Function ViewportAddLandscape

src/viewport.cpp:1210–1320

* Add the landscape to the viewport, i.e. all ground tiles and buildings. */

 * Add the landscape to the viewport, i.e. all ground tiles and buildings.
 */
static void ViewportAddLandscape()
{
	assert(_vd.dpi.top <= _vd.dpi.top + _vd.dpi.height);
	assert(_vd.dpi.left <= _vd.dpi.left + _vd.dpi.width);

	Point upper_left = InverseRemapCoords(_vd.dpi.left, _vd.dpi.top);
	Point upper_right = InverseRemapCoords(_vd.dpi.left + _vd.dpi.width, _vd.dpi.top);

	/* Transformations between tile coordinates and viewport rows/columns: See vp_column_row
	 *   column = y - x
	 *   row    = x + y
	 *   x      = (row - column) / 2
	 *   y      = (row + column) / 2
	 * Note: (row, columns) pairs are only valid, if they are both even or both odd.
	 */

	/* Columns overlap with neighbouring columns by a half tile.
	 *  - Left column is column of upper_left (rounded down) and one column to the left.
	 *  - Right column is column of upper_right (rounded up) and one column to the right.
	 * Note: Integer-division does not round down for negative numbers, so ensure rounding with another increment/decrement.
	 */
	int left_column = (upper_left.y - upper_left.x) / (int)TILE_SIZE - 2;
	int right_column = (upper_right.y - upper_right.x) / (int)TILE_SIZE + 2;

	int potential_bridge_height = ZOOM_BASE * TILE_HEIGHT * _settings_game.construction.max_bridge_height;

	/* Rows overlap with neighbouring rows by a half tile.
	 * The first row that could possibly be visible is the row above upper_left (if it is at height 0).
	 * Due to integer-division not rounding down for negative numbers, we need another decrement.
	 */
	int row = (upper_left.x + upper_left.y) / (int)TILE_SIZE - 2;
	bool last_row = false;
	for (; !last_row; row++) {
		last_row = true;
		for (int column = left_column; column <= right_column; column++) {
			/* Valid row/column? */
			if ((row + column) % 2 != 0) continue;

			Point tilecoord;
			tilecoord.x = (row - column) / 2;
			tilecoord.y = (row + column) / 2;
			assert(column == tilecoord.y - tilecoord.x);
			assert(row == tilecoord.y + tilecoord.x);

			TileType tile_type;
			_cur_ti.x = tilecoord.x * TILE_SIZE;
			_cur_ti.y = tilecoord.y * TILE_SIZE;

			if (IsInsideBS(tilecoord.x, 0, Map::SizeX()) && IsInsideBS(tilecoord.y, 0, Map::SizeY())) {
				/* This includes the south border at Map::MaxX / Map::MaxY. When terraforming we still draw tile selections there. */
				_cur_ti.tile = TileXY(tilecoord.x, tilecoord.y);
				tile_type = GetTileType(_cur_ti.tile);
			} else {
				_cur_ti.tile = INVALID_TILE;
				tile_type = MP_VOID;
			}

			if (tile_type != MP_VOID) {