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/fire.go

@@ -0,0 +1,103 @@
+package fx
+
+import (
+	"github.com/egoist/mygo/ui"
+
+	"git.zacharyzhang.com/ZacharyZhang-NY/8bitMyGoUI/pixel"
+)
+
+type FireOptions struct {
+	// Scale multiplies the 16×20 campfire; zero means 2.
+	Scale int
+	Label string
+}
+
+// tongues are each flicker frame's three tongue heights.
+var tongues = [3][3]int{{3, 6, 2}, {4, 5, 3}, {2, 7, 4}}
+
+// bases are the flame's half widths from row 6 down.
+var bases = [8]int{3, 4, 5, 5, 6, 6, 5, 4}
+
+// flames are flicker frames: a Bad rim, a Warn body.
+var flames = func() (out [3]*pixel.Sprite) {
+	for f := range out {
+		in := func(x, y int) bool {
+			if y < 0 || y > 13 || x < 0 || x > 12 {
+				return false
+			}
+			if y >= 6 && abs(x-6) <= bases[y-6] {
+				return true
+			}
+			for i, h := range tongues[f] {
+				if tip := 6 - h; y >= tip && y <= 6 && abs(x-3-3*i) <= (y-tip)/2 {
+					return true
+				}
+			}
+			return false
+		}
+		out[f] = pixel.SpriteOf(13, 14, func(x, y int) (pixel.Slot, bool) {
+			switch {
+			case !in(x, y):
+				return 0, false
+			case !in(x-1, y) || !in(x+1, y) || !in(x, y-1) || !in(x, y+1):
+				return pixel.Bad, true
+			}
+			return pixel.Warn, true
+		})
+	}
+	return out
+}()
+
+// logs cross under the fire; s marks the cut ends.
+var logs = pixel.MustSprite(`
+ss............ss
+s###........###s
+..####....####..
+....########....
+..####....####..
+s###........###s
+`)
+
+// Fire burns a campfire: flicker frames, heat rising through it.
+func Fire(c *ui.Context, o FireOptions) *ui.Element {
+	k := pixel.K(c)
+	sc := scale("Fire", o.Scale, 2)
+	return box(c, k, o.Label, 16*sc, 20*sc).Draw(func(p *ui.Painter, r ui.Rect) {
+		g := k.Canvas(p, r)
+		fire(g, k, sc, g.Step(10))
+	})
+}
+
+// fire lights a third of every fourth body row, rising.
+func fire(g pixel.Canvas, k pixel.Kit, sc, step int) {
+	px := func(x, y, w, h int, s pixel.Slot) { g.Rect(x*sc, y*sc, w*sc, h*sc, s) }
+	wood := g
+	if k.Palette().Night {
+		wood = g.Cycled([]pixel.Slot{pixel.Shade, pixel.Lit}, 1)
+	}
+	wood.Sprite(0, 14*sc, logs, 0, pick(k, pixel.Faint, pixel.Face), sc)
+	sp, hot := flames[wrap(step, 3)], nightLit(g, k)
+	hot.Sprite(sc, 2*sc, sp, 0, pixel.Ink, sc)
+	// Body rows index the band; turning it lifts the heat.
+	heat := pixel.Cycle([]pixel.Slot{pixel.Lit, pixel.Warn, pixel.Warn, pixel.Warn}, step)
+	for y := range sp.H {
+		for x := range sp.W {
+			if s, ok := sp.At(0, x, y, pixel.Ink); ok && s == pixel.Warn && rnd(16*y+x, 200)%3 == 0 && heat[y%4] == pixel.Lit {
+				hot.Rect((1+x)*sc, (2+y)*sc, sc, sc, pixel.Lit)
+			}
+		}
+	}
+	// Sparks rise beside the tips.
+	for i := range 2 {
+		if t := wrap(step+5*i, 8); t < 5 {
+			px(4+8*i+sway(step+3*i, 8, 1), 5-t, 1, 1, pixel.Warn)
+		}
+	}
+}
+
+func abs(v int) int {
+	if v < 0 {
+		return -v
+	}
+	return v
+}