I want to change the alpha of individual pixels on a texture based on a particle effect

So I have a texture, to be able to visualise the problem a bit more let’s say it is a solid vertical blue rectangle.

What i want to do is have it start off invisible (0 alpha), then i’d like it to start becoming visible from the top and crawl downwards, imagine nannites crawling down it and eating a layer of dirt off the top as they go so it becomes visible where they are… that kind of thing.

My first thought was to try and use a particle effect, setting the alpha of any pixel that has a particle over it to 1.

So i guess what i’m really asking is, is it possible to edit alpha levels of a texture pixel by pixel. And can you tell it to detect if there is a particle there and react to that?

Many thanks

You need to do texture.Apply() after SetPixel()!