uidriver/glfw: Force to swap buffer or recreate an window after toggling fullscreen

This change resolves a bug that an image lag remains after
toggling fullscreen.

On OpenGL, swapping buffer is necessary after toggling fullscreen.

On Metal, recreating a window works after toggling fullscreen.

Fixes #1004

internal/uidriver/glfw/ui.go

@@ -21,6 +21,7 @@ package glfw
 
 import (
 	"context"
+	"fmt"
 	"image"
 	"math"
 	"os"
@@ -323,22 +324,14 @@ func (u *UserInterface) SetScreenSize(width, height int) {
 	if !u.isRunning() {
 		panic("glfw: SetScreenSize can't be called before the main loop starts")
 	}
-	_ = u.t.Call(func() error {
-		// TODO: What if the window is maximized? (#320)
 	u.setScreenSize(width, height, u.scale, u.isFullscreen(), u.vsync)
-		return nil
-	})
 }
 
 func (u *UserInterface) SetScreenScale(scale float64) {
 	if !u.isRunning() {
 		panic("glfw: SetScreenScale can't be called before the main loop starts")
 	}
-	_ = u.t.Call(func() error {
-		// TODO: What if the window is maximized? (#320)
 	u.setScreenSize(u.width, u.height, scale, u.isFullscreen(), u.vsync)
-		return nil
-	})
 }
 
 func (u *UserInterface) ScreenScale() float64 {
@@ -378,10 +371,7 @@ func (u *UserInterface) SetFullscreen(fullscreen bool) {
 		u.setInitFullscreen(fullscreen)
 		return
 	}
-	_ = u.t.Call(func() error {
 	u.setScreenSize(u.width, u.height, u.scale, fullscreen, u.vsync)
-		return nil
-	})
 }
 
 func (u *UserInterface) SetRunnableInBackground(runnableInBackground bool) {
@@ -403,10 +393,7 @@ func (u *UserInterface) SetVsyncEnabled(enabled bool) {
 		u.m.Unlock()
 		return
 	}
-	_ = u.t.Call(func() error {
 	u.setScreenSize(u.width, u.height, u.scale, u.isFullscreen(), enabled)
-		return nil
-	})
 }
 
 func (u *UserInterface) IsVsyncEnabled() bool {
@@ -676,6 +663,12 @@ func (u *UserInterface) createWindow() error {
 }
 
 func (u *UserInterface) run(width, height int, scale float64, title string, context driver.UIContext) error {
+	var (
+		m      *glfw.Monitor
+		mx, my int
+		v      *glfw.VidMode
+	)
+
 	if err := u.t.Call(func() error {
 		if u.graphics.IsGL() {
 			glfw.WindowHint(glfw.ContextVersionMajor, 2)
@@ -728,13 +721,20 @@ func (u *UserInterface) run(width, height int, scale float64, title string, cont
 		// there is not the active window but the foreground window. After showing the current window, the
 		// current window will be the active window. Thus, currentMonitor result varies before and after
 		// showing the window.
-		m := u.currentMonitor()
-		mx, my := m.GetPos()
-		v := m.GetVideoMode()
+		m = u.currentMonitor()
+		mx, my = m.GetPos()
+		v = m.GetVideoMode()
+
+		return nil
+	}); err != nil {
+		return err
+	}
 
 	// The game is in window mode (not fullscreen mode) at the first state.
 	// Don't refer u.initFullscreen here to avoid some GLFW problems.
 	u.setScreenSize(width, height, scale, false, u.vsync)
+
+	_ = u.t.Call(func() error {
 		// Get the window size before showing since window.Show might change the current
 		// monitor which affects glfwSize result.
 		w, h := u.glfwSize()
@@ -754,9 +754,7 @@ func (u *UserInterface) run(width, height int, scale float64, title string, cont
 		u.window.SetPos(x, y)
 
 		return nil
-	}); err != nil {
-		return err
-	}
+	})
 
 	var w unsafe.Pointer
 	_ = u.t.Call(func() error {
@@ -807,10 +805,10 @@ func (u *UserInterface) monitorScale() float64 {
 }
 
 func (u *UserInterface) updateSize(context driver.UIContext) {
-	sizeChanged := false
-	_ = u.t.Call(func() error {
 	u.setScreenSize(u.width, u.height, u.scale, u.isFullscreen(), u.vsync)
 
+	sizeChanged := false
+	_ = u.t.Call(func() error {
 		if !u.toChangeSize {
 			return nil
 		}
@@ -839,13 +837,10 @@ func (u *UserInterface) update(context driver.UIContext) error {
 		return driver.RegularTermination
 	}
 
-	_ = u.t.Call(func() error {
 	if u.isInitFullscreen() {
 		u.setScreenSize(u.width, u.height, u.scale, true, u.vsync)
 		u.setInitFullscreen(false)
 	}
-		return nil
-	})
 
 	// This call is needed for initialization.
 	u.updateSize(context)
@@ -876,7 +871,7 @@ func (u *UserInterface) update(context driver.UIContext) error {
 	}
 
 	// Update the screen size when the window is resizable.
-	_ = u.t.Call(func() error {
+	// TODO: Need locks.
 	w, h := u.reqWidth, u.reqHeight
 	if w != 0 || h != 0 {
 		u.setScreenSize(w, h, u.scale, u.isFullscreen(), u.vsync)
@@ -884,8 +879,6 @@ func (u *UserInterface) update(context driver.UIContext) error {
 	u.reqWidth = 0
 	u.reqHeight = 0
 	return nil
-	})
-	return nil
 }
 
 func (u *UserInterface) loop(context driver.UIContext) error {
@@ -941,10 +934,12 @@ func (u *UserInterface) swapBuffers() {
 	}
 }
 
-// setScreenSize must be called from the main thread.
 func (u *UserInterface) setScreenSize(width, height int, scale float64, fullscreen bool, vsync bool) {
+	windowRecreated := false
+
+	_ = u.t.Call(func() error {
 		if u.width == width && u.height == height && u.scale == scale && u.isFullscreen() == fullscreen && u.vsync == vsync && u.lastMonitorScale == u.monitorScale() {
-		return
+			return nil
 		}
 
 		// On Windows, giving a too small width doesn't call a callback (#165).
@@ -985,11 +980,33 @@ func (u *UserInterface) setScreenSize(width, height int, scale float64, fullscre
 			m := u.currentMonitor()
 			v := m.GetVideoMode()
 			u.window.SetMonitor(m, 0, 0, v.Width, v.Height, v.RefreshRate)
+
+			// Swapping buffer is necesary to prevent the image lag (#1004).
+			if u.graphics.IsGL() {
+				glfw.PollEvents()
+				u.swapBuffers()
+			}
 		} else {
 			if u.window.GetMonitor() != nil {
-			// Give dummy values as the window position and size.
-			// The new window position should be specifying after SetSize.
+				if u.graphics.IsGL() {
+					// When OpenGL is used, swapping buffer is enough to solve the image-lag
+					// issue (#1004). Rather, recreating window destroys GPU resources.
 					u.window.SetMonitor(nil, 0, 0, 16, 16, 0)
+					glfw.PollEvents()
+					u.swapBuffers()
+				} else {
+					// Recreate the window since an image lag remains after coming back from
+					// fullscreen (#1004).
+					if u.window != nil {
+						u.window.Destroy()
+						u.window = nil
+					}
+					if err := u.createWindow(); err != nil {
+						// TODO: This should return an error.
+						panic(fmt.Sprintf("glfw: failed to recreate window: %v", err))
+					}
+					windowRecreated = true
+				}
 			}
 
 			oldW, oldH := u.window.GetSize()
@@ -1016,8 +1033,8 @@ func (u *UserInterface) setScreenSize(width, height int, scale float64, fullscre
 				x := u.origPosX
 				y := u.origPosY
 				u.window.SetPos(x, y)
-			// Dirty hack for macOS (#703). Rendering doesn't work correctly with one SetPos, but work
-			// with two or more SetPos.
+				// Dirty hack for macOS (#703). Rendering doesn't work correctly with one SetPos, but
+				// work with two or more SetPos.
 				if runtime.GOOS == "darwin" {
 					u.window.SetPos(x+1, y)
 					u.window.SetPos(x, y)
@@ -1047,6 +1064,12 @@ func (u *UserInterface) setScreenSize(width, height int, scale float64, fullscre
 		u.graphics.SetVsyncEnabled(vsync)
 
 		u.toChangeSize = true
+		return nil
+	})
+
+	if windowRecreated {
+		u.graphics.SetWindow(u.nativeWindow())
+	}
 }
 
 // currentMonitor returns the monitor most suitable with the current window.