Continuing on my multi-part blog about rendering space, now I’ll talk about building the Milky Way.

Rendering the galaxy was much simpler than rendering the stars. Basically, put a texture of the Milky Way on the inside of a sphere, and you’re done!

Okay, not a sphere, but a rough approximation of a sphere. Start with a cube, and since the GPU will only draw triangles, construct each square facet from two triangles. Subdivide each triangle into two more triangles, and then subdivide all those triangles into two more triangles. Now turn it into a pseudo-sphere by normalizing all the vectors to be a distance of 1 from the center. Presto–a 48-sided polyhedron, or “sphere”.

The Milky Way gets plastered on the inside surface of the sphere, since we’re viewing it from the inside. We use a great image from the European Southern Observatory. This gets cut up into a cube map so we can use it within our shader.

Add noise to the render so we break up the pixelation. See my GLSL random number blog for more details on this and the noise function itself.

And we’re done! Much simpler than the stars. The earth won’t be so simple.

(Here’s my dirty little secret–I never checked the milkyway texture with the actual stars, so I’m quite certain they are misaligned. It was on my list of things to check for the longest time, but I had so much else to finish that I just dropped it at some point. My bad.)