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MRPAS-FOV-Algorithm

What is this?

A straightforward, 2D implementation of Mingos' Restrictive Precise Angle Shadowcasting (MRPAS), a common roguelike Field of View (FOV) algorithm, in C++. An FOV computation algorithm, given a 2D grid of tiles with a set of source coordinates and points marked as view-blocking obstacles, will determine all of the points visible from those coordinates. This implementation is lightweight, headers-only, and can be easily dragged-and-dropped into your project. Based on MRPAS code written by Dominik "Mingos" Marczuk in 2008 and posted on the website of the unreleased roguelike game Umbrarum Regnum in April 2009. (Source Post)

MRPAS was originally written with performance in mind, and is very efficient. It processes as few points as possible, quickly discarding the ones obviously out of FOV, and tends to match or outperform all popular FOV algorithms. It is part of the overall family of Restrictive Precise Angle Shadowcasting algorithms, in that instead of calculating one approximated slope for each cell, it uses three extremely exact slopes, or angles, to determine a cell's visibility from the player's coordinates.

How does the algorithm work?

The MRPAS algorithm begins at the starting point - that is, the player's current coordinates - and iterates over shadowcasted lines of tiles in an octant, from nearest to furthest, from a slope of 0 to a slope of 1. If it encounters an opaque or obstructed tile that blocks the player's vision in that line, it finds the two slopes touching it on the edge and adds that range to a list of obstructed regions. For each tile it traverses, it checks to see if that tile is obstructed by any of those regions. A visible tile needs to have its middle slope fall outside all obstructions to be visible to the player, and an opaque tile only needs not to be fully contained in any obstruction. As MRPAS is a restrictive algorithm, it attempts to minimize the amount of visible tiles, while permissive algorithms maximize them.

How do I use this?

  1. Include the header file FieldOfView.h.
  2. Create a Map object with width and height parameters corresponding to your terrain map dimensions, and fill the cells with the walkable (can the player walk through this tile?) and transparent (can the player see through this tile?) values of your terrain map.
  3. Create a FieldOfView object and call the computeFOV method with your desired parameters.
    • playerX: The player's x-coordinate.
    • playerY: The player's y-coordinate.
    • maxRadius: The maximum FOV radius. Lower values result in lower vision.
    • lightWalls: Are obstacles lit? (false makes obstacles dark.)
  4. The resulting Map cells will contain fov values corresponding to whether they are visible in the player's FOV cone.

Read more

MRPAS License

MRPAS Copyright (c) 2009, 2010 Dominik Marczuk All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: * Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. * Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. * The name of Dominik Marczuk may not be used to endorse or promote products derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY DOMINIK MARCZUK ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL DOMINIK MARCZUK BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.