Function SplitGroundSpriteForOverlay

src/station_cmd.cpp:3131–3185

* Check whether a sprite is a track sprite, which can be replaced by a non-track ground sprite and a rail overlay. * If the ground sprite is suitable, \a ground is replaced with the new non-track ground sprite, and \a overlay_offset * is set to the overlay to draw. * @param ti Positional info for the tile to decide snowyness etc. May be nullptr. * @param[in,out] ground

 * @return true if overlay can be drawn.
 */
bool SplitGroundSpriteForOverlay(const TileInfo *ti, SpriteID *ground, RailTrackOffset *overlay_offset)
{
	bool snow_desert;
	switch (*ground) {
		case SPR_RAIL_TRACK_X:
		case SPR_MONO_TRACK_X:
		case SPR_MGLV_TRACK_X:
			snow_desert = false;
			*overlay_offset = RTO_X;
			break;

		case SPR_RAIL_TRACK_Y:
		case SPR_MONO_TRACK_Y:
		case SPR_MGLV_TRACK_Y:
			snow_desert = false;
			*overlay_offset = RTO_Y;
			break;

		case SPR_RAIL_TRACK_X_SNOW:
		case SPR_MONO_TRACK_X_SNOW:
		case SPR_MGLV_TRACK_X_SNOW:
			snow_desert = true;
			*overlay_offset = RTO_X;
			break;

		case SPR_RAIL_TRACK_Y_SNOW:
		case SPR_MONO_TRACK_Y_SNOW:
		case SPR_MGLV_TRACK_Y_SNOW:
			snow_desert = true;
			*overlay_offset = RTO_Y;
			break;

		default:
			return false;
	}

	if (ti != nullptr) {
		/* Decide snow/desert from tile */
		switch (_settings_game.game_creation.landscape) {
			case LandscapeType::Arctic:
				snow_desert = (uint)ti->z > GetSnowLine() * TILE_HEIGHT;
				break;

			case LandscapeType::Tropic:
				snow_desert = GetTropicZone(ti->tile) == TROPICZONE_DESERT;
				break;

			default:
				break;
		}
	}

	*ground = snow_desert ? SPR_FLAT_SNOW_DESERT_TILE : SPR_FLAT_GRASS_TILE;
	return true;
}

/**
 * Get blocked pillar information for a station tile.