tsplot: Option for font size. (#14)

Add option for setting the font size.

Author: jharshman

tscli/main.go

@@ -163,6 +163,7 @@ func executeQuery(cmd *cobra.Command, args []string) error {
 
 	p, err := ts.Plot([]tsplot.PlotOption{tsplot.WithXAxisName("UTC"),
 		tsplot.WithXTimeTicks(time.Kitchen),
+		tsplot.WithFontSize(float64(12)),
 		tsplot.WithGrid(colornames.Darkgrey),
 		tsplot.WithTitle(metric)}...)
 	if err != nil {

tsplot/options.go

@@ -5,6 +5,7 @@ import (
 	"time"
 
 	"gonum.org/v1/plot"
+	"gonum.org/v1/plot/font"
 	"gonum.org/v1/plot/plotter"
 	monitoringpb "google.golang.org/genproto/googleapis/monitoring/v3"
 	"google.golang.org/protobuf/types/known/durationpb"
@@ -84,6 +85,16 @@ func WithXTimeTicks(format string) PlotOption {
 	}
 }
 
+// WithFontSize configures the font sizes for the plot's Title, Axis', and Legend.
+func WithFontSize(size float64) PlotOption {
+	return func(p *plot.Plot) {
+		p.Title.TextStyle.Font.Size = font.Length(size)
+		p.X.Label.TextStyle.Font.Size = font.Length(size)
+		p.Y.Label.TextStyle.Font.Size = font.Length(size)
+		p.Legend.TextStyle.Font.Size = font.Length(size)
+	}
+}
+
 // ApplyDefaultHighContrast applies the default high contrast color scheme to the *plot.Plot.
 func ApplyDefaultHighContrast(p *plot.Plot) {
 	opts := []PlotOption{