Windows: Fix tablet position in relative (mouse) mode.

When in "mouse" or "relative" mode with the pen position information
would not be calculated correctly resulting in a significant offset
between the tablet pen location and the mouse cursor location. Logic
was added to detect when the two were not in sync and use the mouse
location when this happens.

Change-Id: Icb7129e8cce186c0099953769e215649d9347c8e
Reviewed-by: Laszlo Agocs <laszlo.agocs@digia.com>

2 files changed, 30 insertions, 4 deletions

diff --git a/src/plugins/platforms/windows/qwindowstabletsupport.cpp b/src/plugins/platforms/windows/qwindowstabletsupport.cpp
index 4a5d7b5a78..1a5c1a2e0c 100644
--- a/src/plugins/platforms/windows/qwindowstabletsupport.cpp
+++ b/src/plugins/platforms/windows/qwindowstabletsupport.cpp
@@ -395,8 +395,19 @@ bool QWindowsTabletSupport::translateTabletPacketEvent()
     const int currentDevice = m_devices.at(m_currentDevice).currentDevice;
     const int currentPointer = m_devices.at(m_currentDevice).currentPointerType;
 
-    // When entering proximity, the tablet driver snaps the mouse pointer to the
-    // tablet position scaled to the virtual desktop and keeps it in sync.
+    // The tablet can be used in 2 different modes, depending on it settings:
+    // 1) Absolute (pen) mode:
+    //    The coordinates are scaled to the virtual desktop (by default). The user
+    //    can also choose to scale to the monitor or a region of the screen.
+    //    When entering proximity, the tablet driver snaps the mouse pointer to the
+    //    tablet position scaled to that area and keeps it in sync.
+    // 2) Relative (mouse) mode:
+    //    The pen follows the mouse. The constant 'absoluteRange' specifies the
+    //    manhattanLength difference for detecting if a tablet input device is in this mode,
+    //    in which case we snap the position to the mouse position.
+    // It seems there is no way to find out the mode programmatically, the LOGCONTEXT orgX/Y/Ext
+    // area is always the virtual desktop.
+    enum { absoluteRange = 20 };
     const QRect virtualDesktopArea = QGuiApplication::primaryScreen()->virtualGeometry();
 
     if (QWindowsContext::verboseTablet)
@@ -409,10 +420,24 @@ bool QWindowsTabletSupport::translateTabletPacketEvent()
         const PACKET &packet = localPacketBuf[i];
 
         const int z = currentDevice == QTabletEvent::FourDMouse ? int(packet.pkZ) : 0;
-        const QPointF globalPosF = m_devices.at(m_currentDevice).scaleCoordinates(packet.pkX, packet.pkY, virtualDesktopArea);
+
+        // This code is to delay the tablet data one cycle to sync with the mouse location.
+        QPointF globalPosF = m_oldGlobalPosF;
+        m_oldGlobalPosF = m_devices.at(m_currentDevice).scaleCoordinates(packet.pkX, packet.pkY, virtualDesktopArea);
 
         QWindow *target = QGuiApplicationPrivate::tabletPressTarget; // Pass to window that grabbed it.
-        const QPoint globalPos = globalPosF.toPoint();
+        QPoint globalPos = globalPosF.toPoint();
+
+        // Get Mouse Position and compare to tablet info
+        const QPoint mouseLocation = QWindowsCursor::mousePosition();
+
+        // Positions should be almost the same if we are in absolute
+        // mode. If they are not, use the mouse location.
+        if ((mouseLocation - globalPos).manhattanLength() > absoluteRange) {
+            globalPos = mouseLocation;
+            globalPosF = globalPos;
+        }
+
         if (!target)
             if (QPlatformWindow *pw = QWindowsContext::instance()->findPlatformWindowAt(GetDesktopWindow(), globalPos, CWP_SKIPINVISIBLE | CWP_SKIPTRANSPARENT))
                 target = pw->window();
diff --git a/src/plugins/platforms/windows/qwindowstabletsupport.h b/src/plugins/platforms/windows/qwindowstabletsupport.h
index 12f96b618d..5e29cd9554 100644
--- a/src/plugins/platforms/windows/qwindowstabletsupport.h
+++ b/src/plugins/platforms/windows/qwindowstabletsupport.h
@@ -134,6 +134,7 @@ private:
     bool m_tiltSupport;
     QVector<QWindowsTabletDeviceData> m_devices;
     int m_currentDevice;
+    QPointF m_oldGlobalPosF;
 };
 
 QT_END_NAMESPACE