WIP motion 1

typewriter.go

@@ -0,0 +1,86 @@
+package mujica
+
+import (
+	"log/slog"
+	"strings"
+	"time"
+
+	"github.com/egoist/mygo/ui"
+)
+
+// TypewriterOptions configure a Typewriter.
+type TypewriterOptions struct {
+	// Speed is characters per second; zero means 40.
+	Speed float64
+	// Skippable adds a Skip button that shows the rest at once.
+	Skippable bool
+}
+
+// TypewriterResult is a built Typewriter and its events.
+type TypewriterResult struct {
+	Element *ui.Element
+	done    bool
+}
+
+// Finished reports the frame the whole text came into view.
+func (r TypewriterResult) Finished() bool { return r.done }
+
+type typewriterState struct {
+	text    []rune
+	shown   int
+	last    time.Time
+	skipped bool
+	done    bool
+}
+
+// Typewriter reveals text a character at a time; text that grows continues where it was.
+func Typewriter(c *ui.Context, text string, opts TypewriterOptions) TypewriterResult {
+	speed := opts.Speed
+	if speed == 0 {
+		speed = 40
+	}
+	if speed < 0 {
+		panic("mujica: Typewriter Speed is negative")
+	}
+	col := ui.Column(c).AlignItems(ui.Start).Gap(Density(c).Unit() * 2)
+	res := TypewriterResult{Element: col}
+	st := ui.Local(col, "typing", func() *typewriterState { return &typewriterState{last: c.Now()} })
+	s := *st
+	runes := []rune(text)
+	if !strings.HasPrefix(text, string(s.text)) {
+		s.shown, s.skipped, s.done = 0, false, false
+		slog.Debug("mujica: typewriter restart")
+	}
+	if len(runes) > len(s.text) {
+		s.done = false
+	}
+	s.text = runes
+	now := c.Now()
+	if c.Preferences().ReduceMotion || s.skipped {
+		s.shown = len(runes)
+	} else if s.shown < len(runes) {
+		step := time.Duration(float64(time.Second) / speed)
+		if n := int(now.Sub(s.last) / step); n > 0 {
+			s.shown = min(len(runes), s.shown+n)
+			s.last = s.last.Add(time.Duration(n) * step)
+		}
+		if s.shown < len(runes) {
+			c.After(s.last.Add(step).Sub(now))
+		}
+	} else {
+		s.last = now
+	}
+	col.Children(func() {
+		ui.Text(c, string(runes[:s.shown])).Label(text)
+		if opts.Skippable && s.shown < len(runes) {
+			if Button(c, msg(c, "typewriter.skip"), ButtonOptions{Variant: Ghost}).Clicked() {
+				s.skipped, s.shown = true, len(runes)
+				slog.Debug("mujica: typewriter skip")
+			}
+		}
+	})
+	if s.shown == len(runes) && !s.done {
+		s.done, res.done = true, true
+	}
+	return res
+}