can rotate text + add y axis names

_examples/min_max/main.go

@@ -32,8 +32,12 @@ func drawChart(res http.ResponseWriter, req *http.Request) {
 	}
 
 	graph := chart.Chart{
+		Width:  1920,
+		Height: 1080,
 		YAxis: chart.YAxis{
-			Style: chart.StyleShow(),
+			Name:      "Random Values",
+			NameStyle: chart.StyleShow(),
+			Style:     chart.StyleShow(),
 			Range: &chart.ContinuousRange{
 				Min: 25,
 				Max: 175,
@@ -51,8 +55,10 @@ func drawChart(res http.ResponseWriter, req *http.Request) {
 		},
 	}
 
-	res.Header().Set("Content-Type", "image/png")
-	graph.Render(chart.PNG, res)
+	graph.Elements = []chart.Renderable{chart.Legend(&graph)}
+
+	res.Header().Set("Content-Type", "image/svg+xml")
+	graph.Render(chart.SVG, res)
 }
 
 func main() {

drawing/matrix.go

@@ -161,10 +161,10 @@ func (tr *Matrix) Translate(tx, ty float64) {
 	tr[5] = ty*tr[3] + tx*tr[1] + tr[5]
 }
 
-// Rotate adds a rotation to the matrix. angle is in radian
-func (tr *Matrix) Rotate(angle float64) {
-	c := math.Cos(angle)
-	s := math.Sin(angle)
+// Rotate adds a rotation to the matrix.
+func (tr *Matrix) Rotate(radians float64) {
+	c := math.Cos(radians)
+	s := math.Sin(radians)
 	t0 := c*tr[0] + s*tr[2]
 	t1 := s*tr[3] + c*tr[1]
 	t2 := c*tr[2] - s*tr[0]

drawing/text.go

@@ -22,14 +22,10 @@ func DrawContour(path PathBuilder, ps []truetype.Point, dx, dy float64) {
 			} else {
 				path.QuadCurveTo(q0X+dx, q0Y+dy, qX+dx, qY+dy)
 			}
-		} else {
-			if on0 {
-				// No-op.
-			} else {
-				midX := (q0X + qX) / 2
-				midY := (q0Y + qY) / 2
-				path.QuadCurveTo(q0X+dx, q0Y+dy, midX+dx, midY+dy)
-			}
+		} else if !on0 {
+			midX := (q0X + qX) / 2
+			midY := (q0Y + qY) / 2
+			path.QuadCurveTo(q0X+dx, q0Y+dy, midX+dx, midY+dy)
 		}
 		q0X, q0Y, on0 = qX, qY, on
 	}

raster_renderer.go

@@ -28,6 +28,8 @@ type rasterRenderer struct {
 	i  *image.RGBA
 	gc *drawing.RasterGraphicContext
 
+	rotateRadians float64
+
 	s Style
 }
 
@@ -139,10 +141,11 @@ func (rr *rasterRenderer) SetFontColor(c drawing.Color) {
 
 // Text implements the interface method.
 func (rr *rasterRenderer) Text(body string, x, y int) {
+	xf, yf := rr.getCoords(x, y)
 	rr.gc.SetFont(rr.s.Font)
 	rr.gc.SetFontSize(rr.s.FontSize)
 	rr.gc.SetFillColor(rr.s.FontColor)
-	rr.gc.CreateStringPath(body, float64(x), float64(y))
+	rr.gc.CreateStringPath(body, float64(xf), float64(yf))
 	rr.gc.Fill()
 }
 
@@ -182,6 +185,29 @@ func (rr *rasterRenderer) MeasureText(body string) Box {
 	}
 }
 
+// SetTextRotation sets a text rotation.
+func (rr *rasterRenderer) SetTextRotation(radians float64) {
+	rr.rotateRadians = radians
+}
+
+func (rr *rasterRenderer) getCoords(x, y int) (xf, yf int) {
+	if rr.rotateRadians == 0 {
+		xf = x
+		yf = y
+		return
+	}
+
+	rr.gc.Translate(float64(x), float64(y))
+	rr.gc.Rotate(rr.rotateRadians)
+	return
+}
+
+// ClearTextRotation clears text rotation.
+func (rr *rasterRenderer) ClearTextRotation() {
+	rr.gc.SetMatrixTransform(drawing.NewIdentityMatrix())
+	rr.rotateRadians = 0
+}
+
 // Save implements the interface method.
 func (rr *rasterRenderer) Save(w io.Writer) error {
 	return png.Encode(w, rr.i)

renderer.go

@@ -72,6 +72,12 @@ type Renderer interface {
 	// MeasureText measures text.
 	MeasureText(body string) Box
 
+	// SetTextRotatation sets a rotation for drawing elements.
+	SetTextRotation(radians float64)
+
+	// ClearTextRotation clears rotation.
+	ClearTextRotation()
+
 	// Save writes the image to the given writer.
 	Save(w io.Writer) error
 }

vector_renderer.go

@@ -32,6 +32,7 @@ type vectorRenderer struct {
 	b   *bytes.Buffer
 	c   *canvas
 	s   *Style
+	r   float64
 	p   []string
 	fc  *font.Drawer
 }
@@ -171,6 +172,16 @@ func (vr *vectorRenderer) MeasureText(body string) (box Box) {
 	return
 }
 
+// SetTextRotation sets the text rotation.
+func (vr *vectorRenderer) SetTextRotation(radians float64) {
+	vr.c.r = radians
+}
+
+// ClearTextRotation clears the text rotation.
+func (vr *vectorRenderer) ClearTextRotation() {
+	vr.c.r = 0
+}
+
 // Save saves the renderer's contents to a writer.
 func (vr *vectorRenderer) Save(w io.Writer) error {
 	vr.c.End()
@@ -187,6 +198,7 @@ func newCanvas(w io.Writer) *canvas {
 type canvas struct {
 	w      io.Writer
 	dpi    float64
+	r      float64
 	width  int
 	height int
 }
@@ -206,7 +218,12 @@ func (c *canvas) Path(d string, style Style) {
 }
 
 func (c *canvas) Text(x, y int, body string, style Style) {
-	c.w.Write([]byte(fmt.Sprintf(`<text x="%d" y="%d" style="%s">%s</text>`, x, y, c.styleAsSVG(style), body)))
+	if c.r == 0 {
+		c.w.Write([]byte(fmt.Sprintf(`<text x="%d" y="%d" style="%s">%s</text>`, x, y, c.styleAsSVG(style), body)))
+	} else {
+		transform := fmt.Sprintf(` transform="rotate(%0.2f,%d,%d)"`, Math.RadiansToDegrees(c.r), x, y)
+		c.w.Write([]byte(fmt.Sprintf(`<text x="%d" y="%d" style="%s"%s>%s</text>`, x, y, c.styleAsSVG(style), transform, body)))
+	}
 }
 
 func (c *canvas) Circle(x, y, r int, style Style) {

yaxis.go

@@ -8,7 +8,9 @@ import (
 // YAxis is a veritcal rule of the range.
 // There can be (2) y-axes; a primary and secondary.
 type YAxis struct {
-	Name  string
+	Name      string
+	NameStyle Style
+
 	Style Style
 
 	Zero GridLine
@@ -30,6 +32,11 @@ func (ya YAxis) GetName() string {
 	return ya.Name
 }
 
+// GetNameStyle returns the name style.
+func (ya YAxis) GetNameStyle() Style {
+	return ya.NameStyle
+}
+
 // GetStyle returns the style.
 func (ya YAxis) GetStyle() Style {
 	return ya.Style
@@ -73,6 +80,7 @@ func (ya YAxis) Measure(r Renderer, canvasBox Box, ra Range, defaults Style, tic
 	}
 
 	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)
@@ -83,6 +91,10 @@ func (ya YAxis) Measure(r Renderer, canvasBox Box, ra Range, defaults Style, tic
 			finalTextX = tx - tb.Width()
 		}
 
+		if tb.Height() > maxTextHeight {
+			maxTextHeight = tb.Height()
+		}
+
 		if ya.AxisType == YAxisPrimary {
 			minx = canvasBox.Right
 			maxx = Math.MaxInt(maxx, tx+tb.Width())
@@ -94,6 +106,10 @@ func (ya YAxis) Measure(r Renderer, canvasBox Box, ra Range, defaults Style, tic
 		maxy = Math.MaxInt(maxy, ly+tb.Height()>>1)
 	}
 
+	if ya.NameStyle.Show && len(ya.Name) > 0 {
+		maxx += (DefaultYAxisMargin + maxTextHeight)
+	}
+
 	return Box{
 		Top:    miny,
 		Left:   minx,
@@ -124,12 +140,17 @@ func (ya YAxis) Render(r Renderer, canvasBox Box, ra Range, defaults Style, tick
 	r.LineTo(lx, canvasBox.Top)
 	r.Stroke()
 
+	var maxTextWidth int
 	for _, t := range ticks {
 		v := t.Value
 		ly := canvasBox.Bottom - ra.Translate(v)
 
 		tb := r.MeasureText(t.Label)
 
+		if tb.Width() > maxTextWidth {
+			maxTextWidth = tb.Width()
+		}
+
 		finalTextX := tx
 		finalTextY := ly + tb.Height()>>1
 		if ya.AxisType == YAxisSecondary {
@@ -147,8 +168,18 @@ func (ya YAxis) Render(r Renderer, canvasBox Box, ra Range, defaults Style, tick
 		r.Stroke()
 	}
 
-	if ya.Zero.Style.Show {
-		ya.Zero.Render(r, canvasBox, ra, Style{})
+	nameStyle := ya.NameStyle.InheritFrom(defaults)
+	if ya.NameStyle.Show && len(ya.Name) > 0 {
+		nameStyle.GetTextOptions().WriteToRenderer(r)
+
+		r.SetTextRotation(Math.DegreesToRadians(90))
+
+		tb := r.MeasureText(ya.Name)
+		tx := canvasBox.Right + int(sw) + DefaultYAxisMargin + maxTextWidth + DefaultYAxisMargin
+		ty := canvasBox.Bottom - (canvasBox.Height()>>1 + tb.Width()>>1)
+
+		r.Text(ya.Name, tx, ty)
+		r.ClearTextRotation()
 	}
 
 	if ya.GridMajorStyle.Show || ya.GridMinorStyle.Show {