adding a helper method, DrawBoundedSeries to help w/ bounded series drawing.

bollinger_band_series.go

@@ -110,54 +110,14 @@ func (bbs *BollingerBandsSeries) GetLastBoundedValue() (x, y1, y2 float64) {
 }
 
 // Render renders the series.
-func (bbs BollingerBandsSeries) Render(r Renderer, canvasBox Box, xrange, yrange Range, defaults Style) {
+func (bbs *BollingerBandsSeries) Render(r Renderer, canvasBox Box, xrange, yrange Range, defaults Style) {
-	s := bbs.Style.WithDefaultsFrom(defaults)
+	s := bbs.Style.WithDefaultsFrom(defaults.WithDefaultsFrom(Style{
+		StrokeWidth: 1.0,
+		StrokeColor: DefaultAxisColor.WithAlpha(64),
+		FillColor:   DefaultAxisColor.WithAlpha(32),
+	}))
 
-	r.SetStrokeColor(s.GetStrokeColor())
+	DrawBoundedSeries(r, canvasBox, xrange, yrange, s, bbs, bbs.GetWindowSize())
-	r.SetStrokeDashArray(s.GetStrokeDashArray())
-	r.SetStrokeWidth(s.GetStrokeWidth())
-	r.SetFillColor(s.GetFillColor())
-
-	cb := canvasBox.Bottom
-	cl := canvasBox.Left
-
-	v0x, v0y1, v0y2 := bbs.GetBoundedValue(0)
-	x0 := cl + xrange.Translate(v0x)
-	y0 := cb - yrange.Translate(v0y1)
-
-	var vx, vy1, vy2 float64
-	var x, y int
-
-	xvalues := make([]float64, bbs.Len())
-	xvalues[0] = v0x
-	y2values := make([]float64, bbs.Len())
-	y2values[0] = v0y2
-
-	r.MoveTo(x0, y0)
-	for i := 1; i < bbs.Len(); i++ {
-		vx, vy1, vy2 = bbs.GetBoundedValue(i)
-
-		xvalues[i] = vx
-		y2values[i] = vy2
-
-		x = cl + xrange.Translate(vx)
-		y = cb - yrange.Translate(vy1)
-		if i > bbs.GetWindowSize() {
-			r.LineTo(x, y)
-		} else {
-			r.MoveTo(x, y)
-		}
-	}
-	y = cb - yrange.Translate(vy2)
-	r.LineTo(x, y)
-	for i := bbs.Len() - 1; i >= bbs.GetWindowSize(); i-- {
-		vx, vy2 = xvalues[i], y2values[i]
-		x = cl + xrange.Translate(vx)
-		y = cb - yrange.Translate(vy2)
-		r.LineTo(x, y)
-	}
-	r.Close()
-	r.FillStroke()
 }
 
 func (bbs BollingerBandsSeries) getAverage(valueBuffer *RingBuffer) float64 {

drawing_helpers.go

@@ -48,6 +48,60 @@ func DrawLineSeries(r Renderer, canvasBox Box, xrange, yrange Range, s Style, vs
 	r.Stroke()
 }
 
+// DrawBoundedSeries draws a series that implements BoundedValueProvider.
+func DrawBoundedSeries(r Renderer, canvasBox Box, xrange, yrange Range, s Style, bbs BoundedValueProvider, drawOffsetIndexes ...int) {
+	drawOffsetIndex := 0
+	if len(drawOffsetIndexes) > 0 {
+		drawOffsetIndex = drawOffsetIndexes[0]
+	}
+
+	r.SetStrokeColor(s.GetStrokeColor())
+	r.SetStrokeDashArray(s.GetStrokeDashArray())
+	r.SetStrokeWidth(s.GetStrokeWidth())
+	r.SetFillColor(s.GetFillColor())
+
+	cb := canvasBox.Bottom
+	cl := canvasBox.Left
+
+	v0x, v0y1, v0y2 := bbs.GetBoundedValue(0)
+	x0 := cl + xrange.Translate(v0x)
+	y0 := cb - yrange.Translate(v0y1)
+
+	var vx, vy1, vy2 float64
+	var x, y int
+
+	xvalues := make([]float64, bbs.Len())
+	xvalues[0] = v0x
+	y2values := make([]float64, bbs.Len())
+	y2values[0] = v0y2
+
+	r.MoveTo(x0, y0)
+	for i := 1; i < bbs.Len(); i++ {
+		vx, vy1, vy2 = bbs.GetBoundedValue(i)
+
+		xvalues[i] = vx
+		y2values[i] = vy2
+
+		x = cl + xrange.Translate(vx)
+		y = cb - yrange.Translate(vy1)
+		if i > drawOffsetIndex {
+			r.LineTo(x, y)
+		} else {
+			r.MoveTo(x, y)
+		}
+	}
+	y = cb - yrange.Translate(vy2)
+	r.LineTo(x, y)
+	for i := bbs.Len() - 1; i >= drawOffsetIndex; i-- {
+		vx, vy2 = xvalues[i], y2values[i]
+		x = cl + xrange.Translate(vx)
+		y = cb - yrange.Translate(vy2)
+		r.LineTo(x, y)
+	}
+	r.Close()
+	r.FillStroke()
+}
+
 // MeasureAnnotation measures how big an annotation would be.
 func MeasureAnnotation(r Renderer, canvasBox Box, s Style, lx, ly int, label string) Box {
 	r.SetFillColor(s.GetFillColor(DefaultAnnotationFillColor))