Reduce Mini 2 volume tap latency

station/panel.go

@@ -17,14 +17,15 @@ const (
 	panelPlus   = 115
 	panelCenter = 582
 
-	panelMinTap   = 18 * time.Millisecond
-	panelGap      = 205 * time.Millisecond
-	panelMaxSwipe = 520 * time.Millisecond
-	panelHold     = 500 * time.Millisecond
-	panelRepeat   = 250 * time.Millisecond
-	panelWakeHold = 3 * time.Second
-	panelCooldown = 170 * time.Millisecond
-	panelMaxHold  = 6 * time.Second
+	panelMinTap    = 18 * time.Millisecond
+	panelVolumeGap = 115 * time.Millisecond
+	panelGap       = 205 * time.Millisecond
+	panelMaxSwipe  = 520 * time.Millisecond
+	panelHold      = 500 * time.Millisecond
+	panelRepeat    = 250 * time.Millisecond
+	panelWakeHold  = 3 * time.Second
+	panelCooldown  = 170 * time.Millisecond
+	panelMaxHold   = 6 * time.Second
 )
 
 type panelAction string
@@ -46,6 +47,8 @@ type panelGesture struct {
 	lastRelease  time.Time
 	nextHold     time.Time
 	cooldown     time.Time
+	volumeTail   time.Time
+	volumeZone   uint16
 	held         bool
 	invalid      bool
 	ignoreToSync bool
@@ -85,10 +88,16 @@ func (g *panelGesture) finish(now time.Time) panelAction {
 		}
 	}
 	cooldown := g.cooldown
+	var volumeTail time.Time
+	var volumeZone uint16
 	if action == panelNext || action == panelPrevious {
 		cooldown = now.Add(panelCooldown)
 	}
-	*g = panelGesture{cooldown: cooldown}
+	if action == panelQuieter || action == panelLouder {
+		volumeTail = g.lastRelease.Add(panelGap)
+		volumeZone = g.path[0]
+	}
+	*g = panelGesture{cooldown: cooldown, volumeTail: volumeTail, volumeZone: volumeZone}
 	return action
 }
 
@@ -96,7 +105,11 @@ func (g *panelGesture) tick(now time.Time) panelAction {
 	if g.count == 0 {
 		return ""
 	}
-	if g.down == 0 && !now.Before(g.lastRelease.Add(panelGap)) {
+	gap := panelGap
+	if g.count == 1 && !g.invalid && !g.held && g.path[0] != panelCenter {
+		gap = panelVolumeGap
+	}
+	if g.down == 0 && !now.Before(g.lastRelease.Add(gap)) {
 		return g.finish(now)
 	}
 	if g.down == 0 || g.invalid || g.count != 1 || now.Before(g.nextHold) {
@@ -142,7 +155,9 @@ func (g *panelGesture) key(now time.Time, code uint16, value uint32) {
 		if code == panelCenter {
 			g.nextHold = now.Add(panelWakeHold)
 		}
-		g.invalid = now.Before(g.cooldown)
+		// A late second zone belongs to the same ambiguous motion. Another
+		// touch on the original volume zone can still be an independent tap.
+		g.invalid = now.Before(g.cooldown) || (now.Before(g.volumeTail) && code != g.volumeZone)
 	}
 	// A moving finger can leave and re-enter the center zone while crossing it.
 	if g.count == 2 && code == panelCenter && g.path[1] == panelCenter {

station/panel_test.go

@@ -96,3 +96,25 @@ func TestPanelHoldRepeatsWithoutReleaseTap(t *testing.T) {
 		t.Fatalf("center hold emitted %q", got)
 	}
 }
+
+func TestPanelVolumeRespondsBeforeSwipeWindowEnds(t *testing.T) {
+	start := time.Unix(100, 0)
+	release := start.Add(75 * time.Millisecond)
+	var g panelGesture
+	g.key(start, panelPlus, 1)
+	g.key(release, panelPlus, 0)
+	if got := g.tick(release.Add(panelVolumeGap - time.Millisecond)); got != "" {
+		t.Fatalf("emitted before adjacent-zone window: %q", got)
+	}
+	if got := g.tick(release.Add(panelVolumeGap)); got != panelLouder {
+		t.Fatalf("volume did not respond after the shorter gap: %q", got)
+	}
+	center := release.Add(160 * time.Millisecond)
+	g.key(center, panelCenter, 1)
+	g.key(center.Add(30*time.Millisecond), panelCenter, 0)
+	g.key(center.Add(55*time.Millisecond), panelMinus, 1)
+	g.key(center.Add(80*time.Millisecond), panelMinus, 0)
+	if got := g.tick(center.Add(time.Second)); got != "" {
+		t.Fatalf("late swipe continuation emitted a second action: %q", got)
+	}
+}