From 9c4da76964c63e41015acc07d8c0193ab3e77119 Mon Sep 17 00:00:00 2001
From: Nigel Tao <nigeltao@golang.org>
Date: Wed, 19 May 2010 17:37:01 -0700
Subject: [PATCH] Freetype-Go: gamma is now a float instead of a float64.

R=r
CC=golang-dev
http://codereview.appspot.com/1236042
---
 example/freetype/main.go |  2 ++
 example/gamma/main.go    |  2 +-
 freetype/freetype.go     | 24 ++++++++++++-------
 freetype/raster/paint.go | 52 ++++++++++++++++++++++++----------------
 4 files changed, 50 insertions(+), 30 deletions(-)

diff --git a/example/freetype/main.go b/example/freetype/main.go
index aabef20..cd7f60c 100644
--- a/example/freetype/main.go
+++ b/example/freetype/main.go
@@ -16,6 +16,7 @@ import (
 var (
 	dpi      = flag.Int("dpi", 72, "screen resolution in Dots Per Inch")
 	fontfile = flag.String("fontfile", "../../luxi-fonts/luxisr.ttf", "filename of the ttf font")
+	gamma    = flag.Float("gamma", 1.0, "gamma correction")
 	size     = flag.Float("size", 12, "font size in points")
 	spacing  = flag.Float("spacing", 1.5, "line spacing (e.g. 2 means double spaced)")
 	wonb     = flag.Bool("whiteonblack", false, "white text on a black background")
@@ -87,6 +88,7 @@ func main() {
 	c.SetDPI(*dpi)
 	c.SetFont(font)
 	c.SetFontSize(*size)
+	c.SetGamma(*gamma)
 
 	// Draw the guidelines.
 	for i := 0; i < 200; i++ {
diff --git a/example/gamma/main.go b/example/gamma/main.go
index 99c97af..2d5e14d 100644
--- a/example/gamma/main.go
+++ b/example/gamma/main.go
@@ -53,7 +53,7 @@ func main() {
 	mask := image.NewAlpha(50, 50)
 	painter := raster.NewAlphaPainter(mask)
 	painter.Op = draw.Src
-	gammas := []float64{1.0 / 10.0, 1.0 / 3.0, 1.0 / 2.0, 2.0 / 3.0, 4.0 / 5.0, 1.0, 5.0 / 4.0, 3.0 / 2.0, 2.0, 3.0, 10.0}
+	gammas := []float{1.0 / 10.0, 1.0 / 3.0, 1.0 / 2.0, 2.0 / 3.0, 4.0 / 5.0, 1.0, 5.0 / 4.0, 3.0 / 2.0, 2.0, 3.0, 10.0}
 	for i, g := range gammas {
 		clear(mask)
 		r.Rasterize(raster.NewGammaCorrectionPainter(painter, g))
diff --git a/freetype/freetype.go b/freetype/freetype.go
index 5a2d45b..192e39b 100644
--- a/freetype/freetype.go
+++ b/freetype/freetype.go
@@ -32,7 +32,8 @@ func Pt(x, y int) raster.Point {
 // given size.
 type RGBAContext struct {
 	r        *raster.Rasterizer
-	p        *raster.RGBAPainter
+	rp       *raster.RGBAPainter
+	gp       *raster.GammaCorrectionPainter
 	font     *truetype.Font
 	glyphBuf *truetype.GlyphBuf
 	fontSize float
@@ -144,7 +145,7 @@ func (c *RGBAContext) DrawText(pt raster.Point, s string) (err os.Error) {
 	advance, x0 := 0, pt.X
 	dx := raster.Fixed(-c.xmin << 8)
 	dy := raster.Fixed(-c.ymin << 8)
-	c.p.Dy, y = c.ymin+int(pt.Y>>8), pt.Y&0xff
+	c.rp.Dy, y = c.ymin+int(pt.Y>>8), pt.Y&0xff
 	y += dy
 	prev, hasPrev := truetype.Index(0), false
 	for _, ch := range s {
@@ -169,7 +170,7 @@ func (c *RGBAContext) DrawText(pt raster.Point, s string) (err os.Error) {
 		x = x0 + c.FUnitToFixed(advance)
 		// Break the co-ordinate down into an integer pixel part and a
 		// sub-pixel part, making sure that the latter is non-negative.
-		c.p.Dx, x = c.xmin+int(x>>8), x&0xff
+		c.rp.Dx, x = c.xmin+int(x>>8), x&0xff
 		x += dx
 		// Draw the contours.
 		c.r.Clear()
@@ -178,7 +179,7 @@ func (c *RGBAContext) DrawText(pt raster.Point, s string) (err os.Error) {
 			c.drawContour(c.glyphBuf.Point[e0:e], x, y)
 			e0 = e
 		}
-		c.r.Rasterize(c.p)
+		c.r.Rasterize(c.gp)
 		// Advance the cursor.
 		advance += int(c.font.HMetric(index).AdvanceWidth)
 		prev, hasPrev = index, true
@@ -204,7 +205,7 @@ func (c *RGBAContext) recalc() {
 
 // SetColor sets the color to draw text.
 func (c *RGBAContext) SetColor(color image.Color) {
-	c.p.SetColor(color)
+	c.rp.SetColor(color)
 }
 
 // SetDPI sets the screen resolution in dots per inch.
@@ -229,20 +230,27 @@ func (c *RGBAContext) SetFontSize(fontSize float) {
 	c.recalc()
 }
 
+// SetGamma sets the gamma correction parameter.
+func (c *RGBAContext) SetGamma(g float) {
+	c.gp.SetGamma(g)
+}
+
 // SetRGBA sets the image that the RGBAContext draws onto.
 func (c *RGBAContext) SetRGBA(m *image.RGBA) {
-	c.p.Image = m
+	c.rp.Image = m
 }
 
 // NewRGBAContext creates a new RGBAContext.
 func NewRGBAContext(m *image.RGBA) *RGBAContext {
-	return &RGBAContext{
+	c := &RGBAContext{
 		r:        raster.NewRasterizer(0, 0),
-		p:        raster.NewRGBAPainter(m),
+		rp:       raster.NewRGBAPainter(m),
 		glyphBuf: truetype.NewGlyphBuf(),
 		fontSize: 12,
 		dpi:      72,
 		upe:      2048,
 		scale:    (12 * 72 * 256 * 256) / (2048 * 72),
 	}
+	c.gp = raster.NewGammaCorrectionPainter(c.rp, 1.0)
+	return c
 }
diff --git a/freetype/raster/paint.go b/freetype/raster/paint.go
index 5639a0b..5d417c7 100644
--- a/freetype/raster/paint.go
+++ b/freetype/raster/paint.go
@@ -215,46 +215,56 @@ type GammaCorrectionPainter struct {
 	Painter Painter
 	// Precomputed alpha values for linear interpolation, with fully opaque == 1<<16-1.
 	a [256]uint16
+	// Whether gamma correction is a no-op.
+	gammaIsOne bool
 }
 
 // Paint delegates to the wrapped Painter after performing gamma-correction
 // on each Span.
 func (g *GammaCorrectionPainter) Paint(ss []Span) {
-	const (
-		M = 0x1010101 // 255*M == 1<<32-1
-		N = 0x8080    // N = M>>9, and N < 1<<16-1
-	)
-	for i, _ := range ss {
-		if ss[i].A == 0 || ss[i].A == 1<<32-1 {
-			continue
+	if !g.gammaIsOne {
+		const (
+			M = 0x1010101 // 255*M == 1<<32-1
+			N = 0x8080    // N = M>>9, and N < 1<<16-1
+		)
+		for i, _ := range ss {
+			if ss[i].A == 0 || ss[i].A == 1<<32-1 {
+				continue
+			}
+			p, q := ss[i].A/M, (ss[i].A%M)>>9
+			// The resultant alpha is a linear interpolation of g.a[p] and g.a[p+1].
+			a := uint32(g.a[p])*(N-q) + uint32(g.a[p+1])*q
+			a = (a + N/2) / N
+			// Convert the alpha from 16-bit (which is g.a's range) to 32-bit.
+			a |= a << 16
+			// A non-final Span can't have zero alpha.
+			if a == 0 {
+				a = 1
+			}
+			ss[i].A = a
 		}
-		p, q := ss[i].A/M, (ss[i].A%M)>>9
-		// The resultant alpha is a linear interpolation of g.a[p] and g.a[p+1].
-		a := uint32(g.a[p])*(N-q) + uint32(g.a[p+1])*q
-		a = (a + N/2) / N
-		// Convert the alpha from 16-bit (which is g.a's range) to 32-bit.
-		a |= a << 16
-		// A non-final Span can't have zero alpha.
-		if a == 0 {
-			a = 1
-		}
-		ss[i].A = a
 	}
 	g.Painter.Paint(ss)
 }
 
 // SetGamma sets the gamma value.
-func (g *GammaCorrectionPainter) SetGamma(gamma float64) {
+func (g *GammaCorrectionPainter) SetGamma(gamma float) {
+	if gamma == 1.0 {
+		g.gammaIsOne = true
+		return
+	}
+	g.gammaIsOne = false
+	gamma64 := float64(gamma)
 	for i := 0; i < 256; i++ {
 		a := float64(i) / 0xff
-		a = math.Pow(a, gamma)
+		a = math.Pow(a, gamma64)
 		g.a[i] = uint16(0xffff * a)
 	}
 }
 
 // NewGammaCorrectionPainter creates a new GammaCorrectionPainter that wraps
 // the given Painter.
-func NewGammaCorrectionPainter(p Painter, gamma float64) *GammaCorrectionPainter {
+func NewGammaCorrectionPainter(p Painter, gamma float) *GammaCorrectionPainter {
 	g := &GammaCorrectionPainter{Painter: p}
 	g.SetGamma(gamma)
 	return g