Method ComputeScroll

src/smallmap_gui.cpp:1180–1200

* Compute base parameters of the smallmap such that tile (\a tx, \a ty) starts at pixel (\a x, \a y). * @param tx Tile x coordinate. * @param ty Tile y coordinate. * @param x Non-negative horizontal position in the display where the tile starts. * @param y Non-negative vertical position in the display where the tile starts. * @param[out] sub Value of #subscroll

	 * @return #scroll_x, #scroll_y values.
	 */
	Point ComputeScroll(int tx, int ty, int x, int y, int *sub) const
	{
		assert(x >= 0 && y >= 0);

		int new_sub;
		Point tile_xy = PixelToTile(x, y, &new_sub, false);
		tx -= tile_xy.x;
		ty -= tile_xy.y;

		Point scroll;
		if (new_sub == 0) {
			*sub = 0;
			scroll.x = (tx + this->zoom) * TILE_SIZE;
			scroll.y = (ty - this->zoom) * TILE_SIZE;
		} else {
			*sub = 4 - new_sub;
			scroll.x = (tx + 2 * this->zoom) * TILE_SIZE;
			scroll.y = (ty - 2 * this->zoom) * TILE_SIZE;
		}
		return scroll;
	}

	/**
	 * Initialize or change the zoom level.