Separation of DotColorProvider and ColorProvider Interfaces (#34)

* fully functioning Viridis

* pure functions

_examples/basic/main.go

@@ -26,8 +26,8 @@ func drawChartWide(res http.ResponseWriter, req *http.Request) {
 		Width: 1920, //this overrides the default.
 		Series: []chart.Series{
 			chart.ContinuousSeries{
-				XValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
-				YValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+				XValues: []float64{1.0, 2.0, 3.0, 4.0},
+				YValues: []float64{1.0, 2.0, 3.0, 4.0},
 			},
 		},
 	}

_examples/scatter/main.go

@@ -7,9 +7,15 @@ import (
 	_ "net/http/pprof"
 
 	"github.com/wcharczuk/go-chart"
+	"github.com/wcharczuk/go-chart/drawing"
 )
 
 func drawChart(res http.ResponseWriter, req *http.Request) {
+
+	viridisByY := func(xr, yr chart.Range, x, y float64) drawing.Color {
+		return chart.Viridis(y, yr.GetMin(), yr.GetMax())
+	}
+
 	graph := chart.Chart{
 		Series: []chart.Series{
 			chart.ContinuousSeries{
@@ -17,7 +23,7 @@ func drawChart(res http.ResponseWriter, req *http.Request) {
 					Show:             true,
 					StrokeWidth:      chart.Disabled,
 					DotWidth:         5,
-					DotColorProvider: chart.Jet,
+					DotColorProvider: viridisByY,
 				},
 				XValues: chart.Sequence.Random(128, 1024),
 				YValues: chart.Sequence.Random(128, 1024),

jet.go

@@ -3,11 +3,7 @@ package chart
 import "github.com/wcharczuk/go-chart/drawing"
 
 // Jet is a color map provider based on matlab's jet color map.
-func Jet(xr, yr Range, x, y float64) drawing.Color {
-	return getJetColour(y, yr.GetMin(), yr.GetMax())
-}
-
-func getJetColour(v, vmin, vmax float64) drawing.Color {
+func Jet(v, vmin, vmax float64) drawing.Color {
 	c := drawing.Color{R: 0xff, G: 0xff, B: 0xff, A: 0xff} // white
 	var dv float64
 

style.go

@@ -46,7 +46,7 @@ type Style struct {
 	DotWidth float64
 
 	DotWidthProvider SizeProvider
-	DotColorProvider ColorProvider
+	DotColorProvider DotColorProvider
 
 	FillColor drawing.Color
 

value_provider.go

@@ -39,5 +39,8 @@ type FullBoundedValueProvider interface {
 // SizeProvider is a provider for integer size.
 type SizeProvider func(xrange, yrange Range, x, y float64) float64
 
-// ColorProvider is a provider for dot size.
-type ColorProvider func(xrange, yrange Range, x, y float64) drawing.Color
+// ColorProvider is a general provider for color ranges based on values.
+type ColorProvider func(v, vmin, vmax float64) drawing.Color
+
+// DotColorProvider is a provider for dot color.
+type DotColorProvider func(xrange, yrange Range, x, y float64) drawing.Color

viridis.go

@@ -262,8 +262,8 @@ var viridisColors = [256]drawing.Color{
 }
 
 // Viridis creates a color map provider.
-func Viridis(xr, yr Range, x, y float64) drawing.Color {
-	normalized := (y - yr.GetMin()) / yr.GetDelta()
+func Viridis(v, vmin, vmax float64) drawing.Color {
+	normalized := (v - vmin) / (vmax - vmin)
 	index := uint8(normalized * 255)
 	return viridisColors[index]
 }