kerning

src/pixie/fontformats/opentype.nim

@@ -15,6 +15,7 @@ type
     numTables*: uint16
     encodingRecords*: seq[EncodingRecord]
     runeToGlyphId*: Table[Rune, uint16]
+    glyphIdToRune*: Table[uint16, Rune]
 
   HeadTable* = ref object
     majorVersion*: uint16
@@ -295,6 +296,7 @@ proc parseCmapTable(buf: string, offset: int): CmapTable =
 
             if c != 65535:
               result.runeToGlyphId[Rune(c)] = glyphId.uint16
+              result.glyphIdToRune[glyphId.uint16] = Rune(c)
       else:
         # TODO implement other Windows encodingIDs
         discard
@@ -563,13 +565,13 @@ proc parseKernTable(buf: string, offset: int): KernTable =
   else:
     failUnsupported()
 
-proc getGlyphId*(opentype: OpenType, rune: Rune): int =
+proc getGlyphId*(opentype: OpenType, rune: Rune): uint16 =
   if rune in opentype.cmap.runeToGlyphId:
-    result = opentype.cmap.runeToGlyphId[rune].int
+    result = opentype.cmap.runeToGlyphId[rune]
   else:
     discard # Index 0 is the "missing character" glyph
 
-proc parseGlyph(opentype: OpenType, glyphId: int): Path
+proc parseGlyph(opentype: OpenType, glyphId: uint16): Path
 
 proc parseGlyphPath(buf: string, offset, numberOfContours: int): Path =
   if numberOfContours < 0:
@@ -781,7 +783,7 @@ proc parseCompositeGlyph(opentype: OpenType, offset: int): Path =
     # elif (flags and 0b1000000000000) != 0: # UNSCALED_COMPONENT_OFFSET
     #   discard
 
-    var subPath = opentype.parseGlyph(component.glyphId.int)
+    var subPath = opentype.parseGlyph(component.glyphId)
     subPath.transform(mat3(
       component.xScale, component.scale10, 0.0,
       component.scale01, component.yScale, 0.0,
@@ -792,8 +794,8 @@ proc parseCompositeGlyph(opentype: OpenType, offset: int): Path =
 
     moreComponents = (flags and 0b100000) != 0
 
-proc parseGlyph(opentype: OpenType, glyphId: int): Path =
-  if glyphId < 0 or glyphId >= opentype.glyf.offsets.len:
+proc parseGlyph(opentype: OpenType, glyphId: uint16): Path =
+  if glyphId.int >= opentype.glyf.offsets.len:
     raise newException(PixieError, "Invalid glyph ID " & $glyphId)
 
   let glyphOffset = opentype.glyf.offsets[glyphId]

src/pixie/fonts.nim

@@ -6,6 +6,7 @@ type
   Font* = ref object
     opentype: OpenType
     glyphPaths: Table[Rune, Path]
+    kerningPairs: Table[(Rune, Rune), float32]
     size*: float32 ## Font size in pixels.
     lineHeight*: float32 ## The line height in pixels or AutoLineHeight for the font's default line height.
 
@@ -46,12 +47,17 @@ proc getGlyphPath*(font: Font, rune: Rune): Path =
   font.glyphPaths[rune]
 
 proc getGlyphAdvance*(font: Font, rune: Rune): float32 =
-  let glyphId = font.opentype.getGlyphId(rune)
+  let glyphId = font.opentype.getGlyphId(rune).int
   if glyphId < font.opentype.hmtx.hMetrics.len:
     font.opentype.hmtx.hMetrics[glyphId].advanceWidth.float32
   else:
     font.opentype.hmtx.hMetrics[^1].advanceWidth.float32
 
+proc getKerningAdjustment*(font: Font, left, right: Rune): float32 =
+  let pair = (left, right)
+  if pair in font.kerningPairs:
+    result = font.kerningPairs[pair]
+
 proc scale*(font: Font): float32 =
   ## The scale factor to transform font units into pixels.
   font.size / font.opentype.head.unitsPerEm.float32
@@ -104,6 +110,9 @@ proc typeset*(
     if rune.canWrap():
       prevCanWrap = i
 
+    if i > 0:
+      at.x += font.getKerningAdjustment(runes[i - 1], rune) * font.scale
+
     let advance = font.getGlyphAdvance(rune) * font.scale
     if bounds.x > 0 and at.x + advance > bounds.x: # Wrap to new line
       at.x = 0
@@ -112,6 +121,8 @@ proc typeset*(
       # Go back and wrap glyphs after the wrap index down to the next line
       if prevCanWrap > 0 and prevCanWrap != i:
         for j in prevCanWrap + 1 ..< i:
+          if j > 0:
+            at.x += font.getKerningAdjustment(runes[j - 1], runes[j]) * font.scale
           positions[j] = at
           at.x += font.getGlyphAdvance(runes[j]) * font.scale
 
@@ -129,5 +140,16 @@ proc parseOtf*(buf: string): Font =
   result.size = 12
   result.lineHeight = AutoLineHeight
 
+  if result.opentype.kern != nil:
+    for table in result.opentype.kern.subTables:
+      for pair in table.kernPairs:
+        if pair.value != 0 and
+          pair.left in result.opentype.cmap.glyphIdToRune and
+          pair.right in result.opentype.cmap.glyphIdToRune:
+          result.kerningPairs[(
+            result.opentype.cmap.glyphIdToRune[pair.left],
+            result.opentype.cmap.glyphIdToRune[pair.right]
+          )] = pair.value.float32
+
 proc parseTtf*(buf: string): Font =
   parseOtf(buf)