| gridLayout | Grid that the brush is being used on. |
| brushTarget | Target of the GridBrushBase.Tool operation. By default the currently selected GameObject. |
| position | Current selected location of the brush. |
| tool | Current GridBrushBase.Tool selected. |
| executing | Whether is brush is being used. |
Callback for painting the GUI for the GridBrush in the Scene view.
Implement this for any special behaviours when the GridBrush is used on the Scene view.