vector renderer works

examples/pie_chart/main.go

@@ -14,17 +14,18 @@ func drawChart(res http.ResponseWriter, req *http.Request) {
 			FillColor: chart.ColorLightGray,
 		},
 		Values: []chart.PieChartValue{
-			{Value: 0.3, Label: "Blue"},
+			{Value: 0.2, Label: "Blue"},
 			{Value: 0.2, Label: "Green"},
 			{Value: 0.2, Label: "Gray"},
 			{Value: 0.1, Label: "Orange"},
+			{Value: 0.1, Label: "HEANG"},
 			{Value: 0.1, Label: "??"},
 			{Value: 0.1, Label: "!!"},
 		},
 	}
 
-	res.Header().Set("Content-Type", "image/png")
+	res.Header().Set("Content-Type", "image/svg+xml")
-	err := pie.Render(chart.PNG, res)
+	err := pie.Render(chart.SVG, res)
 	if err != nil {
 		fmt.Printf("Error rendering pie chart: %v\n", err)
 	}

pie_chart.go

@@ -3,7 +3,6 @@ package chart
 import (
 	"errors"
 	"io"
-	"math"
 
 	"github.com/golang/freetype/truetype"
 )
@@ -142,14 +141,15 @@ func (pc PieChart) drawSlices(r Renderer, canvasBox Box, values []PieChartValue)
 	cx, cy := canvasBox.Center()
 	diameter := MinInt(canvasBox.Width(), canvasBox.Height())
 	radius := float64(diameter >> 1)
-	radius2 := (radius * 2.0) / 3.0
+	labelRadius := (radius * 2.0) / 3.0
 
+	// draw the pie slices
 	var rads, delta, delta2, total float64
 	var lx, ly int
 	for index, v := range values {
 		v.Style.InheritFrom(pc.stylePieChartValue(index)).PersistToRenderer(r)
-		r.MoveTo(cx, cy)
 
+		r.MoveTo(cx, cy)
 		rads = PercentToRadians(total)
 		delta = PercentToRadians(v.Value)
 
@@ -161,13 +161,14 @@ func (pc PieChart) drawSlices(r Renderer, canvasBox Box, values []PieChartValue)
 		total = total + v.Value
 	}
 
+	// draw the labels
 	total = 0
 	for index, v := range values {
 		v.Style.InheritFrom(pc.stylePieChartValue(index)).PersistToRenderer(r)
 		if len(v.Label) > 0 {
-			delta2 = RadianAdd(PercentToRadians(total+(v.Value/2.0)), _pi2)
+			delta2 = PercentToRadians(total + (v.Value / 2.0))
-			lx = cx + int(radius2*math.Sin(delta2))
+			delta2 = RadianAdd(delta2, _pi2)
-			ly = cy - int(radius2*math.Cos(delta2))
+			lx, ly = CirclePoint(cx, cy, labelRadius, delta2)
 
 			tb := r.MeasureText(v.Label)
 			lx = lx - (tb.Width() >> 1)

util.go

@@ -191,18 +191,30 @@ func PercentDifference(v1, v2 float64) float64 {
 	return (v2 - v1) / v1
 }
 
-// DegreesToRadians returns degrees as radians.
-func DegreesToRadians(degrees float64) float64 {
-	return degrees * (math.Pi / 180.0)
-}
-
 const (
+	_pi   = math.Pi
 	_2pi  = 2 * math.Pi
 	_3pi4 = (3 * math.Pi) / 4.0
+	_4pi3 = (4 * math.Pi) / 3.0
+	_3pi2 = (3 * math.Pi) / 2.0
+	_5pi4 = (5 * math.Pi) / 4.0
+	_7pi4 = (7 * math.Pi) / 4.0
 	_pi2  = math.Pi / 2.0
 	_pi4  = math.Pi / 4.0
+	_d2r  = (math.Pi / 180.0)
+	_r2d  = (180.0 / math.Pi)
 )
 
+// DegreesToRadians returns degrees as radians.
+func DegreesToRadians(degrees float64) float64 {
+	return degrees * _d2r
+}
+
+// RadiansToDegrees translates a radian value to a degree value.
+func RadiansToDegrees(value float64) float64 {
+	return math.Mod(value, _2pi) * _r2d
+}
+
 // PercentToRadians converts a normalized value (0,1) to radians.
 func PercentToRadians(pct float64) float64 {
 	return DegreesToRadians(360.0 * pct)
@@ -214,7 +226,31 @@ func RadianAdd(base, delta float64) float64 {
 	if value > _2pi {
 		return math.Mod(value, _2pi)
 	} else if value < 0 {
-		return _2pi + value
+		return math.Mod(_2pi+value, _2pi)
 	}
 	return value
 }
+
+// DegreesAdd adds a delta to a base in radians.
+func DegreesAdd(baseDegrees, deltaDegrees float64) float64 {
+	value := baseDegrees + deltaDegrees
+	if value > _2pi {
+		return math.Mod(value, 360.0)
+	} else if value < 0 {
+		return math.Mod(360.0+value, 360.0)
+	}
+	return value
+}
+
+// DegreesToCompass returns the degree value in compass / clock orientation.
+func DegreesToCompass(deg float64) float64 {
+	return DegreesAdd(deg, -90.0)
+}
+
+// CirclePoint returns the absolute position of a circle diameter point given
+// by the radius and the angle.
+func CirclePoint(cx, cy int, radius, angleRadians float64) (x, y int) {
+	x = cx + int(radius*math.Sin(angleRadians))
+	y = cy - int(radius*math.Cos(angleRadians))
+	return
+}

util_test.go

@@ -100,3 +100,60 @@ func TestPercentDifference(t *testing.T) {
 	assert.Equal(0.5, PercentDifference(1.0, 1.5))
 	assert.Equal(-0.5, PercentDifference(2.0, 1.0))
 }
+
+var (
+	_degreesToRadians = map[float64]float64{
+		0:   0, // !_2pi b/c no irrational nums in floats.
+		45:  _pi4,
+		90:  _pi2,
+		135: _3pi4,
+		180: _pi,
+		225: _5pi4,
+		270: _3pi2,
+		315: _7pi4,
+	}
+
+	_compassToRadians = map[float64]float64{
+		0:   _pi2,
+		45:  _pi4,
+		90:  0, // !_2pi b/c no irrational nums in floats.
+		135: _7pi4,
+		180: _3pi2,
+		225: _5pi4,
+		270: _pi,
+		315: _3pi4,
+	}
+)
+
+func TestDegreesToRadians(t *testing.T) {
+	assert := assert.New(t)
+
+	for d, r := range _degreesToRadians {
+		assert.Equal(r, DegreesToRadians(d))
+	}
+}
+
+func TestPercentToRadians(t *testing.T) {
+	assert := assert.New(t)
+
+	for d, r := range _degreesToRadians {
+		assert.Equal(r, PercentToRadians(d/360.0))
+	}
+}
+
+func TestRadiansToDegrees(t *testing.T) {
+	assert := assert.New(t)
+
+	for d, r := range _degreesToRadians {
+		assert.Equal(d, RadiansToDegrees(r))
+	}
+}
+
+func TestRadianAdd(t *testing.T) {
+	assert := assert.New(t)
+
+	assert.Equal(_pi, RadianAdd(_pi2, _pi2))
+	assert.Equal(_3pi2, RadianAdd(_pi2, _pi))
+	assert.Equal(_pi, RadianAdd(_pi, _2pi))
+	assert.Equal(_pi, RadianAdd(_pi, -_2pi))
+}

vector_renderer.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"fmt"
 	"io"
+	"math"
 	"strings"
 
 	"golang.org/x/image/font"
@@ -82,7 +83,24 @@ func (vr *vectorRenderer) QuadCurveTo(cx, cy, x, y int) {
 }
 
 func (vr *vectorRenderer) ArcTo(cx, cy int, rx, ry, startAngle, delta float64) {
-	vr.p = append(vr.p, fmt.Sprintf("A %d %d %0.2f 1 1 %d %d", int(rx), int(ry), delta, cx, cy))
+	startAngle = RadianAdd(startAngle, _pi2)
+	endAngle := RadianAdd(startAngle, delta)
+
+	startx := cx + int(rx*math.Sin(startAngle))
+	starty := cy - int(ry*math.Cos(startAngle))
+
+	if len(vr.p) > 0 {
+		vr.p = append(vr.p, fmt.Sprintf("L %d %d", startx, starty))
+	} else {
+		vr.p = append(vr.p, fmt.Sprintf("M %d %d", startx, starty))
+	}
+
+	endx := cx + int(rx*math.Sin(endAngle))
+	endy := cy - int(ry*math.Cos(endAngle))
+
+	dd := RadiansToDegrees(delta)
+
+	vr.p = append(vr.p, fmt.Sprintf("A %d %d %0.2f 0 1 %d %d", int(rx), int(ry), dd, endx, endy))
 }
 
 // Close closes a shape.