Buffer/ticker-based renderer

examples/go.mod

@@ -8,5 +8,5 @@ require (
 	github.com/charmbracelet/bubbles v0.0.0-20200526000837-87c7cd778f80
 	github.com/charmbracelet/bubbletea v0.6.4-0.20200525234836-3b8b011b5a26
 	github.com/fogleman/ease v0.0.0-20170301025033-8da417bf1776
-	github.com/muesli/termenv v0.5.2
+	github.com/muesli/termenv v0.5.3-0.20200526053627-d728968dcf83
 )

examples/go.sum

@@ -10,6 +10,8 @@ github.com/mattn/go-isatty v0.0.12 h1:wuysRhFDzyxgEmMf5xjvJ2M9dZoWAXNNr5LSBS7uHX
 github.com/mattn/go-isatty v0.0.12/go.mod h1:cbi8OIDigv2wuxKPP5vlRcQ1OAZbq2CE4Kysco4FUpU=
 github.com/muesli/termenv v0.5.2 h1:N1Y1dHRtx6OizOgaIQXd8SkJl4T/cCOV+YyWXiuLUEA=
 github.com/muesli/termenv v0.5.2/go.mod h1:O1/I6sw+6KcrgAmcs6uiUVr7Lui+DNVbHTzt9Lm/PlI=
+github.com/muesli/termenv v0.5.3-0.20200526053627-d728968dcf83 h1:AfshZBlqAwhCZ27NJ1aPlMcPBihF1squ1GpaollhLQk=
+github.com/muesli/termenv v0.5.3-0.20200526053627-d728968dcf83/go.mod h1:O1/I6sw+6KcrgAmcs6uiUVr7Lui+DNVbHTzt9Lm/PlI=
 github.com/pkg/term v0.0.0-20200520122047-c3ffed290a03 h1:pd4YKIqCB0U7O2I4gWHgEUA2mCEOENmco0l/bM957bU=
 github.com/pkg/term v0.0.0-20200520122047-c3ffed290a03/go.mod h1:Z9+Ul5bCbBKnbCvdOWbLqTHhJiYV414CURZJba6L8qA=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
@@ -22,4 +24,6 @@ golang.org/x/sys v0.0.0-20200116001909-b77594299b42 h1:vEOn+mP2zCOVzKckCZy6YsCtD
 golang.org/x/sys v0.0.0-20200116001909-b77594299b42/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20200519105757-fe76b779f299 h1:DYfZAGf2WMFjMxbgTjaC+2HC7NkNAQs+6Q8b9WEB/F4=
 golang.org/x/sys v0.0.0-20200519105757-fe76b779f299/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20200523222454-059865788121 h1:rITEj+UZHYC927n8GT97eC3zrpzXdb/voyeOuVKS46o=
+golang.org/x/sys v0.0.0-20200523222454-059865788121/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=

renderer.go

@@ -0,0 +1,99 @@
+package tea
+
+import (
+	"bytes"
+	"io"
+	"sync"
+	"time"
+
+	"github.com/muesli/termenv"
+)
+
+const (
+	defaultFramerate = time.Millisecond * 16
+)
+
+type renderer struct {
+	out           io.Writer
+	buf           bytes.Buffer
+	framerate     time.Duration
+	ticker        *time.Ticker
+	mtx           sync.Mutex
+	done          chan struct{}
+	lastRender    string
+	linesRendered int
+}
+
+func newRenderer(out io.Writer) *renderer {
+	return &renderer{
+		out:       out,
+		framerate: defaultFramerate,
+	}
+}
+
+func (r *renderer) start() {
+	if r.ticker == nil {
+		r.ticker = time.NewTicker(r.framerate)
+	}
+	r.done = make(chan struct{})
+	go r.listen()
+}
+
+func (r *renderer) stop() {
+	r.flush()
+	r.done <- struct{}{}
+}
+
+func (r *renderer) listen() {
+	for {
+		select {
+		case <-r.ticker.C:
+			if r.ticker != nil {
+				r.flush()
+			}
+		case <-r.done:
+			r.mtx.Lock()
+			r.ticker.Stop()
+			r.ticker = nil
+			r.mtx.Unlock()
+			close(r.done)
+			return
+		}
+	}
+}
+
+func (r *renderer) flush() {
+	if r.buf.Len() == 0 || r.buf.String() == r.lastRender {
+		// Nothing to do
+		return
+	}
+
+	r.mtx.Lock()
+	defer r.mtx.Unlock()
+
+	if r.linesRendered > 0 {
+		termenv.ClearLines(r.linesRendered)
+	}
+	r.linesRendered = 0
+
+	var out bytes.Buffer
+	for _, b := range r.buf.Bytes() {
+		if b == '\n' {
+			r.linesRendered++
+			out.Write([]byte("\r\n"))
+		} else {
+			// TODO: don't write past the terminal width
+			_, _ = out.Write([]byte{b})
+		}
+	}
+
+	_, _ = r.out.Write(out.Bytes())
+	r.lastRender = r.buf.String()
+	r.buf.Reset()
+}
+
+func (w *renderer) write(s string) {
+	w.mtx.Lock()
+	defer w.mtx.Unlock()
+	w.buf.WriteString(s)
+}

tea.go

@@ -1,9 +1,7 @@
 package tea
 
 import (
-	"io"
 	"os"
-	"strings"
 	"sync"
 
 	"github.com/muesli/termenv"
@@ -76,12 +74,13 @@ func NewProgram(init Init, update Update, view View) *Program {
 // Start initializes the program.
 func (p *Program) Start() error {
 	var (
-		model Model
-		cmd   Cmd
-		cmds  = make(chan Cmd)
-		msgs  = make(chan Msg)
-		errs  = make(chan error)
-		done  = make(chan struct{})
+		model      Model
+		cmd        Cmd
+		cmds       = make(chan Cmd)
+		msgs       = make(chan Msg)
+		errs       = make(chan error)
+		done       = make(chan struct{})
+		mrRenderer = newRenderer(os.Stdout)
 	)
 
 	err := initTerminal()
@@ -98,8 +97,11 @@ func (p *Program) Start() error {
 		}()
 	}
 
+	// Start renderer
+	mrRenderer.start()
+
 	// Render initial view
-	p.render(model)
+	mrRenderer.write(p.view(model))
 
 	// Subscribe to user input
 	go func() {
@@ -152,36 +154,11 @@ func (p *Program) Start() error {
 
 			model, cmd = p.update(msg, model) // run update
 			cmds <- cmd                       // process command (if any)
-			p.render(model)                   // render to terminal
+			mrRenderer.write(p.view(model))   // send to renderer
 		}
 	}
 }
 
-// Render a view to the terminal. Returns the number of lines rendered.
-func (p *Program) render(model Model) {
-	view := p.view(model)
-
-	// The view hasn't changed; no need to render
-	if view == p.currentRender {
-		return
-	}
-
-	p.currentRender = view
-	linesRendered := strings.Count(p.currentRender, "\n")
-
-	// Add carriage returns to ensure that the cursor travels to the start of a
-	// column after a newline. Keep in mind that this means that in the rest
-	// of the Tea program newlines should be a normal unix newline (\n).
-	view = strings.Replace(view, "\n", "\r\n", -1)
-
-	p.mutex.Lock()
-	if linesRendered > 0 {
-		termenv.ClearLines(linesRendered)
-	}
-	_, _ = io.WriteString(os.Stdout, view)
-	p.mutex.Unlock()
-}
-
 // AltScreen exits the altscreen. This is just a wrapper around the termenv
 // function.
 func AltScreen() {