Add Marquee decorator for long message scrolling

_examples/marqueeDecorator/go.mod

@@ -0,0 +1,13 @@
+module github.com/vbauerster/mpb/_examples/marqueeDecorator
+
+go 1.17
+
+require github.com/vbauerster/mpb/v8 v8.3.0
+
+require (
+	github.com/VividCortex/ewma v1.2.0 // indirect
+	github.com/acarl005/stripansi v0.0.0-20180116102854-5a71ef0e047d // indirect
+	github.com/mattn/go-runewidth v0.0.14 // indirect
+	github.com/rivo/uniseg v0.4.4 // indirect
+	golang.org/x/sys v0.6.0 // indirect
+)

_examples/marqueeDecorator/main.go

@@ -0,0 +1,55 @@
+package main
+
+import (
+	"fmt"
+	"math/rand"
+	"sync"
+	"time"
+
+	"github.com/vbauerster/mpb/v8"
+	"github.com/vbauerster/mpb/v8/decor"
+)
+
+func main() {
+	var wg sync.WaitGroup
+	// passed wg will be accounted at p.Wait() call
+	p := mpb.New(mpb.WithWaitGroup(&wg), mpb.WithWidth(64))
+	total, numBars := 100, 3
+	wg.Add(numBars)
+
+	fileToDownload := []string{
+		"One Hundred Years of Solitude by Gabriel Garcia Marquez",
+		"The Brothers Karamazov by Fyodor Dostoyevsky",
+		"Alice's Adventures in Wonderland by Lewis Carroll",
+	}
+
+	for i := 0; i < numBars; i++ {
+		name := fmt.Sprintf("Bar#%d:", i)
+		bar := p.AddBar(int64(total),
+			mpb.PrependDecorators(
+				// simple name decorator
+				decor.Name(name),
+				decor.OnComplete(
+					// Marquee decorator with default style
+					Marquee(fileToDownload[i], 20, decor.WCSyncSpace), "done",
+				),
+			),
+			mpb.AppendDecorators(
+				// decor.DSyncWidth bit enables column width synchronization
+				decor.Percentage(decor.WCSyncWidth),
+			),
+		)
+		// simulating some work
+		go func() {
+			defer wg.Done()
+			rng := rand.New(rand.NewSource(time.Now().UnixNano()))
+			max := 100 * time.Millisecond
+			for i := 0; i < total; i++ {
+				time.Sleep(time.Duration(rng.Intn(10)+1) * max / 10)
+				bar.Increment()
+			}
+		}()
+	}
+	// wait for passed wg and for all bars to complete and flush
+	p.Wait()
+}

decor/marquee.go

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+package decor
+
+// Marquee returns marquee decorator that will scroll text right to left.
+//
+// `text` is the scrolling message
+//
+// `ws` controls the showing window size
+func Marquee(text string, ws uint, wcc ...WC) Decorator {
+	bytes := []byte(text)
+	buf := make([]byte, ws)
+	var count uint
+	f := func(s Statistics) string {
+		start := count % uint(len(bytes))
+		var i uint = 0
+		for ; i < ws && start+i < uint(len(bytes)); i++ {
+			buf[i] = bytes[start+i]
+		}
+		for ; i < ws; i++ {
+			buf[i] = ' '
+		}
+		count++
+		return string(buf)
+	}
+	return Any(f, wcc...)
+}