switch( FEAT_CANALS, SELF, switch_riverbank_grid_terrain_arctic,
  [
   STORE_TEMP( (tile_height > (snowline_height - 2)), 0),
   STORE_TEMP( LOAD_TEMP(0) + (tile_height > (snowline_height - 1)), 0),
   STORE_TEMP( LOAD_TEMP(0) + (tile_height > (snowline_height )), 0),
   STORE_TEMP( LOAD_TEMP(0) + (tile_height > (snowline_height + 1)), 0),
   LOAD_TEMP(0)
  ] ) {
 0: switch_riverbank_grid_height_arctic;
 1: switch_riverbank_grid_arctic_snow14;
 2: switch_riverbank_grid_arctic_snow24;
 3: switch_riverbank_grid_arctic_snow34;
 switch_riverbank_grid_height_snow;
}