Graphics Reference
In-Depth Information
6
II
Wire Antialiasing
Emil Persson
6.1 Introduction
There are many sources of aliasing in rendered images. The two most common
culprits are geometric edges and shading. Historically these sources of aliasing
have been resolved by Multi-Sample Antialiasing (MSAA) and mip-mapping with
trilinear filtering respectively. With mip-mapping and trilinear filtering, which
were supported on consumer-level hardware even way back in the 1990s, textures
on surfaces were essentially free from aliasing. In the early 2000s, as consumer-
level hardware gained MSAA support, the remaining problem of edge aliasing,
often referred to as “jaggies,” was more or less a solved problem. Games of this
era could then be relatively aliasing free since the geometric detail was limited
enough that MSAA effectively eliminated all geometric aliasing, and shading was
typically simple and low frequency and did not introduce any additional aliasing
on top of the surface texture. The main exception was alpha-tested objects, such
as fences and foliage, which sorely stood out in an otherwise relatively aliasing-
free environment.
As games have adopted increasingly more sophisticated lighting models and
with geometric density constantly on the rise, aliasing has unfortunately made
a strong comeback in modern games. Mip-mapping alone no longer fully solves
the shader aliasing problem. Complex lighting introduces aliasing where the mip-
mapped textures alone exhibit none. In particular the specular component tends
to cause lots of aliasing. This field is poorly researched and only a few approaches
exist to properly deal with the problem. The most notable work here is LEAN
mapping [Olano and Baker 10]. On the geometry side we are getting increasingly
denser geometry, and as geometry gets down to the sub-pixel level, MSAA is no
longer su
cient.
Muchresearchremainstobedonetosolvetheseproblemsonceandforall.
This chapter does not present a final solution to all these problems; however, it
presents a technique for solving one specific, but common, subset of geometric
aliasing in games, namely that of phone wires and similar long and thin objects.
