I need help with creating a 2d shader that looks like a planet.

Question

I'm making a 2d platformer, and I would like the level to look like you are standing on a small planet. I'm thinking about using a shader to accomplish this. I had never used them before so, with help from this post, I managed to create something similar to what I was imagining:

This is the code I used. The shader is applied in a ColorRect node that is parented by a CanvasLayer node, in order to apply the effect to the entire viewport.

This is the result. It works as intended, but it's not exactly what I wanted. The effect is too extreme. I want to have at least some control over how big the "planet" is. I don't really want everything just come crashing down when it hits the border. This is especially noticeable when we resize the screen:

The ColorRect resizes along with it, making the effect even more extreme.

So I want to know either how I can improve this shader, or if there already exist resources that do something similar so I can implement them in my game. If neither, I can just ditch this idea altogether, no problem. I don't know if I'm asking for too much...

Comments

Eu não sei nada sobre shaders mas só um comentário: tu sabe que tu pode usar PI pra pegar o valor de pi né? Tu não precisa definir uma variável que nem tu ta usando float pi = 3.14.

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Eu sei, mas acho que só tem no GDscript, porque quando eu tento colocar no editor de shader ele dá um erro: Unknown identifier in expression: PI

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@Fupicat English pls?

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They were just saying that I could have used PI instead of creating a variable for storing pi, but that only works in GDscript.

Anyway, you got any ideas on my issue?