descending

tick.go

@@ -1,6 +1,10 @@
 package chart
 
-import "math"
+import (
+	"fmt"
+	"math"
+	"strings"
+)
 
 // TicksProvider is a type that provides ticks.
 type TicksProvider interface {
@@ -31,6 +35,15 @@ func (t Ticks) Less(i, j int) bool {
 	return t[i].Value < t[j].Value
 }
 
+// String returns a string representation of the set of ticks.
+func (t Ticks) String() string {
+	var values []string
+	for i, tick := range t {
+		values = append(values, fmt.Sprintf("[%d: %s]", i, tick.Label))
+	}
+	return strings.Join(values, ", ")
+}
+
 // GenerateContinuousTicks generates a set of ticks.
 func GenerateContinuousTicks(r Renderer, ra Range, isVertical bool, style Style, vf ValueFormatter) []Tick {
 	if vf == nil {
@@ -40,10 +53,17 @@ func GenerateContinuousTicks(r Renderer, ra Range, isVertical bool, style Style,
 	var ticks []Tick
 	min, max := ra.GetMin(), ra.GetMax()
 
-	ticks = append(ticks, Tick{
-		Value: min,
-		Label: vf(min),
-	})
+	if ra.IsDescending() {
+		ticks = append(ticks, Tick{
+			Value: max,
+			Label: vf(max),
+		})
+	} else {
+		ticks = append(ticks, Tick{
+			Value: min,
+			Label: vf(min),
+		})
+	}
 
 	minLabel := vf(min)
 	style.GetTextOptions().WriteToRenderer(r)
@@ -67,17 +87,29 @@ func GenerateContinuousTicks(r Renderer, ra Range, isVertical bool, style Style,
 	intermediateTickCount = Math.MinInt(intermediateTickCount, 1<<10)
 
 	for x := 1; x < intermediateTickCount; x++ {
-		tickValue := min + Math.RoundUp(tickStep*float64(x), roundTo)
+		var tickValue float64
+		if ra.IsDescending() {
+			tickValue = max - Math.RoundUp(tickStep*float64(x), roundTo)
+		} else {
+			tickValue = min + Math.RoundUp(tickStep*float64(x), roundTo)
+		}
 		ticks = append(ticks, Tick{
 			Value: tickValue,
 			Label: vf(tickValue),
 		})
 	}
 
-	ticks = append(ticks, Tick{
-		Value: max,
-		Label: vf(max),
-	})
+	if ra.IsDescending() {
+		ticks = append(ticks, Tick{
+			Value: min,
+			Label: vf(min),
+		})
+	} else {
+		ticks = append(ticks, Tick{
+			Value: max,
+			Label: vf(max),
+		})
+	}
 
 	return ticks
 }