# Ruby shadowcasting implementation

From RogueBasin

This is a Ruby implementation of Bjorn Bergstrom's recursive shadowcasting FOV algorithm. It is basically a straight port of the Python version, implemented as a module, and could probably do with some optimisation.

To use the module, create a Map class or somesuch and provide two methods:

`blocked?(x, y)` returns true if the tile at (x, y) blocks view of tiles beyond it (e.g. walls)
`light(x, y)` marks (x, y) as visible to the player (e.g. lit up on screen)

On both Ruby 1.8 and 1.9, shadowcasting runs slightly faster than Precise Permissive FOV and boasts a circular FOV shape, 8-directions of FOV casting, and is easier to understand. On the other hand, it has artifacts and is not symmetric ... but it is the more popular roguelike algorithm.

module ShadowCastingFieldOfView # Multipliers for transforming coordinates into other octants @@mult = [ [1, 0, 0, -1, -1, 0, 0, 1], [0, 1, -1, 0, 0, -1, 1, 0], [0, 1, 1, 0, 0, -1, -1, 0], [1, 0, 0, 1, -1, 0, 0, -1], ] # Determines which co-ordinates on a 2D grid are visible # from a particular co-ordinate. # start_x, start_y: center of view # radius: how far field of view extends def do_fov(start_x, start_y, radius) light start_x, start_y 8.times do |oct| cast_light start_x, start_y, 1, 1.0, 0.0, radius, @@mult[0][oct],@@mult[1][oct], @@mult[2][oct], @@mult[3][oct], 0 end end private # Recursive light-casting function def cast_light(cx, cy, row, light_start, light_end, radius, xx, xy, yx, yy, id) return if light_start < light_end radius_sq = radius * radius (row..radius).each do |j| # .. is inclusive dx, dy = -j - 1, -j blocked = false while dx <= 0 dx += 1 # Translate the dx, dy co-ordinates into map co-ordinates mx, my = cx + dx * xx + dy * xy, cy + dx * yx + dy * yy # l_slope and r_slope store the slopes of the left and right # extremities of the square we're considering: l_slope, r_slope = (dx-0.5)/(dy+0.5), (dx+0.5)/(dy-0.5) if light_start < r_slope next elsif light_end > l_slope break else # Our light beam is touching this square; light it light(mx, my) if (dx*dx + dy*dy) < radius_sq if blocked # We've scanning a row of blocked squares if blocked?(mx, my) new_start = r_slope next else blocked = false light_start = new_start end else if blocked?(mx, my) and j < radius # This is a blocking square, start a child scan blocked = true cast_light(cx, cy, j+1, light_start, l_slope, radius, xx, xy, yx, yy, id+1) new_start = r_slope end end end end # while dx <= 0 break if blocked end # (row..radius+1).each end end