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#3271772 - 04/16/11 05:23 PM (SSAO) Screen Space Ambient Occlusion?  
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Scoobe Offline
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What does this do? It say screen space abient occlusion, but I can not really tell whats its doing?

Rob


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#3271789 - 04/16/11 06:01 PM Re: (SSAO) Screen Space Ambient Occlusion? [Re: Scoobe]  
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It's a full buffer effect that uses z-order to produce complex occlusion with sparse data points.

Hmm, that made no sense. It's a relatively subtle shading technique used to give a greater sense of depth by coloring/shadowing based on the depth of the image and ambient light sources. It was 'pioneered' in Crysis, made a bit better in BFBC2 but worked probably best in Just Cause 2 (Man, I have to buy less games).

For a flight sim it's too subtle (or rather the darkening/atmospheric use it could have is too light) and because it's a post-processing full buffer effect (i.e. it's something relatively easy to add coding wise) it also has a frames per second impact that doesn't really justify its use just yet.

SSAO is streamlined in DX11, which COD doesn't have a released render path for just yet. For DX10.1, it's definitely on the wrong side of the 'cost/benefit' ratio.

#3271791 - 04/16/11 06:10 PM Re: (SSAO) Screen Space Ambient Occlusion? [Re: Scoobe]  
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Scoobe Offline
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OK cool, Thanks for the detail explanation. Never heard of it before.

Rob


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#3271832 - 04/16/11 07:22 PM Re: (SSAO) Screen Space Ambient Occlusion? [Re: Scoobe]  
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Maybe not the best examples, but...

The shading is a bit nicer with it on, but on my rig (i7 920 @ 3.8 GHz, GTX285, Wi 7) the difference is hard to notice when actually playing and it costs an awful lot of FPS. I have turned it off smile.

86 FPS with SSAO off:


54 FPS with it on






Beyond gliding distance
#3271837 - 04/16/11 07:39 PM Re: (SSAO) Screen Space Ambient Occlusion? [Re: RocketDog]  
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Here is a mathematical difference between the before and after SSAO comparison shots.

Note that the 'yellow' in the bottom right is the frames counter difference.



Science shows there is actually no difference whatsoever, apart from about 30 frames per second.

Now, normally SSAO is subtle, but it's not that subtle. My guess is that the test is broke or that (more likely) the SSAO rendering in COD is not working at all (apart from impacting performance on cards that don't have the feature.

Maybe it's a horizon effect, i.e. try a different angle shot with a longer focal length.

smile

#3271845 - 04/16/11 07:50 PM Re: (SSAO) Screen Space Ambient Occlusion? [Re: Scoobe]  
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_michal Offline
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ON | OFF




Screenshots made by RashbaNor from Polish il2forum.xt.pl forums.

#3271851 - 04/16/11 08:01 PM Re: (SSAO) Screen Space Ambient Occlusion? [Re: _michal]  
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@empeck, Again, I've run those images through an analytics comparison tool and (I've only done the moth) and they are exactly the same.

The SSAO goggles do nothing. smile

PS I could post a solid rectangle of black showing not one pixel difference between the before/after's but thought not much point.

Hmm, I wonder how many placebo comparisons are happening - people are odd that way...

#3271853 - 04/16/11 08:05 PM Re: (SSAO) Screen Space Ambient Occlusion? [Re: Scoobe]  
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Actually there is a difference, but it's very small in that the difference was so low the 'dark black' on 'darker black' makes it hard to see.

If you look real (real) close you can see the yellow underbelly of the moth (just above where the lower wing joins) has a darker shadow. It helps to use a 'swipe' style tool, as that helped me spot it.

Man, that's subtle..

(Edit: attached a 'swipe' where the red box highlights the difference on the left/right of vertical line is image 1 / 2)



Last edited by FearlessFrog; 04/16/11 08:09 PM.
#3271856 - 04/16/11 08:09 PM Re: (SSAO) Screen Space Ambient Occlusion? [Re: Scoobe]  
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There are differences. SSAO adds more contrast to areas in corners. It's clearly visible on the cockpit floor.

#3271859 - 04/16/11 08:14 PM Re: (SSAO) Screen Space Ambient Occlusion? [Re: _michal]  
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Originally Posted By: empeck
There are differences. SSAO adds more contrast to areas in corners. It's clearly visible on the cockpit floor.


Yep, got it - my image difference tool doesn't help so much as SSAO adds dark shadows and it's better at detecting non-black addition/subtractions smile

#3271903 - 04/16/11 09:28 PM Re: (SSAO) Screen Space Ambient Occlusion? [Re: Scoobe]  
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Yep - if I switch backwards and forwards between the two Defiant screenshots (at full size) I can see small differences. On the two I posted, it's harder to spot because of the reduced size, but if you look at the insides of the cockpit and turret you can see it's darker with SSAO on and also the wing root is a touch darker. I actually rather like the effect, but as implemented in ColD it is so very subtle as to be scarecely noticeable and is definitely not worth > 30% of my FPS.


Beyond gliding distance
#3272268 - 04/17/11 12:19 PM Re: (SSAO) Screen Space Ambient Occlusion? [Re: Scoobe]  
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Its a complete waste of processing power.


"It's life, Jim, but not as we know it!"

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#3273095 - 04/18/11 02:56 PM Re: (SSAO) Screen Space Ambient Occlusion? [Re: Scoobe]  
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Wow, that's a lot of extra power for a whole lotta nothing in the looks department.

SSAO really appears to have no place in a pure flight sim like this.



The Jedi Master


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#3273112 - 04/18/11 03:15 PM Re: (SSAO) Screen Space Ambient Occlusion? [Re: Scoobe]  
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As a photographer, maybe I can explain SSAO in a different way, and explain what it SHOULD be doing (not that people here haven't done a good job).

Basically, SSAO as I understand it takes into account the natural real world effect that there is usually "ambient" light playing a part in what we see. As in, the interior of your car is not only lit by direct sun light coming trough the window (and everything not in the sun would be pitch black) but actually your car's "not in the sun" part are lit by reflections of sunlight coming from other surfaces and from "stray light" for example caused by a cloud or by other refraction, rough surfaces and so on. When you start working with precisely defined light sources (as I do for a picture) you really are initially surprised how much light hits an object "roundabout" even though you have no direct ray going from the bulb to the surface.

So even with an theoretically idealistic single light source (a pin-point small sun) surfaces not touched by direct light are never fully dark in our real world, if the primary light is powerful.

What SSAO does is to calculate the amount of geometry around a given 3d plane. You can see that good on Empeck's top two footwell shots from the cockpit interior. The metal deep inside the footwell has less chance of being caught by "stray rays" so it is notable darker when using SSAO. Actually SSAO likely works the other way round, brightening everything up that has a chance of being lit by "stray rays".

The problem here seems to be that the outside of an aircraft, smooth shapes and all, is particularly bad at causing ambient light occlusion. So the effect - even in reality - is just not very much present there. It still costs the same amount to compute though.


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