Function glowFalloff

glowFalloff(distance: number, radius: number): number
How much light a soft glow still carries at distance from its centre: 1 at the centre, easing to exactly 0 at radius, 0 past it. Pure, so a sign's falloff is checkable as arithmetic: the middle of a tube is always brighter than its rim.
Parameters
- distance: number
- radius: number
Returns number
Example
```
import { glowFalloff } from '@datamoc/mwg/two-d/render';

console.log(glowFalloff(0, 24)); // 1 - the centre burns full
console.log(glowFalloff(24, 24)); // 0 - the rim carries nothing
console.log(glowFalloff(48, 24)); // 0 - past the rim stays dark
```
- Defined in src/two-d/render/NeonGlow.ts:27