Approach to rendering a planet texture

Question

I'm making a space game using Godot 4, and I need to capture the "hugeness" of planets. I figured I'd use spheres with textures on them for planets. The textures have identifiable landmasses on them, because that's consistent with what planets have. You should be able to recognize the same landmass when you see it again.

The planets all need to spin, as planets are wont to do. I figure I'd just rotate the mesh itself while the player space ship is still far enough away.

My difficulty begins with approaching the planet closely enough. I don't want to land on any planet, but I do want to be able to achieve a low enough orbit that gives the sense of a horizon. The little picture should illustrate it well enough. I figure I could "squash" the sphere into basically a flat circle when the ship gets close enough to the planet, and you wouldn't notice. I'd point this flattened sphere at the player's position, so it would function like a billboard in that sense. This flattened sphere could then be scaled up in the right directions, to give the sense of a vast circular plane almost.

I figure I could do some kind of trickery with UV offset and scale to keep the texture "in the right place", but i don't have any idea where to start, especially because it would need to be scaled up when you get close to it AND it would need to be in the same place as it was when you were further away from it AND...the uv would need to be offset by the rotation of the planet constantly because when the mesh is squashed, you can't rotate the mesh itself anymore. truthfully, i don't have much experience with uv shenanigans, nor with optical perspective. This whole approach is just an intuitive attempt, but i have to do SOMETHING because just "really big spheres" doesn't give a good enough impression of the hugeness of planets and stars and moons, and I don't know any of that shader black magic that could do the sphere-imposter trick on a quad (especially one you could freely orbit around).

The textures don't need to be super sharp: maybe i could stylize them somehow to be acceptable, but they DO need to have those recognizable landmasses which you can revisit, hence the difficulty.

Does anyone have any pointers for how to do this? Alternatively, does anyone know of a better solution for giving that "vastness of planets" feeling that emerges seamlessly once you get close enough to a planet?

Answer 1

One way to approach this would be to generate the surface of the planet procedurally, using weighted octaves of noise;

Start with a noise function like Perlin or Simplex that takes an x/y[/z] coordinate and returns a value (usually 0-1) for that position.

By scaling the sample coordinates, you can generate different "octaves" of noise.

Blending those together with different weights can give a texture that works very much like a height map, except it can be sampled at arbitrary levels of detail...

Pick a cutoff height as a water level and you now have randomly shaped, but deterministic/repeatable continents with mountainous features.

If you want to go a step farther, you can also calculate erosion and other effects. It'll give you a more realistic result, but it'll be a lot more compute intensive and may require pre-calculating.

For more info on the approach see:

• Continents with Simplex noise (The question I lifted the images from, credit to @Janis Taranda/@DMGregory)
• Procedural Planet Generation Series, especially E03: layered noise (Sebastian Lague, again)

You can either use a 2D noise function and map a 2D coordinate system to your sphere's surface (but you'll get the usual spherical wrapping quirks) OR use a 3D noise function and just sample the points in space for the surface of the sphere, then treat that as a surface height.

Add a random offset to the coordinates for each planet and you'll get unique (but deterministic) results.