# Precise Shadowcasting in JavaScript

From RogueBasin

(Difference between revisions)

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### Determine the corresponding arc <code>[a1,a2]</code> | ### Determine the corresponding arc <code>[a1,a2]</code> | ||

### Consult the shadow queue to determine whether <code>[a1,a2]</code> is fully shadowed | ### Consult the shadow queue to determine whether <code>[a1,a2]</code> is fully shadowed | ||

− | ### If no part of <code>[a1,a2]</code> is visible, mark the cell as | + | ### If no part of <code>[a1,a2]</code> is visible, mark the cell as '''not visible''' and advance to next cell |

− | ### If some part of <code>[a1,a2]</code> is visible, merge it into the shadow queue; mark the cell as visible | + | ### If some part of <code>[a1,a2]</code> is visible, merge it into the shadow queue; mark the cell as '''visible''' |

== Tweaks, tricks and advanced topics == | == Tweaks, tricks and advanced topics == |

## Revision as of 16:26, 3 January 2013

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**not visible**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