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hplot: add Label plotter
This CL exports a new Label type that allows adding text labels on a canvas, either in user data space coordinates or in "normalized" coordinates. Fixes #790.
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lines changed

‎hplot/README.md

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@@ -1110,3 +1110,68 @@ func ExampleHStack_withLogY() {
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}
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}
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```
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## Labels
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![label-example](https://github.com/go-hep/hep/raw/master/hplot/testdata/label_plot_golden.png)
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[embedmd]:# (label_example_test.go go /func ExampleLabel/ /\n}/)
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```go
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func ExampleLabel() {
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// Creating a new plot
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p := hplot.New()
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p.Title.Text = "Plot labels"
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p.X.Min = -10
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p.X.Max = +10
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p.Y.Min = -10
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p.Y.Max = +10
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// Default labels
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l1 := hplot.NewLabel(-8, 5, "(-8,5)\nDefault label")
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p.Add(l1)
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// Label with normalized coordinates.
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l3 := hplot.NewLabel(
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0.5, 0.5,
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"(0.5,0.5)\nLabel with relative coords",
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hplot.WithLabelNormalized(true),
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)
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p.Add(l3)
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// Label with normalized coordinates and auto-adjustement.
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l4 := hplot.NewLabel(
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0.95, 0.95,
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"(0.95,0.95)\nLabel at the canvas edge, with AutoAdjust",
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hplot.WithLabelNormalized(true),
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hplot.WithLabelAutoAdjust(true),
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)
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p.Add(l4)
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// Label with a customed TextStyle
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usrFont, err := vg.MakeFont("Courier-Bold", 12)
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if err != nil {
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panic(fmt.Errorf("could not create font (Courier-Bold, 12): %w", err))
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}
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sty := draw.TextStyle{
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Color: plotutil.Color(2),
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Font: usrFont,
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}
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l5 := hplot.NewLabel(
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0.0, 0.1,
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"(0.0,0.1)\nLabel with a user-defined font",
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hplot.WithLabelTextStyle(sty),
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hplot.WithLabelNormalized(true),
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)
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p.Add(l5)
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p.Add(plotter.NewGlyphBoxes())
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p.Add(hplot.NewGrid())
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// Save the plot to a PNG file.
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err = p.Save(15*vg.Centimeter, -1, "testdata/label_plot.png")
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if err != nil {
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log.Fatalf("error saving plot: %v\n", err)
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}
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}
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```

‎hplot/label.go

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// Copyright ©2020 The go-hep Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package hplot
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import (
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"fmt"
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"image/color"
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"math"
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"gonum.org/v1/plot"
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"gonum.org/v1/plot/plotter"
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"gonum.org/v1/plot/vg/draw"
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)
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// Label displays a user-defined text string on a plot.
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//
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// Fields of Label should not be modified once the Label has been
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// added to an hplot.Plot.
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type Label struct {
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Text string // Text of the label
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X, Y float64 // Position of the label
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TextStyle draw.TextStyle // Text style of the label
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// Normalized indicates whether the label position
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// is in data coordinates or normalized with regard
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// to the canvas space.
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// When normalized, the label position is assumed
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// to fall in the [0, 1] interval. If true, NewLabel
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// panics if x or y are outside [0, 1].
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//
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// Normalized is false by default.
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Normalized bool
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// AutoAdjust enables auto adjustment of the label
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// position, when Normalized is true and when x
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// and/or y are close to 1 and the label is partly
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// outside the canvas. If false and the label doesn't
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// fit in the canvas, an error is returned.
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//
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// AutoAdjust is false by default.
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AutoAdjust bool
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// cache of gonum/plot.Labels
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plt *plotter.Labels
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}
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// NewLabel creates a new txt label at position (x, y).
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func NewLabel(x, y float64, txt string, opts ...LabelOption) *Label {
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style := draw.TextStyle{
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Color: color.Black,
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Font: DefaultStyle.Fonts.Tick, // FIXME(sbinet): add a field in Style?
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}
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cfg := &labelConfig{
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TextStyle: style,
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}
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for _, opt := range opts {
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opt(cfg)
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}
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if cfg.Normalized {
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if !(0 <= x && x <= 1) {
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panic(fmt.Errorf(
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"hplot: normalized label x-position is outside [0,1]: %g", x,
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))
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}
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if !(0 <= y && y <= 1) {
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panic(fmt.Errorf(
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"hplot: normalized label y-position is outside [0,1]: %g", y,
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))
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}
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}
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return &Label{
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Text: txt,
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X: x,
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Y: y,
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TextStyle: cfg.TextStyle,
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Normalized: cfg.Normalized,
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AutoAdjust: cfg.AutoAdjust,
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}
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}
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// Plot implements the Plotter interface,
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// drawing the label on the canvas.
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func (lbl *Label) Plot(c draw.Canvas, p *plot.Plot) {
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lbl.labels(c, p).Plot(c, p)
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}
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// DataRange returns the minimum and maximum x and
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// y values, implementing the plot.DataRanger interface.
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func (lbl *Label) DataRange() (xmin, xmax, ymin, ymax float64) {
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if lbl.Normalized {
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return math.Inf(+1), math.Inf(-1), math.Inf(+1), math.Inf(-1)
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}
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return lbl.labels(draw.Canvas{}, nil).DataRange()
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}
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// GlyphBoxes returns a GlyphBox, corresponding to the label.
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// GlyphBoxes implements the plot.GlyphBoxer interface.
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func (lbl *Label) GlyphBoxes(p *plot.Plot) []plot.GlyphBox {
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if lbl.plt == nil {
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return nil
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}
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// we expect Label.Plot(c,p) has already been called.
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return lbl.labels(draw.Canvas{}, p).GlyphBoxes(p)
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}
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// Internal helper function to get plotter.Labels type.
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func (lbl *Label) labels(c draw.Canvas, p *plot.Plot) *plotter.Labels {
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if lbl.plt != nil {
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return lbl.plt
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}
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var (
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x = lbl.X
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y = lbl.Y
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err error
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)
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if lbl.Normalized {
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// Check whether the label fits in the canvas
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box := lbl.TextStyle.Rectangle(lbl.Text)
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rect := c.Rectangle.Size()
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xmax := lbl.X + box.Max.X.Points()/rect.X.Points()
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ymax := lbl.Y + box.Max.Y.Points()/rect.Y.Points()
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if xmax > 1 || ymax > 1 {
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switch {
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case lbl.AutoAdjust:
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x, y = lbl.adjust(1/rect.X.Points(), 1/rect.Y.Points())
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default:
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panic(fmt.Errorf(
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"hplot: label (%g, %g) falls outside data canvas",
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x, y,
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))
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}
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}
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// Turn relative into absolute coordinates
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x = lbl.scale(x, p.X.Min, p.X.Max, p.X.Scale)
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y = lbl.scale(y, p.Y.Min, p.Y.Max, p.Y.Scale)
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}
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lbl.plt, err = plotter.NewLabels(plotter.XYLabels{
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XYs: []plotter.XY{{X: x, Y: y}},
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Labels: []string{lbl.Text},
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})
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if err != nil {
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panic(fmt.Errorf("hplot: could not create labels: %w", err))
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}
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lbl.plt.TextStyle = []draw.TextStyle{lbl.TextStyle}
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return lbl.plt
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}
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func (lbl *Label) adjust(xnorm, ynorm float64) (x, y float64) {
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x = lbl.adjustX(xnorm)
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y = lbl.adjustY(ynorm)
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return x, y
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}
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func (lbl *Label) adjustX(xnorm float64) float64 {
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var (
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box = lbl.TextStyle.Rectangle(lbl.Text)
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size = box.Size().X.Points() * xnorm
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x = lbl.X
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dx = size - (1 - x)
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)
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if x+size > 1 {
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x -= dx
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}
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if x < 0 {
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x = 0
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}
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return x
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}
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func (lbl *Label) adjustY(ynorm float64) float64 {
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var (
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box = lbl.TextStyle.Rectangle(lbl.Text)
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size = box.Size().Y.Points() * ynorm
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y = lbl.Y
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dy = size - (1 - y)
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)
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if y+size > 1 {
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y -= dy
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}
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if y < 0 {
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y = 0
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}
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return y
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}
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func (Label) scale(v, min, max float64, scaler plot.Normalizer) float64 {
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mid := min + 0.5*(max-min)
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if math.Abs(scaler.Normalize(min, max, mid)-0.5) < 1e-12 {
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return min + v*(max-min)
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}
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// log-scale
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min = math.Log(min)
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max = math.Log(max)
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return math.Exp(min + v*(max-min))
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}
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type labelConfig struct {
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TextStyle draw.TextStyle
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Normalized bool
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AutoAdjust bool
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}
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// LabelOption handles various options to configure a Label.
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type LabelOption func(cfg *labelConfig)
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// WithLabelTextStyle specifies the text style of the label.
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func WithLabelTextStyle(style draw.TextStyle) LabelOption {
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return func(cfg *labelConfig) {
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cfg.TextStyle = style
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}
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}
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// WithLabelNormalized specifies whether the coordinates are
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// normalized to the canvas size.
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func WithLabelNormalized(norm bool) LabelOption {
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return func(cfg *labelConfig) {
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cfg.Normalized = norm
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}
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}
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// WithLabelAutoAdjust specifies whether the coordinates are
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// automatically adjusted to the canvas size.
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func WithLabelAutoAdjust(auto bool) LabelOption {
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return func(cfg *labelConfig) {
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cfg.AutoAdjust = auto
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}
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}
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var (
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_ plot.Plotter = (*Label)(nil)
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_ plot.DataRanger = (*Label)(nil)
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_ plot.GlyphBoxer = (*Label)(nil)
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)

‎hplot/label_example_test.go

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// Copyright ©2020 The go-hep Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package hplot_test
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import (
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"fmt"
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"log"
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"gonum.org/v1/plot/plotter"
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"gonum.org/v1/plot/plotutil"
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"gonum.org/v1/plot/vg"
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"gonum.org/v1/plot/vg/draw"
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"go-hep.org/x/hep/hplot"
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)
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func ExampleLabel() {
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// Creating a new plot
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p := hplot.New()
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p.Title.Text = "Plot labels"
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p.X.Min = -10
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p.X.Max = +10
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p.Y.Min = -10
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p.Y.Max = +10
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// Default labels
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l1 := hplot.NewLabel(-8, 5, "(-8,5)\nDefault label")
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p.Add(l1)
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// Label with normalized coordinates.
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l3 := hplot.NewLabel(
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0.5, 0.5,
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"(0.5,0.5)\nLabel with relative coords",
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hplot.WithLabelNormalized(true),
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)
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p.Add(l3)
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// Label with normalized coordinates and auto-adjustement.
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l4 := hplot.NewLabel(
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0.95, 0.95,
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"(0.95,0.95)\nLabel at the canvas edge, with AutoAdjust",
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hplot.WithLabelNormalized(true),
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hplot.WithLabelAutoAdjust(true),
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)
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p.Add(l4)
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// Label with a customed TextStyle
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usrFont, err := vg.MakeFont("Courier-Bold", 12)
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if err != nil {
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panic(fmt.Errorf("could not create font (Courier-Bold, 12): %w", err))
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}
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sty := draw.TextStyle{
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Color: plotutil.Color(2),
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Font: usrFont,
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}
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l5 := hplot.NewLabel(
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0.0, 0.1,
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"(0.0,0.1)\nLabel with a user-defined font",
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hplot.WithLabelTextStyle(sty),
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hplot.WithLabelNormalized(true),
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)
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p.Add(l5)
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p.Add(plotter.NewGlyphBoxes())
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p.Add(hplot.NewGrid())
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// Save the plot to a PNG file.
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err = p.Save(15*vg.Centimeter, -1, "testdata/label_plot.png")
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if err != nil {
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log.Fatalf("error saving plot: %v\n", err)
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}
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}

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