pie charts!

defaults.go

@@ -65,43 +65,86 @@ const (
 	DefaultPercentValueFormat = "%0.2f%%"
 )
 
+var (
+	// 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 (
 	// 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}
+	DefaultBackgroundColor = ColorWhite
 	// DefaultBackgroundStrokeColor is the default chart border color.
 	// It is equivalent to color:white.
-	DefaultBackgroundStrokeColor = drawing.Color{R: 255, G: 255, B: 255, A: 255}
+	DefaultBackgroundStrokeColor = ColorWhite
 	// 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}
+	DefaultCanvasColor = ColorWhite
 	// 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}
+	DefaultCanvasStrokeColor = ColorWhite
 	// DefaultTextColor is the default chart text color.
 	// It is equivalent to #333333.
-	DefaultTextColor = drawing.Color{R: 51, G: 51, B: 51, A: 255}
+	DefaultTextColor = ColorBlack
 	// DefaultAxisColor is the default chart axis line color.
 	// It is equivalent to #333333.
-	DefaultAxisColor = drawing.Color{R: 51, G: 51, B: 51, A: 255}
+	DefaultAxisColor = ColorBlack
 	// DefaultStrokeColor is the default chart border color.
 	// It is equivalent to #efefef.
-	DefaultStrokeColor = drawing.Color{R: 239, G: 239, B: 239, A: 255}
+	DefaultStrokeColor = ColorLightGray
 	// DefaultFillColor is the default fill color.
 	// It is equivalent to #0074d9.
-	DefaultFillColor = drawing.Color{R: 0, G: 217, B: 116, A: 255}
+	DefaultFillColor = ColorBlue
 	// DefaultAnnotationFillColor is the default annotation background color.
-	DefaultAnnotationFillColor = drawing.Color{R: 255, G: 255, B: 255, A: 255}
+	DefaultAnnotationFillColor = ColorWhite
 	// DefaultGridLineColor is the default grid line color.
-	DefaultGridLineColor = drawing.Color{R: 239, G: 239, B: 239, A: 255}
+	DefaultGridLineColor = ColorLightGray
 )
 
 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},
+	// 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))
+}