From 7946394216f347739cfd0e45357bafc3a15bafbf Mon Sep 17 00:00:00 2001
From: "Randall C. O'Reilly" <randy.oreilly@colorado.edu>
Date: Thu, 16 Aug 2018 23:41:02 -0600
Subject: [PATCH] add advanceCache map[rune] -- easy and major speedup; add
 reading of lineGap; fix Height computation to use ascent - descent + lineGap

---
 truetype/face.go     | 14 +++++++++++++-
 truetype/truetype.go |  6 +++++-
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/truetype/face.go b/truetype/face.go
index 20611fa..f8697d1 100644
--- a/truetype/face.go
+++ b/truetype/face.go
@@ -229,6 +229,7 @@ type face struct {
 	maxh          int
 	glyphBuf      GlyphBuf
 	indexCache    [indexCacheLen]indexCacheEntry
+	advanceCache  map[rune]fixed.Int26_6
 
 	// TODO: clip rectangle?
 }
@@ -255,9 +256,12 @@ func (a *face) Metrics() font.Metrics {
 	scale := float64(a.scale)
 	fupe := float64(a.f.FUnitsPerEm())
 	return font.Metrics{
-		Height:  a.scale,
+		Height:  fixed.Int26_6(math.Ceil(scale * float64(a.f.ascent-a.f.descent+a.f.lineGap) / fupe)),
 		Ascent:  fixed.Int26_6(math.Ceil(scale * float64(+a.f.ascent) / fupe)),
 		Descent: fixed.Int26_6(math.Ceil(scale * float64(-a.f.descent) / fupe)),
+		// TODO: Metrics should include LineGap as a separate measure
+		// TODO: Would also be great to include Ex as in the height of an "x" --
+		// used widely for layout
 	}
 }
 
@@ -342,9 +346,17 @@ func (a *face) GlyphBounds(r rune) (bounds fixed.Rectangle26_6, advance fixed.In
 }
 
 func (a *face) GlyphAdvance(r rune) (advance fixed.Int26_6, ok bool) {
+	if a.advanceCache == nil {
+		a.advanceCache = make(map[rune]fixed.Int26_6, 1024)
+	}
+	advance, ok = a.advanceCache[r]
+	if ok {
+		return
+	}
 	if err := a.glyphBuf.Load(a.f, a.scale, a.index(r), a.hinting); err != nil {
 		return 0, false
 	}
+	a.advanceCache[r] = a.glyphBuf.AdvanceWidth
 	return a.glyphBuf.AdvanceWidth, true
 }
 
diff --git a/truetype/truetype.go b/truetype/truetype.go
index 703fee8..2ae677a 100644
--- a/truetype/truetype.go
+++ b/truetype/truetype.go
@@ -187,6 +187,7 @@ type Font struct {
 	fUnitsPerEm             int32
 	ascent                  int32               // In FUnits.
 	descent                 int32               // In FUnits; typically negative.
+	lineGap                 int32               // In FUnits.
 	bounds                  fixed.Rectangle26_6 // In FUnits.
 	// Values from the maxp section.
 	maxTwilightPoints, maxStorage, maxFunctionDefs, maxStackElements uint16
@@ -294,6 +295,7 @@ func (f *Font) parseHhea() error {
 	}
 	f.ascent = int32(int16(u16(f.hhea, 4)))
 	f.descent = int32(int16(u16(f.hhea, 6)))
+	f.lineGap = int32(int16(u16(f.hhea, 8)))
 	f.nHMetric = int(u16(f.hhea, 34))
 	if 4*f.nHMetric+2*(f.nGlyph-f.nHMetric) != len(f.hmtx) {
 		return FormatError(fmt.Sprintf("bad hmtx length: %d", len(f.hmtx)))
@@ -323,7 +325,9 @@ func (f *Font) parseKern() error {
 	}
 	version, offset := u16(f.kern, 0), 2
 	if version != 0 {
-		return UnsupportedError(fmt.Sprintf("kern version: %d", version))
+		f.nKern = 0
+		return nil
+		// return UnsupportedError(fmt.Sprintf("kern version: %d", version))
 	}
 
 	n, offset := u16(f.kern, offset), offset+2