internal/ui: bug fix: ignore ERROR_BUSY when deleting a GL context

Closes #2518

internal/glfwwin/wglcontext_windows.go

@@ -6,10 +6,13 @@
 package glfwwin
 
 import (
+	"errors"
 	"fmt"
 	"strings"
 	"unsafe"
 
+	"golang.org/x/sys/windows"
+
 	"github.com/hajimehoshi/ebiten/v2/internal/microsoftgdk"
 )
 
@@ -321,7 +324,10 @@ func getProcAddressWGL(procname string) uintptr {
 
 func destroyContextWGL(window *Window) error {
 	if window.context.wgl.handle != 0 {
-		if err := wglDeleteContext(window.context.wgl.handle); err != nil {
+		// Ignore ERROR_BUSY. This happens when the thread is different from the context thread (#2518).
+		// This is a known issue of GLFW (glfw/glfw#2239).
+		// TODO: Delete the context on an appropriate thread.
+		if err := wglDeleteContext(window.context.wgl.handle); err != nil && !errors.Is(err, windows.ERROR_BUSY) {
 			return err
 		}
 		window.context.wgl.handle = 0

internal/ui/ui_glfw.go

@@ -1004,8 +1004,7 @@ func (u *userInterfaceImpl) update() (float64, float64, error) {
 
 func (u *userInterfaceImpl) loopGame() error {
 	defer u.mainThread.Call(func() {
-		// An explicit destorying a window tries to delete a GL context on the main thread on Windows (wglDeleteContext),
+		u.window.Destroy()
-		// but this causes an error unfortunately.
 		glfw.Terminate()
 	})
 	for {