ui/app: (wayland) avoid excessive key repeats

Wayland requires its clients to handle key repeating themselves.
Our strategy is simple: start a timer on key down and fire key
events at regular intervals until another key event arrives.

However, if the program blocks the event loop while processing a
synchronous event, key repeats might pile up before the stopping
key event is processed.

This change use the timestamp of the stopping key event to only
dispatch the repeats queued up before the stop time.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

ui/app/os_wayland.go

@@ -77,9 +77,22 @@ type wlConn struct {
 	xkbCompTable *C.struct_xkb_compose_table
 	xkbCompState *C.struct_xkb_compose_state
 	utf8Buf      []byte
-	repeatRate   int
-	repeatDelay  time.Duration
-	repeatStop   chan struct{}
+
+	repeat repeatState
+}
+
+type repeatState struct {
+	rate  int
+	delay time.Duration
+
+	key   C.uint32_t
+	win   *window
+	stopC chan struct{}
+
+	start time.Duration
+	last  time.Duration
+	mu    sync.Mutex
+	now   time.Duration
 }
 
 type window struct {
@@ -569,7 +582,7 @@ func gio_onPointerAxisDiscrete(data unsafe.Pointer, pointer *C.struct_wl_pointer
 
 //export gio_onKeyboardKeymap
 func gio_onKeyboardKeymap(data unsafe.Pointer, keyboard *C.struct_wl_keyboard, format C.uint32_t, fd C.int32_t, size C.uint32_t) {
-	conn.stopRepeat()
+	conn.repeat.Stop(0)
 	defer syscall.Close(int(fd))
 	if conn.xkbCompState != nil {
 		C.xkb_compose_state_unref(conn.xkbCompState)
@@ -628,19 +641,20 @@ func gio_onKeyboardKeymap(data unsafe.Pointer, keyboard *C.struct_wl_keyboard, f
 
 //export gio_onKeyboardEnter
 func gio_onKeyboardEnter(data unsafe.Pointer, keyboard *C.struct_wl_keyboard, serial C.uint32_t, surf *C.struct_wl_surface, keys *C.struct_wl_array) {
-	conn.stopRepeat()
+	conn.repeat.Stop(0)
 	w := winMap[surf]
 	winMap[keyboard] = w
 }
 
 //export gio_onKeyboardLeave
 func gio_onKeyboardLeave(data unsafe.Pointer, keyboard *C.struct_wl_keyboard, serial C.uint32_t, surf *C.struct_wl_surface) {
-	conn.stopRepeat()
+	conn.repeat.Stop(0)
 }
 
 //export gio_onKeyboardKey
 func gio_onKeyboardKey(data unsafe.Pointer, keyboard *C.struct_wl_keyboard, serial, timestamp, keyCode, state C.uint32_t) {
-	conn.stopRepeat()
+	t := time.Duration(timestamp) * time.Millisecond
+	conn.repeat.Stop(t)
 	w := winMap[keyboard]
 	if state != C.WL_KEYBOARD_KEY_STATE_PRESSED || conn.xkbMap == nil || conn.xkbState == nil || conn.xkbCompState == nil {
 		return
@@ -648,24 +662,78 @@ func gio_onKeyboardKey(data unsafe.Pointer, keyboard *C.struct_wl_keyboard, seri
 	// According to the xkb_v1 spec: "to determine the xkb keycode, clients must add 8 to the key event keycode."
 	keyCode += 8
 	w.dispatchKey(keyCode)
-	if conn.repeatRate > 0 && C.xkb_keymap_key_repeats(conn.xkbMap, C.xkb_keycode_t(keyCode)) == 1 {
-		stop := make(chan struct{})
-		conn.repeatStop = stop
-		rate, delay := conn.repeatRate, conn.repeatDelay
-		go func() {
-			timer := time.NewTimer(delay)
-			for {
-				select {
-				case <-timer.C:
-				case <-stop:
-					close(stop)
-					return
-				}
-				w.dispatchKey(keyCode)
-				delay = time.Second / time.Duration(rate)
-				timer.Reset(delay)
+	if C.xkb_keymap_key_repeats(conn.xkbMap, C.xkb_keycode_t(keyCode)) == 1 {
+		conn.repeat.Start(w, keyCode, t)
+	}
+}
+
+func (r *repeatState) Start(w *window, keyCode C.uint32_t, t time.Duration) {
+	if r.rate <= 0 {
+		return
+	}
+	stopC := make(chan struct{})
+	r.start = t
+	r.last = 0
+	r.now = 0
+	r.stopC = stopC
+	r.key = keyCode
+	r.win = w
+	rate, delay := r.rate, r.delay
+	go func() {
+		timer := time.NewTimer(delay)
+		for {
+			select {
+			case <-timer.C:
+			case <-stopC:
+				close(stopC)
+				return
 			}
-		}()
+			r.Advance(delay)
+			w.notify()
+			delay = time.Second / time.Duration(rate)
+			timer.Reset(delay)
+		}
+	}()
+}
+
+func (r *repeatState) Stop(t time.Duration) {
+	if r.stopC == nil {
+		return
+	}
+	r.stopC <- struct{}{}
+	<-r.stopC
+	r.stopC = nil
+	t -= r.start
+	if r.now > t {
+		r.now = t
+	}
+}
+
+func (r *repeatState) Advance(dt time.Duration) {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	r.now += dt
+}
+
+func (r *repeatState) Repeat() {
+	if r.rate <= 0 {
+		return
+	}
+	r.mu.Lock()
+	now := r.now
+	r.mu.Unlock()
+	for {
+		var delay time.Duration
+		if r.last < r.delay {
+			delay = r.delay
+		} else {
+			delay = time.Second / time.Duration(r.rate)
+		}
+		if r.last+delay > now {
+			break
+		}
+		r.win.dispatchKey(r.key)
+		r.last += delay
 	}
 }
 
@@ -725,6 +793,7 @@ loop:
 		case *dispEvents&(syscall.POLLERR|syscall.POLLHUP) != 0:
 			break loop
 		}
+		conn.repeat.Repeat()
 		if redraw {
 			w.draw(false)
 		}
@@ -827,7 +896,7 @@ func (w *window) dispatchKey(keyCode C.uint32_t) {
 
 //export gio_onKeyboardModifiers
 func gio_onKeyboardModifiers(data unsafe.Pointer, keyboard *C.struct_wl_keyboard, serial, depressed, latched, locked, group C.uint32_t) {
-	conn.stopRepeat()
+	conn.repeat.Stop(0)
 	if conn.xkbState == nil {
 		return
 	}
@@ -837,8 +906,9 @@ func gio_onKeyboardModifiers(data unsafe.Pointer, keyboard *C.struct_wl_keyboard
 
 //export gio_onKeyboardRepeatInfo
 func gio_onKeyboardRepeatInfo(data unsafe.Pointer, keyboard *C.struct_wl_keyboard, rate, delay C.int32_t) {
-	conn.repeatRate = int(rate)
-	conn.repeatDelay = time.Duration(delay) * time.Millisecond
+	conn.repeat.Stop(0)
+	conn.repeat.rate = int(rate)
+	conn.repeat.delay = time.Duration(delay) * time.Millisecond
 }
 
 //export gio_onTextInputEnter
@@ -1080,17 +1150,8 @@ func waylandConnect() error {
 	return nil
 }
 
-func (c *wlConn) stopRepeat() {
-	if c.repeatStop == nil {
-		return
-	}
-	c.repeatStop <- struct{}{}
-	<-c.repeatStop
-	c.repeatStop = nil
-}
-
 func (c *wlConn) destroy() {
-	c.stopRepeat()
+	c.repeat.Stop(0)
 	if c.xkbCompState != nil {
 		C.xkb_compose_state_unref(c.xkbCompState)
 		c.xkbCompState = nil