I think I have finally worked out how to use this filter. I often leave things at the default settings because they give pleasing enough results - or don't use them at all.
I did this tonight

I played with the settings this time until I got it as I wanted.

The perfect effect for a cute fluffy dog. I don't go far beyond defaults myself when I use filters so you are not alone.

Thank you Erisian. Say Hello to Anmal
I wanted some sparkle but only a little

AnMal says Hi

Very nice sallyanne. That's a cute little dog too.

I was just looking at the rodilius filter yesterday! Did not get time to play with it though. I like your image, Sallyanne. Not overdone, just right for "Highlights" as refer to it with humans.

sallyanne, I saw the first post soon after it went up. What I had immediately liked and most remembered was the star in the eye. Today, a week later, boyoboy was my face red when I read more closely and realized that Rodilius is not the name of the doggie but the name of the effect ...

I wanted to appropriate the sparkle for use in some other pictures and wanted to ask your permission. Now I can ask, boldly, like I was so much better informed all along: "Was the eye-light sparkle part of the well-known Rodilius effect or was it added separately?"

And if I can't recreate it on my own, may I borrow your sparkle?

It was part of the effect. Why I had to take the sliders back as far as possible becase everything that was 'white' was affected.
Again the sparkle was just a white spot originally.
In gimp under lighting effects there is a sparkle filter. Try that first.

sallyanne, I got Rodilius to work as I wanted. I also tend to stick with defaults, which means I've no doubt overlooked a lot of what plugins can actually do. For the effect I was trying for, the plugin is just barely on. From time to time I print snapshots of family pets and what to do with the eye-lights seems to require special attention. I much liked the star effect I saw in your photo. It can be subtle enough to not be noticed at all (which was what I wanted) but then may get a little extra smile when it is noticed (which is also what I wanted).

I did this for a person who had just lost their dog. Which was my main reson for not over doing it. They were happy with it too
I'm glad I have been useful in a small way for you neurolurker.

I used Rod's effect in creating this for GMIC. Roddy, named after Rod, of course.

Aaaaah. Roddy is almost as cute as AnMal.

Roddy is very cute, Mahvin!