internal/ui: bug fix: preserve a captured cursor positions for toggling fullscreening for browsers

Closes #2475

internal/ui/input_js.go

@@ -15,6 +15,7 @@
 package ui
 
 import (
+	"math"
 	"syscall/js"
 	"unicode"
 )
@@ -230,10 +231,50 @@ func UpdateInputFromEvent(e js.Value) {
 	theUI.updateInputFromEvent(e)
 }
 
+func (u *userInterfaceImpl) saveCursorPosition() {
+	u.savedCursorX = u.inputState.CursorX
+	u.savedCursorY = u.inputState.CursorY
+	w, h := u.outsideSize()
+	u.savedOutsideWidth = w
+	u.savedOutsideHeight = h
+}
+
 func (u *userInterfaceImpl) updateInputState() error {
 	s := u.DeviceScaleFactor()
-	cx, cy := u.context.clientPositionToLogicalPosition(u.cursorXInClient, u.cursorYInClient, s)
-	u.inputState.CursorX, u.inputState.CursorY = cx, cy
+
+	if !math.IsNaN(u.savedCursorX) && !math.IsNaN(u.savedCursorY) {
+		// If savedCursorX and savedCursorY are valid values, the cursor is saved just before entering or exiting from fullscreen.
+		// Even after entering or exiting from fullscreening, the outside (body) size is not updated for a while.
+		// Wait for the outside size updated.
+		if w, h := u.outsideSize(); u.savedOutsideWidth != w || u.savedOutsideHeight != h {
+			u.inputState.CursorX = u.savedCursorX
+			u.inputState.CursorY = u.savedCursorY
+			cx, cy := u.context.logicalPositionToClientPosition(u.inputState.CursorX, u.inputState.CursorY, s)
+			u.cursorXInClient = cx
+			u.cursorYInClient = cy
+			u.savedCursorX = math.NaN()
+			u.savedCursorY = math.NaN()
+			u.savedOutsideWidth = 0
+			u.savedOutsideHeight = 0
+			u.outsideSizeUnchangedCount = 0
+		} else {
+			u.outsideSizeUnchangedCount++
+
+			// If the outside size is not changed for a while, probably the screen size is not actually changed.
+			// Reset the state.
+			if u.outsideSizeUnchangedCount > 60 {
+				u.savedCursorX = math.NaN()
+				u.savedCursorY = math.NaN()
+				u.savedOutsideWidth = 0
+				u.savedOutsideHeight = 0
+				u.outsideSizeUnchangedCount = 0
+			}
+		}
+	} else {
+		cx, cy := u.context.clientPositionToLogicalPosition(u.cursorXInClient, u.cursorYInClient, s)
+		u.inputState.CursorX = cx
+		u.inputState.CursorY = cy
+	}
 
 	u.inputState.Touches = u.inputState.Touches[:0]
 	for _, t := range u.touchesInClient {

internal/ui/ui_js.go

@@ -16,6 +16,7 @@ package ui
 
 import (
 	"image"
+	"math"
 	"sync"
 	"syscall/js"
 	"time"
@@ -106,6 +107,12 @@ type userInterfaceImpl struct {
 	origCursorYInClient float64
 	touchesInClient     []touchInClient
 
+	savedCursorX              float64
+	savedCursorY              float64
+	savedOutsideWidth         float64
+	savedOutsideHeight        float64
+	outsideSizeUnchangedCount int
+
 	keyboardLayoutMap js.Value
 
 	m         sync.Mutex
@@ -115,6 +122,8 @@ type userInterfaceImpl struct {
 func init() {
 	theUI.userInterfaceImpl = userInterfaceImpl{
 		runnableOnUnfocused: true,
+		savedCursorX:        math.NaN(),
+		savedCursorY:        math.NaN(),
 	}
 }
 
@@ -150,6 +159,11 @@ func (u *userInterfaceImpl) SetFullscreen(fullscreen bool) {
 	if fullscreen == u.IsFullscreen() {
 		return
 	}
+
+	if theUI.cursorMode == CursorModeCaptured {
+		theUI.saveCursorPosition()
+	}
+
 	if fullscreen {
 		f := canvas.Get("requestFullscreen")
 		if !f.Truthy() {
@@ -158,6 +172,7 @@ func (u *userInterfaceImpl) SetFullscreen(fullscreen bool) {
 		f.Call("bind", canvas).Invoke()
 		return
 	}
+
 	f := document.Get("exitFullscreen")
 	if !f.Truthy() {
 		f = document.Get("webkitExitFullscreen")