Hey all,
Just wanted to post a quick link to my latest paper entitled "Layered Variance Shadow Maps", to be published/presented at Graphics Interface 2008 this year. The paper and accompanying video can be grabbed from the following URL:
http://www.punkuser.net/lvsm/
I apologize for the lack of a spiffy web page yet, but I've been working hard on completing my Masters thesis.
In any case, the idea is kind of neat - namely that you can apply monotonic warps to the depth distribution and plug them into Chebyshev's inequality to get different upper bounds on the visibility function, some better than others. The concept of "layered" VSMs is to exploit this fact and effective use a piecewise reconstruction of the visibility function to reduce or eliminate light bleeding. The advantage of the chosen representation is that it scales up the quality of VSMs arbitrarily at a primary cost of the more storage. Because of the chosen representation, only a single sample is needed to evaluate the visibility function at one point (i.e. when shading a pixel) unlike basis-function approaches like Convolution Shadow Maps that require all of the basis coefficients to resolve such a visibility (and thus scale up poorly). Another side advantage is that since each of the pieces represents a smaller depth range, you don't need as much precision, so the technique can be applied to older hardware that may not support fp32 filtering.
The other thing contained in the paper is some preliminary work on "Exponential Variance Shadow Maps", as inspired by Marco Salvi's work. The idea is that an exponential warping of the depth distribution is another application of the above idea. In particular it does a great job of eliminating light bleeding while still not suffering from leakage near castors (since we're still using two moments and Chebyshev's inequality, as usual). The other advantage that I mentioned in another thread is that you can also use the "dual" of the exponential warp to eliminate the "non-planar receiver" artifacts that stock Exponential Shadow Maps suffers from. The EVSM results are preliminary (as I said, I'm trying to graduate here, even though research is more fun), but extremely promising.
Anyways enjoy the paper and I'd be interested to hear any feedback. My current take is that the most useful application of the layered stuff is just to create a few uniform subdivisions, particularly on hardware without fp32 filtering support. Indeed a 2-layer LVSM using 16-bit per component storage fits nicely into a single texture and uses the same amount of memory as a standard VSM, but filters on a much wider range of hardware and provides a bit of light bleeding reduction "for free". The EVSM stuff is probably the most useful moving forward, although you *really* need fp32 filtering for it to shine, and 4xfp32 shadow maps are probably going to be a bit abusive for a few more years. It's pretty clear to me that the benefits will be worth it down the road though (people said VSMs were impractical not even two years ago now - but they are being used increasingly). Interestingly, layers can be used with other warps, so there might be some other fun to be had there, particularly in the offline rendering world where huge filters are common.
Anyways this will be my last paper for now. I'm finishing off my thesis in the next few weeks (a summary of my shadows work mostly), and then I'm off to work at Intel with the ex-Neoptica guys. I'm very much looking forward to the work and the cool opportunities to make a difference in real-time graphics that I expect it will afford in the coming few years
Cheers!
Andrew Lauritzen
PS: Sorry there's no demo yet... particularly embarrassing after Humus posted a cool one today. It needs some cleanup though before I post it publicly and I'm not sure when I'll have the time. The video should give you a good idea of how it works though.
PPS: The "_web" version of the paper is the same one with compressed images. Thus if you just want to browse through the paper and results, grab it. If you want to zoom in and see the uncompressed pixels of the 1920x1200 images, grab the big one Also the WMV is the high quality video. The DivX one is of lower quality for submission into the ACM Digital Library.
[Edit] This thread needs more pictures for people who would otherwise not bother to check out the paper... scroll down to find them!
Just wanted to post a quick link to my latest paper entitled "Layered Variance Shadow Maps", to be published/presented at Graphics Interface 2008 this year. The paper and accompanying video can be grabbed from the following URL:
http://www.punkuser.net/lvsm/
I apologize for the lack of a spiffy web page yet, but I've been working hard on completing my Masters thesis.
In any case, the idea is kind of neat - namely that you can apply monotonic warps to the depth distribution and plug them into Chebyshev's inequality to get different upper bounds on the visibility function, some better than others. The concept of "layered" VSMs is to exploit this fact and effective use a piecewise reconstruction of the visibility function to reduce or eliminate light bleeding. The advantage of the chosen representation is that it scales up the quality of VSMs arbitrarily at a primary cost of the more storage. Because of the chosen representation, only a single sample is needed to evaluate the visibility function at one point (i.e. when shading a pixel) unlike basis-function approaches like Convolution Shadow Maps that require all of the basis coefficients to resolve such a visibility (and thus scale up poorly). Another side advantage is that since each of the pieces represents a smaller depth range, you don't need as much precision, so the technique can be applied to older hardware that may not support fp32 filtering.
The other thing contained in the paper is some preliminary work on "Exponential Variance Shadow Maps", as inspired by Marco Salvi's work. The idea is that an exponential warping of the depth distribution is another application of the above idea. In particular it does a great job of eliminating light bleeding while still not suffering from leakage near castors (since we're still using two moments and Chebyshev's inequality, as usual). The other advantage that I mentioned in another thread is that you can also use the "dual" of the exponential warp to eliminate the "non-planar receiver" artifacts that stock Exponential Shadow Maps suffers from. The EVSM results are preliminary (as I said, I'm trying to graduate here, even though research is more fun), but extremely promising.
Anyways enjoy the paper and I'd be interested to hear any feedback. My current take is that the most useful application of the layered stuff is just to create a few uniform subdivisions, particularly on hardware without fp32 filtering support. Indeed a 2-layer LVSM using 16-bit per component storage fits nicely into a single texture and uses the same amount of memory as a standard VSM, but filters on a much wider range of hardware and provides a bit of light bleeding reduction "for free". The EVSM stuff is probably the most useful moving forward, although you *really* need fp32 filtering for it to shine, and 4xfp32 shadow maps are probably going to be a bit abusive for a few more years. It's pretty clear to me that the benefits will be worth it down the road though (people said VSMs were impractical not even two years ago now - but they are being used increasingly). Interestingly, layers can be used with other warps, so there might be some other fun to be had there, particularly in the offline rendering world where huge filters are common.
Anyways this will be my last paper for now. I'm finishing off my thesis in the next few weeks (a summary of my shadows work mostly), and then I'm off to work at Intel with the ex-Neoptica guys. I'm very much looking forward to the work and the cool opportunities to make a difference in real-time graphics that I expect it will afford in the coming few years
Cheers!
Andrew Lauritzen
PS: Sorry there's no demo yet... particularly embarrassing after Humus posted a cool one today. It needs some cleanup though before I post it publicly and I'm not sure when I'll have the time. The video should give you a good idea of how it works though.
PPS: The "_web" version of the paper is the same one with compressed images. Thus if you just want to browse through the paper and results, grab it. If you want to zoom in and see the uncompressed pixels of the 1920x1200 images, grab the big one
Also the WMV is the high quality video. The DivX one is of lower quality for submission into the ACM Digital Library.[Edit] This thread needs more pictures for people who would otherwise not bother to check out the paper... scroll down to find them!
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