Compositor: Fix various input-related rounding errors

QPointF::toPoint (which is what the QPoint versions of the events use
internally) uses qRound, which is not the right kind of rounding to
use with the QRegion we use for the input region.

This switches to use QPointF variants instead of QPoint wherever
possible, and then the correct conversion (with qFloor) is done once in
the new QPointF version of QWaylandSurface::inputRegionContains().

The compositor inputRegion test has now been updated to test the new
API.

[ChangeLog][Compositor] Fixed various rounding errors related to touch
and mouse input.

Fixes: QTBUG-77457
Change-Id: Ife2365abd56a239c34eee91310ab0e698a50d4ff
Reviewed-by: Paul Olav Tvete <paul.tvete@qt.io>

1 files changed, 18 insertions, 0 deletions

diff --git a/src/compositor/compositor_api/qwaylandsurface.cpp b/src/compositor/compositor_api/qwaylandsurface.cpp
index c79787e6e..a82c93f7b 100644
--- a/src/compositor/compositor_api/qwaylandsurface.cpp
+++ b/src/compositor/compositor_api/qwaylandsurface.cpp
@@ -67,6 +67,7 @@
 #include <QtGui/QScreen>
 
 #include <QtCore/QDebug>
+#include <QtCore/QtMath>
 
 QT_BEGIN_NAMESPACE
 
@@ -706,6 +707,23 @@ bool QWaylandSurface::inputRegionContains(const QPoint &p) const
     return d->inputRegion.contains(p);
 }
 
+//TODO: Add appropriate \since version when this is made public.
+/*!
+ * Returns \c true if the QWaylandSurface's input region contains the point \a position.
+ * Otherwise returns \c false.
+ */
+bool QWaylandSurface::inputRegionContains(const QPointF &position) const
+{
+    Q_D(const QWaylandSurface);
+    // QRegion::contains operates in integers. If a region has a rect (0,0,10,10), (0,0) is
+    // inside while (10,10) is outside. Therefore, we can't use QPoint::toPoint(), which will
+    // round upwards, meaning the point (-0.25,-0.25) would be rounded to (0,0) and count as
+    // being inside the region, and similarly, a point (9.75,9.75) inside the region would be
+    // rounded upwards and count as being outside the region.
+    const QPoint floored(qFloor(position.x()), qFloor(position.y()));
+    return d->inputRegion.contains(floored);
+}
+
 /*!
  * \qmlmethod void QtWaylandCompositor::WaylandSurface::destroy()
  *