feature; solving issue #121

There is now a way to allow gaps in charts due to missing
measurements. A style setting (StrokeMaxSpanGap) determines
whether a gap is stroked or not.

An example is included in examples/custom_styles.

draw.go

@@ -47,12 +47,26 @@ func (d draw) LineSeries(r Renderer, canvasBox Box, xrange, yrange Range, style
 	if style.ShouldDrawStroke() {
 		style.GetStrokeOptions().WriteDrawingOptionsToRenderer(r)
 
+                vxprev := 0.0
+                if vs.Len() > 0 {
+  	                vxprev, _ = vs.GetValues( 1 ) // make sure vxprev starts at the beginning
+	        }
+	        maxspan := style.GetStrokeMaxSpanGap()
 		r.MoveTo(x0, y0)
 		for i := 1; i < vs.Len(); i++ {
 			vx, vy = vs.GetValues(i)
 			x = cl + xrange.Translate(vx)
-			y = cb - yrange.Translate(vy)
+		        y = cb - yrange.Translate(vy)
-			r.LineTo(x, y)
+		        df := vxprev - vx
+		        if df < 0 {
+			  df *= -1 // make it work, regardless of direction ox X-axis
+			}
+                        if df <= maxspan { // span the gap i.e. connect the two points
+  			  r.LineTo(x, y)
+                        } else {           // do not span the gap
+  			  r.MoveTo(x, y)
+                        }
+                        vxprev = vx
 		}
 		r.Stroke()
 	}

examples/custom_styles/main.go

@@ -25,9 +25,10 @@ func main() {
 				Style: chart.Style{
 					StrokeColor: drawing.ColorRed,               // will supercede defaults
 					FillColor:   drawing.ColorRed.WithAlpha(64), // will supercede defaults
+                                        StrokeMaxSpanGap: 2, // do not span gaps more than 2.0 wide
 				},
-				XValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+				XValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0, 8.0, 10.0},
-				YValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+				YValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0, 8.0, 10.0},
 			},
 		},
 	}

style.go

@@ -51,6 +51,7 @@ type Style struct {
 	StrokeWidth     float64
 	StrokeColor     drawing.Color
 	StrokeDashArray []float64
+        StrokeMaxSpanGap float64 // in xvalue unit, nano second for timeseries
 
 	DotColor drawing.Color
 	DotWidth float64
@@ -122,6 +123,12 @@ func (s Style) String() string {
 		output = append(output, "\"stroke_color\": null")
 	}
 
+        if s.StrokeMaxSpanGap >= 0 {
+		output = append(output, fmt.Sprintf("\"stroke_maxspangap\": %.02f", s.StrokeMaxSpanGap))
+	} else {
+		output = append(output, "\"stroke_maxspangap\": null")
+	}
+
 	if len(s.StrokeDashArray) > 0 {
 		var elements []string
 		for _, v := range s.StrokeDashArray {
@@ -194,6 +201,11 @@ func (s Style) GetStrokeColor(defaults ...drawing.Color) drawing.Color {
 	return s.StrokeColor
 }
 
+// GetStrokeMaxSpanGap returns the max span gap, smaller or equal gaps are connected, larger ones are not.
+func (s Style) GetStrokeMaxSpanGap() float64 {
+	return s.StrokeMaxSpanGap
+}
+
 // GetFillColor returns the fill color.
 func (s Style) GetFillColor(defaults ...drawing.Color) drawing.Color {
 	if s.FillColor.IsZero() {
@@ -388,6 +400,7 @@ 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.StrokeMaxSpanGap = s.GetStrokeMaxSpanGap()
 
 	final.DotColor = s.GetDotColor(defaults.DotColor)
 	final.DotWidth = s.GetDotWidth(defaults.DotWidth)
@@ -416,6 +429,7 @@ func (s Style) GetStrokeOptions() Style {
 		StrokeDashArray: s.StrokeDashArray,
 		StrokeColor:     s.StrokeColor,
 		StrokeWidth:     s.StrokeWidth,
+	        StrokeMaxSpanGap:s.StrokeMaxSpanGap,
 	}
 }
 
@@ -443,7 +457,8 @@ func (s Style) GetFillAndStrokeOptions() Style {
 	return Style{
 		ClassName:       s.ClassName,
 		StrokeDashArray: s.StrokeDashArray,
-		FillColor:       s.FillColor,
+	        StrokeMaxSpanGap:s.StrokeMaxSpanGap,
+	        FillColor:       s.FillColor,
 		StrokeColor:     s.StrokeColor,
 		StrokeWidth:     s.StrokeWidth,
 	}