Api For Hit Testing

specs/NonClientHitTestKind.md

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+Hit Test Kind
+===
+
+# Background
+The ability to ask WebView2 for information on a hit test is an important feature for 
+visually hosted apps. It can be used to support features related to mouse activity in 
+regions that are traditionally Non-Client areas. Features like Draggable Regions, 
+Resize, Minimize/Maximize functionality, and more.
+
+
+# Examples
+## Draggable regions (HWND)
+Draggable regions are marked regions on a webpage that will move the app window when the 
+user clicks and drags on them. It also opens up the system menu if right-clicked. This 
+API is designed to provide draggable regions support for apps that are directly hosting 
+the CoreWebView2 via visual hosting and for UI framework WebView2 controls that use visual 
+hosting, like the WinUI2 and WinUI3 WebView2 control.If your app uses windowed hosting, 
+draggable regions are supported by default, no need to follow this guide.
+
+NOTE: This API is not currently supported for environments that use a CoreWindow like UWP.
+
+#### Win32 C++
+```cpp
+LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
+{
+....
+    // We need to forward relevant mouse messages to the webview
+
+    // handle the range of mouse messages & WM_NCRBUTTONDOWN
+    if (message == WM_NCRBUTTONDOWN || message == WM_NCRBUTTONUP) 
+    {
+        POINT point {GET_X_LPARAM(lParam), GET_Y_LPARAM(lParam)};
+        // WM_NCRBUTTONDOWN/UP have poitns in screen coordinates we need
+        // to convert the point to client coordinates to match the others
+        ScreenToClient(hwnd, &point);
+
+        // IsPointInWebview is an example of a function which your app can implement that checks if 
+        // the mouse message point lies inside the rect of the visual that hosts the WebView2
+        if (IsPointInWebView(point)) 
+        {
+            // Adjust the point from app client coordinates to webview client coordinates.
+            // m_webViewBounds is a rect that represents the bounds that you app has set for 
+            // the webveiw
+            point.x -= m_webViewBounds.left;
+            point.y -= m_webViewBounds.top;
+
+            // forward mouse messages to WebView2
+            CHECK_FAILURE(m_compositionController->SendMouseInput(
+                static_cast<COREWEBVIEW2_MOUSE_EVENT_KIND>(message),
+                static_cast<COREWEBVIEW2_MOUSE_EVENT_VIRTUAL_KEYS>(GET_KEYSTATE_WPARAM(wParam)),
+                0, point));
+            return 0;
+        }
+
+    }
+
+    switch(message) 
+    {
+        ....
+        // Handling this message is important for enabling dragging
+        case WM_NCHITTEST:
+            POINT point {GET_X_LPARAM(lParam), GET_Y_LPARAM(lParam)};
+            COREWEBVIEW2_NON_CLIENT_REGION_KIND result = COREWEBVIEW2_NON_CLIENT_REGION_KIND_NOWHERE;
+            CHECK_FAILURE(m_compositionController->GetNonClientRegionAtPoint(&point, &result));
+            return result;
+        ....
+    }
+....
+}
+```
+#### C#
+```c#
+protected override void WndProc(ref Message m)
+{
+....
+
+if (m.Msg == WM_NCHITTEST)
+{
+    Point point = new Point(GET_X_LPARAM(m.lParam), GET_Y_LPARAM(m.lParam));
+    if (m_compositionController.GetNonClientRegionAtPoint(point) == 
+        CoreWebView2NonClientRegionKind.Caption) 
+    {
+        m.Result = (IntPtr)HTCAPTION;
+    }
+}
+else if (m.msg == WM_NCRBUTTONDOWN || m.msg == WM_NCRBUTTONUP) 
+{
+
+    Point point = new Point(GET_X_LPARAM(m.lParam), GET_Y_LPARAM(m.lParam));
+
+    // WM_NCRBUTTONDOWN/UP have poitns in screen coordinates we need
+    // to convert the point to client coordinates to match the others
+    ScreenToClient(m.hwnd, ref point);
+
+
+    // IsPointInWebview is an example of a function which your app can implement that 
+    // checks if the mouse message point lies inside the rect of the visual that hosts
+    // the WebView.
+    if (IsPointInWebView(point)) 
+    {
+        // Adjust the point from app client coordinates to webview client coordinates.
+        // m_webViewBounds is a rect that represents the bounds that you app has set for 
+        // the webveiw
+        point.x -= m_webViewBounds.left;
+        point.y -= m_webViewBounds.top;
+
+        // forward mouse messages to WebView2
+        m_compositionController.SendMouseInput(
+            (CoreWebView2MouseEventKind)m.msg,
+            (CoreWebView2MouseEventVirtualKeys)GET_KEYSTATE_WPARAM(wParam),
+            0,
+            point);
+
+        m.Result = 0;
+        return;
+    }
+
+}
+// The following code forwards mouse messages to the WebView2 - Start
+    ....
+}
+```
+#### C#/WinRT
+
+```c#
+void DraggableRegionSample() {
+
+    m_compositionController.NonClientRegionChanged += (object sender, CoreWebView2NonClientRegionChangedEventArgs arg) => {
+        CoreWebView2NonClientRegionKind kind = arg.Region;
+        IVector<Windows.Foundation.Rect> region_rects = m_compositionController.QueryNonClientRegion(kind);
+        // use kind & region_rects to ConfigureRegion on the InputNonClientPointerSource
+    }
+
+}
+```
+# API Notes
+## Marking regions In Your App
+Draggable regions in WebView2 are HTML elements marked with the CSS style
+`-webkit-app-region: drag`. WebView2 will treat any element with this style as a 
+drag handle for the window.
+
+See Documentation [here](https://learn.microsoft.com/en-us/microsoft-edge/progressive-web-apps-chromium/how-to/window-controls-overlay#make-regions-of-your-app-drag-handlers-for-the-window)
+
+# API Details
+## Win32 C++
+```cpp
+/// This enum contains values representing possible regions a given
+/// point lies within
+typedef enum COREWEBVIEW2_NON_CLIENT_REGION_KIND {
+    /// A hit test region in the WebView2 which has the CSS style 
+    /// `-webkit-app-region: drag` set. Web content should use this CSS 
+    /// style to identify regions that should be treated like the app 
+    /// window's title bar. This has the same value as the Win32 HTCAPTION 
+    /// constant. 
+    COREWEBVIEW2_NON_CLIENT_REGION_KIND_CAPTION = 2,
+    /// A hit test region in the WebView2 which does not have the CSS style 
+    /// `-webkit-app-region: drag` set. This is normal web content that should not be 
+    /// considered part of the app window's title bar. This has the same value 
+    /// as the Win32 HTCLIENT constant.
+    COREWEBVIEW2_NON_CLIENT_REGION_KIND_CLIENT = 1,
+    /// A hit test region out of bounds of the WebView2.
+    /// This has the same value as the Win32 HTNOWHERE
+    COREWEBVIEW2_NON_CLIENT_REGION_KIND_NOWHERE = 0
+} COREWEBVIEW2_NON_CLIENT_REGION_KIND;
+
+[uuid(0BEA1283-39DC-48D1-9893-16275505CBBC), object, pointer_default(unique)]
+interface ICoreWebView2NonClientRegionChangedEventHandler : IUnknown {
+  /// Called to provide the implementer with the event args for the
+  /// corresponding event.
+  HRESULT Invoke(
+      [in] ICoreWebView2StagingCompositionController* sender,
+      [in] ICoreWebView2NonClientRegionChangedEventArgs* args);
+}
+
+/// Interface for status bar text change event args
+[uuid(E404B00C-669E-43EC-BE43-FB8CD7DBB480), object, pointer_default(unique)]
+interface ICoreWebView2NonClientRegionChangedEventArgs : IUnknown {
+    [propget] HRESULT Region(
+                    [out, retval] COREWEBVIEW2_NON_CLIENT_REGION_KIND* value);
+}
+// Interface that Represents a Collection of Regoin Rects
+[uuid(A990DA9D-4243-4FCD-B895-2E7E87EAAB14), object, pointer_default(unique)]
+interface ICoreWebView2RegionRectCollection : IUnknown {
+  /// Gets the number of `RegionRect` objects contained in the `RegionRectCollection`.
+  [propget] HRESULT Count([out, retval] UINT32* value);
+
+  /// Gets the `RegionRect` at the specified index.
+  HRESULT GetValueAtIndex([in] UINT32 index,
+      [out, retval] RECT* value);
+
+}
+
+/// This interface includes the new API for enabling WebView2 support for hit-testing regions
+[uuid(42BF7BA5-917A-4C27-ADA1-EA6969854C16), object, pointer_default(unique)]
+interface ICoreWebView2CompositionController4 : ICoreWebView2CompositionController3 {
+  /// If you are hosting a WebView2 using CoreWebView2CompositionController, you can call
+  /// this method in your Win32 WndProc to determine if the mouse is moving over or
+  /// clicking on WebView2 web content that should be considered part of the app window's
+  /// title bar.
+
+  /// The point parameter is expected to be in the client coordinate space of WebView2.
+  /// The method sets the out parameter value as follows:
+  ///     - COREWEBVIEW2_NON_CLIENT_REGION_KIND_CAPTION when point corresponds to
+  ///         a region (HTML element) within the WebView2 with
+  ///         `-webkit-app-region: drag` CSS style set
+  ///     - COREWEBVIEW2_NON_CLIENT_REGION_KIND_CLIENT when point corresponds to
+  ///         a region (HTML element) within the WebView2 without
+  ///         `-webkit-app-region: drag` CSS style set
+  ///     - COREWEBVIEW2_NON_CLIENT_REGION_KIND_NOWHERE when point is not within the WebView2
+  HRESULT GetNonClientRegionAtPoint(
+                      [in] POINT point,
+                      [out, retval] COREWEBVIEW2_NON_CLIENT_REGION_KIND* value);
+
+  HRESULT QueryNonClientRegion(
+    [in] COREWEBVIEW2_NON_CLIENT_REGION_KIND kind,
+    [out, retval] ICoreWebView2RegionRectCollection** rects);
+
+  /// Use to add a listener to be notified when NonClientRegion change
+  HRESULT add_NonClientRegionChanged(
+      [in] ICoreWebView2NonClientRegionChangedEventHandler* eventHandler,
+      [out] EventRegistrationToken* token);
+
+  /// Removing an event handler for `NonClientRegionChanged` event
+  HRESULT remove_NonClientRegionChanged(
+      [in] EventRegistrationToken token);
+}
+
+/// Mouse event type used by SendMouseInput to convey the type of mouse event
+/// being sent to WebView. The values of this enum align with the matching
+/// WM_* window messages.
+typedef enum COREWEBVIEW2_MOUSE_EVENT_KIND {
+    ....
+    /// Mouse Right Button Down event over a nonclient area, WM_NCRBUTTONDOWN.
+    COREWEBVIEW2_MOUSE_EVENT_KIND_NON_CLIENT_RIGHT_BUTTON_DOWN = 0x00A4,
+    /// Mouse Right Button up event over a nonclient area, WM_NCRBUTTONUP.
+    COREWEBVIEW2_MOUSE_EVENT_KIND_NON_CLIENT_RIGHT_BUTTON_UP = 0x00A5,
+    ....
+} COREWEBVIEW2_MOUSE_EVENT_KIND;
+```
+## .Net/ WinRT
+```c#
+namespace Microsoft.Web.WebView2.Core {
+    enum CoreWebView2NonClientRegionKind
+    {
+        Caption = 2,
+        Client = 1,
+        Nowhere = 0,
+    }
+    enum CoreWebView2MouseEventKind
+    {
+        ...
+        NonClientRightButtonDown = 0x00A4,
+        NonClientRightButtonUp = 0x00A5,
+        ...
+    }
+    runtimeclass CoreWebView2NonClientRegionChangedEventArgs
+    {
+        // ICoreWebView2NonClientRegionChangedEventArgs members
+        CoreWebView2NonClientRegionKind Region { get; };
+
+    }
+    runtimeclass CoreWebView2CompositionController {
+
+        [interface_name("Microsoft.Web.WebView2.Core.ICoreWebView2CompositionController4")]
+        {
+            /// ICoreWebView2CompositionController4 members
+            event Windows.Foundation.TypedEventHandler<CoreWebView2CompositionController, CoreWebView2NonClientRegionChangedEventArgs> NonClientRegionChanged;
+            CoreWebView2NonClientRegionKind GetNonClientRegionAtPoint(Windows.Foundation.Point point);
+            IVector<Windows.Foundation.Rect> QueryNonClientRegion(CoreWebView2NonClientRegionKind Kind);
+        }
+    }
+}
+```