vector: add benchmarks.

Change-Id: I4946ccc3a915c7e9365cd5fe860da673a2270fbb
Reviewed-on: https://go-review.googlesource.com/29631
Reviewed-by: David Crawshaw <crawshaw@golang.org>

vector/vector_test.go

@@ -8,8 +8,10 @@ package vector
 
 import (
 	"image"
+	"image/color"
 	"image/draw"
 	"image/png"
+	"math"
 	"os"
 	"testing"
 
@@ -93,3 +95,109 @@ func TestBasicPath(t *testing.T) {
 		}
 	}
 }
+
+const (
+	benchmarkGlyphWidth  = 893
+	benchmarkGlyphHeight = 1122
+)
+
+// benchmarkGlyphData is the 'a' glyph from the Roboto Regular font, translated
+// so that its top left corner is (0, 0).
+var benchmarkGlyphData = []struct {
+	// n being 0, 1 or 2 means moveTo, lineTo or quadTo.
+	n uint32
+	p f32.Vec2
+	q f32.Vec2
+}{
+	{0, f32.Vec2{699, 1102}, f32.Vec2{0, 0}},
+	{2, f32.Vec2{683, 1070}, f32.Vec2{673, 988}},
+	{2, f32.Vec2{544, 1122}, f32.Vec2{365, 1122}},
+	{2, f32.Vec2{205, 1122}, f32.Vec2{102.5, 1031.5}},
+	{2, f32.Vec2{0, 941}, f32.Vec2{0, 802}},
+	{2, f32.Vec2{0, 633}, f32.Vec2{128.5, 539.5}},
+	{2, f32.Vec2{257, 446}, f32.Vec2{490, 446}},
+	{1, f32.Vec2{670, 446}, f32.Vec2{0, 0}},
+	{1, f32.Vec2{670, 361}, f32.Vec2{0, 0}},
+	{2, f32.Vec2{670, 264}, f32.Vec2{612, 206.5}},
+	{2, f32.Vec2{554, 149}, f32.Vec2{441, 149}},
+	{2, f32.Vec2{342, 149}, f32.Vec2{275, 199}},
+	{2, f32.Vec2{208, 249}, f32.Vec2{208, 320}},
+	{1, f32.Vec2{22, 320}, f32.Vec2{0, 0}},
+	{2, f32.Vec2{22, 239}, f32.Vec2{79.5, 163.5}},
+	{2, f32.Vec2{137, 88}, f32.Vec2{235.5, 44}},
+	{2, f32.Vec2{334, 0}, f32.Vec2{452, 0}},
+	{2, f32.Vec2{639, 0}, f32.Vec2{745, 93.5}},
+	{2, f32.Vec2{851, 187}, f32.Vec2{855, 351}},
+	{1, f32.Vec2{855, 849}, f32.Vec2{0, 0}},
+	{2, f32.Vec2{855, 998}, f32.Vec2{893, 1086}},
+	{1, f32.Vec2{893, 1102}, f32.Vec2{0, 0}},
+	{1, f32.Vec2{699, 1102}, f32.Vec2{0, 0}},
+	{0, f32.Vec2{392, 961}, f32.Vec2{0, 0}},
+	{2, f32.Vec2{479, 961}, f32.Vec2{557, 916}},
+	{2, f32.Vec2{635, 871}, f32.Vec2{670, 799}},
+	{1, f32.Vec2{670, 577}, f32.Vec2{0, 0}},
+	{1, f32.Vec2{525, 577}, f32.Vec2{0, 0}},
+	{2, f32.Vec2{185, 577}, f32.Vec2{185, 776}},
+	{2, f32.Vec2{185, 863}, f32.Vec2{243, 912}},
+	{2, f32.Vec2{301, 961}, f32.Vec2{392, 961}},
+}
+
+// benchGlyph benchmarks rasterizing a TrueType glyph.
+//
+// Note that, compared to the github.com/google/font-go prototype, the height
+// here is the height of the bounding box, not the pixels per em used to scale
+// a glyph's vectors. A height of 64 corresponds to a ppem greater than 64.
+func benchGlyph(b *testing.B, cm color.Model, height int, op draw.Op) {
+	scale := float32(height) / benchmarkGlyphHeight
+
+	// Clone the benchmarkGlyphData slice and scale its coordinates.
+	data := append(benchmarkGlyphData[:0:0], benchmarkGlyphData...)
+	for i := range data {
+		data[i].p[0] *= scale
+		data[i].p[1] *= scale
+		data[i].q[0] *= scale
+		data[i].q[1] *= scale
+	}
+
+	width := int(math.Ceil(float64(benchmarkGlyphWidth * scale)))
+	z := NewRasterizer(width, height)
+
+	dst, src := draw.Image(nil), image.Image(nil)
+	switch cm {
+	case color.AlphaModel:
+		dst = image.NewAlpha(z.Bounds())
+		src = image.Opaque
+	default:
+		b.Fatal("unsupported color model")
+	}
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		z.Reset(width, height)
+		z.DrawOp = op
+		for _, d := range data {
+			switch d.n {
+			case 0:
+				z.MoveTo(d.p)
+			case 1:
+				z.LineTo(d.p)
+			case 2:
+				z.QuadTo(d.p, d.q)
+			}
+		}
+		z.Draw(dst, dst.Bounds(), src, image.Point{})
+	}
+}
+
+func BenchmarkGlyphAlpha16Over(b *testing.B)  { benchGlyph(b, color.AlphaModel, 16, draw.Over) }
+func BenchmarkGlyphAlpha16Src(b *testing.B)   { benchGlyph(b, color.AlphaModel, 16, draw.Src) }
+func BenchmarkGlyphAlpha32Over(b *testing.B)  { benchGlyph(b, color.AlphaModel, 32, draw.Over) }
+func BenchmarkGlyphAlpha32Src(b *testing.B)   { benchGlyph(b, color.AlphaModel, 32, draw.Src) }
+func BenchmarkGlyphAlpha64Over(b *testing.B)  { benchGlyph(b, color.AlphaModel, 64, draw.Over) }
+func BenchmarkGlyphAlpha64Src(b *testing.B)   { benchGlyph(b, color.AlphaModel, 64, draw.Src) }
+func BenchmarkGlyphAlpha128Over(b *testing.B) { benchGlyph(b, color.AlphaModel, 128, draw.Over) }
+func BenchmarkGlyphAlpha128Src(b *testing.B)  { benchGlyph(b, color.AlphaModel, 128, draw.Src) }
+func BenchmarkGlyphAlpha256Over(b *testing.B) { benchGlyph(b, color.AlphaModel, 256, draw.Over) }
+func BenchmarkGlyphAlpha256Src(b *testing.B)  { benchGlyph(b, color.AlphaModel, 256, draw.Src) }
+
+// TODO: color.RGBAModel benchmarks.