In reply to my first reply, I got to thinking that I would like to know how to do this, too. So after experimenting for a while, I came up with a solution. It may have been covered in other posts, or it may not be exactly what you’re looking for, but it is a way to fill text with particles. I use Corel Photo Paint for still editing. I’m not familiar with Photoshop, but the concepts should be the same. These are the steps I took to make a waterfall form some text in Pi3:
1. Create a text object on a background that is 720×486 pixels. 486 is to make sure that the edges of a 720×480 movie are covered.
2. Center your object so it will paste into the next step centered.
3. Copy and paste it into a new background with no background, ie. onto a transparent background, of the same size.
4. Create a mask from the object and keep the object selected.
5. Invert the mask so that the mask will cover everything BUT the object.
6. Feather the mask from the inside a little, otherwise you end up with a hairline outline when added to Pi3 as a layer. This will make the edges a little fuzzy, though.
7. Save the mask to Alpha channel 1.
8. Save the file as a Photoshop file, (PSD). This will save the alpha or transparency of your text. I couldn’t seem to get a PNG to work. Maybe I missed something.
9. Use this file as a layer in Pi3, with your particles underneath on a lower layer. The particles will “form” your text as they emit.
Hope this helps. I know I learned something valuable.