Add a helper function to convert QPointF to QPoint using floor instead of round

In a bunch of cases, we want to floor when converting to QPoint rather
than rounding. As it gets tedious to repeat the same code over and over,
add a helper function.

src/libkwineffects/kwineffects.h

@@ -206,6 +206,17 @@ KWINEFFECTS_EXPORT inline QVector2D roundVector(const QVector2D &input)
     return QVector2D(std::round(input.x()), std::round(input.y()));
 }
 
+/**
+ * Convert a QPointF to a QPoint by flooring instead of rounding.
+ *
+ * By default, QPointF::toPoint() rounds which can cause problems in certain
+ * cases.
+ */
+KWINEFFECTS_EXPORT inline QPoint flooredPoint(const QPointF &point)
+{
+    return QPoint(std::floor(point.x()), std::floor(point.y()));
+}
+
 /**
  * @short Base class for all KWin effects
  *