154 replies to this topic

[Altair]

XORcist said:

Does that mean you are gonna stop your stuff ?? If thats what you meant, then GREAT:yes: . No more posts from me dude. :surrender

What it means is that even after a year, you don't have a clue what I'm saying. I just find it frustratingly unbelievable.

[anubis]

Altair : One of the first principles of information technology is : The message is created by the receiver... Meaning : Since some people here apparently constantly misinterpret your posts, you should start to think about whether you are broadcasting at the right frequency. Just my two cents.

[Altair]

anubis said:

Altair : One of the first principles of information technology is : The message is created by the receiver... Meaning : Since some people here apparently constantly misinterpret your posts, you should start to think about whether you are broadcasting at the right frequency. Just my two cents.

You need reasonable amount of background information to be able to understand the message and I was relying on that to get my message across. Apparently I was radically wrong. It's like trying to teach linear algebra to someone who doesn't even know how to multiply numbers together.

That's a problem in discussion forums in general because there's vastly different level of experienced people involved. Btw, no offence intended against inexperienced people. I definately like to have chats with them as well because they often got fresh view on things and might actually bring some nice thoughts on the table sometimes.

Cheers, Altair

[Nameless]

Altair:

How do you propose to handle complex reflection/refraction/transparency without raytracing? Sure we have cubemapping and depth peeling and other hacks for coarse effects, but it's impractical to scale this up to movie quality levels. I don't find cache coherency and other arguments for performance compelling if there's a show-stopper like that looming ahead.

Also, it seems to me that a hardware raytracer capable of rendering modern games at rt speeds, is already halfway to real time photon mapping, soft shadows and so on -- all of which benefit from the tree you calculate per frame (the performance hit of which is minimal when you start talking about gi and such).

Thoughts?

[Altair]

Nameless said:

How do you propose to handle complex reflection/refraction/transparency without raytracing? Sure we have cubemapping and depth peeling and other hacks for coarse effects, but it's impractical to scale this up to movie quality levels.

I wish I had answers to those questions. It doesn't mean that raytracing is the way to solve those problems though. Possibilities in rasterization have been taken huge leaps recently and people are actively researching how those possibilities can be utilized to their best effect. Not only that, but there are also huge leaps ahead, so there's no reason dispair that those specific features you are talking about wont be solvable (at least to a degree) with rasterization approach. Note, I'm not saying that raytracing doesn't solve elegantly some of the issues, but rather that it has huge pile of issues on its own, which in my opinion are the "show-stopper".

Nameless said:

I don't find cache coherency and other arguments for performance compelling if there's a show-stopper like that looming ahead.

Coherency has huge importancy in realtime computer graphics as well as in any realtime application. GPU vendors have been made huge effort to maximize this in order to avoid memory access becoming the bottleneck in rendering.

Nameless said:

Also, it seems to me that a hardware raytracer capable of rendering modern games at rt speeds, is already halfway to real time photon mapping, soft shadows and so on

There's LONG way to go for HW raytracer to be even close to performance of modern GPUs, or rather render similar scenes with comparable framerate. Even if we would assume that there would be HW raytracer capable for it, GI would totally bring it to its knees.

Nameless said:

all of which benefit from the tree you calculate per frame (the performance hit of which is minimal when you start talking about gi and such).

The kd-tree isn't computed per frame (it's very expensive process), since then you would end up processing all the geometry every frame and one of the inherent advantage of raytracer is the hierarchical scene traversal which prevents you from touching all the data. However, not building kd-tree per frame has its problems which has been discussed in this thread.

It's not really good supporting argument for raytracing to say that building kd-tree is nothing in comparison in computing to GI. It makes you sound more like you are taking my stance by saying that building kd-tree is very slow but hey look we got something even much more radically slower we can do! ;)

Cheers, Altair

[davepermen]

a simple "photonmap everything" is "just another" raytracing pass.. doesn't really cost much more.. say if you would SLI your rpu's, you could have one photonmapping, one raytracing, and continue at the same speed and res with (more or less) full gi.

[Altair]

davepermen said:

a simple "photonmap everything" is "just another" raytracing pass.. doesn't really cost much more.. say if you would SLI your rpu's, you could have one photonmapping, one raytracing, and continue at the same speed and res with (more or less) full gi.

Do you realize how awfully wrong that statement is? Now I can understand why you think HW raytracing is such a great idea ;) Just think of a completely diffuse white wall and red box next to it. You don't get reddish GI effects on the wall with "just another" raytracing pass.

Cheers, Altair

[Nameless]

>>It's not really good supporting argument for raytracing to say that building kd-tree is nothing in comparison in computing to GI. It makes you sound more like you are taking my stance by saying that building kd-tree is very slow but hey look we got something even much more radically slower we can do!

I agree; I don't doubt that realistically we're years away from raytracing what modern rasterizers do effortlessly. On the other hand, it does provide *elegant* solutions to ugly, ugly hacks (and after all, we're talking about the next *BIG* thing in rt graphics). Dynamic cube-maps, parallax mapping, and so on are great for making things look 95% realistic, but I think that last 5% is what will be the next *BIG* thing.

I think the next *BIG* thing is definitely light transport. Raytracing provides a natural solution to a problem as simple as reflections of reflections (a simple case is just looking at a concave object from the right angle). Something fancier, like dispersion, is trivial: just have your glass shader re-emit more refractive rays to cover a nice variety of wavelengths. I know there's hacks for all of this that look 'okay', but again it's the last 5%.

Here's another problem: how do you stencil shadow translucent objects, or even just something with a 1-bit mask on it -- like leaves on a tree (without modelling each leaf with a huge number of polygons, which would eliminate your performance advantage anyway)?

[Altair]

I'm not really an advocate of stencil shadows but rather lean towards shadow mapping. Both have their advantages/issues though, but there has been some proposals how to solve issues in shadow mapping (irregular z-buffer, alias-free shadow mapping). It's not that pixel perfect shadows or translucency wouldn't be doable on rasterization technique, but rather that current implementations on GPU doesn't quite support it due to practical reasons.

Cheers, Altair

[davepermen]

Altair said:

Do you realize how awfully wrong that statement is? Now I can understand why you think HW raytracing is such a great idea ;) Just think of a completely diffuse white wall and red box next to it. You don't get reddish GI effects on the wall with "just another" raytracing pass.

Cheers, Altair

uhm.. how old is photonmapping now, that you don't know how it works.. it's a twopass algorithm, wich works about exactly that way. one pass generates the map, the second reads and uses it. and yes, photonmapping generates about all gi effects possible (depending on implementation, of course). and it doesn't have to be slow in doing so.

[Reedbeta]

Altair has a point. You have to emit photons from each light source, sampling across all points on the surface and all directions in the hemisphere above each point, and then trace their interactions with surfaces to whichever depth you want. To get a good distribution requires shooting a LOT more photons than there are primary rays in a typical rendered scene. So generating the photon map is quite nontrivial. It re-uses basically the same algorithm, but you need a lot more horsepower.

[anubis]

Quote

You need reasonable amount of background information to be able to understand the message and I was relying on that to get my message across. Apparently I was radically wrong. It's like trying to teach linear algebra to someone who doesn't even know how to multiply numbers together.

Altair : It must be really lonely up there, huh ? If you think that diminishing people let's you appear any wiser... well... you have my pitty.

[Altair]

anubis said:

Altair : It must be really lonely up there, huh ?

There are a lot of way more experienced people than I am who are/have been working in game/hw industry and with whom I keep talking frequently, so no, not really. There's a lot you can learn as hobbyist developer and there are some really talented ones, but industry experience is hard to replace. No offense intended and I try to be less blunt in the future ;)

Cheers, Altair

[juhnu]

Could it be possible for the moderators to close this thread? It has long gone too personal and occasionally quite insulting.

Maybe time for people to step back and chill out a bit.

[anubis]

Quote

There are a lot of way more experienced people than I am who are/have been working in game/hw industry and with whom I keep talking frequently, so no, not really. There's a lot you can learn as hobbyist developer and there are some really talented ones, but industry experience is hard to replace. No offense intended and I try to be less blunt in the future

Cheers, Altair

That's fine then... I'm really just trying to act as a moderator here. Personally I don't have any preferences in this dicussion.

Quote

Could it be possible for the moderators to close this thread? It has long gone too personal and occasionally quite insulting.

Maybe time for people to step back and chill out a bit.

Yeah... it's about time.