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laeuchli

OpenGL Best way to render stars?

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laeuchli    338
Dear All, I'm trying to render a realistic star field ,as seen from earth. I have the positions and magnitudes from a star catalogue, and am currently rendering them as points with various levels of alpha. This works ok, but doesnt look great, and I'm trying to think of a better rendering method. One way I considered was using point sprites, however then I'd need a star texture, and I'm not sure what would look good. Another thought I have on this is that I should increase/decrease the size of the points based on thier magnitude, and not just fade them out. I think theres a good way to do this in DirectX while keeping just one DrawPrimitive call. Is theres a way to do this in OpenGL? It seems like I'd have to keep calling a glPointSize, or setup the quads myself, which seems like kind of a pain. Any suggestions would be greatly apprciated. Regards, Jesse

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Gagyi    192
Well, stars ARE really little points (sub-pixel), most of their "size" is coming from lens flare and atmospheric scattering.
So the texture you need is either a lens flare texture or a simple blurry circle. (but you can try other things and experiment what LOOKS good in practice)

P.S.: I guess the vertex attribute called D3DFVF_PSIZE is exactly what you need. Of course you can always use the distance from the viewer to set the point sizes ;)

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laeuchli    338
</P.S.: I guess the vertex attribute called D3DFVF_PSIZE is exactly what you need. Of course you can always use the distance from the viewer to set the point sizes ;)/>
Haha doh, of course. I'm silly. Thats probably the way to go, as theres no D3DFVF_PSIZE equiv as I understand it in opengl. Anyway have any point sprite star textures that worked well?
Regards,
Jesse

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Gagyi    192
Download the trial of the game "Pax Galaxia" or "Pax Solaris" It has 4 or 5 nice star textures with alpha maps.
Hope this helps ;)

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Trurl    208
I did a stellar renderer a few years ago using point sprites. I used a vertex program to compute the sprite size based on magnitude (and in the 3D case, distance), a mipmapped texture encoding a gaussian, and a fragment program to modulate the color of the gaussian based on spectral type. The end result closely resembles long-exposure astro photography, and easily runs realtime, even for millions of stars. Screeny. I've been meaning to convert this over to GLSL, but I haven't gotten around to it. If you'd like to look at the code, it is part of Electro.

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Mike.Popoloski    3258
Quote:
Original post by Trurl
I did a stellar renderer a few years ago using point sprites. I used a vertex program to compute the sprite size based on magnitude (and in the 3D case, distance), a mipmapped texture encoding a gaussian, and a fragment program to modulate the color of the gaussian based on spectral type. The end result closely resembles long-exposure astro photography, and easily runs realtime, even for millions of stars. Screeny. I've been meaning to convert this over to GLSL, but I haven't gotten around to it. If you'd like to look at the code, it is part of Electro.


Holy crap! That looks awesome!

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laeuchli    338
Wow that does look incredibly good Trurl. Where in the source is the texture you used? I've been pawing though, and cant seem to find it.
Regards,
JEsse

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Trurl    208
The texture is just a gaussian, so it's easy to generate procedurally. No need to store it on disk. The gaussian texture generator is star_make_texture() in star.c.

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