Visual shader to cutoff specific color level

[GammaGames]

Godot Version

4.5

Question

I have a black and white texture from itch for a blood pool. Black is transparent while white is solid, mapping to the alpha works.

I want to be able to set a cutoff color that will make it so values below a certain lightness are transparent, letting me animate the pool. Currently I have a step op combining with a darken color op, which seems to work:

Some previews:

But I have a few questions:

1. Is there a better way/more efficient way to achieve the same effect?
2. The color is backward and you have to use black to show the entire image. How do I invert that?
3. How can I make the transition smoother so it’s not 100% white at the limit of the cutoff?

[normalized]

1. Step is extremely efficient.
2. Flip parameters to step.
3. Use smoothstep instead.

[GammaGames]

Flipping the inputs on the step had weird effects!

Smoothstep worked but I ended up liking the non-smooth version, my final shader (for now) is:

Now to save them out to textures, since I can’t use it on a decal