Add media components 346-365; input.SlideBase, guarded Pad

An audio player with transport, scrubber and volume; an equalizer and
a visualizer; a playlist; a cassette, cartridge and record that turn
while they play and hold where they stop; piano keys, a step sequencer
and a tracker you can type into; a waveform, a 16:9 video frame, an
image compare, a gallery, a filmstrip, a record button and an FM tuner.

input exports SlideBase, the undrawn rail its sliders share; the
gallery treats exported Bases as building blocks, not components.
pixel's micro font gains '#' for notes like C#4. pixel.Pad and the
slide rail read input only while their base is enabled, so Inert or a
fresh Disabled stops a drag or a key already sent. AGENTS records why
a drawn container keeps the DISABLED description: MyGo paints a
disabled subtree at half opacity.

media/views_test.go

@@ -0,0 +1,96 @@
+package media_test
+
+import (
+	"testing"
+
+	"github.com/egoist/mygo/ui"
+
+	"git.zacharyzhang.com/ZacharyZhang-NY/8bitMyGoUI/media"
+	"git.zacharyzhang.com/ZacharyZhang-NY/8bitMyGoUI/pixel"
+)
+
+// solid is a w by h picture in one slot.
+func solid(w, h int, s pixel.Slot) *pixel.Sprite {
+	return pixel.SpriteOf(w, h, func(x, y int) (pixel.Slot, bool) { return s, true })
+}
+
+func TestImageCompareSplitsWhereDragged(t *testing.T) {
+	wd := newWorld()
+	split, changed := 0.5, false
+	tt := view(300, 200, wd, func(c *ui.Context) {
+		changed = media.ImageCompare(c, "Compare", solid(10, 6, pixel.Good), solid(10, 6, pixel.Bad), &split, media.ImageCompareOptions{Scale: 2}).Changed || changed
+	})
+	r := find(t, tt, "Compare")
+	x, y, w, h := dots(r)
+	img := tt.Image()
+	// Row 0 is above the grip.
+	if w != 20 || h != 12 || at(img, wd.pal, x+2, y) != pixel.Good || at(img, wd.pal, x+10, y) != pixel.Edge || at(img, wd.pal, x+15, y) != pixel.Bad {
+		t.Fatal("before is not left of the split, after right")
+	}
+	tt.Press(r.X+r.W/4, r.Y+2)
+	tt.Release(r.X+r.W/4, r.Y+2)
+	if split != 0.25 || !changed || at(tt.Image(), wd.pal, x+7, y) != pixel.Bad {
+		t.Fatalf("pressing a quarter in split at %v", split)
+	}
+	tt.Key(0, ui.KeyHome)
+	if split != 0 || at(tt.Image(), wd.pal, x+2, y) != pixel.Bad || at(tt.Image(), wd.pal, x+6, y+h/2) != pixel.Edge {
+		t.Fatal("at 0, all is after and the grip stays whole")
+	}
+	tt.Key(0, ui.KeyEnd)
+	if split != 1 || at(tt.Image(), wd.pal, x+17, y) != pixel.Good {
+		t.Fatal("at 1, all is before")
+	}
+	mustPanic(t, "pictures of two sizes", func() {
+		view(300, 200, newWorld(), func(c *ui.Context) {
+			s := 0.5
+			media.ImageCompare(c, "C", solid(2, 2, pixel.Ink), solid(3, 2, pixel.Ink), &s, media.ImageCompareOptions{})
+		})
+	})
+}
+
+func TestGalleryChoosesByArrowsAndClicks(t *testing.T) {
+	wd := newWorld()
+	pics := []*pixel.Sprite{solid(4, 3, pixel.Good), solid(4, 3, pixel.Bad), solid(4, 3, pixel.Info)}
+	chosen, changed := 0, false
+	tt := view(300, 200, wd, func(c *ui.Context) {
+		changed = media.Gallery(c, "Views", pics, []string{"Green", "Red", "Blue"}, &chosen, media.GalleryOptions{Scale: 2}).Changed || changed
+	})
+	big := func(name string) pixel.Slot {
+		x, y, _, _ := dots(find(t, tt, name))
+		return at(tt.Image(), wd.pal, x+4, y+4)
+	}
+	if big("Green") != pixel.Good {
+		t.Fatal("the big picture is not the chosen one")
+	}
+	// The middle of the strip is the second thumbnail.
+	click(t, tt, "Views")
+	if chosen != 1 || !changed || big("Red") != pixel.Bad {
+		t.Fatalf("clicking the middle chose %d", chosen)
+	}
+	tt.Key(0, ui.KeyRight)
+	if chosen != 2 || big("Blue") != pixel.Info {
+		t.Fatalf("Right chose %d", chosen)
+	}
+	changed = false
+	tt.Key(0, ui.KeyRight)
+	if chosen != 2 || changed {
+		t.Fatalf("Right at the end: %d, changed %v", chosen, changed)
+	}
+	// The chosen thumbnail wears the cursor ring.
+	x, y, _, _ := dots(find(t, tt, "Views"))
+	if at(tt.Image(), wd.pal, x+2*10, y) != pixel.Accent || at(tt.Image(), wd.pal, x, y) == pixel.Accent {
+		t.Fatal("the ring is not on the chosen thumbnail")
+	}
+	for name, fn := range map[string]func(c *ui.Context){
+		"names short of pictures": func(c *ui.Context) {
+			n := 0
+			media.Gallery(c, "V", pics, []string{"Green"}, &n, media.GalleryOptions{})
+		},
+		"a choice past the end": func(c *ui.Context) {
+			n := 3
+			media.Gallery(c, "V", pics, []string{"Green", "Red", "Blue"}, &n, media.GalleryOptions{})
+		},
+	} {
+		mustPanic(t, name, func() { view(300, 200, newWorld(), fn) })
+	}
+}