[probably solved] How to render a huge planet?

OpenGL Development
#1

Hi guys, this is kind of a newbie OpenGL question, so please bear with me.

I’m currently fooling around with LibGDX trying some new things out and building a little 2D lander game. The lander is no problem (its basically 128 x 128 pixels), but I do have an issue with rendering a planet that is comparatively huge compared to the lander (as in, 1000+ * larger):

Edit: forgot to mention, heh, it’s 2D

The problem is that I have no idea on how to best approach this. I would guess that I could draw the planet as a circular polygon using a mipmap texture (i.e. a detailed texture when zoomed in, less detailed when zoomed out) repeated over the surface. But I’m curious as to how you guys would approach this. Any ideas would be appreciated!

#2

I would use noise, since my texture would probably be derived from noise anyways if I had to create it. You can use as much or as little detail as you need without creating repetition.

#3

You need to render detail using an very smart LOD system so you dont eat al resources.
Best thing would be to make an quad tree for all lod levels, and generate these on the fly.
But this is 3D stuff…

With a planet you get really fast at texture limits, so using one texture would only work if you wont zoom in (much).

#4

@Several KB: good idea, but I have some doubts it will look very nice. But it may be worth a try.

@RobinB: sorry! forgot to mention its 2D in fact. But that may not change anything fundamentally. I’ll look into quad trees and see what they can do for me…

#5

Just use simple texture with mipmaps.

#6

If your planet truly needs to be 100k + pixels and you need to be able to see the entire thing (be it through zooming or panning)… then use a mesh with a repeating planet texture, scale the texcoords accordingly.

Generating the points of a circle looks somewhat like this:

To determine an approximate number of steps given your radius, you can use something like this:
[icode]int steps = (int)(12 * Math.pow(radius/2f, 1/3f));[/icode]

Alternatively:
[icode]int steps = (int)(12 * Math.cbrt(radius/2f));[/icode]

You can read about LibGDX meshes here:

You can use triangles or triangle fan. Triangle fan is easy; just put a point in the center, then points for each circle segment (just like in the Code Pen). Triangles is not too much more difficult; the benefit of them is that you can place many in the same batch (in this case it doesn’t seem necessary, since you’ve only got one planet).

Texcoords would be calculated kind of like this:

float u = (((x-centerX) / radius) / 2f + 0.5f) * repeatCount;
float v = (((y-centerY) / radius) / 2f + 0.5f) * repeatCount;

Which leads to 0.0 - 1.0 values, multiplied by the number of times you want the texture to repeat. Make sure TextureFilter.Repeat is set! :slight_smile:

If you only ever see the tip of the planet, then forgo the above and just use a half-circle texture that makes the ship look small in comparison (SpriteBatch).

#7

@davedes:

Thanks a lot for the detailed explanation! I can see how this can be done, especially the texture coordinate part is interesting. I’ll go and try it out.