works more or less

_examples/scatter/main.go

@@ -0,0 +1,39 @@
+package main
+
+import (
+	"log"
+	"net/http"
+
+	"github.com/wcharczuk/go-chart"
+	"github.com/wcharczuk/go-chart/drawing"
+)
+
+func drawChart(res http.ResponseWriter, req *http.Request) {
+	println("drawing scatter plot")
+	graph := chart.Chart{
+		Series: []chart.Series{
+			chart.ContinuousSeries{
+				Style: chart.Style{
+					Show:        true,
+					StrokeWidth: chart.Disabled,
+					DotWidth:    3,
+					DotColor:    drawing.ColorRed,
+				},
+				XValues: chart.Sequence.Random(32, 1024),
+				YValues: chart.Sequence.Random(32, 1024),
+			},
+		},
+	}
+
+	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)
+	log.Fatal(http.ListenAndServe(":8080", nil))
+}

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")

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++ {
@@ -52,7 +52,22 @@ func (d draw) LineSeries(r Renderer, canvasBox Box, xrange, yrange Range, style
 			y = cb - yrange.Translate(vy)
 			r.LineTo(x, y)
 		}
-	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.

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)

raster_renderer.go

@@ -1,6 +1,7 @@
 package chart
 
 import (
+	"fmt"
 	"image"
 	"image/png"
 	"io"
@@ -116,17 +117,17 @@ func (rr *rasterRenderer) FillStroke() {
 	rr.gc.FillStroke()
 }
 
-// Circle implements the interface method.
+// Circle fully draws and strokes a circle at a given point.
 func (rr *rasterRenderer) Circle(radius float64, x, y int) {
+	fmt.Printf("RasterRenderer.Circle(%f, %d, %d)\n", radius, x, y)
 	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
 	}
 

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()
+}