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// 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 (
"math"
"gonum.org/v1/plot/vg"
"gonum.org/v1/plot/vg/draw"
)
// A Legend gives a description of the meaning of different
// data elements of the plot. Each legend entry has a name
// and a thumbnail, where the thumbnail shows a small
// sample of the display style of the corresponding data.
type Legend struct {
// TextStyle is the style given to the legend
// entry texts.
draw.TextStyle
// Padding is the amount of padding to add
// between each entry in the legend. If Padding
// is zero then entries are spaced based on the
// font size.
Padding vg.Length
// Top and Left specify the location of the legend.
// If Top is true the legend is located along the top
// edge of the plot, otherwise it is located along
// the bottom edge. If Left is true then the legend
// is located along the left edge of the plot, and the
// text is positioned after the icons, otherwise it is
// located along the right edge and the text is
// positioned before the icons.
Top, Left bool
// XOffs and YOffs are added to the legend's
// final position.
XOffs, YOffs vg.Length
// ThumbnailWidth is the width of legend thumbnails.
ThumbnailWidth vg.Length
// entries are all of the legendEntries described
// by this legend.
entries []legendEntry
}
// A legendEntry represents a single line of a legend, it
// has a name and an icon.
type legendEntry struct {
// text is the text associated with this entry.
text string
// thumbs is a slice of all of the thumbnails styles
thumbs []Thumbnailer
}
// Thumbnailer wraps the Thumbnail method, which
// draws the small image in a legend representing the
// style of data.
type Thumbnailer interface {
// Thumbnail draws an thumbnail representing
// a legend entry. The thumbnail will usually show
// a smaller representation of the style used
// to plot the corresponding data.
Thumbnail(c *draw.Canvas)
}
// NewLegend returns a legend with the default
// parameter settings.
func NewLegend() (Legend, error) {
font, err := vg.MakeFont(DefaultFont, vg.Points(12))
if err != nil {
return Legend{}, err
}
return Legend{
ThumbnailWidth: vg.Points(20),
TextStyle: draw.TextStyle{Font: font},
}, nil
}
// Draw draws the legend to the given draw.Canvas.
func (l *Legend) Draw(c draw.Canvas) {
iconx := c.Min.X
sty := l.TextStyle
textx := iconx + l.ThumbnailWidth + sty.Rectangle(" ").Max.X
if !l.Left {
iconx = c.Max.X - l.ThumbnailWidth
textx = iconx - l.TextStyle.Rectangle(" ").Max.X
sty.XAlign--
}
textx += l.XOffs
iconx += l.XOffs
enth := l.entryHeight()
y := c.Max.Y - enth
if !l.Top {
y = c.Min.Y + (enth+l.Padding)*(vg.Length(len(l.entries))-1)
}
y += l.YOffs
icon := &draw.Canvas{
Canvas: c.Canvas,
Rectangle: vg.Rectangle{
Min: vg.Point{X: iconx, Y: y},
Max: vg.Point{X: iconx + l.ThumbnailWidth, Y: y + enth},
},
}
for _, e := range l.entries {
for _, t := range e.thumbs {
t.Thumbnail(icon)
}
yoffs := (enth - sty.Rectangle(e.text).Max.Y) / 2
c.FillText(sty, vg.Point{X: textx, Y: icon.Min.Y + yoffs}, e.text)
icon.Min.Y -= enth + l.Padding
icon.Max.Y -= enth + l.Padding
}
}
// Rectangle returns the extent of the Legend.
func (l *Legend) Rectangle(c draw.Canvas) vg.Rectangle {
var width, height vg.Length
sty := l.TextStyle
entryHeight := l.entryHeight()
for i, e := range l.entries {
width = vg.Length(math.Max(float64(width), float64(l.ThumbnailWidth+sty.Rectangle(" "+e.text).Max.X)))
height += entryHeight
if i != 0 {
height += l.Padding
}
}
var r vg.Rectangle
if l.Left {
r.Max.X = c.Max.X
r.Min.X = c.Max.X - width
} else {
r.Max.X = c.Min.X + width
r.Min.X = c.Min.X
}
if l.Top {
r.Max.Y = c.Max.Y
r.Min.Y = c.Max.Y - height
} else {
r.Max.Y = c.Min.Y + height
r.Min.Y = c.Min.Y
}
return r
}
// entryHeight returns the height of the tallest legend
// entry text.
func (l *Legend) entryHeight() (height vg.Length) {
for _, e := range l.entries {
if h := l.TextStyle.Rectangle(e.text).Max.Y; h > height {
height = h
}
}
return
}
// Add adds an entry to the legend with the given name.
// The entry's thumbnail is drawn as the composite of all of the
// thumbnails.
func (l *Legend) Add(name string, thumbs ...Thumbnailer) {
l.entries = append(l.entries, legendEntry{text: name, thumbs: thumbs})
}
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