Adds the ability to draw an XY scatter plot. (#27)

* works more or less

* updating comment

* removing debugging printf

* adding output

* tweaks

* missed a couple series validations

* testing auto coloring

* updated output.png

* color tests etc.

* sanity check tests.

* should not use unkeyed fields anyway.

_examples/request_timings/main.go

@@ -23,7 +23,7 @@ func parseFloat64(str string) float64 {
 func readData() ([]time.Time, []float64) {
 	var xvalues []time.Time
 	var yvalues []float64
-	chart.File.ReadByLines("requests.csv", func(line string) {
+	err := chart.File.ReadByLines("requests.csv", func(line string) {
 		parts := strings.Split(line, ",")
 		year := parseInt(parts[0])
 		month := parseInt(parts[1])
@@ -33,6 +33,9 @@ func readData() ([]time.Time, []float64) {
 		xvalues = append(xvalues, time.Date(year, time.Month(month), day, hour, 0, 0, 0, time.UTC))
 		yvalues = append(yvalues, elapsedMillis)
 	})
+	if err != nil {
+		fmt.Println(err.Error())
+	}
 	return xvalues, yvalues
 }
 

_examples/scatter/main.go

@@ -0,0 +1,80 @@
+package main
+
+import (
+	"log"
+	"net/http"
+
+	"github.com/wcharczuk/go-chart"
+)
+
+func drawChart(res http.ResponseWriter, req *http.Request) {
+	graph := chart.Chart{
+		Series: []chart.Series{
+			chart.ContinuousSeries{
+				Style: chart.Style{
+					Show:        true,
+					StrokeWidth: chart.Disabled,
+					DotWidth:    3,
+				},
+				XValues: chart.Sequence.Random(32, 1024),
+				YValues: chart.Sequence.Random(32, 1024),
+			},
+			chart.ContinuousSeries{
+				Style: chart.Style{
+					Show:        true,
+					StrokeWidth: chart.Disabled,
+					DotWidth:    5,
+				},
+				XValues: chart.Sequence.Random(16, 1024),
+				YValues: chart.Sequence.Random(16, 1024),
+			},
+			chart.ContinuousSeries{
+				Style: chart.Style{
+					Show:        true,
+					StrokeWidth: chart.Disabled,
+					DotWidth:    7,
+				},
+				XValues: chart.Sequence.Random(8, 1024),
+				YValues: chart.Sequence.Random(8, 1024),
+			},
+		},
+	}
+
+	res.Header().Set("Content-Type", "image/png")
+	err := graph.Render(chart.PNG, res)
+	if err != nil {
+		log.Println(err.Error())
+	}
+
+}
+
+func unit(res http.ResponseWriter, req *http.Request) {
+	graph := chart.Chart{
+		Height: 50,
+		Width:  50,
+		Canvas: chart.Style{
+			Padding: chart.Box{IsSet: true},
+		},
+		Background: chart.Style{
+			Padding: chart.Box{IsSet: true},
+		},
+		Series: []chart.Series{
+			chart.ContinuousSeries{
+				XValues: chart.Sequence.Float64(0, 4, 1),
+				YValues: chart.Sequence.Float64(0, 4, 1),
+			},
+		},
+	}
+
+	res.Header().Set("Content-Type", "image/png")
+	err := graph.Render(chart.PNG, res)
+	if err != nil {
+		log.Println(err.Error())
+	}
+}
+
+func main() {
+	http.HandleFunc("/", drawChart)
+	http.HandleFunc("/unit", unit)
+	log.Fatal(http.ListenAndServe(":8080", nil))
+}

box.go

@@ -5,16 +5,36 @@ import (
 	"math"
 )
 
+var (
+	// BoxZero is a preset box that represents an intentional zero value.
+	BoxZero = Box{IsSet: true}
+)
+
+// NewBox returns a new (set) box.
+func NewBox(top, left, right, bottom int) Box {
+	return Box{
+		IsSet:  true,
+		Top:    top,
+		Left:   left,
+		Right:  right,
+		Bottom: bottom,
+	}
+}
+
 // Box represents the main 4 dimensions of a box.
 type Box struct {
 	Top    int
 	Left   int
 	Right  int
 	Bottom int
+	IsSet  bool
 }
 
 // IsZero returns if the box is set or not.
 func (b Box) IsZero() bool {
+	if b.IsSet {
+		return false
+	}
 	return b.Top == 0 && b.Left == 0 && b.Right == 0 && b.Bottom == 0
 }
 
@@ -25,7 +45,7 @@ func (b Box) String() string {
 
 // GetTop returns a coalesced value with a default.
 func (b Box) GetTop(defaults ...int) int {
-	if b.Top == 0 {
+	if !b.IsSet && b.Top == 0 {
 		if len(defaults) > 0 {
 			return defaults[0]
 		}
@@ -36,7 +56,7 @@ func (b Box) GetTop(defaults ...int) int {
 
 // GetLeft returns a coalesced value with a default.
 func (b Box) GetLeft(defaults ...int) int {
-	if b.Left == 0 {
+	if !b.IsSet && b.Left == 0 {
 		if len(defaults) > 0 {
 			return defaults[0]
 		}
@@ -47,7 +67,7 @@ func (b Box) GetLeft(defaults ...int) int {
 
 // GetRight returns a coalesced value with a default.
 func (b Box) GetRight(defaults ...int) int {
-	if b.Right == 0 {
+	if !b.IsSet && b.Right == 0 {
 		if len(defaults) > 0 {
 			return defaults[0]
 		}
@@ -58,7 +78,7 @@ func (b Box) GetRight(defaults ...int) int {
 
 // GetBottom returns a coalesced value with a default.
 func (b Box) GetBottom(defaults ...int) int {
-	if b.Bottom == 0 {
+	if !b.IsSet && b.Bottom == 0 {
 		if len(defaults) > 0 {
 			return defaults[0]
 		}
@@ -91,6 +111,7 @@ func (b Box) Aspect() float64 {
 // Clone returns a new copy of the box.
 func (b Box) Clone() Box {
 	return Box{
+		IsSet:  b.IsSet,
 		Top:    b.Top,
 		Left:   b.Left,
 		Right:  b.Right,

box_test.go

@@ -109,9 +109,9 @@ func TestBoxConstrain(t *testing.T) {
 func TestBoxOuterConstrain(t *testing.T) {
 	assert := assert.New(t)
 
-	box := Box{0, 0, 100, 100}
+	box := NewBox(0, 0, 100, 100)
-	canvas := Box{5, 5, 95, 95}
+	canvas := NewBox(5, 5, 95, 95)
-	taller := Box{-10, 5, 50, 50}
+	taller := NewBox(-10, 5, 50, 50)
 
 	c := canvas.OuterConstrain(box, taller)
 	assert.Equal(15, c.Top, c.String())
@@ -119,7 +119,7 @@ func TestBoxOuterConstrain(t *testing.T) {
 	assert.Equal(95, c.Right, c.String())
 	assert.Equal(95, c.Bottom, c.String())
 
-	wider := Box{5, 5, 110, 50}
+	wider := NewBox(5, 5, 110, 50)
 	d := canvas.OuterConstrain(box, wider)
 	assert.Equal(5, d.Top, d.String())
 	assert.Equal(5, d.Left, d.String())

chart.go

@@ -141,8 +141,10 @@ func (c Chart) Render(rp RendererProvider, w io.Writer) error {
 
 func (c Chart) checkHasVisibleSeries() error {
 	hasVisibleSeries := false
+	var style Style
 	for _, s := range c.Series {
-		hasVisibleSeries = hasVisibleSeries || (s.GetStyle().IsZero() || s.GetStyle().Show)
+		style = s.GetStyle()
+		hasVisibleSeries = hasVisibleSeries || (style.IsZero() || style.Show)
 	}
 	if !hasVisibleSeries {
 		return fmt.Errorf("must have (1) visible series; make sure if you set a style, you set .Show = true")
@@ -511,6 +513,7 @@ func (c Chart) styleDefaultsCanvas() Style {
 func (c Chart) styleDefaultsSeries(seriesIndex int) Style {
 	strokeColor := GetDefaultColor(seriesIndex)
 	return Style{
+		DotColor:    strokeColor,
 		StrokeColor: strokeColor,
 		StrokeWidth: DefaultSeriesLineWidth,
 		Font:        c.GetFont(),

chart_test.go

@@ -2,6 +2,8 @@ package chart
 
 import (
 	"bytes"
+	"image"
+	"image/png"
 	"math"
 	"testing"
 	"time"
@@ -483,3 +485,91 @@ func TestChartCheckRangesWithRanges(t *testing.T) {
 	xr, yr, yra := c.getRanges()
 	assert.Nil(c.checkRanges(xr, yr, yra))
 }
+
+func at(i image.Image, x, y int) drawing.Color {
+	return drawing.ColorFromAlphaMixedRGBA(i.At(x, y).RGBA())
+}
+
+func TestChartE2ELine(t *testing.T) {
+	assert := assert.New(t)
+
+	c := Chart{
+		Height: 50,
+		Width:  50,
+		Canvas: Style{
+			Padding: Box{IsSet: true},
+		},
+		Background: Style{
+			Padding: Box{IsSet: true},
+		},
+		Series: []Series{
+			ContinuousSeries{
+				XValues: Sequence.Float64(0, 4, 1),
+				YValues: Sequence.Float64(0, 4, 1),
+			},
+		},
+	}
+
+	var buffer = &bytes.Buffer{}
+	err := c.Render(PNG, buffer)
+	assert.Nil(err)
+
+	// do color tests ...
+
+	i, err := png.Decode(buffer)
+	assert.Nil(err)
+
+	// test the bottom and top of the line
+	assert.Equal(drawing.ColorWhite, at(i, 0, 0))
+	assert.Equal(drawing.ColorWhite, at(i, 49, 49))
+
+	// test a line mid point
+	defaultSeriesColor := GetDefaultColor(0)
+	assert.Equal(defaultSeriesColor, at(i, 0, 49))
+	assert.Equal(defaultSeriesColor, at(i, 49, 0))
+	assert.Equal(drawing.ColorFromHex("bddbf6"), at(i, 24, 24))
+}
+
+func TestChartE2ELineWithFill(t *testing.T) {
+	assert := assert.New(t)
+
+	c := Chart{
+		Height: 50,
+		Width:  50,
+		Canvas: Style{
+			Padding: Box{IsSet: true},
+		},
+		Background: Style{
+			Padding: Box{IsSet: true},
+		},
+		Series: []Series{
+			ContinuousSeries{
+				Style: Style{
+					Show:        true,
+					StrokeColor: drawing.ColorBlue,
+					FillColor:   drawing.ColorRed,
+				},
+				XValues: Sequence.Float64(0, 4, 1),
+				YValues: Sequence.Float64(0, 4, 1),
+			},
+		},
+	}
+
+	var buffer = &bytes.Buffer{}
+	err := c.Render(PNG, buffer)
+	assert.Nil(err)
+
+	// do color tests ...
+
+	i, err := png.Decode(buffer)
+	assert.Nil(err)
+
+	// test the bottom and top of the line
+	assert.Equal(drawing.ColorWhite, at(i, 0, 0))
+	assert.Equal(drawing.ColorRed, at(i, 49, 49))
+
+	// test a line mid point
+	defaultSeriesColor := drawing.ColorBlue
+	assert.Equal(defaultSeriesColor, at(i, 0, 49))
+	assert.Equal(defaultSeriesColor, at(i, 49, 0))
+}

defaults.go

@@ -14,6 +14,8 @@ const (
 	DefaultChartWidth = 1024
 	// DefaultStrokeWidth is the default chart stroke width.
 	DefaultStrokeWidth = 0.0
+	// DefaultDotWidth is the default chart dot width.
+	DefaultDotWidth = 0.0
 	// DefaultSeriesLineWidth is the default line width.
 	DefaultSeriesLineWidth = 1.0
 	// DefaultAxisLineWidth is the line width of the axis lines.

draw.go

@@ -27,9 +27,8 @@ func (d draw) LineSeries(r Renderer, canvasBox Box, xrange, yrange Range, style
 	var vx, vy float64
 	var x, y int
 
-	fill := style.GetFillColor()
+	if style.ShouldDrawStroke() && style.ShouldDrawFill() {
-	if !fill.IsZero() {
+		style.GetFillOptions().WriteDrawingOptionsToRenderer(r)
-		style.GetFillOptions().WriteToRenderer(r)
 		r.MoveTo(x0, y0)
 		for i := 1; i < vs.Len(); i++ {
 			vx, vy = vs.GetValue(i)
@@ -43,7 +42,8 @@ func (d draw) LineSeries(r Renderer, canvasBox Box, xrange, yrange Range, style
 		r.Fill()
 	}
 
-	style.GetStrokeOptions().WriteToRenderer(r)
+	if style.ShouldDrawStroke() {
+		style.GetStrokeOptions().WriteDrawingOptionsToRenderer(r)
 
 		r.MoveTo(x0, y0)
 		for i := 1; i < vs.Len(); i++ {
@@ -55,6 +55,22 @@ func (d draw) LineSeries(r Renderer, canvasBox Box, xrange, yrange Range, style
 		r.Stroke()
 	}
 
+	if style.ShouldDrawDot() {
+		dotWidth := style.GetDotWidth()
+
+		style.GetDotOptions().WriteDrawingOptionsToRenderer(r)
+
+		for i := 0; i < vs.Len(); i++ {
+			vx, vy = vs.GetValue(i)
+			x = cl + xrange.Translate(vx)
+			y = cb - yrange.Translate(vy)
+
+			r.Circle(dotWidth, x, y)
+			r.FillStroke()
+		}
+	}
+}
+
 // BoundedSeries draws a series that implements BoundedValueProvider.
 func (d draw) BoundedSeries(r Renderer, canvasBox Box, xrange, yrange Range, style Style, bbs BoundedValueProvider, drawOffsetIndexes ...int) {
 	drawOffsetIndex := 0

drawing/color.go

@@ -46,12 +46,20 @@ func ColorFromHex(hex string) Color {
 	return c
 }
 
+// ColorFromAlphaMixedRGBA returns the system alpha mixed rgba values.
+func ColorFromAlphaMixedRGBA(r, g, b, a uint32) Color {
+	fa := float64(a) / 255.0
+	var c Color
+	c.R = uint8(float64(r) / fa)
+	c.G = uint8(float64(g) / fa)
+	c.B = uint8(float64(b) / fa)
+	c.A = uint8(a | (a >> 8))
+	return c
+}
+
 // Color is our internal color type because color.Color is bullshit.
 type Color struct {
-	R uint8
+	R, G, B, A uint8
-	G uint8
-	B uint8
-	A uint8
 }
 
 // RGBA returns the color as a pre-alpha mixed color set.
@@ -88,6 +96,24 @@ func (c Color) WithAlpha(a uint8) Color {
 	}
 }
 
+// Equals returns true if the color equals another.
+func (c Color) Equals(other Color) bool {
+	return c.R == other.R &&
+		c.G == other.G &&
+		c.B == other.B &&
+		c.A == other.A
+}
+
+// AverageWith averages two colors.
+func (c Color) AverageWith(other Color) Color {
+	return Color{
+		R: (c.R + other.R) >> 1,
+		G: (c.G + other.G) >> 1,
+		B: (c.B + other.B) >> 1,
+		A: c.A,
+	}
+}
+
 // String returns a css string representation of the color.
 func (c Color) String() string {
 	fa := float64(c.A) / float64(255)

drawing/color_test.go

@@ -3,6 +3,8 @@ package drawing
 import (
 	"testing"
 
+	"image/color"
+
 	"github.com/blendlabs/go-assert"
 )
 
@@ -39,3 +41,13 @@ func TestColorFromHex(t *testing.T) {
 	shortBlue := ColorFromHex("00F")
 	assert.Equal(ColorBlue, shortBlue)
 }
+
+func TestColorFromAlphaMixedRGBA(t *testing.T) {
+	assert := assert.New(t)
+
+	black := ColorFromAlphaMixedRGBA(color.Black.RGBA())
+	assert.True(black.Equals(ColorBlack), black.String())
+
+	white := ColorFromAlphaMixedRGBA(color.White.RGBA())
+	assert.True(white.Equals(ColorWhite), white.String())
+}

drawing/curve.go

@@ -1,8 +1,6 @@
 package drawing
 
-import (
+import "math"
-	"math"
-)
 
 const (
 	// CurveRecursionLimit represents the maximum recursion that is really necessary to subsivide a curve into straight lines
@@ -98,31 +96,60 @@ func SubdivideQuad(c, c1, c2 []float64) {
 	return
 }
 
+func traceWindowIndices(i int) (startAt, endAt int) {
+	startAt = i * 6
+	endAt = startAt + 6
+	return
+}
+
+func traceCalcDeltas(c []float64) (dx, dy, d float64) {
+	dx = c[4] - c[0]
+	dy = c[5] - c[1]
+	d = math.Abs(((c[2]-c[4])*dy - (c[3]-c[5])*dx))
+	return
+}
+
+func traceIsFlat(dx, dy, d, threshold float64) bool {
+	return (d * d) < threshold*(dx*dx+dy*dy)
+}
+
+func traceGetWindow(curves []float64, i int) []float64 {
+	startAt, endAt := traceWindowIndices(i)
+	return curves[startAt:endAt]
+}
+
 // TraceQuad generate lines subdividing the curve using a Liner
 // flattening_threshold helps determines the flattening expectation of the curve
 func TraceQuad(t Liner, quad []float64, flatteningThreshold float64) {
+	const curveLen = CurveRecursionLimit * 6
+	const curveEndIndex = curveLen - 1
+	const lastIteration = CurveRecursionLimit - 1
+
 	// Allocates curves stack
-	var curves [CurveRecursionLimit * 6]float64
+	curves := make([]float64, curveLen)
+
+	// copy 6 elements from the quad path to the stack
 	copy(curves[0:6], quad[0:6])
-	i := 0
+
-	// current curve
+	var i int
 	var c []float64
 	var dx, dy, d float64
 
 	for i >= 0 {
-		c = curves[i*6:]
+		c = traceGetWindow(curves, i)
-		dx = c[4] - c[0]
+		dx, dy, d = traceCalcDeltas(c)
-		dy = c[5] - c[1]
 
-		d = math.Abs(((c[2]-c[4])*dy - (c[3]-c[5])*dx))
+		// bail early if the distance is 0
+		if d == 0 {
+			return
+		}
 
 		// if it's flat then trace a line
-		if (d*d) < flatteningThreshold*(dx*dx+dy*dy) || i == len(curves)-1 {
+		if traceIsFlat(dx, dy, d, flatteningThreshold) || i == lastIteration {
 			t.LineTo(c[4], c[5])
 			i--
 		} else {
-			// second half of bezier go lower onto the stack
+			SubdivideQuad(c, traceGetWindow(curves, i+1), traceGetWindow(curves, i))
-			SubdivideQuad(c, curves[(i+1)*6:], curves[i*6:])
 			i++
 		}
 	}

drawing/curve_test.go

@@ -0,0 +1,35 @@
+package drawing
+
+import (
+	"testing"
+
+	assert "github.com/blendlabs/go-assert"
+)
+
+type point struct {
+	X, Y float64
+}
+
+type mockLine struct {
+	inner []point
+}
+
+func (ml *mockLine) LineTo(x, y float64) {
+	ml.inner = append(ml.inner, point{x, y})
+}
+
+func (ml mockLine) Len() int {
+	return len(ml.inner)
+}
+
+func TestTraceQuad(t *testing.T) {
+	assert := assert.New(t)
+
+	// Quad
+	// x1, y1, cpx1, cpy2, x2, y2 float64
+	// do the 9->12 circle segment
+	quad := []float64{10, 20, 20, 20, 20, 10}
+	liner := &mockLine{}
+	TraceQuad(liner, quad, 0.5)
+	assert.NotZero(liner.Len())
+}

drawing/flattener.go

@@ -23,10 +23,10 @@ type Flattener interface {
 // Flatten convert curves into straight segments keeping join segments info
 func Flatten(path *Path, flattener Flattener, scale float64) {
 	// First Point
-	var startX, startY float64 = 0, 0
+	var startX, startY float64
 	// Current Point
-	var x, y float64 = 0, 0
+	var x, y float64
-	i := 0
+	var i int
 	for _, cmp := range path.Components {
 		switch cmp {
 		case MoveToComponent:
@@ -43,6 +43,7 @@ func Flatten(path *Path, flattener Flattener, scale float64) {
 			flattener.LineJoin()
 			i += 2
 		case QuadCurveToComponent:
+			// we include the previous point for the start of the curve
 			TraceQuad(flattener, path.Points[i-2:], 0.5)
 			x, y = path.Points[i+2], path.Points[i+3]
 			flattener.LineTo(x, y)

linear_regression_series.go

@@ -49,7 +49,9 @@ func (lrs LinearRegressionSeries) GetWindow() int {
 
 // GetEndIndex returns the effective window end.
 func (lrs LinearRegressionSeries) GetEndIndex() int {
-	return Math.MinInt(lrs.GetOffset()+(lrs.Len()), (lrs.InnerSeries.Len() - 1))
+	offset := lrs.GetOffset() + lrs.Len()
+	innerSeriesLastIndex := lrs.InnerSeries.Len() - 1
+	return Math.MinInt(offset, innerSeriesLastIndex)
 }
 
 // GetOffset returns the data offset.
@@ -62,7 +64,7 @@ func (lrs LinearRegressionSeries) GetOffset() int {
 
 // GetValue gets a value at a given index.
 func (lrs *LinearRegressionSeries) GetValue(index int) (x, y float64) {
-	if lrs.InnerSeries == nil {
+	if lrs.InnerSeries == nil || lrs.InnerSeries.Len() == 0 {
 		return
 	}
 	if lrs.m == 0 && lrs.b == 0 {
@@ -78,7 +80,7 @@ func (lrs *LinearRegressionSeries) GetValue(index int) (x, y float64) {
 // GetLastValue computes the last moving average value but walking back window size samples,
 // and recomputing the last moving average chunk.
 func (lrs *LinearRegressionSeries) GetLastValue() (x, y float64) {
-	if lrs.InnerSeries == nil {
+	if lrs.InnerSeries == nil || lrs.InnerSeries.Len() == 0 {
 		return
 	}
 	if lrs.m == 0 && lrs.b == 0 {

macd_series.go

@@ -27,6 +27,24 @@ type MACDSeries struct {
 	macdl  *MACDLineSeries
 }
 
+// Validate validates the series.
+func (macd MACDSeries) Validate() error {
+	var err error
+	if macd.signal != nil {
+		err = macd.signal.Validate()
+	}
+	if err != nil {
+		return err
+	}
+	if macd.macdl != nil {
+		err = macd.macdl.Validate()
+	}
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
 // GetPeriods returns the primary and secondary periods.
 func (macd MACDSeries) GetPeriods() (w1, w2, sig int) {
 	if macd.PrimaryPeriod == 0 {
@@ -121,6 +139,14 @@ type MACDSignalSeries struct {
 	signal *EMASeries
 }
 
+// Validate validates the series.
+func (macds MACDSignalSeries) Validate() error {
+	if macds.signal != nil {
+		return macds.signal.Validate()
+	}
+	return nil
+}
+
 // GetPeriods returns the primary and secondary periods.
 func (macds MACDSignalSeries) GetPeriods() (w1, w2, sig int) {
 	if macds.PrimaryPeriod == 0 {
@@ -214,6 +240,27 @@ type MACDLineSeries struct {
 	Sigma float64
 }
 
+// Validate validates the series.
+func (macdl MACDLineSeries) Validate() error {
+	var err error
+	if macdl.ema1 != nil {
+		err = macdl.ema1.Validate()
+	}
+	if err != nil {
+		return err
+	}
+	if macdl.ema2 != nil {
+		err = macdl.ema2.Validate()
+	}
+	if err != nil {
+		return err
+	}
+	if macdl.InnerSeries == nil {
+		return fmt.Errorf("MACDLineSeries: must provide an inner series")
+	}
+	return nil
+}
+
 // GetName returns the name of the time series.
 func (macdl MACDLineSeries) GetName() string {
 	return macdl.Name
@@ -289,11 +336,3 @@ func (macdl *MACDLineSeries) Render(r Renderer, canvasBox Box, xrange, yrange Ra
 	style := macdl.Style.InheritFrom(defaults)
 	Draw.LineSeries(r, canvasBox, xrange, yrange, style, macdl)
 }
-
-// Validate validates the series.
-func (macdl *MACDLineSeries) Validate() error {
-	if macdl.InnerSeries == nil {
-		return fmt.Errorf("macd line series requires InnerSeries to be set")
-	}
-	return nil
-}

raster_renderer.go

@@ -116,17 +116,16 @@ func (rr *rasterRenderer) FillStroke() {
 	rr.gc.FillStroke()
 }
 
-// Circle implements the interface method.
+// Circle fully draws a circle at a given point but does not apply the fill or stroke.
 func (rr *rasterRenderer) Circle(radius float64, x, y int) {
 	xf := float64(x)
 	yf := float64(y)
+
 	rr.gc.MoveTo(xf-radius, yf)                            //9
-	rr.gc.QuadCurveTo(xf, yf, xf, yf-radius) //12
+	rr.gc.QuadCurveTo(xf-radius, yf-radius, xf, yf-radius) //12
-	rr.gc.QuadCurveTo(xf, yf, xf+radius, yf) //3
+	rr.gc.QuadCurveTo(xf+radius, yf-radius, xf+radius, yf) //3
-	rr.gc.QuadCurveTo(xf, yf, xf, yf+radius) //6
+	rr.gc.QuadCurveTo(xf+radius, yf+radius, xf, yf+radius) //6
-	rr.gc.QuadCurveTo(xf, yf, xf-radius, yf) //9
+	rr.gc.QuadCurveTo(xf-radius, yf+radius, xf-radius, yf) //9
-	rr.gc.Close()
-	rr.gc.FillStroke()
 }
 
 // SetFont implements the interface method.

sequence.go

@@ -8,10 +8,14 @@ import (
 var (
 	// Sequence contains some sequence utilities.
 	// These utilities can be useful for generating test data.
-	Sequence = &sequence{}
+	Sequence = &sequence{
+		rnd: rand.New(rand.NewSource(time.Now().Unix())),
+	}
 )
 
-type sequence struct{}
+type sequence struct {
+	rnd *rand.Rand
+}
 
 // Float64 produces an array of floats from [start,end] by optional steps.
 func (s sequence) Float64(start, end float64, steps ...float64) []float64 {
@@ -35,11 +39,10 @@ func (s sequence) Float64(start, end float64, steps ...float64) []float64 {
 
 // Random generates a fixed length sequence of random values between (0, scale).
 func (s sequence) Random(samples int, scale float64) []float64 {
-	rnd := rand.New(rand.NewSource(time.Now().Unix()))
 	values := make([]float64, samples)
 
 	for x := 0; x < samples; x++ {
-		values[x] = rnd.Float64() * scale
+		values[x] = s.rnd.Float64() * scale
 	}
 
 	return values
@@ -47,11 +50,10 @@ func (s sequence) Random(samples int, scale float64) []float64 {
 
 // Random generates a fixed length sequence of random values with a given average, above and below that average by (-scale, scale)
 func (s sequence) RandomWithAverage(samples int, average, scale float64) []float64 {
-	rnd := rand.New(rand.NewSource(time.Now().Unix()))
 	values := make([]float64, samples)
 
 	for x := 0; x < samples; x++ {
-		jitter := scale - (rnd.Float64() * (2 * scale))
+		jitter := scale - (s.rnd.Float64() * (2 * scale))
 		values[x] = average + jitter
 	}
 

sma_series.go

@@ -50,7 +50,7 @@ func (sma SMASeries) GetPeriod(defaults ...int) int {
 
 // GetValue gets a value at a given index.
 func (sma SMASeries) GetValue(index int) (x, y float64) {
-	if sma.InnerSeries == nil {
+	if sma.InnerSeries == nil || sma.InnerSeries.Len() == 0 {
 		return
 	}
 	px, _ := sma.InnerSeries.GetValue(index)
@@ -62,7 +62,7 @@ func (sma SMASeries) GetValue(index int) (x, y float64) {
 // GetLastValue computes the last moving average value but walking back window size samples,
 // and recomputing the last moving average chunk.
 func (sma SMASeries) GetLastValue() (x, y float64) {
-	if sma.InnerSeries == nil {
+	if sma.InnerSeries == nil || sma.InnerSeries.Len() == 0 {
 		return
 	}
 	seriesLen := sma.InnerSeries.Len()

style.go

@@ -8,6 +8,12 @@ import (
 	"github.com/wcharczuk/go-chart/drawing"
 )
 
+const (
+	// Disabled indicates if the value should be interpreted as set intentionally to zero.
+	// this is because golang optionals aren't here yet.
+	Disabled = -1
+)
+
 // StyleShow is a prebuilt style with the `Show` property set to true.
 func StyleShow() Style {
 	return Style{
@@ -24,7 +30,11 @@ type Style struct {
 	StrokeColor     drawing.Color
 	StrokeDashArray []float64
 
+	DotColor drawing.Color
+	DotWidth float64
+
 	FillColor drawing.Color
+
 	FontSize  float64
 	FontColor drawing.Color
 	Font      *truetype.Font
@@ -38,7 +48,14 @@ type Style struct {
 
 // IsZero returns if the object is set or not.
 func (s Style) IsZero() bool {
-	return s.StrokeColor.IsZero() && s.FillColor.IsZero() && s.StrokeWidth == 0 && s.FontColor.IsZero() && s.FontSize == 0 && s.Font == nil
+	return s.StrokeColor.IsZero() &&
+		s.StrokeWidth == 0 &&
+		s.DotColor.IsZero() &&
+		s.DotWidth == 0 &&
+		s.FillColor.IsZero() &&
+		s.FontColor.IsZero() &&
+		s.FontSize == 0 &&
+		s.Font == nil
 }
 
 // String returns a text representation of the style.
@@ -83,6 +100,18 @@ func (s Style) String() string {
 		output = append(output, "\"stroke_dash_array\": null")
 	}
 
+	if s.DotWidth >= 0 {
+		output = append(output, fmt.Sprintf("\"dot_width\": %0.2f", s.DotWidth))
+	} else {
+		output = append(output, "\"dot_width\": null")
+	}
+
+	if !s.DotColor.IsZero() {
+		output = append(output, fmt.Sprintf("\"dot_color\": %s", s.DotColor.String()))
+	} else {
+		output = append(output, "\"dot_color\": null")
+	}
+
 	if !s.FillColor.IsZero() {
 		output = append(output, fmt.Sprintf("\"fill_color\": %s", s.FillColor.String()))
 	} else {
@@ -132,6 +161,17 @@ func (s Style) GetFillColor(defaults ...drawing.Color) drawing.Color {
 	return s.FillColor
 }
 
+// GetDotColor returns the stroke color.
+func (s Style) GetDotColor(defaults ...drawing.Color) drawing.Color {
+	if s.DotColor.IsZero() {
+		if len(defaults) > 0 {
+			return defaults[0]
+		}
+		return drawing.ColorTransparent
+	}
+	return s.DotColor
+}
+
 // GetStrokeWidth returns the stroke width.
 func (s Style) GetStrokeWidth(defaults ...float64) float64 {
 	if s.StrokeWidth == 0 {
@@ -143,6 +183,17 @@ func (s Style) GetStrokeWidth(defaults ...float64) float64 {
 	return s.StrokeWidth
 }
 
+// GetDotWidth returns the dot width for scatter plots.
+func (s Style) GetDotWidth(defaults ...float64) float64 {
+	if s.DotWidth == 0 {
+		if len(defaults) > 0 {
+			return defaults[0]
+		}
+		return DefaultDotWidth
+	}
+	return s.DotWidth
+}
+
 // GetStrokeDashArray returns the stroke dash array.
 func (s Style) GetStrokeDashArray(defaults ...[]float64) []float64 {
 	if len(s.StrokeDashArray) == 0 {
@@ -288,6 +339,10 @@ func (s Style) InheritFrom(defaults Style) (final Style) {
 	final.StrokeColor = s.GetStrokeColor(defaults.StrokeColor)
 	final.StrokeWidth = s.GetStrokeWidth(defaults.StrokeWidth)
 	final.StrokeDashArray = s.GetStrokeDashArray(defaults.StrokeDashArray)
+
+	final.DotColor = s.GetDotColor(defaults.DotColor)
+	final.DotWidth = s.GetDotWidth(defaults.DotWidth)
+
 	final.FillColor = s.GetFillColor(defaults.FillColor)
 	final.FontColor = s.GetFontColor(defaults.FontColor)
 	final.FontSize = s.GetFontSize(defaults.FontSize)
@@ -298,6 +353,7 @@ func (s Style) InheritFrom(defaults Style) (final Style) {
 	final.TextWrap = s.GetTextWrap(defaults.TextWrap)
 	final.TextLineSpacing = s.GetTextLineSpacing(defaults.TextLineSpacing)
 	final.TextRotationDegrees = s.GetTextRotationDegrees(defaults.TextRotationDegrees)
+
 	return
 }
 
@@ -317,6 +373,16 @@ func (s Style) GetFillOptions() Style {
 	}
 }
 
+// GetDotOptions returns the dot components.
+func (s Style) GetDotOptions() Style {
+	return Style{
+		StrokeDashArray: nil,
+		FillColor:       s.DotColor,
+		StrokeColor:     s.DotColor,
+		StrokeWidth:     1.0,
+	}
+}
+
 // GetFillAndStrokeOptions returns the fill and stroke components.
 func (s Style) GetFillAndStrokeOptions() Style {
 	return Style{
@@ -340,3 +406,18 @@ func (s Style) GetTextOptions() Style {
 		TextRotationDegrees: s.TextRotationDegrees,
 	}
 }
+
+// ShouldDrawStroke tells drawing functions if they should draw the stroke.
+func (s Style) ShouldDrawStroke() bool {
+	return !s.StrokeColor.IsZero() && s.StrokeWidth > 0
+}
+
+// ShouldDrawDot tells drawing functions if they should draw the dot.
+func (s Style) ShouldDrawDot() bool {
+	return !s.DotColor.IsZero() && s.DotWidth > 0
+}
+
+// ShouldDrawFill tells drawing functions if they should draw the stroke.
+func (s Style) ShouldDrawFill() bool {
+	return !s.FillColor.IsZero()
+}

xaxis_test.go

@@ -61,7 +61,7 @@ func TestXAxisMeasure(t *testing.T) {
 	assert.Nil(err)
 	ticks := []Tick{{Value: 1.0, Label: "1.0"}, {Value: 2.0, Label: "2.0"}, {Value: 3.0, Label: "3.0"}}
 	xa := XAxis{}
-	xab := xa.Measure(r, Box{0, 0, 100, 100}, &ContinuousRange{Min: 1.0, Max: 3.0, Domain: 100}, style, ticks)
+	xab := xa.Measure(r, NewBox(0, 0, 100, 100), &ContinuousRange{Min: 1.0, Max: 3.0, Domain: 100}, style, ticks)
 	assert.Equal(122, xab.Width())
 	assert.Equal(21, xab.Height())
 }

yaxis_test.go

@@ -61,7 +61,7 @@ func TestYAxisMeasure(t *testing.T) {
 	assert.Nil(err)
 	ticks := []Tick{{Value: 1.0, Label: "1.0"}, {Value: 2.0, Label: "2.0"}, {Value: 3.0, Label: "3.0"}}
 	ya := YAxis{}
-	yab := ya.Measure(r, Box{0, 0, 100, 100}, &ContinuousRange{Min: 1.0, Max: 3.0, Domain: 100}, style, ticks)
+	yab := ya.Measure(r, NewBox(0, 0, 100, 100), &ContinuousRange{Min: 1.0, Max: 3.0, Domain: 100}, style, ticks)
 	assert.Equal(32, yab.Width())
 	assert.Equal(110, yab.Height())
 }
@@ -79,7 +79,7 @@ func TestYAxisSecondaryMeasure(t *testing.T) {
 	assert.Nil(err)
 	ticks := []Tick{{Value: 1.0, Label: "1.0"}, {Value: 2.0, Label: "2.0"}, {Value: 3.0, Label: "3.0"}}
 	ya := YAxis{AxisType: YAxisSecondary}
-	yab := ya.Measure(r, Box{0, 0, 100, 100}, &ContinuousRange{Min: 1.0, Max: 3.0, Domain: 100}, style, ticks)
+	yab := ya.Measure(r, NewBox(0, 0, 100, 100), &ContinuousRange{Min: 1.0, Max: 3.0, Domain: 100}, style, ticks)
 	assert.Equal(32, yab.Width())
 	assert.Equal(110, yab.Height())
 }