Defining an Entity’s Field of View

Hands-on Rust — by Herbert Wolverson (76 / 120)

👈 Chapter 10 Fields of View | TOC | Limiting Monsters’ Fields of View 👉

You need to follow a few steps to determine which tiles are visible from any point on the map. First, you have to denote which tiles are see-through and which are opaque. Second, you need to prepare a component to store the visibility data. Finally, you need a system that runs a field-of-view algorithm and stores the results in the new component type.

Tile Opacity

The first step in implementing visibility is deciding which tiles are see-through and which are opaque. Bracket-lib defines a trait entry for this known as is_opaque. Your map is simple, with tiles being either solid walls or floors. That leads to walls being opaque and floors being transparent (or not opaque). To represent this, bracket-lib requires you to add one more function to your map’s BaseMap implementation: is_opaque:

WhatCanISee/fov/src/map.rs

​ ​impl​ BaseMap ​for​ Map {
​     ​fn​ ​is_opaque​(&​self​, idx: usize) ​->​ bool {
​         ​self​.tiles[idx ​as​ usize] != ​TileType​::Floor
​     }

Opaque and Blocked Are Not the Same

TIP

is_blocked and is_opaque give similar results. In more complicated games, they aren’t the same thing. A closed window is opaque — but blocks an entity from traveling…