Add canvas, dither, sprites, clock and pixel elements

pixel/clock.go

@@ -0,0 +1,71 @@
+package pixel
+
+import (
+	"fmt"
+	"sync/atomic"
+	"time"
+
+	"github.com/egoist/mygo/ui"
+)
+
+var due atomic.Int64
+
+// Due is the earliest repaint asked for since ResetDue.
+func Due() time.Time {
+	n := due.Load()
+	if n == 0 {
+		return time.Time{}
+	}
+	return time.Unix(0, n)
+}
+
+func ResetDue() { due.Store(0) }
+
+func ask(at int64) {
+	for {
+		cur := due.Load()
+		if cur != 0 && cur <= at || due.CompareAndSwap(cur, at) {
+			return
+		}
+	}
+}
+
+// Step is the frame at fps, frozen under Reduce Motion.
+func (g Canvas) Step(fps int) int {
+	checkFPS(fps)
+	if g.k.reduce {
+		return 0
+	}
+	return g.Busy(fps)
+}
+
+// Busy is the frame at fps, ignoring Reduce Motion.
+func (g Canvas) Busy(fps int) int {
+	n, d := frameAt(g.now(), fps)
+	g.p.After(d)
+	ask(g.p.Now().Add(d).UnixNano())
+	return n
+}
+
+// Tick is the frame at fps, rebuilding the view.
+func (k Kit) Tick(c *ui.Context, fps int) int {
+	n, d := frameAt(k.now, fps)
+	c.After(d)
+	ask(c.Now().Add(d).UnixNano())
+	return n
+}
+
+// frameAt is the frame at t and the next wait.
+func frameAt(t time.Time, fps int) (int, time.Duration) {
+	checkFPS(fps)
+	period := int64(time.Second) / int64(fps)
+	ns := t.UnixNano()
+	n := ns / period
+	return int(n), time.Duration((n+1)*period - ns)
+}
+
+func checkFPS(fps int) {
+	if fps < 1 || fps > 60 {
+		panic(fmt.Sprintf("pixel: fps %d outside 1–60", fps))
+	}
+}