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 <andre.rocha@qt.io>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>

1 files changed, 3 insertions, 1 deletions

diff --git a/src/plugins/platforms/windows/qwindowsintegration.cpp b/src/plugins/platforms/windows/qwindowsintegration.cpp
index 0694435427..7d621126b9 100644
--- a/src/plugins/platforms/windows/qwindowsintegration.cpp
+++ b/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);