Add fx components 291-320 and the home scene; Kit.Shot, Kit.Toward

Palette cycling, sky, sun and moon, clouds, starfield, rain, snow,
petals, leaves, fireflies, waterfall, ocean, campfire, lava, aurora,
lightning, mountains and a season scene; scanlines, vignette, screen
shake, flash, dither fades, iris wipes, dissolves, mosaics, glitches,
sparkles, explosions and confetti. Home opens on a live scene in the
palette's season and a strip of all eight palettes.

pixel adds Canvas.Cycled, Sprite.At, SpriteOf, Kit.Toward and
Kit.Shot, which spends a cue under Reduce Motion so it never replays;
display exports Reduce. Gallery grids and the sidebar are one Tab
stop each.

feedback/effects_test.go

@@ -278,6 +278,24 @@ func TestReadyGoReportsDoneAfterAJump(t *testing.T) {
 	}
 }
 
+func TestShakeSpendsCuesUnderReduceMotion(t *testing.T) {
+	clk, cue := newClock(), 0
+	tt := view(300, 100, clk, false, func(c *ui.Context) {
+		feedback.Shake(c, feedback.ShakeOptions{Cue: cue}, func() {
+			ui.Box(c).Size(20, 20).Label("box")
+		})
+	})
+	x := find(t, tt, "box").X
+	tt.SetPreferences(ui.Preferences{ReduceMotion: true, TextScale: 1})
+	cue++
+	tt.Frame()
+	tt.SetPreferences(ui.Preferences{ReduceMotion: false, TextScale: 1})
+	tt.Frame()
+	if find(t, tt, "box").X != x {
+		t.Fatal("a cue spent under Reduce Motion shook later")
+	}
+}
+
 func TestShakeJoltsUnlessReduced(t *testing.T) {
 	for _, reduce := range []bool{false, true} {
 		clk := newClock()

feedback/shake.go

@@ -18,9 +18,6 @@ var shakes = [...]int{2, -2, 2, -2, 1, -1, 0}
 func Shake(c *ui.Context, o ShakeOptions, content func()) *ui.Element {
 	k := pixel.K(c)
 	e := ui.Box(c)
-	dx := 0
-	if step := k.Since(c, k.Cue(e, o.Cue), 20, len(shakes)-1); !k.Reduce() {
-		dx = shakes[step]
-	}
+	dx := shakes[k.Shot(c, e, o.Cue, 20, len(shakes)-1)]
 	return e.Padding(0, k.D(2-dx), 0, k.D(2+dx)).Children(content)
 }