tweaks to range validation.

chart.go

@@ -2,6 +2,7 @@ package chart
 
 import (
 	"errors"
+	"fmt"
 	"io"
 	"math"
 
@@ -69,8 +70,12 @@ func (c Chart) GetHeight() int {
 // Render renders the chart with the given renderer to the given io.Writer.
 func (c Chart) Render(rp RendererProvider, w io.Writer) error {
 	if len(c.Series) == 0 {
-		return errors.New("Please provide at least one series")
+		return errors.New("please provide at least one series")
 	}
+	if visibleSeriesErr := c.checkHasVisibleSeries(); visibleSeriesErr != nil {
+		return visibleSeriesErr
+	}
+
 	c.YAxisSecondary.AxisType = YAxisSecondary
 
 	r, err := rp(c.GetWidth(), c.GetHeight())
@@ -134,6 +139,17 @@ func (c Chart) Render(rp RendererProvider, w io.Writer) error {
 	return r.Save(w)
 }
 
+func (c Chart) checkHasVisibleSeries() error {
+	hasVisibleSeries := false
+	for _, s := range c.Series {
+		hasVisibleSeries = hasVisibleSeries || (s.GetStyle().IsZero() || s.GetStyle().Show)
+	}
+	if !hasVisibleSeries {
+		return fmt.Errorf("must have (1) visible series; make sure if you set a style, you set .Show = true")
+	}
+	return nil
+}
+
 func (c Chart) validateSeries() error {
 	var err error
 	for _, s := range c.Series {
@@ -272,15 +288,29 @@ func (c Chart) getRanges() (xrange, yrange, yrangeAlt Range) {
 }
 
 func (c Chart) checkRanges(xr, yr, yra Range) error {
-	if math.IsInf(xr.GetDelta(), 0) || math.IsNaN(xr.GetDelta()) || xr.GetDelta() == 0 {
-		return errors.New("Invalid (infinite or NaN) x-range delta")
+	xDelta := xr.GetDelta()
+	if math.IsInf(xDelta, 0) {
+		return errors.New("infinite x-range delta")
 	}
-	if math.IsInf(yr.GetDelta(), 0) || math.IsNaN(yr.GetDelta()) || yr.GetDelta() == 0 {
-		return errors.New("Invalid (infinite or NaN) y-range delta")
+	if math.IsNaN(xDelta) {
+		return errors.New("nan x-range delta")
 	}
+
+	yDelta := yr.GetDelta()
+	if math.IsInf(yDelta, 0) {
+		return errors.New("infinite y-range delta")
+	}
+	if math.IsNaN(yDelta) {
+		return errors.New("nan y-range delta")
+	}
+
 	if c.hasSecondarySeries() {
-		if math.IsInf(yra.GetDelta(), 0) || math.IsNaN(yra.GetDelta()) || yra.GetDelta() == 0 {
-			return errors.New("Invalid (infinite or NaN) y-secondary-range delta")
+		yraDelta := yra.GetDelta()
+		if math.IsInf(yraDelta, 0) {
+			return errors.New("infinite secondary y-range delta")
+		}
+		if math.IsNaN(yraDelta) {
+			return errors.New("nan secondary y-range delta")
 		}
 	}