Function GreyscaleToMapHeights

src/heightmap.cpp:307–397

* Converts a given greyscale map to something that fits in OTTD map system * and create a map of that data. * @param img_width the with of the image in pixels/tiles * @param img_height the height of the image in pixels/tiles * @param map the input map */

 * @param map        the input map
 */
static void GreyscaleToMapHeights(uint img_width, uint img_height, std::span<const uint8_t> map)
{
	/* Defines the detail of the aspect ratio (to avoid doubles) */
	const uint num_div = 16384;
	/* Ensure multiplication with num_div does not cause overflows. */
	static_assert(num_div <= std::numeric_limits<uint>::max() / MAX_HEIGHTMAP_SIDE_LENGTH_IN_PIXELS);

	uint width, height;
	uint row, col;
	uint row_pad = 0, col_pad = 0;
	uint img_scale;
	uint img_row, img_col;
	TileIndex tile;

	/* Get map size and calculate scale and padding values */
	switch (_settings_game.game_creation.heightmap_rotation) {
		default: NOT_REACHED();
		case HM_COUNTER_CLOCKWISE:
			width   = Map::SizeX();
			height  = Map::SizeY();
			break;
		case HM_CLOCKWISE:
			width   = Map::SizeY();
			height  = Map::SizeX();
			break;
	}

	if ((img_width * num_div) / img_height > ((width * num_div) / height)) {
		/* Image is wider than map - center vertically */
		img_scale = (width * num_div) / img_width;
		row_pad = (1 + height - ((img_height * img_scale) / num_div)) / 2;
	} else {
		/* Image is taller than map - center horizontally */
		img_scale = (height * num_div) / img_height;
		col_pad = (1 + width - ((img_width * img_scale) / num_div)) / 2;
	}

	if (_settings_game.construction.freeform_edges) {
		for (uint x = 0; x < Map::SizeX(); x++) MakeVoid(TileXY(x, 0));
		for (uint y = 0; y < Map::SizeY(); y++) MakeVoid(TileXY(0, y));
	}

	/* Form the landscape */
	for (row = 0; row < height; row++) {
		for (col = 0; col < width; col++) {
			switch (_settings_game.game_creation.heightmap_rotation) {
				default: NOT_REACHED();
				case HM_COUNTER_CLOCKWISE: tile = TileXY(col, row); break;
				case HM_CLOCKWISE:         tile = TileXY(row, col); break;
			}

			/* Check if current tile is within the 1-pixel map edge or padding regions */
			if ((!_settings_game.construction.freeform_edges && DistanceFromEdge(tile) <= 1) ||
					(row < row_pad) || (row >= (height - row_pad - (_settings_game.construction.freeform_edges ? 0 : 1))) ||
					(col < col_pad) || (col >= (width  - col_pad - (_settings_game.construction.freeform_edges ? 0 : 1)))) {
				SetTileHeight(tile, 0);
			} else {
				/* Use nearest neighbour resizing to scale map data.