getOpaqueRect
Gets an opaque rectangle inside the node that GTK can determine to be fully opaque.
There is no guarantee that this is indeed the largest opaque rectangle or that regions outside the rectangle are not opaque. This function is a best effort with that goal.
The rectangle will be fully contained in the bounds of the node.
Return
true if part or all of the rendernode is opaque, false if no opaque region could be found.
Since
4.16
Parameters
outOpaque
return location for the opaque rect