internal/ui: bug fix: need to delay to capture a cursor

From the spec https://w3c.github.io/pointerlock/#extensions-to-the-element-interface,
capturing a cursor might require a cooltime. This change adds a delay
to capture a cursor just after escaping from a capture.

Closes #2693

internal/ui/ui_js.go

@@ -80,8 +80,10 @@ type userInterfaceImpl struct {
 	running             bool
 	cursorMode          CursorMode
 	cursorPrevMode      CursorMode
+	captureCursorLater  bool
 	cursorShape         CursorShape
 	onceUpdateCalled    bool
+	lastCaptureExitTime time.Time
 
 	lastDeviceScaleFactor float64
 
@@ -189,6 +191,16 @@ func (u *userInterfaceImpl) CursorMode() CursorMode {
 }
 
 func (u *userInterfaceImpl) SetCursorMode(mode CursorMode) {
+	if mode == CursorModeCaptured && !u.canCaptureCursor() {
+		u.captureCursorLater = true
+		return
+	}
+	u.setCursorMode(mode)
+}
+
+func (u *userInterfaceImpl) setCursorMode(mode CursorMode) {
+	u.captureCursorLater = false
+
 	if !canvas.Truthy() {
 		return
 	}
@@ -199,6 +211,7 @@ func (u *userInterfaceImpl) SetCursorMode(mode CursorMode) {
 	u.cursorPrevMode = u.cursorMode
 	if u.cursorMode == CursorModeCaptured {
 		document.Call("exitPointerLock")
+		u.lastCaptureExitTime = time.Now()
 	}
 	u.cursorMode = mode
 	switch mode {
@@ -272,7 +285,25 @@ func (u *userInterfaceImpl) isFocused() bool {
 	return true
 }
 
+// canCaptureCursor reports whether a cursor can be captured or not now.
+// Just after escaping from a capture, a browser might not be able to capture a cursor (#2693).
+// If it is too early to capture a cursor, Ebitengine tries to delay it.
+//
+// See also https://w3c.github.io/pointerlock/#extensions-to-the-element-interface
+//
+// > Pointer lock is a transient activation-gated API, therefore a requestPointerLock() call
+// > MUST fail if the relevant global object of this does not have transient activation.
+// > This prevents locking upon initial navigation or re-acquiring lock without user's attention.
+func (u *userInterfaceImpl) canCaptureCursor() bool {
+	// 1.5 [sec] seems enough in the real world.
+	return time.Now().Sub(u.lastCaptureExitTime) >= 1500*time.Millisecond
+}
+
 func (u *userInterfaceImpl) update() error {
+	if u.captureCursorLater && u.canCaptureCursor() {
+		u.setCursorMode(CursorModeCaptured)
+	}
+
 	if u.suspended() {
 		return hooks.SuspendAudio()
 	}

run.go

@@ -353,6 +353,7 @@ func CursorMode() CursorModeType {
 // CursorModeCaptured also works on browsers.
 // When the user exits the captured mode not by SetCursorMode but by the UI (e.g., pressing ESC),
 // the previous cursor mode is set automatically.
+// On browsers, setting CursorModeCaptured might be delayed especially just after escaping from a capture.
 //
 // SetCursorMode does nothing on mobiles.
 //