examples: remove depdencies on golang.org/x/sys/windows (#278)

Closes #270

examples/libc/main_windows.go

@@ -3,9 +3,11 @@
 
 package main
 
-import "golang.org/x/sys/windows"
+import "syscall"
 
 func openLibrary(name string) (uintptr, error) {
-	handle, err := windows.LoadLibrary(name)
+	// Use [syscall.LoadLibrary] here to avoid external dependencies (#270).
+	// For actual use cases, [golang.org/x/sys/windows.NewLazySystemDLL] is recommended.
+	handle, err := syscall.LoadLibrary(name)
 	return uintptr(handle), err
 }

examples/window/main_windows.go

@@ -5,10 +5,9 @@ package main
 
 import (
 	"runtime"
+	"syscall"
 	"unsafe"
 
-	"golang.org/x/sys/windows"
-
 	"github.com/ebitengine/purego"
 )
 
@@ -78,10 +77,14 @@ var (
 )
 
 func init() {
-	kernel32 := windows.NewLazySystemDLL("kernel32.dll").Handle()
+	// Use [syscall.NewLazyDLL] here to avoid external dependencies (#270).
+	// For actual use cases, [golang.org/x/sys/windows.NewLazySystemDLL] is recommended.
+	kernel32 := syscall.NewLazyDLL("kernel32.dll").Handle()
 	purego.RegisterLibFunc(&GetModuleHandle, kernel32, "GetModuleHandleW")
 
-	user32 := windows.NewLazySystemDLL("user32.dll").Handle()
+	// Use [syscall.NewLazyDLL] here to avoid external dependencies (#270).
+	// For actual use cases, [golang.org/x/sys/windows.NewLazySystemDLL] is recommended.
+	user32 := syscall.NewLazyDLL("user32.dll").Handle()
 	purego.RegisterLibFunc(&RegisterClassEx, user32, "RegisterClassExW")
 	purego.RegisterLibFunc(&CreateWindowEx, user32, "CreateWindowExW")
 	purego.RegisterLibFunc(&AdjustWindowRect, user32, "AdjustWindowRect")
@@ -96,15 +99,15 @@ func init() {
 }
 
 func main() {
-	className, err := windows.UTF16PtrFromString("Sample Window Class")
+	className, err := syscall.UTF16PtrFromString("Sample Window Class")
 	if err != nil {
 		panic(err)
 	}
 	inst := GetModuleHandle(className)
 
 	wc := WNDCLASSEX{
 		Size:      uint32(unsafe.Sizeof(WNDCLASSEX{})),
-		WndProc:   windows.NewCallback(wndProc),
+		WndProc:   syscall.NewCallback(wndProc),
 		Instance:  inst,
 		ClassName: className,
 	}
@@ -117,7 +120,7 @@ func main() {
 		Right:  320,
 		Bottom: 240,
 	}
-	title, err := windows.UTF16PtrFromString("My Title")
+	title, err := syscall.UTF16PtrFromString("My Title")
 	if err != nil {
 		panic(err)
 	}
@@ -130,7 +133,7 @@ func main() {
 		0, 0, inst, nil,
 	)
 	if hwnd == 0 {
-		panic(windows.GetLastError())
+		panic(syscall.GetLastError())
 	}
 
 	ShowWindow(hwnd, SW_SHOW)

go.mod

@@ -1,5 +1,3 @@
 module github.com/ebitengine/purego
 
 go 1.18
-
-require golang.org/x/sys v0.23.0

go.sum

@@ -1,2 +0,0 @@
-golang.org/x/sys v0.23.0 h1:YfKFowiIMvtgl1UERQoTPPToxltDeZfbj4H7dVUCwmM=
-golang.org/x/sys v0.23.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=