text rotation is sucky.

_examples/text_rotation/main.go

@@ -0,0 +1,48 @@
+package main
+
+import (
+	"net/http"
+
+	"github.com/wcharczuk/go-chart"
+)
+
+func drawChart(res http.ResponseWriter, req *http.Request) {
+	/*
+	   In this example we set a rotation on the style for the custom ticks from the `custom_ticks` example.
+	*/
+
+	graph := chart.Chart{
+		YAxis: chart.YAxis{
+			Style: chart.Style{
+				Show:                true,
+				TextRotationDegrees: 45.0,
+			},
+			Range: &chart.ContinuousRange{
+				Min: 0.0,
+				Max: 4.0,
+			},
+			Ticks: []chart.Tick{
+				{0.0, "0.00"},
+				{2.0, "2.00"},
+				{4.0, "4.00"},
+				{6.0, "6.00"},
+				{8.0, "Eight"},
+				{10.0, "Ten"},
+			},
+		},
+		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},
+			},
+		},
+	}
+
+	res.Header().Set("Content-Type", "image/png")
+	graph.Render(chart.PNG, res)
+}
+
+func main() {
+	http.HandleFunc("/", drawChart)
+	http.ListenAndServe(":8080", nil)
+}

box.go

@@ -219,3 +219,17 @@ func (b Box) OuterConstrain(bounds, other Box) Box {
 	}
 	return newBox
 }
+
+// Rotate rotates a box's corners by a given radian rotation angle.
+func (b Box) Rotate(radians float64) Box {
+	cx, cy := b.Center()
+
+	ltx, lty := Math.RotateCoordinate(cx, cy, b.Left, b.Top, radians)
+	rbx, rby := Math.RotateCoordinate(cx, cy, b.Right, b.Bottom, radians)
+	return Box{
+		Top:    lty,
+		Left:   ltx,
+		Right:  rbx,
+		Bottom: rby,
+	}
+}

box_test.go

@@ -143,3 +143,19 @@ func TestBoxShift(t *testing.T) {
 	assert.Equal(11, shifted.Right)
 	assert.Equal(12, shifted.Bottom)
 }
+
+func TestBoxRotate(t *testing.T) {
+	assert := assert.New(t)
+
+	b := Box{
+		Top:    5,
+		Left:   5,
+		Right:  20,
+		Bottom: 10,
+	}
+	rotated := b.Rotate(Math.DegreesToRadians(45))
+	assert.Equal(1, rotated.Top)
+	assert.Equal(4, rotated.Left)
+	assert.Equal(11, rotated.Right)
+	assert.Equal(15, rotated.Bottom)
+}

math.go

@@ -214,9 +214,18 @@ func (m mathUtil) DegreesToCompass(deg float64) float64 {
 }
 
 // CirclePoint returns the absolute position of a circle diameter point given
-// by the radius and the angle.
-func (m mathUtil) CirclePoint(cx, cy int, radius, angleRadians float64) (x, y int) {
-	x = cx + int(radius*math.Sin(angleRadians))
-	y = cy - int(radius*math.Cos(angleRadians))
+// by the radius and the theta.
+func (m mathUtil) CirclePoint(cx, cy int, radius, thetaRadians float64) (x, y int) {
+	x = cx + int(radius*math.Sin(thetaRadians))
+	y = cy - int(radius*math.Cos(thetaRadians))
+	return
+}
+
+func (m mathUtil) RotateCoordinate(cx, cy, x, y int, thetaRadians float64) (rx, ry int) {
+	tempX, tempY := float64(x-cx), float64(y-cy)
+	rotatedX := int(math.Ceil(tempX*math.Cos(thetaRadians) - tempY*math.Sin(thetaRadians)))
+	rotatedY := int(math.Ceil(tempX*math.Sin(thetaRadians) + tempY*math.Cos(thetaRadians)))
+	rx = rotatedX + cy
+	ry = rotatedY + cy
 	return
 }

math_test.go

@@ -160,3 +160,14 @@ func TestRadianAdd(t *testing.T) {
 	assert.Equal(_pi, Math.RadianAdd(_pi, _2pi))
 	assert.Equal(_pi, Math.RadianAdd(_pi, -_2pi))
 }
+
+func TestRotateCoordinate(t *testing.T) {
+	assert := assert.New(t)
+
+	cx, cy := 10, 10
+	x, y := 5, 5
+
+	rx, ry := Math.RotateCoordinate(cx, cy, x, y, Math.DegreesToRadians(45))
+	assert.Equal(10, rx)
+	assert.Equal(3, ry)
+}

raster_renderer.go

@@ -177,12 +177,17 @@ func (rr *rasterRenderer) MeasureText(body string) Box {
 		t = 0
 	}
 
-	return Box{
+	textBox := Box{
 		Top:    int(math.Ceil(t)),
 		Left:   int(math.Ceil(l)),
 		Right:  int(math.Ceil(r)),
 		Bottom: int(math.Ceil(b)),
 	}
+	if rr.rotateRadians == 0 {
+		return textBox
+	}
+
+	return textBox.Rotate(rr.rotateRadians)
 }
 
 // SetTextRotation sets a text rotation.

style.go

@@ -33,6 +33,7 @@ type Style struct {
 	TextVerticalAlign   TextVerticalAlign
 	TextWrap            TextWrap
 	TextLineSpacing     int
+	TextRotationDegrees float64
 }
 
 // IsZero returns if the object is set or not.
@@ -241,6 +242,16 @@ func (s Style) GetTextLineSpacing(defaults ...int) int {
 	return s.TextLineSpacing
 }
 
+// GetTextRotationDegrees returns the text rotation in degrees.
+func (s Style) GetTextRotationDegrees(defaults ...float64) float64 {
+	if s.TextRotationDegrees == 0 {
+		if len(defaults) > 0 {
+			return defaults[0]
+		}
+	}
+	return s.TextRotationDegrees
+}
+
 // WriteToRenderer passes the style's options to a renderer.
 func (s Style) WriteToRenderer(r Renderer) {
 	r.SetStrokeColor(s.GetStrokeColor())
@@ -250,6 +261,12 @@ func (s Style) WriteToRenderer(r Renderer) {
 	r.SetFont(s.GetFont())
 	r.SetFontColor(s.GetFontColor())
 	r.SetFontSize(s.GetFontSize())
+
+	if s.GetTextRotationDegrees() == 0 {
+		r.ClearTextRotation()
+	} else {
+		r.SetTextRotation(Math.DegreesToRadians(s.GetTextRotationDegrees()))
+	}
 }
 
 // WriteDrawingOptionsToRenderer passes just the drawing style options to a renderer.
@@ -281,6 +298,7 @@ func (s Style) InheritFrom(defaults Style) (final Style) {
 	final.TextVerticalAlign = s.GetTextVerticalAlign(defaults.TextVerticalAlign)
 	final.TextWrap = s.GetTextWrap(defaults.TextWrap)
 	final.TextLineSpacing = s.GetTextLineSpacing(defaults.TextLineSpacing)
+	final.TextRotationDegrees = s.GetTextRotationDegrees(defaults.TextRotationDegrees)
 	return
 }
 
@@ -320,5 +338,6 @@ func (s Style) GetTextOptions() Style {
 		TextVerticalAlign:   s.TextVerticalAlign,
 		TextWrap:            s.TextWrap,
 		TextLineSpacing:     s.TextLineSpacing,
+		TextRotationDegrees: s.TextRotationDegrees,
 	}
 }

yaxis.go

@@ -20,6 +20,7 @@ type YAxis struct {
 	ValueFormatter ValueFormatter
 	Range          Range
 
+	TickStyle Style
 	Ticks     []Tick
 	GridLines []GridLine
 
@@ -42,6 +43,11 @@ func (ya YAxis) GetStyle() Style {
 	return ya.Style
 }
 
+// GetTickStyle returns the tick style.
+func (ya YAxis) GetTickStyle() Style {
+	return ya.TickStyle
+}
+
 // GetTicks returns the ticks for a series.
 // The coalesce priority is:
 // 	- User Supplied Ticks (i.e. Ticks array on the axis itself).
@@ -68,8 +74,6 @@ 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 {
-	ya.Style.InheritFrom(defaults).WriteToRenderer(r)
-
 	sort.Sort(Ticks(ticks))
 
 	var tx int
@@ -79,9 +83,12 @@ func (ya YAxis) Measure(r Renderer, canvasBox Box, ra Range, defaults Style, tic
 		tx = canvasBox.Left - DefaultYAxisMargin
 	}
 
+	ya.TickStyle.InheritFrom(ya.Style.InheritFrom(defaults)).WriteToRenderer(r)
+
 	var minx, maxx, miny, maxy = math.MaxInt32, 0, math.MaxInt32, 0
 	var maxTextHeight int
 	for _, t := range ticks {
+
 		v := t.Value
 		ly := canvasBox.Bottom - ra.Translate(v)
 
@@ -142,9 +149,11 @@ func (ya YAxis) Render(r Renderer, canvasBox Box, ra Range, defaults Style, tick
 
 	var maxTextWidth int
 	for _, t := range ticks {
+
 		v := t.Value
 		ly := canvasBox.Bottom - ra.Translate(v)
 
+		ya.TickStyle.InheritFrom(ya.Style.InheritFrom(defaults)).WriteToRenderer(r)
 		tb := r.MeasureText(t.Label)
 
 		if tb.Width() > maxTextWidth {
@@ -158,6 +167,7 @@ func (ya YAxis) Render(r Renderer, canvasBox Box, ra Range, defaults Style, tick
 		}
 
 		r.Text(t.Label, finalTextX, finalTextY)
+		r.ClearTextRotation()
 
 		r.MoveTo(lx, ly)
 		if ya.AxisType == YAxisPrimary {
@@ -168,12 +178,9 @@ func (ya YAxis) Render(r Renderer, canvasBox Box, ra Range, defaults Style, tick
 		r.Stroke()
 	}
 
-	nameStyle := ya.NameStyle.InheritFrom(defaults)
+	nameStyle := ya.NameStyle.InheritFrom(defaults.InheritFrom(Style{TextRotationDegrees: 90}))
 	if ya.NameStyle.Show && len(ya.Name) > 0 {
 		nameStyle.GetTextOptions().WriteToRenderer(r)
-
-		r.SetTextRotation(Math.DegreesToRadians(90))
-
 		tb := r.MeasureText(ya.Name)
 
 		var tx int
@@ -186,7 +193,6 @@ func (ya YAxis) Render(r Renderer, canvasBox Box, ra Range, defaults Style, tick
 		ty := canvasBox.Bottom - (canvasBox.Height()>>1 + tb.Width()>>1)
 
 		r.Text(ya.Name, tx, ty)
-		r.ClearTextRotation()
 	}
 
 	if ya.Zero.Style.Show {