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/lava.go

@@ -0,0 +1,61 @@
+package fx
+
+import (
+	"github.com/egoist/mygo/ui"
+
+	"git.zacharyzhang.com/ZacharyZhang-NY/8bitMyGoUI/pixel"
+)
+
+type LavaOptions struct {
+	// Width and Height are dots; zeros mean 160 by 48.
+	Width, Height int
+	Label         string
+}
+
+// Lava flows in cycling veins while bubbles swell and pop.
+func Lava(c *ui.Context, o LavaOptions) *ui.Element {
+	k := pixel.K(c)
+	w, h := size("Lava", o.Width, o.Height, 160, 48)
+	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() { lava(g, k, g.Step(6)) })
+	})
+}
+
+// lava's veins flow and cycle row by row; crust drifts.
+func lava(g pixel.Canvas, k pixel.Kit, step int) {
+	g.Rect(0, 0, g.W, g.H, pixel.Bad)
+	band := pixel.Cycle([]pixel.Slot{pixel.Warn, pixel.Warn, light(k), pixel.Warn, pixel.Bad, pixel.Bad}, -step)
+	for j := 0; 4*j < g.H; j++ {
+		s, dir := band[j%len(band)], 1-2*(j%2)
+		for i := range g.W/14 + 1 {
+			x := wrap(rnd(i, 130+j)+dir*step, g.W+16) - 8
+			g.Rect(x, 4*j+1+rnd(i, 140+j)%2, 4+rnd(i, 150+j)%8, 1, s)
+		}
+	}
+	crust := pick(k, pixel.Edge, pixel.Shade)
+	for i := range g.W * g.H / 300 {
+		g.Rect(wrap(rnd(i, 160)+step/2, g.W), rnd(i, 161)%g.H, 2+rnd(i, 162)%3, 1, crust)
+	}
+	for i := range max(2, g.W/24) {
+		t := step + rnd(i, 130)
+		// Each life of a bubble rises somewhere new.
+		x, y := rnd(t/12*64+i, 131)%g.W, 4+rnd(t/12*64+i, 132)%max(1, g.H-8)
+		switch wrap(t, 12) {
+		case 4:
+			g.Dot(x, y, pixel.Warn)
+		case 5:
+			g.Disc(x, y, 1, pixel.Warn)
+		case 6:
+			g.Disc(x, y, 2, pixel.Warn)
+			g.Dot(x-1, y-1, light(k))
+		case 7:
+			g.Circle(x, y, 3, pixel.Warn)
+			g.Dot(x-1, y-1, light(k))
+		case 8:
+			for _, d := range [][2]int{{-4, 0}, {4, 0}, {0, -4}, {0, 4}} {
+				g.Dot(x+d[0], y+d[1], pixel.Warn)
+			}
+		}
+	}
+}