Function packColorAdd

packColorAdd(r: number, g: number, b: number, a?: number): number
Packs an additive colour into the form the attribute expects.
Parameters
- r: number
  red, 0 to 1
- g: number
  green, 0 to 1
- b: number
  blue, 0 to 1
- a: number = 0
  how much to add to the sprite's own alpha, 0 to 1; usually 0
Returns number
Example
```
import { packColorAdd } from '@datamoc/mw_games/two-d/render';
import { TintedSprite } from '@datamoc/mw_games/two-d/render';

declare const rat: TintedSprite;

rat.colorAdd = packColorAdd(0, 1, 0); // pull the sprite towards pure green
```
- Defined in src/two-d/render/ColorTransformBatcher.ts:588