can just supply inverted ranges.

axis.go

@@ -25,12 +25,15 @@ const (
 // Axis is a chart feature detailing what values happen where.
 type Axis interface {
 	GetName() string
+	SetName(name string)
+
 	GetStyle() Style
+	SetStyle(style Style)
 
 	GetTicks() []Tick
 	GenerateTicks(r Renderer, ra Range, vf ValueFormatter) []Tick
 
-	// GetGridLines returns the gridlines for the axis.
+	// GenerateGridLines returns the gridlines for the axis.
 	GetGridLines(ticks []Tick) []GridLine
 
 	// Measure should return an absolute box for the axis.

continuous_range.go

@@ -56,7 +56,7 @@ func (r *ContinuousRange) SetDomain(domain int) {
 
 // String returns a simple string for the ContinuousRange.
 func (r ContinuousRange) String() string {
-	return fmt.Sprintf("ContinuousRange [%.2f,%.2f] => %d", r.Min, r.Max, r.Domain)
+	return fmt.Sprintf("ContinuousRange [%.2f,%.2f] => %f", r.Min, r.Max, r.Domain)
 }
 
 // Translate maps a given value into the ContinuousRange space.

range.go

@@ -20,7 +20,7 @@ type Stringable interface {
 	String() string
 }
 
-// Range is a
+// Range is a common interface for a range of values.
 type Range interface {
 	Stringable
 	IsZeroable

tick.go

@@ -49,17 +49,18 @@ func GenerateContinuousTicks(r Renderer, ra Range, isVertical bool, style Style,
 	style.GetTextOptions().WriteToRenderer(r)
 	labelBox := r.MeasureText(minLabel)
 
-	var tickSize int
+	var tickSize float64
 	if isVertical {
-		tickSize = labelBox.Height() + DefaultMinimumTickVerticalSpacing
+		tickSize = float64(labelBox.Height() + DefaultMinimumTickVerticalSpacing)
 	} else {
-		tickSize = labelBox.Width() + DefaultMinimumTickHorizontalSpacing
+		tickSize = float64(labelBox.Width() + DefaultMinimumTickHorizontalSpacing)
 	}
 
-	domainRemainder := (ra.GetDomain()) - (tickSize * 2)
+	domain := float64(ra.GetDomain())
+	domainRemainder := domain - (tickSize * 2)
 	intermediateTickCount := int(math.Floor(float64(domainRemainder) / float64(tickSize)))
 
-	rangeDelta := max - min
+	rangeDelta := math.Abs(max - min)
 	tickStep := rangeDelta / float64(intermediateTickCount)
 
 	roundTo := Math.GetRoundToForDelta(rangeDelta) / 10

tick_test.go

@@ -1,12 +1,57 @@
 package chart
 
-/*
-func TestGenerateTicksWithStep(t *testing.T) {
+import (
+	"testing"
+
+	assert "github.com/blendlabs/go-assert"
+)
+
+func TestGenerateContinuousTicks(t *testing.T) {
 	assert := assert.New(t)
 
+	f, err := GetDefaultFont()
+	assert.Nil(err)
 
+	r, err := PNG(1024, 1024)
+	assert.Nil(err)
+	r.SetFont(f)
 
-	ticks := GenerateContinuousTicksWithStep(&ContinuousRange{Min: 1.0, Max: 10.0, Domain: 100}, 1.0, FloatValueFormatter, false)
-	assert.Len(ticks, 10)
+	ra := &ContinuousRange{
+		Min:    0.0,
+		Max:    10.0,
+		Domain: 256,
+	}
+
+	vf := FloatValueFormatter
+
+	ticks := GenerateContinuousTicks(r, ra, false, Style{}, vf)
+	assert.NotEmpty(ticks)
+	assert.Len(ticks, 11)
+	assert.Equal(0.0, ticks[0].Value)
+	assert.Equal(10, ticks[len(ticks)-1].Value)
+}
+
+func TestGenerateContinuousTicksDescending(t *testing.T) {
+	assert := assert.New(t)
+
+	f, err := GetDefaultFont()
+	assert.Nil(err)
+
+	r, err := PNG(1024, 1024)
+	assert.Nil(err)
+	r.SetFont(f)
+
+	ra := &ContinuousRange{
+		Min:    10.0,
+		Max:    0.0,
+		Domain: 256,
+	}
+
+	vf := FloatValueFormatter
+
+	ticks := GenerateContinuousTicks(r, ra, false, Style{}, vf)
+	assert.NotEmpty(ticks)
+	assert.Len(ticks, 11)
+	assert.Equal(10.0, ticks[0].Value)
+	assert.Equal(0.0, ticks[len(ticks)-1].Value)
 }
-*/

xaxis.go

@@ -1,9 +1,6 @@
 package chart
 
-import (
-	"math"
-	"sort"
-)
+import "math"
 
 // XAxis represents the horizontal axis.
 type XAxis struct {
@@ -71,7 +68,6 @@ func (xa XAxis) GetGridLines(ticks []Tick) []GridLine {
 // Measure returns the bounds of the axis.
 func (xa XAxis) Measure(r Renderer, canvasBox Box, ra Range, defaults Style, ticks []Tick) Box {
 	tickStyle := xa.TickStyle.InheritFrom(xa.Style.InheritFrom(defaults))
-	sort.Sort(Ticks(ticks))
 
 	tp := xa.GetTickPosition()
 
@@ -124,8 +120,6 @@ func (xa XAxis) Render(r Renderer, canvasBox Box, ra Range, defaults Style, tick
 	r.LineTo(canvasBox.Right, canvasBox.Bottom)
 	r.Stroke()
 
-	sort.Sort(Ticks(ticks))
-
 	tp := xa.GetTickPosition()
 
 	var tx, ty int

yaxis.go

@@ -1,9 +1,6 @@
 package chart
 
-import (
-	"math"
-	"sort"
-)
+import "math"
 
 // YAxis is a veritcal rule of the range.
 // There can be (2) y-axes; a primary and secondary.
@@ -15,7 +12,8 @@ type YAxis struct {
 
 	Zero GridLine
 
-	AxisType YAxisType
+	AxisType  YAxisType
+	Ascending bool
 
 	ValueFormatter ValueFormatter
 	Range          Range
@@ -74,8 +72,6 @@ func (ya YAxis) GetGridLines(ticks []Tick) []GridLine {
 
 // Measure returns the bounds of the axis.
 func (ya YAxis) Measure(r Renderer, canvasBox Box, ra Range, defaults Style, ticks []Tick) Box {
-	sort.Sort(Ticks(ticks))
-
 	var tx int
 	if ya.AxisType == YAxisPrimary {
 		tx = canvasBox.Right + DefaultYAxisMargin
@@ -128,8 +124,6 @@ func (ya YAxis) Render(r Renderer, canvasBox Box, ra Range, defaults Style, tick
 	tickStyle := ya.TickStyle.InheritFrom(ya.Style.InheritFrom(defaults))
 	tickStyle.WriteToRenderer(r)
 
-	sort.Sort(Ticks(ticks))
-
 	sw := tickStyle.GetStrokeWidth(defaults.StrokeWidth)
 
 	var lx int