pie charts!

defaults.go

@@ -66,42 +66,85 @@ const (
 )
 
 var (
-	// DefaultBackgroundColor is the default chart background color.
-	// It is equivalent to css color:white.
-	DefaultBackgroundColor = drawing.Color{R: 255, G: 255, B: 255, A: 255}
-	// DefaultBackgroundStrokeColor is the default chart border color.
-	// It is equivalent to color:white.
-	DefaultBackgroundStrokeColor = drawing.Color{R: 255, G: 255, B: 255, A: 255}
-	// DefaultCanvasColor is the default chart canvas color.
-	// It is equivalent to css color:white.
-	DefaultCanvasColor = drawing.Color{R: 255, G: 255, B: 255, A: 255}
-	// DefaultCanvasStrokeColor is the default chart canvas stroke color.
-	// It is equivalent to css color:white.
-	DefaultCanvasStrokeColor = drawing.Color{R: 255, G: 255, B: 255, A: 255}
-	// DefaultTextColor is the default chart text color.
-	// It is equivalent to #333333.
-	DefaultTextColor = drawing.Color{R: 51, G: 51, B: 51, A: 255}
-	// DefaultAxisColor is the default chart axis line color.
-	// It is equivalent to #333333.
-	DefaultAxisColor = drawing.Color{R: 51, G: 51, B: 51, A: 255}
-	// DefaultStrokeColor is the default chart border color.
-	// It is equivalent to #efefef.
-	DefaultStrokeColor = drawing.Color{R: 239, G: 239, B: 239, A: 255}
-	// DefaultFillColor is the default fill color.
-	// It is equivalent to #0074d9.
-	DefaultFillColor = drawing.Color{R: 0, G: 217, B: 116, A: 255}
-	// DefaultAnnotationFillColor is the default annotation background color.
-	DefaultAnnotationFillColor = drawing.Color{R: 255, G: 255, B: 255, A: 255}
-	// DefaultGridLineColor is the default grid line color.
-	DefaultGridLineColor = drawing.Color{R: 239, G: 239, B: 239, A: 255}
+	// ColorWhite is white.
+	ColorWhite = drawing.Color{R: 255, G: 255, B: 255, A: 255}
+	// ColorBlue is the basic theme blue color.
+	ColorBlue = drawing.Color{R: 0, G: 116, B: 217, A: 255}
+	// ColorCyan is the basic theme cyan color.
+	ColorCyan = drawing.Color{R: 0, G: 217, B: 210, A: 255}
+	// ColorGreen is the basic theme green color.
+	ColorGreen = drawing.Color{R: 0, G: 217, B: 101, A: 255}
+	// ColorRed is the basic theme red color.
+	ColorRed = drawing.Color{R: 217, G: 0, B: 116, A: 255}
+	// ColorOrange is the basic theme orange color.
+	ColorOrange = drawing.Color{R: 217, G: 101, B: 0, A: 255}
+	// ColorYellow is the basic theme yellow color.
+	ColorYellow = drawing.Color{R: 217, G: 210, B: 0, A: 255}
+	// ColorBlack is the basic theme black color.
+	ColorBlack = drawing.Color{R: 51, G: 51, B: 51, A: 255}
+	// ColorLightGray is the basic theme light gray color.
+	ColorLightGray = drawing.Color{R: 239, G: 239, B: 239, A: 255}
+
+	// ColorAlternateBlue is a alternate theme color.
+	ColorAlternateBlue = drawing.Color{R: 106, G: 195, B: 203, A: 255}
+	// ColorAlternateGreen is a alternate theme color.
+	ColorAlternateGreen = drawing.Color{R: 42, G: 190, B: 137, A: 255}
+	// ColorAlternateGray is a alternate theme color.
+	ColorAlternateGray = drawing.Color{R: 110, G: 128, B: 139, A: 255}
+	// ColorAlternateYellow is a alternate theme color.
+	ColorAlternateYellow = drawing.Color{R: 240, G: 174, B: 90, A: 255}
+	// ColorAlternateLightGray is a alternate theme color.
+	ColorAlternateLightGray = drawing.Color{R: 187, G: 190, B: 191, A: 255}
 )
 
 var (
-	// DefaultSeriesStrokeColors are a couple default series colors.
-	DefaultSeriesStrokeColors = []drawing.Color{
-		{R: 0, G: 116, B: 217, A: 255},
-		{R: 0, G: 217, B: 116, A: 255},
-		{R: 217, G: 0, B: 116, A: 255},
+	// DefaultBackgroundColor is the default chart background color.
+	// It is equivalent to css color:white.
+	DefaultBackgroundColor = ColorWhite
+	// DefaultBackgroundStrokeColor is the default chart border color.
+	// It is equivalent to color:white.
+	DefaultBackgroundStrokeColor = ColorWhite
+	// DefaultCanvasColor is the default chart canvas color.
+	// It is equivalent to css color:white.
+	DefaultCanvasColor = ColorWhite
+	// DefaultCanvasStrokeColor is the default chart canvas stroke color.
+	// It is equivalent to css color:white.
+	DefaultCanvasStrokeColor = ColorWhite
+	// DefaultTextColor is the default chart text color.
+	// It is equivalent to #333333.
+	DefaultTextColor = ColorBlack
+	// DefaultAxisColor is the default chart axis line color.
+	// It is equivalent to #333333.
+	DefaultAxisColor = ColorBlack
+	// DefaultStrokeColor is the default chart border color.
+	// It is equivalent to #efefef.
+	DefaultStrokeColor = ColorLightGray
+	// DefaultFillColor is the default fill color.
+	// It is equivalent to #0074d9.
+	DefaultFillColor = ColorBlue
+	// DefaultAnnotationFillColor is the default annotation background color.
+	DefaultAnnotationFillColor = ColorWhite
+	// DefaultGridLineColor is the default grid line color.
+	DefaultGridLineColor = ColorLightGray
+)
+
+var (
+	// DefaultColors are a couple default series colors.
+	DefaultColors = []drawing.Color{
+		ColorBlue,
+		ColorGreen,
+		ColorRed,
+		ColorCyan,
+		ColorOrange,
+	}
+
+	// DefaultAlternateColors are a couple alternate colors.
+	DefaultAlternateColors = []drawing.Color{
+		ColorAlternateBlue,
+		ColorAlternateGreen,
+		ColorAlternateGray,
+		ColorAlternateYellow,
+		ColorAlternateLightGray,
 	}
 )
 
@@ -117,10 +160,17 @@ var (
 )
 
 // GetDefaultSeriesStrokeColor returns a color from the default list by index.
-// NOTE: the index will wrap around (using a modulo).g
+// NOTE: the index will wrap around (using a modulo).
 func GetDefaultSeriesStrokeColor(index int) drawing.Color {
-	finalIndex := index % len(DefaultSeriesStrokeColors)
-	return DefaultSeriesStrokeColors[finalIndex]
+	finalIndex := index % len(DefaultColors)
+	return DefaultColors[finalIndex]
+}
+
+// GetDefaultPieChartValueColor returns a color from the default list by index.
+// NOTE: the index will wrap around (using a modulo).
+func GetDefaultPieChartValueColor(index int) drawing.Color {
+	finalIndex := index % len(DefaultAlternateColors)
+	return DefaultAlternateColors[finalIndex]
 }
 
 var (

drawing/path.go

@@ -101,10 +101,10 @@ func (p *Path) CubicCurveTo(cx1, cy1, cx2, cy2, x, y float64) {
 }
 
 // ArcTo adds an arc to the path
-func (p *Path) ArcTo(cx, cy, rx, ry, startAngle, angle float64) {
-	endAngle := startAngle + angle
+func (p *Path) ArcTo(cx, cy, rx, ry, startAngle, delta float64) {
+	endAngle := startAngle + delta
 	clockWise := true
-	if angle < 0 {
+	if delta < 0 {
 		clockWise = false
 	}
 	// normalize
@@ -124,7 +124,7 @@ func (p *Path) ArcTo(cx, cy, rx, ry, startAngle, angle float64) {
 	} else {
 		p.MoveTo(startX, startY)
 	}
-	p.appendToPath(ArcToComponent, cx, cy, rx, ry, startAngle, angle)
+	p.appendToPath(ArcToComponent, cx, cy, rx, ry, startAngle, delta)
 	p.x = cx + math.Cos(endAngle)*rx
 	p.y = cy + math.Sin(endAngle)*ry
 }

drawing/stack_graphic_context.go

@@ -171,8 +171,8 @@ func (gc *StackGraphicContext) CubicCurveTo(cx1, cy1, cx2, cy2, x, y float64) {
 }
 
 // ArcTo draws an arc.
-func (gc *StackGraphicContext) ArcTo(cx, cy, rx, ry, startAngle, angle float64) {
-	gc.current.Path.ArcTo(cx, cy, rx, ry, startAngle, angle)
+func (gc *StackGraphicContext) ArcTo(cx, cy, rx, ry, startAngle, delta float64) {
+	gc.current.Path.ArcTo(cx, cy, rx, ry, startAngle, delta)
 }
 
 // Close closes a path.

examples/pie_chart/main.go

@@ -0,0 +1,35 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"net/http"
+
+	"github.com/wcharczuk/go-chart"
+)
+
+func drawChart(res http.ResponseWriter, req *http.Request) {
+	pie := chart.PieChart{
+		Canvas: chart.Style{
+			FillColor: chart.ColorLightGray,
+		},
+		Values: []chart.PieChartValue{
+			{Value: 0.3, Label: "Blue"},
+			{Value: 0.2, Label: "Green"},
+			{Value: 0.2, Label: "Gray"},
+			{Value: 0.1, Label: "Orange"},
+			{Value: 0.1, Label: "??"},
+		},
+	}
+
+	res.Header().Set("Content-Type", "image/png")
+	err := pie.Render(chart.PNG, res)
+	if err != nil {
+		fmt.Printf("Error rendering pie chart: %v\n", err)
+	}
+}
+
+func main() {
+	http.HandleFunc("/", drawChart)
+	log.Fatal(http.ListenAndServe(":8080", nil))
+}

pie_chart.go

@@ -0,0 +1,284 @@
+package chart
+
+import (
+	"errors"
+	"io"
+	"math"
+
+	"github.com/golang/freetype/truetype"
+)
+
+// PieChartValue is a slice of a pie-chart.
+type PieChartValue struct {
+	Style Style
+	Label string
+	Value float64
+}
+
+// PieChart is a chart that draws sections of a circle based on percentages.
+type PieChart struct {
+	Title      string
+	TitleStyle Style
+
+	Width  int
+	Height int
+	DPI    float64
+
+	Background Style
+	Canvas     Style
+
+	Font        *truetype.Font
+	defaultFont *truetype.Font
+
+	Values   []PieChartValue
+	Elements []Renderable
+}
+
+// GetDPI returns the dpi for the chart.
+func (pc PieChart) GetDPI(defaults ...float64) float64 {
+	if pc.DPI == 0 {
+		if len(defaults) > 0 {
+			return defaults[0]
+		}
+		return DefaultDPI
+	}
+	return pc.DPI
+}
+
+// GetFont returns the text font.
+func (pc PieChart) GetFont() *truetype.Font {
+	if pc.Font == nil {
+		return pc.defaultFont
+	}
+	return pc.Font
+}
+
+// GetWidth returns the chart width or the default value.
+func (pc PieChart) GetWidth() int {
+	if pc.Width == 0 {
+		return DefaultChartWidth
+	}
+	return pc.Width
+}
+
+// GetHeight returns the chart height or the default value.
+func (pc PieChart) GetHeight() int {
+	if pc.Height == 0 {
+		return DefaultChartWidth
+	}
+	return pc.Height
+}
+
+// Render renders the chart with the given renderer to the given io.Writer.
+func (pc PieChart) Render(rp RendererProvider, w io.Writer) error {
+	if len(pc.Values) == 0 {
+		return errors.New("Please provide at least one value.")
+	}
+
+	r, err := rp(pc.GetWidth(), pc.GetHeight())
+	if err != nil {
+		return err
+	}
+
+	if pc.Font == nil {
+		defaultFont, err := GetDefaultFont()
+		if err != nil {
+			return err
+		}
+		pc.defaultFont = defaultFont
+	}
+	r.SetDPI(pc.GetDPI(DefaultDPI))
+
+	canvasBox := pc.getDefaultCanvasBox()
+	canvasBox = pc.getCircleAdjustedCanvasBox(canvasBox)
+
+	pc.drawBackground(r)
+	pc.drawCanvas(r, canvasBox)
+
+	valuesWithPlaceholder, err := pc.finalizeValues(pc.Values)
+	if err != nil {
+		return err
+	}
+	pc.drawSlices(r, canvasBox, valuesWithPlaceholder)
+	pc.drawTitle(r)
+	for _, a := range pc.Elements {
+		a(r, canvasBox, pc.styleDefaultsElements())
+	}
+
+	return r.Save(w)
+}
+
+func (pc PieChart) drawBackground(r Renderer) {
+	DrawBox(r, Box{
+		Right:  pc.GetWidth(),
+		Bottom: pc.GetHeight(),
+	}, pc.getBackgroundStyle())
+}
+
+func (pc PieChart) drawCanvas(r Renderer, canvasBox Box) {
+	DrawBox(r, canvasBox, pc.getCanvasStyle())
+}
+
+func (pc PieChart) drawTitle(r Renderer) {
+	if len(pc.Title) > 0 && pc.TitleStyle.Show {
+		r.SetFont(pc.TitleStyle.GetFont(pc.GetFont()))
+		r.SetFontColor(pc.TitleStyle.GetFontColor(DefaultTextColor))
+		titleFontSize := pc.TitleStyle.GetFontSize(DefaultTitleFontSize)
+		r.SetFontSize(titleFontSize)
+
+		textBox := r.MeasureText(pc.Title)
+
+		textWidth := textBox.Width()
+		textHeight := textBox.Height()
+
+		titleX := (pc.GetWidth() >> 1) - (textWidth >> 1)
+		titleY := pc.TitleStyle.Padding.GetTop(DefaultTitleTop) + textHeight
+
+		r.Text(pc.Title, titleX, titleY)
+	}
+}
+
+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
+
+	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)
+
+		rads = PercentToRadians(total)
+		delta = PercentToRadians(v.Value)
+
+		r.ArcTo(cx, cy, radius, radius, rads, delta)
+
+		r.LineTo(cx, cy)
+		r.Close()
+		r.FillStroke()
+		total = total + v.Value
+	}
+
+	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)
+			lx = cx + int(radius2*math.Sin(delta2))
+			ly = cy - int(radius2*math.Cos(delta2))
+
+			tb := r.MeasureText(v.Label)
+			lx = lx - (tb.Width() >> 1)
+
+			r.Text(v.Label, lx, ly)
+		}
+		total = total + v.Value
+	}
+}
+
+func (pc PieChart) finalizeValues(values []PieChartValue) ([]PieChartValue, error) {
+	var total float64
+	for _, v := range values {
+		total += v.Value
+		if total > 1.0 {
+			return nil, errors.New("Values total exceeded 1.0; please normalize pie chart values to [0,1.0)")
+		}
+	}
+	remainder := 1.0 - total
+	if RoundDown(remainder, 0.0001) > 0 {
+		return append(values, PieChartValue{
+			Style: pc.styleDefaultsPieChartValue(),
+			Value: remainder,
+		}), nil
+	}
+	return values, nil
+}
+
+func (pc PieChart) getDefaultCanvasBox() Box {
+	return pc.Box()
+}
+
+func (pc PieChart) getCircleAdjustedCanvasBox(canvasBox Box) Box {
+	circleDiameter := MinInt(canvasBox.Width(), canvasBox.Height())
+
+	square := Box{
+		Right:  circleDiameter,
+		Bottom: circleDiameter,
+	}
+
+	return canvasBox.Fit(square)
+}
+
+func (pc PieChart) getBackgroundStyle() Style {
+	return pc.Background.InheritFrom(pc.styleDefaultsBackground())
+}
+
+func (pc PieChart) getCanvasStyle() Style {
+	return pc.Canvas.InheritFrom(pc.styleDefaultsCanvas())
+}
+
+func (pc PieChart) styleDefaultsCanvas() Style {
+	return Style{
+		FillColor:   DefaultCanvasColor,
+		StrokeColor: DefaultCanvasStrokeColor,
+		StrokeWidth: DefaultStrokeWidth,
+	}
+}
+
+func (pc PieChart) styleDefaultsPieChartValue() Style {
+	return Style{
+		StrokeColor: ColorWhite,
+		StrokeWidth: 5.0,
+		FillColor:   ColorWhite,
+	}
+}
+
+func (pc PieChart) stylePieChartValue(index int) Style {
+	return Style{
+		StrokeColor: ColorWhite,
+		StrokeWidth: 5.0,
+		FillColor:   GetDefaultPieChartValueColor(index),
+		FontSize:    24.0,
+		FontColor:   ColorWhite,
+		Font:        pc.GetFont(),
+	}
+}
+
+func (pc PieChart) styleDefaultsBackground() Style {
+	return Style{
+		FillColor:   DefaultBackgroundColor,
+		StrokeColor: DefaultBackgroundStrokeColor,
+		StrokeWidth: DefaultStrokeWidth,
+	}
+}
+
+func (pc PieChart) styleDefaultsSeries(seriesIndex int) Style {
+	strokeColor := GetDefaultSeriesStrokeColor(seriesIndex)
+	return Style{
+		StrokeColor: strokeColor,
+		StrokeWidth: DefaultStrokeWidth,
+		Font:        pc.GetFont(),
+		FontSize:    DefaultFontSize,
+	}
+}
+
+func (pc PieChart) styleDefaultsElements() Style {
+	return Style{
+		Font: pc.GetFont(),
+	}
+}
+
+// Box returns the chart bounds as a box.
+func (pc PieChart) Box() Box {
+	dpr := pc.Background.Padding.GetRight(DefaultBackgroundPadding.Right)
+	dpb := pc.Background.Padding.GetBottom(DefaultBackgroundPadding.Bottom)
+
+	return Box{
+		Top:    pc.Background.Padding.GetTop(DefaultBackgroundPadding.Top),
+		Left:   pc.Background.Padding.GetLeft(DefaultBackgroundPadding.Left),
+		Right:  pc.GetWidth() - dpr,
+		Bottom: pc.GetHeight() - dpb,
+	}
+}

raster_renderer.go

@@ -71,6 +71,16 @@ func (rr *rasterRenderer) LineTo(x, y int) {
 	rr.gc.LineTo(float64(x), float64(y))
 }
 
+// QuadCurveTo implements the interface method.
+func (rr *rasterRenderer) QuadCurveTo(cx, cy, x, y int) {
+	rr.gc.QuadCurveTo(float64(cx), float64(cy), float64(x), float64(y))
+}
+
+// ArcTo implements the interface method.
+func (rr *rasterRenderer) ArcTo(cx, cy int, rx, ry, startAngle, delta float64) {
+	rr.gc.ArcTo(float64(cx), float64(cy), rx, ry, startAngle, delta)
+}
+
 // Close implements the interface method.
 func (rr *rasterRenderer) Close() {
 	rr.gc.Close()

renderer.go

@@ -34,6 +34,14 @@ type Renderer interface {
 	// from the previous point.
 	LineTo(x, y int)
 
+	// QuadCurveTo draws a quad curve.
+	// cx and cy represent the bezier "control points".
+	QuadCurveTo(cx, cy, x, y int)
+
+	// ArcTo draws an arc with a given center (cx,cy)
+	// a given set of radii (rx,ry), a startAngle and delta (in radians).
+	ArcTo(cx, cy int, rx, ry, startAngle, delta float64)
+
 	// Close finalizes a shape as drawn by LineTo.
 	Close()
 

style.go

@@ -79,11 +79,11 @@ func (s Style) String() string {
 	if s.FontSize != 0 {
 		output = append(output, fmt.Sprintf("\"font_size\": \"%0.2fpt\"", s.FontSize))
 	} else {
-		output = append(output, "\"fill_color\": null")
+		output = append(output, "\"font_size\": null")
 	}
 
-	if !s.FillColor.IsZero() {
-		output = append(output, fmt.Sprintf("\"font_color\": %s", s.FillColor.String()))
+	if !s.FontColor.IsZero() {
+		output = append(output, fmt.Sprintf("\"font_color\": %s", s.FontColor.String()))
 	} else {
 		output = append(output, "\"font_color\": null")
 	}
@@ -190,6 +190,7 @@ func (s Style) PersistToRenderer(r Renderer) {
 	r.SetStrokeColor(s.GetStrokeColor())
 	r.SetStrokeWidth(s.GetStrokeWidth())
 	r.SetStrokeDashArray(s.GetStrokeDashArray())
+	r.SetFillColor(s.GetFillColor())
 	r.SetFont(s.GetFont())
 	r.SetFontColor(s.GetFontColor())
 	r.SetFontSize(s.GetFontSize())

util.go

@@ -99,6 +99,21 @@ func RoundDown(value, roundTo float64) float64 {
 	return d1 * roundTo
 }
 
+// Normalize returns a set of numbers on the interval [0,1] for a given set of inputs.
+// An example: 4,3,2,1 => 0.4, 0.3, 0.2, 0.1
+// Caveat; the total may be < 1.0; there are going to be issues with irrational numbers etc.
+func Normalize(values ...float64) []float64 {
+	var total float64
+	for _, v := range values {
+		total += v
+	}
+	output := make([]float64, len(values))
+	for x, v := range values {
+		output[x] = RoundDown(v/total, 0.001)
+	}
+	return output
+}
+
 // MinInt returns the minimum of a set of integers.
 func MinInt(values ...int) int {
 	min := math.MaxInt32
@@ -175,3 +190,31 @@ func SeqDays(days int) []time.Time {
 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 (
+	_2pi  = 2 * math.Pi
+	_3pi4 = (3 * math.Pi) / 4.0
+	_pi2  = math.Pi / 2.0
+	_pi4  = math.Pi / 4.0
+)
+
+// PercentToRadians converts a normalized value (0,1) to radians.
+func PercentToRadians(pct float64) float64 {
+	return DegreesToRadians(360.0 * pct)
+}
+
+// RadianAdd adds a delta to a base in radians.
+func RadianAdd(base, delta float64) float64 {
+	value := base + delta
+	if value > _2pi {
+		return math.Mod(value, _2pi)
+	} else if value < 0 {
+		return _2pi + value
+	}
+	return value
+}

vector_renderer.go

@@ -76,6 +76,15 @@ func (vr *vectorRenderer) LineTo(x, y int) {
 	vr.p = append(vr.p, fmt.Sprintf("L %d %d", x, y))
 }
 
+// QuadCurveTo draws a quad curve.
+func (vr *vectorRenderer) QuadCurveTo(cx, cy, x, y int) {
+	vr.p = append(vr.p, fmt.Sprintf("Q%d,%d %d,%d", cx, cy, x, y))
+}
+
+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))
+}
+
 // Close closes a shape.
 func (vr *vectorRenderer) Close() {
 	vr.p = append(vr.p, fmt.Sprintf("Z"))