What's the point of SGSSAA ?

[ShePearl]

The short comings of MSAA, to my understanding is that MSAA is not full scene AA. MSAA only applies to polygon edges.

Nvidia's SGSSAA (and OGSSAA) applies to full scene.

How about MSAA with TrSSAA ? Is this combination not considered full scene ?

Performance of 4xMSAA + 4xTrSSAA should be better than 4xSGSSAA. No ?

 

[JayJapanB]

I don't have much experience with SGSSAA
TrSSAA is good in screenshots but I find it creates blur when moving.
At least nvidia's application of it does.

Good topic, op.

 

[demowhc]

trSSAA doesn't create blur, it only applies AA to transparencies with MSAA on the rest.

OP, the point of SGSSAA is it provides superior quality. Try something like Skyrim or Mass Effect with 4xSGSSAA, and then again with 4xMSAA + trSSAA. SGSSAA does a better job and also removes a lot of shimmer that MSAA doesn't, meaning the image is much cleaner, especially in motion.

 

[JayJapanB]

trSSAA doesn't create blur, it only applies AA to transparencies with MSAA on the rest.

OP, the point of SGSSAA is it provides superior quality. Try something like Skyrim or Mass Effect with 4xSGSSAA, and then again with 4xMSAA + trSSAA. SGSSAA does a better job and also removes a lot of shimmer that MSAA doesn't, meaning the image is much cleaner, especially in motion.

I know what it does however I find that, in crysis in particular, it would provide good antialiasing yet cause blurring on transparencies when moving.

I'm not referring to the same sort of blur associated with PPAA

 

[boxleitnerb]

The newer drivers (310 series and above) have automatic LOD adjustment which is needed to improve image sharpness and detail. Sometimes SGSSAA can conflict with PP effects, thus it may blur. In those cases custom AA bits can be employed that reduce or eliminate blur:

It's German, but the list speaks for itself I think
http://www.forum-3dcenter.org/vbulletin/showthread.php?t=490867

 

[evilsofa]

SGSSAA is simply the full scene version of TrSSAA.

TrSSAA chooses which pixels to apply itself to with an alpha test. Nvidia put out a driver version with a bug in the TrSSAA code that disregarded the results of the alpha test and applied itself to all pixels. That buggy version of TrSSAA is SGSSAA.

You would expect TrSSAA to be faster than SGSSAA since one is full scene and the other is not, but how much of the performance hit comes after the alpha test? Has someone done a benchmark on this?

For more in-depth info, see NaturalViolence's page on Nvidia AA modes, particularly the SGSSAA page.

When talking about blurring in SSAA and SGSSAA, it's important to know that it only happens when a game's post-processing shader is not compatible with SGSSAA or has odd framebuffer formats. Also, some games look better with SSAA than SGSSAA, and some games look better with SGSSAA than SSAA. For example, I have read that Skyrim is now very compatible with SGSSAA and has no blurring with LOD set to 0, and no texture shimmering even on bump-mapped textures. While elsewhere, I have read that (at least at one point) Mass Effect 3 was better with SSAA than with SGSSAA, but I don't know if that has changed since then. I also did some testing awhile ago (which I really should redo now) where I found that in Mass Effect 2, 16xCSAA + 4xSGSSAA was the only mode that got rid of all jaggies and seemed to look much better than 4xMSAA + 4xSGSSAA, even though I know you are supposed to match 4x to 4x and not use CSAA.

 

[LuminaryJanitor]

What's the point of SGSSAA ?

It fixes shader aliasing.

 

[ShePearl]

It fixes shader aliasing.

MSAA + TrSSAA can't fix shader aliasing ?

Sometimes SGSSAA can conflict with PP effects, thus it may blur. In those cases custom AA bits can be employed that reduce or eliminate blur

What do you mean by PP effects ?

 

[evilsofa]

PP = post-processing. When a game uses post-processing shaders that conflict with SGSSAA or SSAA, the result is blurring. SGSSAA and SSAA work differently enough that some games will conflict with only one of the two methods.

 

[LuminaryJanitor]

MSAA + TrSSAA can't fix shader aliasing ?

Nope. MSAA only affects the edges of polygons. TrSSAA only targets sprites or polygons with transparent textures. Textures themselves are antialiased through a combination of mipmapping and AF. But dynamically generated pixel shader effects within a polygon, like specular highlights or parallax maps, don't benefit from any of this.

Even shaders applied around polygon edges miss out on the MSAA in some cases; I believe the problem is that the rendering pass which does the shader calculations may (depending on the renderer) be independent of the one which does the multisampling, so the shader pass only calculates one colour value for the pixel (therefore, no AA). Actually, I'm not sure if SGSSAA even helps with this - if it's applied during the same pass as MSAA, I imagine you'd run into the same issue.