Precise Shadowcasting in JavaScript

This pages describes and explains the Precise Shadowcasting algorithm, developed and implemented by Ondřej Žára in rot.js.

WORK IN PROGRESS

General algorithm workflow

1. Let [x,y] be the player coordinates
2. Initialize the empty shadow queue
3. For R=1 up to maximum visibility range do:
   1. Retrieve all cells whose range from [x,y] is R
   2. Make sure these cells are in correct order (clockwise or counter-clockwise; every iteration starting at the same angle)
   3. For every cell in this "ring":
      1. Determine the corresponding arc [a1,a2]
      2. Consult the shadow queue to determine whether [a1,a2] is fully shadowed
      3. If no part of [a1,a2] is visible, mark the cell as not visible and advance to next cell
      4. If some part of [a1,a2] is visible, merge it into the shadow queue; mark the cell as visible