Custom render tooltip events in RDHeaderView

* Because Qt is awful at customising controls, the functions used to fetch the
  index of sections are not virtual so the internal QHeaderView version doesn't
  get the right sections when we have column grouping enabled.

qrenderdoc/Widgets/Extended/RDHeaderView.cpp

@@ -30,6 +30,7 @@
 #include <QPixmap>
 #include <QPointer>
 #include <QScrollBar>
+#include <QToolTip>
 #include <QTreeView>
 #include "Code/QRDUtils.h"
 
@@ -864,6 +865,28 @@ void RDHeaderView::paintEvent(QPaintEvent *e)
   }
 }
 
+bool RDHeaderView::viewportEvent(QEvent *e)
+{
+  if(e->type() == QEvent::ToolTip)
+  {
+    QHelpEvent *h = (QHelpEvent *)e;
+    int section = logicalIndexAt(h->pos());
+    if(section >= 0)
+    {
+      QAbstractItemModel *m = this->model();
+
+      QVariant tooltip = m->headerData(section, orientation(), Qt::ToolTipRole);
+      if(tooltip.isValid())
+      {
+        QToolTip::showText(h->globalPos(), tooltip.toString(), this);
+        return true;
+      }
+    }
+  }
+
+  return QHeaderView::viewportEvent(e);
+}
+
 void RDHeaderView::paintSection(QPainter *painter, const QRect &rect, int section) const
 {
   if(!m_customSizing)