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/fireflies.go

@@ -0,0 +1,38 @@
+package fx
+
+import (
+	"github.com/egoist/mygo/ui"
+
+	"git.zacharyzhang.com/ZacharyZhang-NY/8bitMyGoUI/pixel"
+)
+
+type FirefliesOptions struct {
+	// Width and Height are dots; zeros mean 160 by 96.
+	Width, Height int
+	Label         string
+}
+
+// Fireflies wander and glow: bright, dim, then dark a while.
+func Fireflies(c *ui.Context, o FirefliesOptions) *ui.Element {
+	k := pixel.K(c)
+	w, h := size("Fireflies", 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() { fireflies(g, g.Step(8)) })
+	})
+}
+
+func fireflies(g pixel.Canvas, step int) {
+	for i := range max(3, g.W*g.H/600) {
+		x := rnd(i, 70)%g.W + sway(step+rnd(i, 71), 40+rnd(i, 72)%24, 8)
+		y := rnd(i, 73)%g.H + sway(step+rnd(i, 74), 28+rnd(i, 75)%20, 5)
+		switch t := wrap(step+rnd(i, 76), 16); {
+		case t < 6:
+			g.Rect(x-1, y, 3, 1, pixel.Good)
+			g.Rect(x, y-1, 1, 3, pixel.Good)
+			g.Dot(x, y, pixel.Warn)
+		case t < 9:
+			g.Dot(x, y, pixel.Good)
+		}
+	}
+}