlay
      (var buffer ([] 256 char) (array 0))
      (var mouse-x int 0)
      (var mouse-y int 0)