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Discuss the Star Trek mod(s) for the Vega Strike Engine

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esgaroth
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Post by esgaroth »

Anyone taken a look at this ?
http://en.spaceengine.org/
Opinions ?
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Re: Offtopic

Post by klauss »

esgaroth wrote:Anyone taken a look at this ?
http://en.spaceengine.org/
Opinions ?
It looks like you're asking me to finally add ring shadows once and for all. :p

Anyway, it looks like celestia with fancier graphics.
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esgaroth
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Re: Offtopic

Post by esgaroth »

I´m not asking anything. :-)
I am a scientist, If I ask, I ask directly :-)

And if I´d have a wish for free I´d wish a volumetric shader for nebulae - after a few additional coworkers for the vegatrek project, of course....
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Re: Offtopic

Post by klauss »

If I had a clear idea how to write that shader, I would. I'm still drawing a blank there, short of an imposter cloud, I have no idea how to raytrace the nebula fast enough.
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Re: Offtopic

Post by log0 »

Not sure what effect you are trying to achieve. Glowing clouds in space?

For atmosphere clouds I've been playing with the following idea (originally developed by ATI?). You create a mesh volume for the cloud (for atmosphere clouds this volume is enclosed by two layers displaced by cloud density, think of heightmap). In your main pass you write scene depth into an extra buffer. Then you render the cloud mesh back facing tris depth into one buffer and the forward facing into another. This step can even be done in one pass using normals to differentiate between back/forward facing. In a final pass you use this three depth values to attenuate your scene.

For clouds the only bit that doesn't work is in-scattering, as you would need multiple density samples along view ray and towards light source. But for a generic volumetric fog/cloud/smoke effect the idea might be good enough.

Edit:
Hmm, for in-scattering one could do another cloud depth pass from the light direction, like with shadow mapping. And then sample it a few(3-4) times in the cloud view depth interval, interpolate density towards light. Need to experiment with it.
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Re: Offtopic

Post by klauss »

log0 wrote:Not sure what effect you are trying to achieve. Glowing clouds in space?

For atmosphere clouds I've been playing with the following idea (originally developed by ATI?). You create a mesh volume for the cloud (for atmosphere clouds this volume is enclosed by two layers displaced by cloud density, think of heightmap). In your main pass you write scene depth into an extra buffer. Then you render the cloud mesh back facing tris depth into one buffer and the forward facing into another. This step can even be done in one pass using normals to differentiate between back/forward facing. In a final pass you use this three depth values to attenuate your scene.

For clouds the only bit that doesn't work is in-scattering, as you would need multiple density samples along view ray and towards light source. But for a generic volumetric fog/cloud/smoke effect the idea might be good enough.

Edit:
Hmm, for in-scattering one could do another cloud depth pass from the light direction, like with shadow mapping. And then sample it a few(3-4) times in the cloud view depth interval, interpolate density towards light. Need to experiment with it.
Atmosphere clouds seen from space are already done. Depending on your GPU, the raytracing step will be more or less precise. It works pretty much like you said, albeit greatly optimized since, assuming the camera is in space, lots of things can be approximated. Like, no need to render depth, depth can be computed based on the assumption that the cloud density map is mapped onto a sphere.

But it's not that what I was referring to. Glowing clouds in space indeed is what I was referring to. Planetary nebula, accretion disks, artificial clouds of other kinds.

Planetary nebula don't move while flying in-system, but they would move when you jump from system to system.
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Re: Offtopic

Post by log0 »

klauss wrote:
log0 wrote:Not sure what effect you are trying to achieve. Glowing clouds in space?

For atmosphere clouds I've been playing with the following idea (originally developed by ATI?). You create a mesh volume for the cloud (for atmosphere clouds this volume is enclosed by two layers displaced by cloud density, think of heightmap). In your main pass you write scene depth into an extra buffer. Then you render the cloud mesh back facing tris depth into one buffer and the forward facing into another. This step can even be done in one pass using normals to differentiate between back/forward facing. In a final pass you use this three depth values to attenuate your scene.

For clouds the only bit that doesn't work is in-scattering, as you would need multiple density samples along view ray and towards light source. But for a generic volumetric fog/cloud/smoke effect the idea might be good enough.

Edit:
Hmm, for in-scattering one could do another cloud depth pass from the light direction, like with shadow mapping. And then sample it a few(3-4) times in the cloud view depth interval, interpolate density towards light. Need to experiment with it.
Atmosphere clouds seen from space are already done. Depending on your GPU, the raytracing step will be more or less precise. It works pretty much like you said, albeit greatly optimized since, assuming the camera is in space, lots of things can be approximated. Like, no need to render depth, depth can be computed based on the assumption that the cloud density map is mapped onto a sphere.

But it's not that what I was referring to. Glowing clouds in space indeed is what I was referring to. Planetary nebula, accretion disks, artificial clouds of other kinds.

Planetary nebula don't move while flying in-system, but they would move when you jump from system to system.
Confused... I wasn't talking about atmospheric clouds from space. But about 3D "volume" clouds that you can fly through.

PS: I don't mean this as a feature request of any kind, just sharing some info.
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Re: Offtopic

Post by klauss »

log0 wrote:Confused... I wasn't talking about atmospheric clouds from space. But about 3D "volume" clouds that you can fly through.

PS: I don't mean this as a feature request of any kind, just sharing some info.
For those, in space, in-scattering is the entire effect. Nebulas, more precisely, are glowing clouds interspersed with opaque ones. The whole neat effect is produced by in-scattering and self shadowing, and that's what I don't know how to accomplish.

Dust opaque clouds are easier, but still challenging. An imposter cloud can easily handle direct lighting, and simple tricks can mimic self-shadowing without actually simulating it (ie: paricles closer to the light source aren't shadowed, particles further away are with the shadowing increasing as you go deeper). The challenge here is sort order and overdraw. They can easily kill most GPUs (see VS's leak effect on damaged ships and the effect it has on performance).
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Re: Offtopic

Post by esgaroth »

Not sure what effect you are trying to achieve. Glowing clouds in space?
Not necessarily glowing clouds. Simple clouds would be ok for me. Just a kind of "fog" in space...
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