Implement `DisplayServer.window_start_resize`.

doc/classes/DisplayServer.xml

@@ -1836,8 +1836,17 @@
 			<return type="void" />
 			<param index="0" name="window_id" type="int" default="0" />
 			<description>
-				Starts a drag operation on the window with the given [param window_id], using the current mouse position. Call this method when handling a mouse button being pressed to simulate a pressed event on the window's title bar. Using this method allows the window to participate in space switching, tiling, and other system features.
-				[b]Note:[/b] This method is implemented on Linux(X11/Wayland), macOS, and Windows.
+				Starts an interactive drag operation on the window with the given [param window_id], using the current mouse position. Call this method when handling a mouse button being pressed to simulate a pressed event on the window's title bar. Using this method allows the window to participate in space switching, tiling, and other system features.
+				[b]Note:[/b] This method is implemented on Linux (X11/Wayland), macOS, and Windows.
+			</description>
+		</method>
+		<method name="window_start_resize">
+			<return type="void" />
+			<param index="0" name="edge" type="int" enum="DisplayServer.WindowResizeEdge" />
+			<param index="1" name="window_id" type="int" default="0" />
+			<description>
+				Starts an interactive resize operation on the window with the given [param window_id], using the current mouse position. Call this method when handling a mouse button being pressed to simulate a pressed event on the window's edge.
+				[b]Note:[/b] This method is implemented on Linux (X11/Wayland), macOS, and Windows.
 			</description>
 		</method>
 	</methods>
@@ -2183,6 +2192,33 @@
 			Sent when the window title bar decoration is changed (e.g. [constant WINDOW_FLAG_EXTEND_TO_TITLE] is set or window entered/exited full screen mode).
 			[b]Note:[/b] This flag is implemented only on macOS.
 		</constant>
+		<constant name="WINDOW_EDGE_TOP_LEFT" value="0" enum="WindowResizeEdge">
+			Top-left edge of a window.
+		</constant>
+		<constant name="WINDOW_EDGE_TOP" value="1" enum="WindowResizeEdge">
+			Top edge of a window.
+		</constant>
+		<constant name="WINDOW_EDGE_TOP_RIGHT" value="2" enum="WindowResizeEdge">
+			Top-right edge of a window.
+		</constant>
+		<constant name="WINDOW_EDGE_LEFT" value="3" enum="WindowResizeEdge">
+			Left edge of a window.
+		</constant>
+		<constant name="WINDOW_EDGE_RIGHT" value="4" enum="WindowResizeEdge">
+			Right edge of a window.
+		</constant>
+		<constant name="WINDOW_EDGE_BOTTOM_LEFT" value="5" enum="WindowResizeEdge">
+			Bottom-left edge of a window.
+		</constant>
+		<constant name="WINDOW_EDGE_BOTTOM" value="6" enum="WindowResizeEdge">
+			Bottom edge of a window.
+		</constant>
+		<constant name="WINDOW_EDGE_BOTTOM_RIGHT" value="7" enum="WindowResizeEdge">
+			Bottom-right edge of a window.
+		</constant>
+		<constant name="WINDOW_EDGE_MAX" value="8" enum="WindowResizeEdge">
+			Represents the size of the [enum WindowResizeEdge] enum.
+		</constant>
 		<constant name="VSYNC_DISABLED" value="0" enum="VSyncMode">
 			No vertical synchronization, which means the engine will display frames as fast as possible (tearing may be visible). Framerate is unlimited (regardless of [member Engine.max_fps]).
 		</constant>

platform/linuxbsd/wayland/display_server_wayland.cpp

@@ -993,6 +993,13 @@ void DisplayServerWayland::window_start_drag(WindowID p_window) {
 	wayland_thread.window_start_drag(p_window);
 }
 
+void DisplayServerWayland::window_start_resize(WindowResizeEdge p_edge, WindowID p_window) {
+	MutexLock mutex_lock(wayland_thread.mutex);
+
+	ERR_FAIL_INDEX(int(p_edge), WINDOW_EDGE_MAX);
+	wayland_thread.window_start_resize(p_edge, p_window);
+}
+
 void DisplayServerWayland::cursor_set_shape(CursorShape p_shape) {
 	ERR_FAIL_INDEX(p_shape, CURSOR_MAX);
 

platform/linuxbsd/wayland/display_server_wayland.h

@@ -273,6 +273,7 @@ public:
 	virtual DisplayServer::VSyncMode window_get_vsync_mode(WindowID p_window_id) const override;
 
 	virtual void window_start_drag(WindowID p_window = MAIN_WINDOW_ID) override;
+	virtual void window_start_resize(WindowResizeEdge p_edge, WindowID p_window) override;
 
 	virtual void cursor_set_shape(CursorShape p_shape) override;
 	virtual CursorShape cursor_get_shape() const override;

platform/linuxbsd/wayland/wayland_thread.cpp

@@ -3354,6 +3354,80 @@ void WaylandThread::window_start_drag(DisplayServer::WindowID p_window_id) {
 #endif
 }
 
+void WaylandThread::window_start_resize(DisplayServer::WindowResizeEdge p_edge, DisplayServer::WindowID p_window) {
+	// TODO: Use window IDs for multiwindow support.
+	WindowState &ws = main_window;
+	SeatState *ss = wl_seat_get_seat_state(wl_seat_current);
+
+	if (ss && ws.xdg_toplevel) {
+		xdg_toplevel_resize_edge edge = XDG_TOPLEVEL_RESIZE_EDGE_NONE;
+		switch (p_edge) {
+			case DisplayServer::WINDOW_EDGE_TOP_LEFT: {
+				edge = XDG_TOPLEVEL_RESIZE_EDGE_TOP_LEFT;
+			} break;
+			case DisplayServer::WINDOW_EDGE_TOP: {
+				edge = XDG_TOPLEVEL_RESIZE_EDGE_TOP;
+			} break;
+			case DisplayServer::WINDOW_EDGE_TOP_RIGHT: {
+				edge = XDG_TOPLEVEL_RESIZE_EDGE_TOP_RIGHT;
+			} break;
+			case DisplayServer::WINDOW_EDGE_LEFT: {
+				edge = XDG_TOPLEVEL_RESIZE_EDGE_LEFT;
+			} break;
+			case DisplayServer::WINDOW_EDGE_RIGHT: {
+				edge = XDG_TOPLEVEL_RESIZE_EDGE_RIGHT;
+			} break;
+			case DisplayServer::WINDOW_EDGE_BOTTOM_LEFT: {
+				edge = XDG_TOPLEVEL_RESIZE_EDGE_BOTTOM_LEFT;
+			} break;
+			case DisplayServer::WINDOW_EDGE_BOTTOM: {
+				edge = XDG_TOPLEVEL_RESIZE_EDGE_BOTTOM;
+			} break;
+			case DisplayServer::WINDOW_EDGE_BOTTOM_RIGHT: {
+				edge = XDG_TOPLEVEL_RESIZE_EDGE_BOTTOM_RIGHT;
+			} break;
+			default:
+				break;
+		}
+		xdg_toplevel_resize(ws.xdg_toplevel, ss->wl_seat, ss->pointer_data.button_serial, edge);
+	}
+
+#ifdef LIBDECOR_ENABLED
+	if (ws.libdecor_frame) {
+		libdecor_resize_edge edge = LIBDECOR_RESIZE_EDGE_NONE;
+		switch (p_edge) {
+			case DisplayServer::WINDOW_EDGE_TOP_LEFT: {
+				edge = LIBDECOR_RESIZE_EDGE_TOP_LEFT;
+			} break;
+			case DisplayServer::WINDOW_EDGE_TOP: {
+				edge = LIBDECOR_RESIZE_EDGE_TOP;
+			} break;
+			case DisplayServer::WINDOW_EDGE_TOP_RIGHT: {
+				edge = LIBDECOR_RESIZE_EDGE_TOP_RIGHT;
+			} break;
+			case DisplayServer::WINDOW_EDGE_LEFT: {
+				edge = LIBDECOR_RESIZE_EDGE_LEFT;
+			} break;
+			case DisplayServer::WINDOW_EDGE_RIGHT: {
+				edge = LIBDECOR_RESIZE_EDGE_RIGHT;
+			} break;
+			case DisplayServer::WINDOW_EDGE_BOTTOM_LEFT: {
+				edge = LIBDECOR_RESIZE_EDGE_BOTTOM_LEFT;
+			} break;
+			case DisplayServer::WINDOW_EDGE_BOTTOM: {
+				edge = LIBDECOR_RESIZE_EDGE_BOTTOM;
+			} break;
+			case DisplayServer::WINDOW_EDGE_BOTTOM_RIGHT: {
+				edge = LIBDECOR_RESIZE_EDGE_BOTTOM_RIGHT;
+			} break;
+			default:
+				break;
+		}
+		libdecor_frame_resize(ws.libdecor_frame, ss->wl_seat, ss->pointer_data.button_serial, edge);
+	}
+#endif
+}
+
 void WaylandThread::window_set_max_size(DisplayServer::WindowID p_window_id, const Size2i &p_size) {
 	// TODO: Use window IDs for multiwindow support.
 	WindowState &ws = main_window;

platform/linuxbsd/wayland/wayland_thread.h

@@ -955,6 +955,8 @@ public:
 
 	struct wl_surface *window_get_wl_surface(DisplayServer::WindowID p_window_id) const;
 
+	void window_start_resize(DisplayServer::WindowResizeEdge p_edge, DisplayServer::WindowID p_window);
+
 	void window_set_max_size(DisplayServer::WindowID p_window_id, const Size2i &p_size);
 	void window_set_min_size(DisplayServer::WindowID p_window_id, const Size2i &p_size);
 

platform/linuxbsd/x11/display_server_x11.cpp

@@ -69,6 +69,14 @@
 #define _NET_WM_STATE_REMOVE 0L // remove/unset property
 #define _NET_WM_STATE_ADD 1L // add/set property
 
+#define _NET_WM_MOVERESIZE_SIZE_TOPLEFT 0L
+#define _NET_WM_MOVERESIZE_SIZE_TOP 1L
+#define _NET_WM_MOVERESIZE_SIZE_TOPRIGHT 2L
+#define _NET_WM_MOVERESIZE_SIZE_RIGHT 3L
+#define _NET_WM_MOVERESIZE_SIZE_BOTTOMRIGHT 4L
+#define _NET_WM_MOVERESIZE_SIZE_BOTTOM 5L
+#define _NET_WM_MOVERESIZE_SIZE_BOTTOMLEFT 6L
+#define _NET_WM_MOVERESIZE_SIZE_LEFT 7L
 #define _NET_WM_MOVERESIZE_MOVE 8L
 
 // 2.2 is the first release with multitouch
@@ -5516,6 +5524,70 @@ void DisplayServerX11::window_start_drag(WindowID p_window) {
 	XSync(x11_display, 0);
 }
 
+void DisplayServerX11::window_start_resize(WindowResizeEdge p_edge, WindowID p_window) {
+	_THREAD_SAFE_METHOD_
+
+	ERR_FAIL_INDEX(int(p_edge), WINDOW_EDGE_MAX);
+
+	ERR_FAIL_COND(!windows.has(p_window));
+	WindowData &wd = windows[p_window];
+
+	XClientMessageEvent m;
+	memset(&m, 0, sizeof(m));
+
+	XUngrabPointer(x11_display, CurrentTime);
+
+	Window root_return, child_return;
+	int root_x, root_y, win_x, win_y;
+	unsigned int mask_return;
+
+	Bool xquerypointer_result = XQueryPointer(x11_display, wd.x11_window, &root_return, &child_return, &root_x, &root_y, &win_x, &win_y, &mask_return);
+
+	m.type = ClientMessage;
+	m.window = wd.x11_window;
+	m.message_type = XInternAtom(x11_display, "_NET_WM_MOVERESIZE", True);
+	m.format = 32;
+	if (xquerypointer_result) {
+		m.data.l[0] = root_x;
+		m.data.l[1] = root_y;
+		m.data.l[3] = Button1;
+	}
+
+	switch (p_edge) {
+		case DisplayServer::WINDOW_EDGE_TOP_LEFT: {
+			m.data.l[2] = _NET_WM_MOVERESIZE_SIZE_TOPLEFT;
+		} break;
+		case DisplayServer::WINDOW_EDGE_TOP: {
+			m.data.l[2] = _NET_WM_MOVERESIZE_SIZE_TOP;
+		} break;
+		case DisplayServer::WINDOW_EDGE_TOP_RIGHT: {
+			m.data.l[2] = _NET_WM_MOVERESIZE_SIZE_TOPRIGHT;
+		} break;
+		case DisplayServer::WINDOW_EDGE_LEFT: {
+			m.data.l[2] = _NET_WM_MOVERESIZE_SIZE_LEFT;
+		} break;
+		case DisplayServer::WINDOW_EDGE_RIGHT: {
+			m.data.l[2] = _NET_WM_MOVERESIZE_SIZE_RIGHT;
+		} break;
+		case DisplayServer::WINDOW_EDGE_BOTTOM_LEFT: {
+			m.data.l[2] = _NET_WM_MOVERESIZE_SIZE_BOTTOMLEFT;
+		} break;
+		case DisplayServer::WINDOW_EDGE_BOTTOM: {
+			m.data.l[2] = _NET_WM_MOVERESIZE_SIZE_BOTTOM;
+		} break;
+		case DisplayServer::WINDOW_EDGE_BOTTOM_RIGHT: {
+			m.data.l[2] = _NET_WM_MOVERESIZE_SIZE_BOTTOMRIGHT;
+		} break;
+		default:
+			break;
+	}
+	m.data.l[4] = 1; // Source - normal application.
+
+	XSendEvent(x11_display, DefaultRootWindow(x11_display), False, SubstructureRedirectMask | SubstructureNotifyMask, (XEvent *)&m);
+
+	XSync(x11_display, 0);
+}
+
 pid_t get_window_pid(Display *p_display, Window p_window) {
 	Atom atom = XInternAtom(p_display, "_NET_WM_PID", False);
 	Atom actualType;

platform/linuxbsd/x11/display_server_x11.h

@@ -527,6 +527,7 @@ public:
 	virtual DisplayServer::VSyncMode window_get_vsync_mode(WindowID p_vsync_mode) const override;
 
 	virtual void window_start_drag(WindowID p_window = MAIN_WINDOW_ID) override;
+	virtual void window_start_resize(WindowResizeEdge p_edge, WindowID p_window) override;
 
 	virtual Error embed_process(WindowID p_window, OS::ProcessID p_pid, const Rect2i &p_rect, bool p_visible, bool p_grab_focus) override;
 	virtual Error remove_embedded_process(OS::ProcessID p_pid) override;

platform/macos/display_server_macos.h

@@ -92,6 +92,7 @@ public:
 		Vector<Vector2> mpath;
 
 		Point2i mouse_pos;
+		WindowResizeEdge edge = WINDOW_EDGE_MAX;
 
 		Size2i min_size;
 		Size2i max_size;
@@ -409,6 +410,7 @@ public:
 	virtual bool window_minimize_on_title_dbl_click() const override;
 
 	virtual void window_start_drag(WindowID p_window = MAIN_WINDOW_ID) override;
+	virtual void window_start_resize(WindowResizeEdge p_edge, WindowID p_window = MAIN_WINDOW_ID) override;
 
 	virtual void window_set_window_buttons_offset(const Vector2i &p_offset, WindowID p_window = MAIN_WINDOW_ID) override;
 	virtual Vector3i window_get_safe_title_margins(WindowID p_window = MAIN_WINDOW_ID) const override;

platform/macos/display_server_macos.mm

@@ -2440,6 +2440,16 @@ void DisplayServerMacOS::window_start_drag(WindowID p_window) {
 	[wd.window_object performWindowDragWithEvent:event];
 }
 
+void DisplayServerMacOS::window_start_resize(WindowResizeEdge p_edge, WindowID p_window) {
+	_THREAD_SAFE_METHOD_
+
+	ERR_FAIL_INDEX(int(p_edge), WINDOW_EDGE_MAX);
+	ERR_FAIL_COND(!windows.has(p_window));
+	WindowData &wd = windows[p_window];
+
+	wd.edge = p_edge;
+}
+
 void DisplayServerMacOS::window_set_window_buttons_offset(const Vector2i &p_offset, WindowID p_window) {
 	_THREAD_SAFE_METHOD_
 

platform/macos/godot_content_view.mm

@@ -394,6 +394,11 @@
 }
 
 - (void)mouseDown:(NSEvent *)event {
+	DisplayServerMacOS *ds = (DisplayServerMacOS *)DisplayServer::get_singleton();
+	if (ds && ds->has_window(window_id)) {
+		DisplayServerMacOS::WindowData &wd = ds->get_window(window_id);
+		wd.edge = DisplayServer::WINDOW_EDGE_MAX;
+	}
 	if (([event modifierFlags] & NSEventModifierFlagControl)) {
 		mouse_down_control = true;
 		[self processMouseEvent:event index:MouseButton::RIGHT pressed:true outofstream:false];
@@ -404,10 +409,65 @@
 }
 
 - (void)mouseDragged:(NSEvent *)event {
+	DisplayServerMacOS *ds = (DisplayServerMacOS *)DisplayServer::get_singleton();
+	if (ds && ds->has_window(window_id)) {
+		DisplayServerMacOS::WindowData &wd = ds->get_window(window_id);
+		if (wd.edge != DisplayServer::WINDOW_EDGE_MAX) {
+			Size2i max_size = wd.max_size / ds->screen_get_max_scale();
+			Size2i min_size = wd.min_size / ds->screen_get_max_scale();
+			NSRect frame = [wd.window_object frame];
+			switch (wd.edge) {
+				case DisplayServer::WINDOW_EDGE_TOP_LEFT: {
+					int clamped_dx = CLAMP(frame.size.width - event.deltaX, min_size.x, max_size.x) - frame.size.width;
+					int clamped_dy = CLAMP(frame.size.height - event.deltaY, min_size.y, max_size.y) - frame.size.height;
+					[wd.window_object setFrame:NSMakeRect(frame.origin.x - clamped_dx, frame.origin.y, frame.size.width + clamped_dx, frame.size.height + clamped_dy) display:YES];
+				} break;
+				case DisplayServer::WINDOW_EDGE_TOP: {
+					int clamped_dy = CLAMP(frame.size.height - event.deltaY, min_size.y, max_size.y) - frame.size.height;
+					[wd.window_object setFrame:NSMakeRect(frame.origin.x, frame.origin.y, frame.size.width, frame.size.height + clamped_dy) display:YES];
+				} break;
+				case DisplayServer::WINDOW_EDGE_TOP_RIGHT: {
+					int clamped_dx = CLAMP(frame.size.width + event.deltaX, min_size.x, max_size.x) - frame.size.width;
+					int clamped_dy = CLAMP(frame.size.height - event.deltaY, min_size.y, max_size.y) - frame.size.height;
+					[wd.window_object setFrame:NSMakeRect(frame.origin.x, frame.origin.y, frame.size.width + clamped_dx, frame.size.height + clamped_dy) display:YES];
+				} break;
+				case DisplayServer::WINDOW_EDGE_LEFT: {
+					int clamped_dx = CLAMP(frame.size.width - event.deltaX, min_size.x, max_size.x) - frame.size.width;
+					[wd.window_object setFrame:NSMakeRect(frame.origin.x - clamped_dx, frame.origin.y, frame.size.width + clamped_dx, frame.size.height) display:YES];
+				} break;
+				case DisplayServer::WINDOW_EDGE_RIGHT: {
+					int clamped_dx = CLAMP(frame.size.width + event.deltaX, min_size.x, max_size.x) - frame.size.width;
+					[wd.window_object setFrame:NSMakeRect(frame.origin.x, frame.origin.y, frame.size.width + clamped_dx, frame.size.height) display:YES];
+				} break;
+				case DisplayServer::WINDOW_EDGE_BOTTOM_LEFT: {
+					int clamped_dx = CLAMP(frame.size.width - event.deltaX, min_size.x, max_size.x) - frame.size.width;
+					int clamped_dy = CLAMP(frame.size.height + event.deltaY, min_size.y, max_size.y) - frame.size.height;
+					[wd.window_object setFrame:NSMakeRect(frame.origin.x - clamped_dx, frame.origin.y - clamped_dy, frame.size.width + clamped_dx, frame.size.height + clamped_dy) display:YES];
+				} break;
+				case DisplayServer::WINDOW_EDGE_BOTTOM: {
+					int clamped_dy = CLAMP(frame.size.height + event.deltaY, min_size.y, max_size.y) - frame.size.height;
+					[wd.window_object setFrame:NSMakeRect(frame.origin.x, frame.origin.y - clamped_dy, frame.size.width, frame.size.height + clamped_dy) display:YES];
+				} break;
+				case DisplayServer::WINDOW_EDGE_BOTTOM_RIGHT: {
+					int clamped_dx = CLAMP(frame.size.width + event.deltaX, min_size.x, max_size.x) - frame.size.width;
+					int clamped_dy = CLAMP(frame.size.height + event.deltaY, min_size.y, max_size.y) - frame.size.height;
+					[wd.window_object setFrame:NSMakeRect(frame.origin.x, frame.origin.y - clamped_dy, frame.size.width + clamped_dx, frame.size.height + clamped_dy) display:YES];
+				} break;
+				default:
+					break;
+			}
+			return;
+		}
+	}
 	[self mouseMoved:event];
 }
 
 - (void)mouseUp:(NSEvent *)event {
+	DisplayServerMacOS *ds = (DisplayServerMacOS *)DisplayServer::get_singleton();
+	if (ds && ds->has_window(window_id)) {
+		DisplayServerMacOS::WindowData &wd = ds->get_window(window_id);
+		wd.edge = DisplayServer::WINDOW_EDGE_MAX;
+	}
 	if (mouse_down_control) {
 		[self processMouseEvent:event index:MouseButton::RIGHT pressed:false outofstream:false];
 	} else {

platform/windows/display_server_windows.cpp

@@ -3999,6 +3999,52 @@ void DisplayServerWindows::window_start_drag(WindowID p_window) {
 	SendMessage(wd.hWnd, WM_SYSCOMMAND, SC_MOVE | HTCAPTION, MAKELPARAM(coords.x, coords.y));
 }
 
+void DisplayServerWindows::window_start_resize(WindowResizeEdge p_edge, WindowID p_window) {
+	_THREAD_SAFE_METHOD_
+
+	ERR_FAIL_INDEX(int(p_edge), WINDOW_EDGE_MAX);
+	ERR_FAIL_COND(!windows.has(p_window));
+	WindowData &wd = windows[p_window];
+
+	ReleaseCapture();
+
+	POINT coords;
+	GetCursorPos(&coords);
+	ScreenToClient(wd.hWnd, &coords);
+
+	DWORD op = 0;
+	switch (p_edge) {
+		case DisplayServer::WINDOW_EDGE_TOP_LEFT: {
+			op = WMSZ_TOPLEFT;
+		} break;
+		case DisplayServer::WINDOW_EDGE_TOP: {
+			op = WMSZ_TOP;
+		} break;
+		case DisplayServer::WINDOW_EDGE_TOP_RIGHT: {
+			op = WMSZ_TOPRIGHT;
+		} break;
+		case DisplayServer::WINDOW_EDGE_LEFT: {
+			op = WMSZ_LEFT;
+		} break;
+		case DisplayServer::WINDOW_EDGE_RIGHT: {
+			op = WMSZ_RIGHT;
+		} break;
+		case DisplayServer::WINDOW_EDGE_BOTTOM_LEFT: {
+			op = WMSZ_BOTTOMLEFT;
+		} break;
+		case DisplayServer::WINDOW_EDGE_BOTTOM: {
+			op = WMSZ_BOTTOM;
+		} break;
+		case DisplayServer::WINDOW_EDGE_BOTTOM_RIGHT: {
+			op = WMSZ_BOTTOMRIGHT;
+		} break;
+		default:
+			break;
+	}
+
+	SendMessage(wd.hWnd, WM_SYSCOMMAND, SC_SIZE | op, MAKELPARAM(coords.x, coords.y));
+}
+
 void DisplayServerWindows::set_context(Context p_context) {
 }
 

platform/windows/display_server_windows.h

@@ -819,6 +819,7 @@ public:
 	virtual DisplayServer::VSyncMode window_get_vsync_mode(WindowID p_vsync_mode) const override;
 
 	virtual void window_start_drag(WindowID p_window = MAIN_WINDOW_ID) override;
+	virtual void window_start_resize(WindowResizeEdge p_edge, WindowID p_window = MAIN_WINDOW_ID) override;
 
 	virtual void cursor_set_shape(CursorShape p_shape) override;
 	virtual CursorShape cursor_get_shape() const override;

servers/display_server.cpp

@@ -993,6 +993,7 @@ void DisplayServer::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("window_minimize_on_title_dbl_click"), &DisplayServer::window_minimize_on_title_dbl_click);
 
 	ClassDB::bind_method(D_METHOD("window_start_drag", "window_id"), &DisplayServer::window_start_drag, DEFVAL(MAIN_WINDOW_ID));
+	ClassDB::bind_method(D_METHOD("window_start_resize", "edge", "window_id"), &DisplayServer::window_start_resize, DEFVAL(MAIN_WINDOW_ID));
 
 	ClassDB::bind_method(D_METHOD("ime_get_selection"), &DisplayServer::ime_get_selection);
 	ClassDB::bind_method(D_METHOD("ime_get_text"), &DisplayServer::ime_get_text);
@@ -1170,6 +1171,16 @@ void DisplayServer::_bind_methods() {
 	BIND_ENUM_CONSTANT(WINDOW_EVENT_DPI_CHANGE);
 	BIND_ENUM_CONSTANT(WINDOW_EVENT_TITLEBAR_CHANGE);
 
+	BIND_ENUM_CONSTANT(WINDOW_EDGE_TOP_LEFT);
+	BIND_ENUM_CONSTANT(WINDOW_EDGE_TOP);
+	BIND_ENUM_CONSTANT(WINDOW_EDGE_TOP_RIGHT);
+	BIND_ENUM_CONSTANT(WINDOW_EDGE_LEFT);
+	BIND_ENUM_CONSTANT(WINDOW_EDGE_RIGHT);
+	BIND_ENUM_CONSTANT(WINDOW_EDGE_BOTTOM_LEFT);
+	BIND_ENUM_CONSTANT(WINDOW_EDGE_BOTTOM);
+	BIND_ENUM_CONSTANT(WINDOW_EDGE_BOTTOM_RIGHT);
+	BIND_ENUM_CONSTANT(WINDOW_EDGE_MAX);
+
 	BIND_ENUM_CONSTANT(VSYNC_DISABLED);
 	BIND_ENUM_CONSTANT(VSYNC_ENABLED);
 	BIND_ENUM_CONSTANT(VSYNC_ADAPTIVE);

servers/display_server.h

@@ -499,6 +499,20 @@ public:
 
 	virtual void window_start_drag(WindowID p_window = MAIN_WINDOW_ID) {}
 
+	enum WindowResizeEdge {
+		WINDOW_EDGE_TOP_LEFT,
+		WINDOW_EDGE_TOP,
+		WINDOW_EDGE_TOP_RIGHT,
+		WINDOW_EDGE_LEFT,
+		WINDOW_EDGE_RIGHT,
+		WINDOW_EDGE_BOTTOM_LEFT,
+		WINDOW_EDGE_BOTTOM,
+		WINDOW_EDGE_BOTTOM_RIGHT,
+		WINDOW_EDGE_MAX,
+	};
+
+	virtual void window_start_resize(WindowResizeEdge p_edge, WindowID p_window = MAIN_WINDOW_ID) {}
+
 	// necessary for GL focus, may be able to use one of the existing functions for this, not sure yet
 	virtual void gl_window_make_current(DisplayServer::WindowID p_window_id);
 
@@ -639,6 +653,7 @@ VARIANT_ENUM_CAST(DisplayServer::MouseMode)
 VARIANT_ENUM_CAST(DisplayServer::ScreenOrientation)
 VARIANT_ENUM_CAST(DisplayServer::WindowMode)
 VARIANT_ENUM_CAST(DisplayServer::WindowFlags)
+VARIANT_ENUM_CAST(DisplayServer::WindowResizeEdge)
 VARIANT_ENUM_CAST(DisplayServer::HandleType)
 VARIANT_ENUM_CAST(DisplayServer::VirtualKeyboardType);
 VARIANT_ENUM_CAST(DisplayServer::CursorShape)