Fresnel Sliders

Fresnel effects in video games are implemented by figuring out the angle of a visual surface relative to the camera, and affecting how it looks based on that. For example, making an object glow just on the parts curving away from the camera is a very common look to grab the player's attention for pickups.

A split slider (as used for sound gadgets) could work for this--where you can drag with X as normal. Or drag with L1+X to split the slider in two and have a left edge point and a right edge point, defining a range of values.

As an example, I'll use the glow (referring to the visual rendering, not the light emitting part). So you'd have the left edge of the slider be the minimum for the setting; the entire object's surface will glow that much. The right edge of the slider would be the maximum for the setting, affecting the flecks/surfaces facing side-on from the camera where you can't actually see it. The angle of the surface between face-on and side-on will glow an amount between the min. and max. of that range.

So if you have a ball and its glow is at 0.1 minimum, and 0.5 maximum, the centre is facing you so that will be at 0.1. As it gets toward the edge of the ball it will glow more and more until it's at 0.5 at its edge.

You could set the minimum to 0,and now the middle of the ball will be unaffected.

To have more control, settings to manipulate the angle range could be used. A minimum angle would start at 0 (perfectly facing the camera). But you could up that to say 45 degrees, so that the 0.1 glow would start further out from the middle of the ball. And a maximum angle could be adjusted in the same way. Set it to 50 degrees and now there's a pretty sharp transition to 0.5 glow.

You could have fresnel sliders for other settings too. Tint amount, for example, would allow things like cel shading to work pretty seamlessly. Set the tint colour to black, with a tint of min 0, max 1. And the fresnel angle range to min 80 degrees to max 80 degrees. This will make the surfaces at the edge of the character black, as if with a drawn outline. Parts like noses with a surface facing away more will have a thin outline to them.

And then think about using it with opacity on a painting, to make water that is more reflective of the sky when you look perpendicular to it, and more transparent when you look straight through it!

I appreciate this would be a bigger change, especially for the UI of sculpts and paintings. It's just one of those effects that is so commonly used in video games, and can go that extra step in making something feel more realistic, or more stylised depending on how you use it.