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.

fx/petals.go

@@ -0,0 +1,32 @@
+package fx
+
+import (
+	"github.com/egoist/mygo/ui"
+
+	"git.zacharyzhang.com/ZacharyZhang-NY/8bitMyGoUI/pixel"
+)
+
+type PetalsOptions struct {
+	// Width and Height are dots; zeros mean 160 by 96.
+	Width, Height int
+	Label         string
+}
+
+// Petals fall on a breeze, turning as they go.
+func Petals(c *ui.Context, o PetalsOptions) *ui.Element {
+	k := pixel.K(c)
+	w, h := size("Petals", o.Width, o.Height, 160, 96)
+	return box(c, k, o.Label, w, h).Draw(func(p *ui.Painter, r ui.Rect) {
+		g := k.Canvas(p, r)
+		g.Clip(0, 0, g.W, g.H, func() { petals(g, g.Step(8)) })
+	})
+}
+
+// petals fall a row a step, drifting left every three.
+func petals(g pixel.Canvas, step int) {
+	for i := range g.W * g.H / 260 {
+		y := wrap(rnd(i, 50)+step, g.H+6) - 3
+		x := wrap(rnd(i, 51)-step/3+sway(step+rnd(i, 52), 24, 3), g.W+4) - 2
+		g.Sprite(x, y, petal, step/2+i, pixel.Ink, 1)
+	}
+}