# Precise Shadowcasting in JavaScript

From RogueBasin

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

**WORK IN PROGRESS**

## Contents |

## About

## General algorithm workflow

- Let
`[x,y]`

be the player coordinates - Initialize the empty shadow queue
- For
`R=1`

up to maximum visibility range do:- Retrieve all cells whose range from
`[x,y]`

is`R`

- Make sure these cells are in correct order (clockwise or counter-clockwise; every iteration starting at the same angle)
- For every cell in this "ring":
- Determine the corresponding arc
`[a1,a2]`

- Consult the shadow queue to determine whether
`[a1,a2]`

is fully shadowed - If no part of
`[a1,a2]`

is visible, mark the cell as invisible and advance to next cell - If some part of
`[a1,a2]`

is visible, merge it into the shadow queue; mark the cell as visible

- Determine the corresponding arc

- Retrieve all cells whose range from