the surface of an object to simulate actual
transparent substances, such as glass, as well
as more complex 3D forms that would be too
complicated to render fully, such as wire fences
or foliage. With conventional MSAA, these
textures are left untouched and can produce
some of the worst and most noticeable jaggies
and flickering as you move around a scene.
MSAA also has the most trouble working
effectively with some of the sophisticated
post-processing techniques used in modern
games, so it’s often not available as an AA
choiceingamemenus.Transparencyanti-aliasing
(TSAA, adaptive MSAA)
It should come as no great surprise that the
next big innovation in anti-aliasing was fixing
that inability to apply MSAA to transparent
textures. Both AMD and Nvidia now have
settings that allow you to independently
turn on transparency AA as an extra option
on top of conventional MSAA. AMD calls
this feature ‘adaptive AA’ while Nvidia calls it
simply ‘transparency AA’ (TSAA).
The key here is that, with normal
MSAA, the transparency information of
the textures simply isn’t relevant to the
algorithm – the edge of the textures aren’t
edges of polygons so they aren’t treated as
such. With transparency MSAA, a technique
called alpha-to-coverage is used to create
a mask or template of all the transparent
textures that need AA applying to them.
This mask or template is then injected into
the normal AA algorithm, where it will treat
the edges of the transparent objects as
normal edges.
To make the situation even more
complicated, you can choose whether to
have the transparent parts processed in an
MSAA fashion – so that only the edges of
the transparent part are anti-aliased – or
in a super-sampling fashion, where the
whole texture is just anti-aliased with super
sampling instead. As you can imagine,
the latter looks even better but is more
demanding on your graphics hardware.
In our tests, we stuck to the multi-sampledversion where, because of the relative
simplicity of the scene we were using, it
had almost no performance impact, while
noticeably improving the image quality of the
foliage in the scene. For some reason, the wire
fencing is already anti-aliased in CS:GO when
normal MSAA is applied – further proving
just how much AA is intertwined with the
development of games now – so applying
transparency AA didn’t make a difference here.
Overall, as a general rule of thumb, for
those games that support it, MSAA with
transparencyAAoffersa greatcompromisebetweenimagequalityandperformance.
With AMD’s adaptive AA turned on (8x), we
saw just a 42 per cent drop in performance
compared with no AA, while achieving a
striking improvement in image quality.
Super sampling still looks better on the
whole, but MSAA with transparency AA is a
great compromise, which is why it has been
essentially the pinnacle of conventional AA
methods for many years. For the next wave
of AA options, we have to turn to post-
processing techniques.Morphological AA (MLAA) and
Fast Approximate AA (FXAA)
Now let’s move onto the second class of anti-
aliasing techniques, the single most popular
of which is called Fast Approximate AA or
FXAA. It’s a variation of the more general
morphological class of AA techniques that,
instead of working on the 3D scene, just deal
with the final 2D pixels. It looks to provide an
approximation of conventional AA techniques,
but without the huge performance hit.
It does this by operating purely on the
pixels that have already been rendered earlier
on in the graphics pipeline, rather than the
underlying geometry. This approach vastly
reduces the number of calculations that
need to be performed. Basically, it looks for
places where there’s a high contrast between
neighbouring pixels, and then blends those
areas. It can blend in different directions and
at different rates, and keeps track of edges to
ensure the most natural-looking blends.From top to bottom: No AA, 2x Adaptive
MSAA, 4x Adaptive MSAA and 8x
Adaptive MSAA
MSAA CAN’T CORRECT ANY ALIASING THAT OCCURS
INSIDE A POLYGON, AS THE TECHNIQUE ONLY AFFECTS
THE EDGES OF POLYGONS