plot,plotter: use errors instead of panics for failable plotters

errors.go

@@ -0,0 +1,25 @@
+// Copyright ©2015 The gonum Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package plot
+
+import "fmt"
+
+// Errors is a collection of plotting errors. An Errors value
+// must have a length of at least one.
+type Errors []error
+
+func (e Errors) Error() string {
+	switch len(e) {
+	case 0:
+		panic("plot: invalid error")
+	case 1:
+		return e[0].Error()
+	case 2:
+		return fmt.Sprintf("plot: %v and 1 more error", e[0])
+	default:
+		return fmt.Sprintf("plot: %v and %d more errors", e[0], len(e)-1)
+	}
+
+}

plot.go

@@ -71,7 +71,7 @@ type Plot struct {
 // http://godoc.org/github.com/gonum/plot/plotter
 type Plotter interface {
 	// Plot draws the data to a draw.Canvas.
-	Plot(draw.Canvas, *Plot)
+	Plot(draw.Canvas, *Plot) error
 }
 
 // DataRanger wraps the DataRange method.
@@ -149,7 +149,10 @@ func (p *Plot) Add(ps ...Plotter) {
 // GlyphBoxer interface will have their GlyphBoxes
 // taken into account when padding the plot so that
 // none of their glyphs are clipped.
-func (p *Plot) Draw(c draw.Canvas) {
+//
+// All errors raised during a call to Draw are returned
+// in an Errors slice.
+func (p *Plot) Draw(c draw.Canvas) error {
 	if p.BackgroundColor != nil {
 		c.SetColor(p.BackgroundColor)
 		c.Fill(c.Rectangle.Path())
@@ -171,11 +174,19 @@ func (p *Plot) Draw(c draw.Canvas) {
 	y.draw(padY(p, draw.Crop(c, 0, 0, xheight, 0)))
 
 	dataC := padY(p, padX(p, draw.Crop(c, ywidth, 0, xheight, 0)))
+	var errs Errors
 	for _, data := range p.plotters {
-		data.Plot(dataC, p)
+		err := data.Plot(dataC, p)
+		if err != nil {
+			errs = append(errs, err)
+		}
 	}
 
 	p.Legend.draw(draw.Crop(draw.Crop(c, ywidth, 0, 0, 0), 0, 0, xheight, 0))
+	if errs != nil {
+		return errs
+	}
+	return nil
 }
 
 // DataCanvas returns a new draw.Canvas that
@@ -447,13 +458,15 @@ func (p *Plot) NominalY(names ...string) {
 // Supported formats are:
 //
 //  eps, jpg|jpeg, pdf, png, svg, and tif|tiff.
+//
+// If WriterTo returns an error of type Errors some of
+// the elements of the written plot may be invalid.
 func (p *Plot) WriterTo(w, h vg.Length, format string) (io.WriterTo, error) {
 	c, err := draw.NewFormattedCanvas(w, h, format)
 	if err != nil {
 		return nil, err
 	}
-	p.Draw(draw.New(c))
-	return c, nil
+	return c, p.Draw(draw.New(c))
 }
 
 // Save saves the plot to an image file.  The file format is determined
@@ -462,6 +475,9 @@ func (p *Plot) WriterTo(w, h vg.Length, format string) (io.WriterTo, error) {
 // Supported extensions are:
 //
 //  .eps, .jpg, .jpeg, .pdf, .png, .svg, .tif and .tiff.
+//
+// If Save returns an error of type Errors some of
+// the elements of the saved plot may be invalid.
 func (p *Plot) Save(w, h vg.Length, file string) (err error) {
 	f, err := os.Create(file)
 	if err != nil {
@@ -478,11 +494,15 @@ func (p *Plot) Save(w, h vg.Length, file string) (err error) {
 	if len(format) != 0 {
 		format = format[1:]
 	}
-	c, err := p.WriterTo(w, h, format)
+	c, errs := p.WriterTo(w, h, format)
+	_, err = c.WriteTo(f)
+
+	// If the call to c.WriteTo failed this is a hard
+	// error and we do not care about the plotting
+	// errors, otherwise return any errors that arose
+	// during rendering.
 	if err != nil {
 		return err
 	}
-
-	_, err = c.WriteTo(f)
-	return err
+	return errs
 }

plotter/barchart.go

@@ -96,7 +96,7 @@ func (b *BarChart) StackOn(on *BarChart) {
 }
 
 // Plot implements the plot.Plotter interface.
-func (b *BarChart) Plot(c draw.Canvas, plt *plot.Plot) {
+func (b *BarChart) Plot(c draw.Canvas, plt *plot.Plot) error {
 	trCat, trVal := plt.Transforms(&c)
 	if b.Horizontal {
 		trCat, trVal = trVal, trCat
@@ -151,6 +151,7 @@ func (b *BarChart) Plot(c draw.Canvas, plt *plot.Plot) {
 		}
 		c.StrokeLines(b.LineStyle, outline...)
 	}
+	return nil
 }
 
 // DataRange implements the plot.DataRanger interface.

plotter/boxplot.go

@@ -186,17 +186,16 @@ func median(vs Values) float64 {
 }
 
 // Plot draws the BoxPlot on Canvas c and Plot plt.
-func (b *BoxPlot) Plot(c draw.Canvas, plt *plot.Plot) {
+func (b *BoxPlot) Plot(c draw.Canvas, plt *plot.Plot) error {
 	if b.Horizontal {
 		b := &horizBoxPlot{b}
-		b.Plot(c, plt)
-		return
+		return b.Plot(c, plt)
 	}
 
 	trX, trY := plt.Transforms(&c)
 	x := trX(b.Location)
 	if !c.ContainsX(x) {
-		return
+		return nil
 	}
 	x += b.Offset
 
@@ -234,6 +233,8 @@ func (b *BoxPlot) Plot(c draw.Canvas, plt *plot.Plot) {
 			c.DrawGlyphNoClip(b.GlyphStyle, vg.Point{X: x, Y: y})
 		}
 	}
+
+	return nil
 }
 
 // DataRange returns the minimum and maximum x
@@ -318,11 +319,11 @@ func (o boxPlotOutsideLabels) Label(i int) string {
 // bar charts.
 type horizBoxPlot struct{ *BoxPlot }
 
-func (b horizBoxPlot) Plot(c draw.Canvas, plt *plot.Plot) {
+func (b horizBoxPlot) Plot(c draw.Canvas, plt *plot.Plot) error {
 	trX, trY := plt.Transforms(&c)
 	y := trY(b.Location)
 	if !c.ContainsY(y) {
-		return
+		return nil
 	}
 	y += b.Offset
 
@@ -360,6 +361,8 @@ func (b horizBoxPlot) Plot(c draw.Canvas, plt *plot.Plot) {
 			c.DrawGlyphNoClip(b.GlyphStyle, vg.Point{X: x, Y: y})
 		}
 	}
+
+	return nil
 }
 
 // DataRange returns the minimum and maximum x

plotter/bubbles.go

@@ -61,7 +61,7 @@ func NewBubbles(xyz XYZer, min, max vg.Length) (*Bubbles, error) {
 }
 
 // Plot implements the Plot method of the plot.Plotter interface.
-func (bs *Bubbles) Plot(c draw.Canvas, plt *plot.Plot) {
+func (bs *Bubbles) Plot(c draw.Canvas, plt *plot.Plot) error {
 	trX, trY := plt.Transforms(&c)
 
 	c.SetColor(bs.Color)
@@ -83,6 +83,8 @@ func (bs *Bubbles) Plot(c draw.Canvas, plt *plot.Plot) {
 		p.Close()
 		c.Fill(p)
 	}
+
+	return nil
 }
 
 // radius returns the radius of a bubble by linear interpolation.

plotter/colorbar.go

@@ -53,7 +53,7 @@ func (l *ColorBar) check() {
 }
 
 // Plot implements the Plot method of the plot.Plotter interface.
-func (l *ColorBar) Plot(c draw.Canvas, p *plot.Plot) {
+func (l *ColorBar) Plot(c draw.Canvas, p *plot.Plot) error {
 	l.check()
 	colors := l.colors(c)
 	var img *image.NRGBA64
@@ -98,6 +98,7 @@ func (l *ColorBar) Plot(c draw.Canvas, p *plot.Plot) {
 		Max: vg.Point{X: xmax, Y: ymax},
 	}
 	c.DrawImage(rect, img)
+	return nil
 }
 
 // DataRange implements the DataRange method

plotter/contour.go

@@ -5,6 +5,7 @@
 package plotter
 
 import (
+	"errors"
 	"image/color"
 	"math"
 	"sort"
@@ -121,10 +122,16 @@ func quantilesR7(g GridXYZ, p []float64) []float64 {
 const naive = false
 
 // Plot implements the Plot method of the plot.Plotter interface.
-func (h *Contour) Plot(c draw.Canvas, plt *plot.Plot) {
+func (h *Contour) Plot(c draw.Canvas, plt *plot.Plot) error {
+	if h.Min > h.Max {
+		panic("contour: non-positive Z range")
+	}
+	if h.Min == h.Max {
+		return errors.New("contour: zero Z range")
+	}
 	if naive {
 		h.naivePlot(c, plt)
-		return
+		return nil
 	}
 
 	var pal []color.Color
@@ -178,6 +185,8 @@ func (h *Contour) Plot(c draw.Canvas, plt *plot.Plot) {
 			}
 		}
 	}
+
+	return nil
 }
 
 // naivePlot implements the a naive rendering approach for contours.

plotter/errbars.go

@@ -63,7 +63,7 @@ func NewYErrorBars(yerrs interface {
 }
 
 // Plot implements the Plotter interface, drawing labels.
-func (e *YErrorBars) Plot(c draw.Canvas, p *plot.Plot) {
+func (e *YErrorBars) Plot(c draw.Canvas, p *plot.Plot) error {
 	trX, trY := p.Transforms(&c)
 	for i, err := range e.YErrors {
 		x := trX(e.XYs[i].X)
@@ -75,6 +75,7 @@ func (e *YErrorBars) Plot(c draw.Canvas, p *plot.Plot) {
 		e.drawCap(&c, x, ylow)
 		e.drawCap(&c, x, yhigh)
 	}
+	return nil
 }
 
 // drawCap draws the cap if it is not clipped.
@@ -171,7 +172,7 @@ func NewXErrorBars(xerrs interface {
 }
 
 // Plot implements the Plotter interface, drawing labels.
-func (e *XErrorBars) Plot(c draw.Canvas, p *plot.Plot) {
+func (e *XErrorBars) Plot(c draw.Canvas, p *plot.Plot) error {
 	trX, trY := p.Transforms(&c)
 	for i, err := range e.XErrors {
 		y := trY(e.XYs[i].Y)
@@ -183,6 +184,7 @@ func (e *XErrorBars) Plot(c draw.Canvas, p *plot.Plot) {
 		e.drawCap(&c, xlow, y)
 		e.drawCap(&c, xhigh, y)
 	}
+	return nil
 }
 
 // drawCap draws the cap if it is not clipped.

plotter/functions.go

@@ -30,7 +30,7 @@ func NewFunction(f func(float64) float64) *Function {
 
 // Plot implements the Plotter interface, drawing a line
 // that connects each point in the Line.
-func (f *Function) Plot(c draw.Canvas, p *plot.Plot) {
+func (f *Function) Plot(c draw.Canvas, p *plot.Plot) error {
 	trX, trY := p.Transforms(&c)
 
 	d := (p.X.Max - p.X.Min) / float64(f.Samples-1)
@@ -41,6 +41,7 @@ func (f *Function) Plot(c draw.Canvas, p *plot.Plot) {
 		line[i].Y = trY(f.F(x))
 	}
 	c.StrokeLines(f.LineStyle, c.ClipLinesXY(line)...)
+	return nil
 }
 
 // Thumbnail draws a line in the given style down the

plotter/glyphbox.go

@@ -26,7 +26,7 @@ func NewGlyphBoxes() *GlyphBoxes {
 	return g
 }
 
-func (g GlyphBoxes) Plot(c draw.Canvas, plt *plot.Plot) {
+func (g GlyphBoxes) Plot(c draw.Canvas, plt *plot.Plot) error {
 	for _, b := range plt.GlyphBoxes(plt) {
 		x := c.X(b.X) + b.Rectangle.Min.X
 		y := c.Y(b.Y) + b.Rectangle.Min.Y
@@ -38,4 +38,5 @@ func (g GlyphBoxes) Plot(c draw.Canvas, plt *plot.Plot) {
 			{x, y},
 		})
 	}
+	return nil
 }

plotter/grid.go

@@ -40,7 +40,7 @@ func NewGrid() *Grid {
 }
 
 // Plot implements the plot.Plotter interface.
-func (g *Grid) Plot(c draw.Canvas, plt *plot.Plot) {
+func (g *Grid) Plot(c draw.Canvas, plt *plot.Plot) error {
 	trX, trY := plt.Transforms(&c)
 
 	var (
@@ -66,7 +66,7 @@ func (g *Grid) Plot(c draw.Canvas, plt *plot.Plot) {
 
 horiz:
 	if g.Horizontal.Color == nil {
-		return
+		return nil
 	}
 	for _, tk := range plt.Y.Tick.Marker.Ticks(plt.Y.Min, plt.Y.Max) {
 		if tk.IsMinor() {
@@ -78,4 +78,6 @@ horiz:
 		}
 		c.StrokeLine2(g.Horizontal, xmin, y, xmax, y)
 	}
+
+	return nil
 }