| Parameter | Description | 
|---|---|
| terrain | Active Terrain object. | 
| editContext | Interface for communication between Editor and Paint tools. | 
Custom terrain tool OnSceneGUI callback.
                  Unity calls this method to run tool-specific scene UI and behavior.
                  Additional resources: Editor.OnSceneGUI, SceneView, TerrainPaintTool_1.OnRenderBrushPreview.