Client: Fix touch rounding errors

Touch now accounts for fractional input in the same way as for pointer
input.

Task-number: QTBUG-77457
Change-Id: I18e633bf7c7033187a641f757b8b24f52479971a
Reviewed-by: Paul Olav Tvete <paul.tvete@qt.io>
(cherry picked from commit b1a534a536892035fdf1e826a066bda6ab34b93a)
Reviewed-by: Pier Luigi Fiorini <pierluigi.fiorini@liri.io>

2 files changed, 13 insertions, 7 deletions

diff --git a/src/client/qwaylandinputdevice.cpp b/src/client/qwaylandinputdevice.cpp
index 6016589a6..e781d4768 100644
--- a/src/client/qwaylandinputdevice.cpp
+++ b/src/client/qwaylandinputdevice.cpp
@@ -867,14 +867,15 @@ void QWaylandInputDevice::Touch::touch_down(uint32_t serial,
     mParent->mSerial = serial;
     mFocus = window;
     mParent->mQDisplay->setLastInputDevice(mParent, serial, mFocus);
-    mParent->handleTouchPoint(id, wl_fixed_to_double(x), wl_fixed_to_double(y), Qt::TouchPointPressed);
+    QPointF position(wl_fixed_to_double(x), wl_fixed_to_double(y));
+    mParent->handleTouchPoint(id, Qt::TouchPointPressed, position);
 }
 
 void QWaylandInputDevice::Touch::touch_up(uint32_t serial, uint32_t time, int32_t id)
 {
     Q_UNUSED(serial);
     Q_UNUSED(time);
-    mParent->handleTouchPoint(id, 0, 0, Qt::TouchPointReleased);
+    mParent->handleTouchPoint(id, Qt::TouchPointReleased);
 
     if (allTouchPointsReleased()) {
         mFocus = nullptr;
@@ -893,7 +894,8 @@ void QWaylandInputDevice::Touch::touch_up(uint32_t serial, uint32_t time, int32_
 void QWaylandInputDevice::Touch::touch_motion(uint32_t time, int32_t id, wl_fixed_t x, wl_fixed_t y)
 {
     Q_UNUSED(time);
-    mParent->handleTouchPoint(id, wl_fixed_to_double(x), wl_fixed_to_double(y), Qt::TouchPointMoved);
+    QPointF position(wl_fixed_to_double(x), wl_fixed_to_double(y));
+    mParent->handleTouchPoint(id, Qt::TouchPointMoved, position);
 }
 
 void QWaylandInputDevice::Touch::touch_cancel()
@@ -907,7 +909,7 @@ void QWaylandInputDevice::Touch::touch_cancel()
     QWindowSystemInterface::handleTouchCancelEvent(nullptr, mParent->mTouchDevice);
 }
 
-void QWaylandInputDevice::handleTouchPoint(int id, double x, double y, Qt::TouchPointState state)
+void QWaylandInputDevice::handleTouchPoint(int id, Qt::TouchPointState state, const QPointF &surfacePosition)
 {
     auto end = mTouch->mPendingTouchPoints.end();
     auto it = std::find_if(mTouch->mPendingTouchPoints.begin(), end, [id](auto tp){ return tp.id == id; });
@@ -919,7 +921,6 @@ void QWaylandInputDevice::handleTouchPoint(int id, double x, double y, Qt::Touch
 
     // Only moved and pressed needs to update/set position
     if (state == Qt::TouchPointMoved || state == Qt::TouchPointPressed) {
-        // x and y are surface relative.
         // We need a global (screen) position.
         QWaylandWindow *win = mTouch->mFocus;
 
@@ -933,7 +934,12 @@ void QWaylandInputDevice::handleTouchPoint(int id, double x, double y, Qt::Touch
 
         tp.area = QRectF(0, 0, 8, 8);
         QMargins margins = win->frameMargins();
-        tp.area.moveCenter(win->window()->mapToGlobal(QPoint(x - margins.left(), y - margins.top())));
+        QPointF localPosition = surfacePosition - QPointF(margins.left(), margins.top());
+        // TODO: This doesn't account for high dpi scaling for the delta, but at least it matches
+        // what we have for mouse input.
+        QPointF delta = localPosition - localPosition.toPoint();
+        QPointF globalPosition = win->window()->mapToGlobal(localPosition.toPoint()) + delta;
+        tp.area.moveCenter(globalPosition);
     }
 
     tp.state = state;
diff --git a/src/client/qwaylandinputdevice_p.h b/src/client/qwaylandinputdevice_p.h
index d9bae9836..b6bd514c3 100644
--- a/src/client/qwaylandinputdevice_p.h
+++ b/src/client/qwaylandinputdevice_p.h
@@ -165,7 +165,7 @@ private:
     uint32_t mSerial = 0;
 
     void seat_capabilities(uint32_t caps) override;
-    void handleTouchPoint(int id, double x, double y, Qt::TouchPointState state);
+    void handleTouchPoint(int id, Qt::TouchPointState state, const QPointF &surfacePosition = QPoint());
 
     QTouchDevice *mTouchDevice = nullptr;