Spherical Coordinates (Splitting a sphere into eights)

[severe marsh]

I've been trying to code a sphere mesh in gd script, but it's really difficult. The thing is I need it to be able to be split into eights so I need to print out each part separately, and that's proving to be quite difficult. The code is in the post if you want to see it.

[upper pulsar]

How many rings and segments are you thinking. (Easier if segments is a multiple of 8)

[severe marsh]

Maybe 32 for segments, 16 for rings

I might up it to 64 and 32 tho

But 32 and 16 seems to be good

[upper pulsar]

Do you need faces inside the sphere on either side of the segments?

[severe marsh]

Yep

Otherwise it'll be hollow

So like think of it more like sowing the missing parts

That's the big issue. Splitting is one thing, but adding the faces might also be tricky

I could probably just draw to spheres with cylindrical coordinates, convert it to rectangular coordinates, and use those. I would need three circles. The issue is then we need to remove extranious parts of the circles too. So we need to do it off a case by case basis

What I'm thinking is we calculate which octant we're in

while we're generating the mesh

and if we don't need it, we don't calculate it

Then we just need to figure out which quarter circles to add

and then it's done

[rotund pilot]

octogonal spheres are easier to cut up

[upper pulsar]

I just started writing the code to generate it and realized something do you need UVs because I'm terrible at setting up UVs

[rotund pilot]

let me find the exact math description

how far did you get

[upper pulsar]

I was about to declare the arrays

[rotund pilot]

Why do you need a sphere mesh? What purpose do you want it for

I'm assuming you want it

[upper pulsar]

I'm not the one asking I was trying to help

[rotund pilot]

ah

print out each part separately for an existing godot csg sphere or a https://docs.godotengine.org/en/4.4/classes/class_spheremesh.html sounds a lot easier than generating one and then printing one

So I was curious why was there a need to both generate and print

If all you needed was the sphere in blender, you can even export the current scene to gtlf2

[severe marsh]

Oh me?

[rotund pilot]

yeah

[severe marsh]

I'm making a program that makes custom 3d models in the anime style

think of vroid

[rotund pilot]

sure

what's stopping you?

[severe marsh]

wdym?

[rotund pilot]

We wrote a character generator once for work. Then the project meandered so we decided to https://github.com/V-Sekai/godot-vrm and do other godot engine related things

there's also the makehuman project

https://github.com/NitroxNova/humanizer/

[severe marsh]

I know but I just want it as a challenge you know? Plus I want the full rights to the things created in it

[rotund pilot]

We've done a lot of those steps to make a godot engine character generator. ask me anything

[severe marsh]

What parametes did you add?

[upper pulsar]

I'm thinking @iFire may be more helpful but if it doesn't work (and you don't need UVs) at me and I'll resume making the generation code I'm fairly quick at it because It's my go-to method

[rotund pilot]

previously godot engine only had a collada importer. So we added fbx and gltf2

[severe marsh]

I have this for the things people can customize

[rotund pilot]

that looks like a lot like the make human blend shapes

[severe marsh]

Well anyhow, I got it partially working

except theirs this weird triangle?

It's like an artifact

[rotund pilot]

are you aware of the various godot engine axis conventions

it's ok to say no

[severe marsh]

nope not at all

Anyhow here's the weird triangle

[rotund pilot]

https://docs.godotengine.org/en/stable/tutorials/3d/introduction_to_3d.html#coordinate-system

[rotund pilot]

are you sure that's a triangle? looks like multiple triangles

Turn on wireframe mode

Godot Engine doesn't have n-gons (not even quads)

[severe marsh]

How?

[rotund pilot]

you probably are using the wrong triangle order or forward axis

it's an editor viewport debug mode

[severe marsh]

I'm generating it, I can't see it in the editor

[rotund pilot]

this is here, so you can see it so you can turn on wireframe mode

[severe marsh]

No this is in the running instance

[rotund pilot]

hm, uh writing your wireframe shader is a bit annoying

[rotund pilot]

anyways as far as I can tell something is either cutting out the mesh or it's missing

[severe marsh]

Yeah

[rotund pilot]

like a camera clip plane

[severe marsh]

I'm thinking it's either one of two things

either my function for checking octants is wrong

or it's just in multiple octants at once, which defaults it to true

[rotund pilot]

can you do only one octant

it should be possible.

so standard tricks are divide and conquer and use the identity trick (make something that returns the input like 5 * 1 = 5)

[severe marsh]

Let me check

1 octant works

2 octants work

3 works

4 works

Wait nvm?

Octants can only print horizontally for some reason

[rotund pilot]

that might be it

[severe marsh]

So what do I do then?

Yeah not sure what to do

I've tried debugging it

but it's kinda hard to

[rotund pilot]

try doing only vertically

[severe marsh]

It get's the triangle issue then

[rotund pilot]

did divide conquer work

[severe marsh]

Wait now I'm confused

Okay so it works

so long as everything

is on the same hemisphere

otherwise it breaks

[rotund pilot]

sounds like backface culling

[severe marsh]

what's that?

[rotund pilot]

you know when you have a mesh and go inside it and it turns transparent

[severe marsh]

Yep

[rotund pilot]

one common optimization is don't draw the back face because someone assumed the mesh is manifold so it will never show

[severe marsh]

Yeah, I mean ideally I want that too

How would backface culling fix this?

[rotund pilot]

it doesn't

I wanted to know if you flippd the triangles inside out

[severe marsh]

Correction: How does it relate to this

[severe marsh]

good point

[rotund pilot]

if you reversed the winding order or whatever

[severe marsh]

I don't think so

I could send you a copy of the project

That way you can debug it in godot

[rotund pilot]

I'm a bit ragged so you can send it but I'll probably do more progress in this chat

[severe marsh]

https://github.com/zorauthedeveloper/testingforspheircalcoordinatesingodot

[foggy flicker]

hi, dropping in from the math channel, the length of this conversation is intimidating...
this page from the doc ends with a simple code to generate a spherical mesh that you may want to take inspiration from : https://docs.godotengine.org/en/latest/tutorials/3d/procedural_geometry/arraymesh.html

[severe marsh]

That does help quite a lot

I FIXED IT

I think

kinda

No more weird triangle thing

[foggy flicker]

I also have a few questions :

• does it have to be a mesh (writing a shader to render a perfect sphere isn't very hard, though I get you may need to get aquainted with shaders first)
• is the "UV sphere" you seem to be going for really fitting your needs ? another nice approach to meshing a sphere would be this (I've seen it called the "icosphere"): https://upload.wikimedia.org/wikipedia/commons/f/ff/Geodesic_icosahedral_polyhedron_example.png , or you could also use the popular fibonacci spiral (as seen here for example https://extremelearning.com.au/evenly-distributing-points-on-a-sphere/)

[rotund pilot]

there's no gdscript in the project

I recommend icosphere too

I forgot the name and the algorithm

[severe marsh]

nvm

[severe marsh]

To the question does it have to be a mesh, yes it does. I'm merging it with other meshes later so it will have to be. Number 2, I'd like to stick to the UV Sphere if possible. I just personally don't like the icosphere method. I still have no clue whats wrong though. Even the one godot provided, adding the changes makes the triangle error. I think it's a error with the octant detection

[foggy flicker]

well, I'm going to bed now ; please try to somewhat sum up what you've done and how it misbehaves, I don't think I'll ever want to read the whole thread

[severe marsh]

Yeah bassically we got the script to generate the sphere, we tried detecting when it split into octants, it did, but then their was this weird triangle artifact left behind. I then just noticed that a entire strip is missing. So I think it's the octant detection

[severe marsh]

Yo @rotund pilot

I think I fixed it

Well not me...

Sadly I had to get help from Claude

It fixed it though

But I don't like using AI

What's your opinion on it?

[rotund pilot]

Your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.

[severe marsh]

What's that supposed to mean?

[rotund pilot]

AI will magnify the power of the powerful and the individual. I can't predict the future.

[severe marsh]

Either way it's fixed

It was a kinda of easy yet complicated fix

[rotund pilot]

yay

[severe marsh]

Bassically we create a 2d grid, and fill it with -1

[rotund pilot]

To be honest I still would prefer the strategy of generating csg meshes then auto rigging them in godot engine.

[severe marsh]

As in?

[rotund pilot]

for character generation

I think you're trying to generate meshes via gdscript

[severe marsh]

Correct

[rotund pilot]

a flaw of this approach is you won't keep water tightness "manifold"

secondly it's kinda annoying and you can't get the engine to help you with skinning or morphing

but you've gone further than me, so don't let tell you what to do

[severe marsh]

I mean your right

[rotund pilot]

I'd detoured into making the avatars work in game

[severe marsh]

Wdym?

[rotund pilot]

Like character controllers.

We decided not to make a character generator and like directly import vrm from vroid etc or unity packages from booth.pm

[severe marsh]

I'm still a little confused on what your trying to say

[rotund pilot]

nevermind.

great work!

[severe marsh]

Thanks

[severe marsh]

Turns out, it was broken

Just in disguise

[severe marsh]

I fixed it

Jeez this is a loop