FEAATURE//ANALYSSIS
sharp, such as textures, aren’t blurred and
softened. Moreover, it means there’s far less of
a performance hit, as the extra calculations that
are required are only performed on some pixels.
MSAA still samples at a higher resolution,
as with SSAA, but for any instance where only
one polygon of the 3D scene covers all the
sub-samples, the renderer only performs the
required calculations once and applies it to all
the sub-samples. However, where more than
one polygon covers the sub-samples – as with
the edges of objects – the full sub-sample
rendering process is undertaken.
As a result, performance is massively
improved over SSAA in most instances
although, in theory, a scene could have so
many edges that the whole scene effectively
still needs to be fully super-sampled. Even
outsideofextremecases,theperformancehitfromMSAAcanstillbesubstantialin
today’shighlycomplex3Dgames,where
a significantproportionofpixelsmaystill
intersecttheedgesofpolygons.Inourtesting,
wesawa dropof 42 percentfromrunning
withnoAAtousing8xMSAA.
What’smore,MSAAhasseveralimage
qualityissues.Thefirstis thatit can’tcorrect
anyaliasingthatoccursinsidea polygon,asthe
techniqueonlyaffectstheedgesofpolygons.
So,if a texturethat’susedtopaintthesurfaceof
a polygonproducesanaliased,jagged-looking
image,MSAAcan’tfixthisproblem.
Thiseffectis oftenparticularlynoticeable
whenviewingobjectsthatusetransparent
textures.Thesetexturesareappliedtosuper sampling. Moreover, because DSR is
applied after the game has finished rendering,
you can apply DSR on top of other anti-
aliasing, or indeed on top of any other post-
processing effects that aren’t captured by
conventional AA techniques.
Nonetheless, it does seem a bit odd that
Nvidia doesn’t offer conventional SSAA as
well, because DSR on its own simply doesn’t
do the single most important job you want
from an AA technique: get rid of the jaggies.
Testing at a 4x DSR factor – equivalent to
4x SSAA – there are still very clearly visible
jagged lines in our test images. We also found
that, at 2x DSR (the game ran at a resolution
of 2,715 x 1,527 and downscaled to 1,920 x
1,080), image quality was noticeably worse
than with 2x SSAA, while the performance hit
wasroughlythesame.
Weweren’tabletodirectlytestthe
performancescalingofDSRversusSSAA,as
AMDdoesn’tofferDSRandNvidiadoesn’t
offerSSAA,butourtestssuggestthatthey
haveroughlythesameimpactforanygiven
samplingrate/DSRfactor.
Multi-sampleAA(MSAA)
Thesecondmostcommonformofanti-aliasing
is knownasmulti-sampleanti-aliasing,andit
improvesonbothofthemainshortcomings
ofSSAA,althoughit alsointroducesitsown
issues.Insteadofsofteningthewholescene,it
specificallyonlyworksontheedgesofobjects
in a 3Dscene.Thisapproachensuresthat
elementsofthescenethatshouldremain
From left to right: No AA, 2x DSR, 4x DSR, 4x SSAA
From top to bottom: No AA, 2x MSAA, 4x MSAA
and 8x MSAADSR ON ITS OWN SIMPLY DOESN’T DO THE SINGLE MOST
IMPORTANT JOB YOU WANT FROM AN AA TECHNIQUE:
GET RID OF THE JAGGIES