[v3 windows] Support frameless drag

v3/internal/runtime/desktop/drag.js

@@ -51,7 +51,14 @@ function onMouseDown(e) {
 }
 
 function onMouseUp(e) {
-    document.body.style.cursor = window.wails.previousCursor || 'auto';
+    let mousePressed = e.buttons !== undefined ? e.buttons : e.which;
+    if (mousePressed > 0) {
+        endDrag();
+    }
+}
+
+export function endDrag() {
+    document.body.style.cursor = 'default';
     shouldDrag = false;
 }
 
@@ -60,10 +67,7 @@ function onMouseMove(e) {
         shouldDrag = false;
         let mousePressed = e.buttons !== undefined ? e.buttons : e.which;
         if (mousePressed > 0) {
-            window.wails.previousCursor = document.body.style.cursor;
-            document.body.style.cursor = 'grab';
             invoke("drag");
-            return;
         }
     }
 }

v3/internal/runtime/desktop/invoke.js

@@ -13,7 +13,7 @@ The electron alternative for Go
 // defined in the Taskfile
 export let invoke = function(input) {
     if(WINDOWS) {
-        chrome.external.invoke(input);
+        chrome.webview.postMessage(input);
     } else {
         webkit.messageHandlers.external.postMessage(input);
     }

v3/internal/runtime/desktop/main.js

@@ -20,7 +20,7 @@ import {dispatchWailsEvent, Emit, Off, OffAll, On, Once, OnMultiple} from "./eve
 import {dialogCallback, dialogErrorCallback, Error, Info, OpenFile, Question, SaveFile, Warning,} from "./dialogs";
 import {enableContextMenus} from "./contextmenu";
 import {reloadWML} from "./wml";
-import {setupDrag} from "./drag";
+import {setupDrag, endDrag} from "./drag";
 
 window.wails = {
     ...newRuntime(null),
@@ -33,6 +33,7 @@ window._wails = {
     dispatchWailsEvent,
     callCallback,
     callErrorCallback,
+    endDrag,
 };
 
 export function newRuntime(windowName) {

v3/pkg/application/application.go

@@ -666,6 +666,17 @@ func invokeSyncWithResult[T any](fn func() T) (res T) {
 	return res
 }
 
+func invokeSyncWithError(fn func() error) (err error) {
+	var wg sync.WaitGroup
+	wg.Add(1)
+	globalApplication.dispatchOnMainThread(func() {
+		err = fn()
+		wg.Done()
+	})
+	wg.Wait()
+	return
+}
+
 func invokeSyncWithResultAndError[T any](fn func() (T, error)) (res T, err error) {
 	var wg sync.WaitGroup
 	wg.Add(1)

v3/pkg/application/webview_window.go

@@ -62,6 +62,7 @@ type (
 		setFrameless(bool)
 		openContextMenu(menu *Menu, data *ContextMenuData)
 		nativeWindowHandle() uintptr
+		startDrag() error
 	}
 )
 
@@ -437,12 +438,17 @@ func (w *WebviewWindow) SetBackgroundColour(colour RGBA) *WebviewWindow {
 func (w *WebviewWindow) handleMessage(message string) {
 	w.info(message)
 	// Check for special messages
-	if message == "test" {
-		invokeSync(func() {
-			w.SetTitle("Hello World")
-		})
+	if message == "drag" {
+		if !w.IsFullscreen() {
+			invokeSync(func() {
+				err := w.startDrag()
+				if err != nil {
+					w.error("Failed to start drag: %s", err)
+				}
+			})
+		}
 	}
-	w.info("ProcessMessage from front end:", message)
+	w.info("ProcessMessage from front end: %s", message)
 
 }
 
@@ -842,3 +848,10 @@ func (w *WebviewWindow) emit(eventType events.WindowEventType) {
 		EventID:  uint(eventType),
 	}
 }
+
+func (w *WebviewWindow) startDrag() error {
+	if w.impl == nil {
+		return nil
+	}
+	return invokeSyncWithError(w.impl.startDrag)
+}

v3/pkg/application/webview_window_darwin.go

@@ -1222,3 +1222,8 @@ func (w *macosWebviewWindow) setHTML(html string) {
 	// Render HTML
 	C.windowRenderHTML(w.nsWindow, cHTML)
 }
+
+func (w *macosWebviewWindow) startDrag() error {
+	// Unused - handled by the native code
+	return nil
+}

v3/pkg/application/webview_window_darwin.m

@@ -64,6 +64,8 @@ extern bool hasListeners(unsigned int);
 // Handle script messages from the external bridge
 - (void)userContentController:(nonnull WKUserContentController *)userContentController didReceiveScriptMessage:(nonnull WKScriptMessage *)message {
     NSString *m = message.body;
+
+    // TODO: Standardise drag by sending the drag event back to Go
     if ( [m isEqualToString:@"drag"] ) {
         /*
         if( [self IsFullScreen] ) {

v3/pkg/application/webview_window_windows.go

@@ -45,6 +45,15 @@ type windowsWebviewWindow struct {
 	resizeDebouncer func(func())
 }
 
+func (w *windowsWebviewWindow) startDrag() error {
+	if !w32.ReleaseCapture() {
+		return fmt.Errorf("unable to release mouse capture")
+	}
+	// Use PostMessage because we don't want to block the caller until dragging has been finished.
+	w32.PostMessage(w.hwnd, w32.WM_NCLBUTTONDOWN, w32.HTCAPTION, 0)
+	return nil
+}
+
 func (w *windowsWebviewWindow) nativeWindowHandle() uintptr {
 	return w.hwnd
 }
@@ -660,6 +669,8 @@ func (w *windowsWebviewWindow) WndProc(msg uint32, wparam, lparam uintptr) uintp
 		windowsApp.unregisterWindow(w)
 	case w32.WM_NCLBUTTONDOWN:
 		w32.SetFocus(w.hwnd)
+	case w32.WM_NCLBUTTONUP:
+
 	case w32.WM_MOVE, w32.WM_MOVING:
 		_ = w.chromium.NotifyParentWindowPositionChanged()
 	case w32.WM_SIZE: