legend_example_test.go

// Copyright ©2018 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_test

import (
	"image/color"
	"os"

	"gonum.org/v1/plot"
	"gonum.org/v1/plot/vg"
	"gonum.org/v1/plot/vg/draw"
	"gonum.org/v1/plot/vg/vgimg"
)

type exampleThumbnailer struct {
	color.Color
}

// Thumbnail fulfills the plot.Thumbnailer interface.
func (et exampleThumbnailer) Thumbnail(c *draw.Canvas) {
	pts := []vg.Point{
		{X: c.Min.X, Y: c.Min.Y},
		{X: c.Min.X, Y: c.Max.Y},
		{X: c.Max.X, Y: c.Max.Y},
		{X: c.Max.X, Y: c.Min.Y},
	}
	poly := c.ClipPolygonY(pts)
	c.FillPolygon(et.Color, poly)

	pts = append(pts, vg.Point{X: c.Min.X, Y: c.Min.Y})
	outline := c.ClipLinesY(pts)
	c.StrokeLines(draw.LineStyle{
		Color: color.Black,
		Width: vg.Points(1),
	}, outline...)
}

// This example creates a some standalone legends with borders around them.
func ExampleLegend_standalone() {
	c := vgimg.New(vg.Points(120), vg.Points(100))
	dc := draw.New(c)

	// These example thumbnailers could be replaced with any of Plotters
	// in the plotter subpackage.
	red := exampleThumbnailer{Color: color.NRGBA{R: 255, A: 255}}
	green := exampleThumbnailer{Color: color.NRGBA{G: 255, A: 255}}
	blue := exampleThumbnailer{Color: color.NRGBA{B: 255, A: 255}}

	l := plot.NewLegend()
	l.Add("red", red)
	l.Add("green", green)
	l.Add("blue", blue)
	l.Padding = vg.Millimeter
	l.YPosition = draw.PosCenter

	// purpleRectangle draws a purple rectangle around the given Legend.
	purpleRectangle := func(l plot.Legend) {
		r := l.Rectangle(dc)
		dc.StrokeLines(draw.LineStyle{
			Color: color.NRGBA{R: 255, B: 255, A: 255},
			Width: vg.Points(1),
		}, []vg.Point{
			{X: r.Min.X, Y: r.Min.Y}, {X: r.Min.X, Y: r.Max.Y}, {X: r.Max.X, Y: r.Max.Y},
			{X: r.Max.X, Y: r.Min.Y}, {X: r.Min.X, Y: r.Min.Y},
		})
	}

	l.Draw(dc)
	purpleRectangle(l)

	l.Left = true
	l.Draw(dc)
	purpleRectangle(l)

	l.Top = true
	l.Draw(dc)
	purpleRectangle(l)

	l.Left = false
	l.Draw(dc)
	purpleRectangle(l)

	w, err := os.Create("testdata/legend_standalone.png")
	if err != nil {
		panic(err)
	}
	defer w.Close()

	png := vgimg.PngCanvas{Canvas: c}
	if _, err := png.WriteTo(w); err != nil {
		panic(err)
	}
}