| sourceRect | The part of the active Render Texture to copy. | 
| dest | The X and Y coordinates of the heightmap texture to copy into. | 
| syncControl | Controls how CPU synchronization is performed. | 
Copies the specified part of the active RenderTexture to the Terrain heightmap texture.
        This functions calls DirtyHeightmapRegion internally and sends out the OnTerrainChanged message accordingly.
See Also: TerrainHeightmapSyncControl, DirtyHeightmapRegion, SyncHeightmap.