set_allocation
Description:
Sets the widget’s allocation.
This should not be used directly, but from within a widget’s size_allocate method.
The allocation set should be the “adjusted” or actual allocation. If you’re implementing a 
      Container, you want to use 
      size_allocate instead of set_allocation. The 
      GtkWidgetClass:GtkWidget:adjust_size_allocation virtual method adjusts the allocation inside 
      size_allocate to create an adjusted allocation.
Parameters:
| this | a Widget | 
| allocation | a pointer to a Allocation to copy from |