+
+ // TODO: allow to disable
+ if (1) {
+ painter->setPen(QPen(Qt::red, 2, Qt::SolidLine));
+ QPointF c = getCentroid();
+ handleSize *= 1.5;
+ painter->drawLine(QLineF(c - QPointF(handleSize, handleSize), c + QPointF(handleSize, handleSize)));
+ painter->drawLine(QLineF(c - QPointF(-handleSize, handleSize), c + QPointF(-handleSize, handleSize)));
+ }
+}
+
+QPointF OnMonitorCornersItem::getCentroid()
+{
+ QList <QPointF> p = sortedClockwise();
+
+ /*
+ * See: http://local.wasp.uwa.edu.au/~pbourke/geometry/polyarea/
+ */
+
+ double A = 0;
+ int i, j;
+ for (i = 0; i < 4; ++i) {
+ j = (i + 1) % 4;
+ A += p[j].x() * p[i].y() - p[i].x() * p[j].y();
+ }
+ A /= 2.;
+ A = qAbs(A);
+
+ double x = 0, y = 0, f;
+ for (i = 0; i < 4; ++i) {
+ j = (i + 1) % 4;
+ f = (p[i].x() * p[j].y() - p[j].x() * p[i].y());
+ x += f * (p[i].x() + p[j].x());
+ y += f * (p[i].y() + p[j].y());
+ }
+ x /= 6*A;
+ y /= 6*A;
+ return QPointF(x, y);
+}
+
+QList <QPointF> OnMonitorCornersItem::sortedClockwise()
+{
+ QList <QPointF> points = polygon().toList();
+ QPointF& a = points[0];
+ QPointF& b = points[1];
+ QPointF& c = points[2];
+ QPointF& d = points[3];
+
+ /*
+ * http://stackoverflow.com/questions/242404/sort-four-points-in-clockwise-order
+ */
+
+ double abc = a.x() * b.y() - a.y() * b.x() + b.x() * c.y() - b.y() * c.x() + c.x() * a.y() - c.y() * a.x();
+ if (abc > 0) {
+ double acd = a.x() * c.y() - a.y() * c.x() + c.x() * d.y() - c.y() * d.x() + d.x() * a.y() - d.y() * a.x();
+ if (acd > 0) {
+ ;
+ } else {
+ double abd = a.x() * b.y() - a.y() * b.x() + b.x() * d.y() - b.y() * d.x() + d.x() * a.y() - d.y() * a.x();
+ if (abd > 0) {
+ std::swap(d, c);
+ } else{
+ std::swap(a, d);
+ }
+ }
+ } else {
+ double acd = a.x() * c.y() - a.y() * c.x() + c.x() * d.y() - c.y() * d.x() + d.x() * a.y() - d.y() * a.x();
+ if (acd > 0) {
+ double abd = a.x() * b.y() - a.y() * b.x() + b.x() * d.y() - b.y() * d.x() + d.x() * a.y() - d.y() * a.x();
+ if (abd > 0) {
+ std::swap(b, c);
+ } else {
+ std::swap(a, b);
+ }
+ } else {
+ std::swap(a, c);
+ }
+ }