feat: add svgclock example

twpayne · May 13, 2024 · 34df65f · 34df65f
1 parent cd02e9e
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diff --git a/cmd/svgclock/README.md b/cmd/svgclock/README.md
@@ -0,0 +1,11 @@
+# svgclock
+
+This example demonstrates dynamic generation of an SVG file.
+
+Run it:
+
+```console
+$ go run github.com/twpayne/go-svg/cmd/svgclock
+```
+
+and visit http://localhost:8080 in your web browser.
diff --git a/cmd/svgclock/index.html.tmpl b/cmd/svgclock/index.html.tmpl
@@ -0,0 +1,9 @@
+<html>
+    <head>
+        <title>Clock</title>
+        <meta http-equiv="refresh" content="1">
+    </head>
+    <body>
+        {{ now | svgClock }}
+    </body>
+</html>
diff --git a/cmd/svgclock/main.go b/cmd/svgclock/main.go
@@ -0,0 +1,95 @@
+package main
+
+import (
+	_ "embed"
+	"flag"
+	"fmt"
+	"html/template"
+	"math"
+	"net/http"
+	"os"
+	"time"
+
+	"github.com/twpayne/go-svg"
+	"github.com/twpayne/go-svg/svgpath"
+)
+
+//go:embed index.html.tmpl
+var indexHTML string
+
+func rad(deg int) float64 {
+	return math.Pi * float64(deg) / 180
+}
+
+func svgClock(t time.Time) *svg.SVGElement {
+	width := 128.0
+	height := 128.0
+	buffer := 4.0
+	diameter := min(width-2*buffer, height-2*buffer)
+	radius := diameter / 2
+	hour, minute, second := t.Hour(), t.Minute(), t.Second()
+	handElements := make([]svg.Element, 0, 3)
+	for _, hand := range []struct {
+		angle       float64
+		length      float64
+		stroke      svg.String
+		strokeWidth svg.Length
+	}{
+		{
+			length:      0.8,
+			angle:       rad(360*second/60 - 90),
+			stroke:      svg.String("red"),
+			strokeWidth: svg.Number(1),
+		},
+		{
+			length:      0.9,
+			angle:       rad(360*(60*minute+second)/(60*60) - 90),
+			stroke:      svg.String("black"),
+			strokeWidth: svg.Number(3),
+		},
+		{
+			length:      0.6,
+			angle:       rad(360*((hour%12)*60*60+minute*60+second)/(12*60*60) - 90),
+			stroke:      svg.String("black"),
+			strokeWidth: svg.Number(5),
+		},
+	} {
+		handElement := svg.Path().D(svgpath.New().
+			MoveToAbs([]float64{width / 2, height / 2}).
+			LineToRel([]float64{hand.length * radius * math.Cos(hand.angle), hand.length * radius * math.Sin(hand.angle)}).
+			ClosePath(),
+		).Stroke(hand.stroke).StrokeWidth(hand.strokeWidth)
+		handElements = append(handElements, handElement)
+	}
+	return svg.New().WidthHeight(width, height, svg.Number).ViewBox(0, 0, width, height).Children(
+		svg.Circle().CXCYR(width/2, height/2, radius, svg.Number).Fill("none").Stroke("black"),
+	).AppendChildren(handElements...)
+}
+
+func run() error {
+	addr := flag.String("addr", ":8080", "address")
+	flag.Parse()
+
+	indexTemplate, err := template.New("").Funcs(template.FuncMap{
+		"now": time.Now,
+		"svgClock": func(t time.Time) template.HTML {
+			return template.HTML(svgClock(t).String())
+		},
+	}).Parse(indexHTML)
+	if err != nil {
+		return err
+	}
+
+	http.HandleFunc("GET /", func(w http.ResponseWriter, r *http.Request) {
+		_ = indexTemplate.Execute(w, nil)
+	})
+
+	return http.ListenAndServe(*addr, nil)
+}
+
+func main() {
+	if err := run(); err != nil {
+		fmt.Println(err)
+		os.Exit(1)
+	}
+}