ui: Panic on MaximizeWindow when the window is not resizable

On Windows, the window could be maximized even when the window was
not resizable. This behavior is confusing. Forbid it so that the
behavior will be clearer.

examples/windowsize/main.go

@@ -251,7 +251,7 @@ func (g *game) Update(screen *ebiten.Image) error {
 	ebiten.SetWindowDecorated(decorated)
 	ebiten.SetWindowPosition(positionX, positionY)
 	ebiten.SetWindowFloating(floating)
-	if maximize {
+	if maximize && ebiten.IsWindowResizable() {
 		ebiten.MaximizeWindow()
 	}
 	if minimize {
@@ -294,7 +294,7 @@ func (g *game) Draw(screen *ebiten.Image) {
 	}
 
 	var lines []string
-	if !ebiten.IsWindowMaximized() {
+	if !ebiten.IsWindowMaximized() && ebiten.IsWindowResizable() {
 		lines = append(lines, "[M] Maximize the window")
 	}
 	if !ebiten.IsWindowMinimized() {
@@ -403,6 +403,7 @@ func main() {
 		ebiten.SetWindowFloating(true)
 	}
 	if *flagMaximize {
+		ebiten.SetWindowResizable(true)
 		ebiten.MaximizeWindow()
 	}
 	if *flagAutoAdjusting {

internal/uidriver/glfw/window.go

@@ -129,6 +129,9 @@ func (w *window) IsMaximized() bool {
 }
 
 func (w *window) Maximize() {
+	if !w.IsResizable() {
+		panic("glfw: a window to maximize must be resizable")
+	}
 	if !w.ui.isRunning() {
 		w.ui.setInitWindowMaximized(true)
 		return

window.go

@@ -262,12 +262,15 @@ func SetWindowFloating(float bool) {
 
 // MaximizeWindow maximizes the window.
 //
-// On some environments like macOS, MaximizeWindow requres that the window is resizable.
+// MaximizeWindow panics when the window is not resizable.
 //
 // MaximizeWindow does nothing on browsers or mobiles.
 //
 // MaximizeWindow is concurrent-safe.
 func MaximizeWindow() {
+	if !IsWindowResizable() {
+		panic("ebiten: a window to maximize must be resizable")
+	}
 	if w := uiDriver().Window(); w != nil {
 		w.Maximize()
 	}