Windows QPA: Dispatch skipped touch/pen events if compression is off

If the hardware produces events faster than the app can consume between
two updates, Windows automatically coalesces them into a single message
with the latest touch/pen pointer state and coordinates, effectively
compressing those events. But the pointer API also supports querying
and retrieving the skipped individual touch and pen frames.

There are cases where keeping all the events generated by the hardware
is desired, especially for pen events where having the most sampled
points available is critical to precisely rendering curves.

Qt already defines application attributes to control event compression
for general high frequency events and for tablet events in particular.
Use them on Windows also to control whether to retrieve skipped frames.

[ChangeLog][Windows] The application attributes AA_CompressTabletEvents
and AA_CompressHighFrequencyEvents are now supported on Windows 8 and
above for touch/pen input, with the same defaults as on X11 (compress
touch events, don't compress tablet events)

Task-number: QTBUG-44964
Task-number: QTBUG-60437
Change-Id: I1b11a043e2d71ee502895971fafb3a46306a89d8
Reviewed-by: Andre de la Rocha <[email protected]>
Reviewed-by: Friedemann Kleint <[email protected]>

src/corelib/global/qnamespace.qdoc

@@ -245,7 +245,10 @@
            QEvent::MouseMove, QEvent::TouchUpdate, and changes in window size and
            position will be combined whenever they occur more frequently than the
            application handles them, so that they don't accumulate and overwhelm the
-           application later. On other platforms, the default is false.
+           application later.
+           On Windows 8 and above the default value is also true, but it only applies
+           to touch events. Mouse and window events remain unaffected by this flag.
+           On other platforms, the default is false.
            (In the future, the compression feature may be implemented across platforms.)
            You can test the attribute to see whether compression is enabled.
            If your application needs to handle all events with no compression,
@@ -256,8 +259,9 @@
 
     \value AA_CompressTabletEvents Enables compression of input events from tablet devices.
            Notice that AA_CompressHighFrequencyEvents must be true for events compression
-           to be enabled, and that this flag extends the former to tablet events. Its default
-           value is false.
+           to be enabled, and that this flag extends the former to tablet events.
+           Currently supported on the X11 windowing system, Windows 8 and above.
+           The default value is false.
            This value was added in Qt 5.10.
 
     \value AA_DontCheckOpenGLContextThreadAffinity When making a context

src/plugins/platforms/windows/qwindowscontext.cpp

@@ -201,7 +201,9 @@ void QWindowsUser32DLL::init()
         getPointerDeviceRects = (GetPointerDeviceRects)library.resolve("GetPointerDeviceRects");
         getPointerTouchInfo = (GetPointerTouchInfo)library.resolve("GetPointerTouchInfo");
         getPointerFrameTouchInfo = (GetPointerFrameTouchInfo)library.resolve("GetPointerFrameTouchInfo");
+        getPointerFrameTouchInfoHistory = (GetPointerFrameTouchInfoHistory)library.resolve("GetPointerFrameTouchInfoHistory");
         getPointerPenInfo = (GetPointerPenInfo)library.resolve("GetPointerPenInfo");
+        getPointerPenInfoHistory = (GetPointerPenInfoHistory)library.resolve("GetPointerPenInfoHistory");
         skipPointerFrameMessages = (SkipPointerFrameMessages)library.resolve("SkipPointerFrameMessages");
     }
 
@@ -216,8 +218,8 @@ void QWindowsUser32DLL::init()
 bool QWindowsUser32DLL::supportsPointerApi()
 {
     return enableMouseInPointer && getPointerType && getPointerInfo && getPointerDeviceRects
-            && getPointerTouchInfo && getPointerFrameTouchInfo && getPointerPenInfo
-            && skipPointerFrameMessages;
+            && getPointerTouchInfo && getPointerFrameTouchInfo && getPointerFrameTouchInfoHistory
+            && getPointerPenInfo && getPointerPenInfoHistory && skipPointerFrameMessages;
 }
 
 void QWindowsShcoreDLL::init()

src/plugins/platforms/windows/qwindowscontext.h

@@ -92,7 +92,9 @@ struct QWindowsUser32DLL
     typedef BOOL (WINAPI *GetPointerDeviceRects)(HANDLE, RECT *, RECT *);
     typedef BOOL (WINAPI *GetPointerTouchInfo)(UINT32, PVOID);
     typedef BOOL (WINAPI *GetPointerFrameTouchInfo)(UINT32, UINT32 *, PVOID);
+    typedef BOOL (WINAPI *GetPointerFrameTouchInfoHistory)(UINT32, UINT32 *, UINT32 *, PVOID);
     typedef BOOL (WINAPI *GetPointerPenInfo)(UINT32, PVOID);
+    typedef BOOL (WINAPI *GetPointerPenInfoHistory)(UINT32, UINT32 *, PVOID);
     typedef BOOL (WINAPI *SkipPointerFrameMessages)(UINT32);
     typedef BOOL (WINAPI *SetProcessDPIAware)();
     typedef BOOL (WINAPI *AddClipboardFormatListener)(HWND);
@@ -110,7 +112,9 @@ struct QWindowsUser32DLL
     GetPointerDeviceRects getPointerDeviceRects = nullptr;
     GetPointerTouchInfo getPointerTouchInfo = nullptr;
     GetPointerFrameTouchInfo getPointerFrameTouchInfo = nullptr;
+    GetPointerFrameTouchInfoHistory getPointerFrameTouchInfoHistory = nullptr;
     GetPointerPenInfo getPointerPenInfo = nullptr;
+    GetPointerPenInfoHistory getPointerPenInfoHistory = nullptr;
     SkipPointerFrameMessages skipPointerFrameMessages = nullptr;
 
     // Windows Vista onwards

src/plugins/platforms/windows/qwindowsintegration.cpp

@@ -236,7 +236,9 @@ QWindowsIntegrationPrivate::QWindowsIntegrationPrivate(const QStringList &paramL
     m_options = parseOptions(paramList, &tabletAbsoluteRange, &dpiAwareness);
     QWindowsFontDatabase::setFontOptions(m_options);
 
-    if (!m_context.initPointer(m_options)) {
+    if (m_context.initPointer(m_options)) {
+        QCoreApplication::setAttribute(Qt::AA_CompressHighFrequencyEvents);
+    } else {
         m_context.initTablet(m_options);
         if (tabletAbsoluteRange >= 0)
             m_context.setTabletAbsoluteRange(tabletAbsoluteRange);

src/plugins/platforms/windows/qwindowspointerhandler.cpp

@@ -106,6 +106,32 @@ bool QWindowsPointerHandler::translatePointerEvent(QWindow *window, HWND hwnd, Q
             qWarning() << "GetPointerFrameTouchInfo() failed:" << qt_error_string();
             return false;
         }
+
+        if (!pointerCount)
+            return false;
+
+        // The history count is the same for all the touchpoints in touchInfo
+        quint32 historyCount = touchInfo[0].pointerInfo.historyCount;
+        // dispatch any skipped frames if event compression is disabled by the app
+        if (historyCount > 1 && !QCoreApplication::testAttribute(Qt::AA_CompressHighFrequencyEvents)) {
+            touchInfo.resize(pointerCount * historyCount);
+            if (!QWindowsContext::user32dll.getPointerFrameTouchInfoHistory(pointerId,
+                                                                            &historyCount,
+                                                                            &pointerCount,
+                                                                            touchInfo.data())) {
+                qWarning() << "GetPointerFrameTouchInfoHistory() failed:" << qt_error_string();
+                return false;
+            }
+
+            // history frames are returned with the most recent frame first so we iterate backwards
+            bool result = true;
+            for (auto it = touchInfo.rbegin(), end = touchInfo.rend(); it != end; it += pointerCount) {
+                result &= translateTouchEvent(window, hwnd, et, msg,
+                                              &(*(it + (pointerCount - 1))), pointerCount);
+            }
+            return result;
+        }
+
         return translateTouchEvent(window, hwnd, et, msg, touchInfo.data(), pointerCount);
     }
     case QT_PT_PEN: {
@@ -114,6 +140,29 @@ bool QWindowsPointerHandler::translatePointerEvent(QWindow *window, HWND hwnd, Q
             qWarning() << "GetPointerPenInfo() failed:" << qt_error_string();
             return false;
         }
+
+        quint32 historyCount = penInfo.pointerInfo.historyCount;
+        // dispatch any skipped frames if generic or tablet event compression is disabled by the app
+        if (historyCount > 1
+            && (!QCoreApplication::testAttribute(Qt::AA_CompressHighFrequencyEvents)
+                || !QCoreApplication::testAttribute(Qt::AA_CompressTabletEvents))) {
+            QVarLengthArray<POINTER_PEN_INFO, 10> penInfoHistory(historyCount);
+
+            if (!QWindowsContext::user32dll.getPointerPenInfoHistory(pointerId,
+                                                                     &historyCount,
+                                                                     penInfoHistory.data())) {
+                qWarning() << "GetPointerPenInfoHistory() failed:" << qt_error_string();
+                return false;
+            }
+
+            // history frames are returned with the most recent frame first so we iterate backwards
+            bool result = true;
+            for (auto it = penInfoHistory.rbegin(), end = penInfoHistory.rend(); it != end; ++it) {
+                result &= translatePenEvent(window, hwnd, et, msg, &(*(it)));
+            }
+            return result;
+        }
+
         return translatePenEvent(window, hwnd, et, msg, &penInfo);
     }
     }