ui: Bug fix: wrong scaling when a window move across monitors

Fixes #701

internal/devicescale/impl_windows.go

@@ -24,7 +24,6 @@ import (
 
 const (
 	logPixelsX              = 88
-	monitorDefaultToNull    = 0
 	monitorDefaultToNearest = 2
 	mdtEffectiveDpi         = 0
 )
@@ -178,7 +177,7 @@ func impl(x, y int) float64 {
 
 	// MonitorFromPoint requires to pass a POINT value, and there seems no portable way to
 	// do this with Cgo. Use MonitorFromRect instead.
-	m, err := monitorFromRect(uintptr(unsafe.Pointer(&lprc)), monitorDefaultToNull)
+	m, err := monitorFromRect(uintptr(unsafe.Pointer(&lprc)), monitorDefaultToNearest)
 	if err != nil {
 		panic(err)
 	}

internal/ui/ui_glfw.go

@@ -774,14 +774,6 @@ func (u *userInterface) currentMonitor() *glfw.Monitor {
 	if m := w.GetMonitor(); m != nil {
 		return m
 	}
-
-	wx, wy := w.GetPos()
-	for _, m := range glfw.GetMonitors() {
-		mx, my := m.GetPos()
-		v := m.GetVideoMode()
-		if mx <= wx && wx < mx+v.Width && my <= wy && wy < my+v.Height {
-			return m
-		}
-	}
-	return glfw.GetPrimaryMonitor()
+	// Get the monitor which the current window belongs to. This requires OS API.
+	return currentMonitor()
 }

internal/ui/ui_mac.go

@@ -18,6 +18,25 @@
 
 package ui
 
+// #cgo CFLAGS: -x objective-c
+// #cgo LDFLAGS: -framework AppKit
+//
+// #import <AppKit/AppKit.h>
+//
+// static void currentMonitorPos(int* x, int* y) {
+//   NSDictionary* screenDictionary = [[NSScreen mainScreen] deviceDescription];
+//   NSNumber* screenID = [screenDictionary objectForKey:@"NSScreenNumber"];
+//   CGDirectDisplayID aID = [screenID unsignedIntValue];
+//   const CGRect bounds = CGDisplayBounds(aID);
+//   *x = bounds.origin.x;
+//   *y = bounds.origin.y;
+// }
+import "C"
+
+import (
+	"github.com/go-gl/glfw/v3.2/glfw"
+)
+
 func glfwScale() float64 {
 	return 1
 }
@@ -25,3 +44,16 @@ func glfwScale() float64 {
 func adjustWindowPosition(x, y int) (int, int) {
 	return x, y
 }
+
+func currentMonitor() *glfw.Monitor {
+	x := C.int(0)
+	y := C.int(0)
+	C.currentMonitorPos(&x, &y)
+	for _, m := range glfw.GetMonitors() {
+		mx, my := m.GetPos()
+		if int(x) == mx && int(y) == my {
+			return m
+		}
+	}
+	return nil
+}

internal/ui/ui_unix.go

@@ -19,6 +19,8 @@
 package ui
 
 import (
+	"github.com/go-gl/glfw/v3.2/glfw"
+
 	"github.com/hajimehoshi/ebiten/internal/devicescale"
 )
 
@@ -30,3 +32,17 @@ func glfwScale() float64 {
 func adjustWindowPosition(x, y int) (int, int) {
 	return x, y
 }
+
+func currentMonitor() *glfw.Monitor {
+	// TODO: Return more appropriate display.
+	w := glfw.GetCurrentContext()
+	wx, wy := w.GetPos()
+	for _, m := range glfw.GetMonitors() {
+		mx, my := m.GetPos()
+		v := m.GetVideoMode()
+		if mx <= wx && wx < mx+v.Width && my <= wy && wy < my+v.Height {
+			return m
+		}
+	}
+	return nil
+}

internal/ui/ui_windows.go

@@ -16,21 +16,81 @@
 
 package ui
 
-// TODO: Use golang.org/x/sys/windows (NewLazyDLL) instead of cgo.
-
-// #cgo LDFLAGS: -lgdi32
-//
-// #include <windows.h>
-//
-// static int getCaptionHeight() {
-//   return GetSystemMetrics(SM_CYCAPTION);
-// }
-import "C"
-
 import (
+	"fmt"
+	"syscall"
+	"unsafe"
+
+	"github.com/go-gl/glfw/v3.2/glfw"
+
 	"github.com/hajimehoshi/ebiten/internal/devicescale"
 )
 
+const (
+	smCyCaption             = 4
+	monitorDefaultToNearest = 2
+)
+
+type rect struct {
+	left   int32
+	top    int32
+	right  int32
+	bottom int32
+}
+
+type monitorInfo struct {
+	cbSize    uint32
+	rcMonitor rect
+	rcWork    rect
+	dwFlags   uint32
+}
+
+var (
+	// user32 is defined at hideconsole_windows.go
+	procGetSystemMetrics  = user32.NewProc("GetSystemMetrics")
+	procGetActiveWindow   = user32.NewProc("GetActiveWindow")
+	procMonitorFromWindow = user32.NewProc("MonitorFromWindow")
+	procGetMonitorInfoW   = user32.NewProc("GetMonitorInfoW")
+)
+
+func getSystemMetrics(nIndex int) (int, error) {
+	r, _, e := syscall.Syscall(procGetSystemMetrics.Addr(), 1, uintptr(nIndex), 0, 0)
+	if e != 0 {
+		return 0, fmt.Errorf("ui: GetSystemMetrics failed: error code: %d", e)
+	}
+	return int(r), nil
+}
+
+func getActiveWindow() (uintptr, error) {
+	r, _, e := syscall.Syscall(procGetActiveWindow.Addr(), 0, 0, 0, 0)
+	if e != 0 {
+		return 0, fmt.Errorf("ui: GetActiveWindow failed: error code: %d", e)
+	}
+	return r, nil
+}
+
+func monitorFromWindow(hwnd uintptr, dwFlags uint32) (uintptr, error) {
+	r, _, e := syscall.Syscall(procMonitorFromWindow.Addr(), 2, hwnd, uintptr(dwFlags), 0)
+	if e != 0 {
+		return 0, fmt.Errorf("ui: MonitorFromWindow failed: error code: %d", e)
+	}
+	if r == 0 {
+		return 0, fmt.Errorf("ui: MonitorFromWindow failed: returned value: %d", r)
+	}
+	return r, nil
+}
+
+func getMonitorInfoW(hMonitor uintptr, lpmi *monitorInfo) error {
+	r, _, e := syscall.Syscall(procGetMonitorInfoW.Addr(), 2, hMonitor, uintptr(unsafe.Pointer(lpmi)), 0)
+	if e != 0 {
+		return fmt.Errorf("ui: GetMonitorInfoW failed: error code: %d", e)
+	}
+	if r == 0 {
+		return fmt.Errorf("ui: GetMonitorInfoW failed: returned value: %d", r)
+	}
+	return nil
+}
+
 func glfwScale() float64 {
 	// This function must be called on the main thread.
 	return devicescale.GetAt(currentUI.currentMonitor().GetPos())
@@ -42,9 +102,43 @@ func adjustWindowPosition(x, y int) (int, int) {
 	if x < 0 {
 		x = 0
 	}
-	t := int(C.getCaptionHeight())
+	t, err := getSystemMetrics(smCyCaption)
+	if err != nil {
+		panic(err)
+	}
 	if y < t {
 		y = t
 	}
 	return x, y
 }
+
+func currentMonitor() *glfw.Monitor {
+	w, err := getActiveWindow()
+	if err != nil {
+		panic(err)
+	}
+	if w == 0 {
+		// There is no window at launching.
+		return glfw.GetPrimaryMonitor()
+	}
+
+	m, err := monitorFromWindow(w, monitorDefaultToNearest)
+	if err != nil {
+		panic(err)
+	}
+
+	mi := monitorInfo{}
+	mi.cbSize = uint32(unsafe.Sizeof(mi))
+	if err := getMonitorInfoW(m, &mi); err != nil {
+		panic(err)
+	}
+
+	x, y := int(mi.rcMonitor.left), int(mi.rcMonitor.top)
+	for _, m := range glfw.GetMonitors() {
+		mx, my := m.GetPos()
+		if mx == x && my == y {
+			return m
+		}
+	}
+	return nil
+}