Game Development Reference
In-Depth Information
2
II
Real-Time Ptex and
Vector Displacement
Karl Hillesland
2.1
Introduction
A fundamental texture authoring problem is that it's dicult to unwrap a mesh
with arbitrary topology onto a continuous 2D rectangular texture domain. Meshes
are broken into pieces that are unwrapped into “charts” and packed into a rect-
angular texture domain as an “atlas” as shown in Figure 2.4(b) . Artists spend
time setting up UVs to minimize distortion and wasted space in the texture when
they should ideally be focusing on the actual painting and modeling.
Another problem is that edges of each chart in the atlas introduce seam arti-
facts. This seam problem becomes much worse when the texture is a displacement
map used for hardware tessellation, as any discrepancy manifests as a crack in
the surface.
This chapter describes an implicit texture parametrization system to solve
these problems that we call packed Ptex . It builds on the Ptex method developed
by Disney Animation Studios for production rendering [Burley and Lacewell 08].
Ptex associates a small independent texture map with each face of the mesh.
Each texture map has its own mip chain. In the original Ptex method, adjacency
information is used for filtering across the edge of one face texture and into the
next.
There are two main advantages of Ptex relative to conventional texture atlas-
ing. First, there is no need for explicit UV. Second, there are no seaming issues
arising from unwrapping a complete mesh of arbitrary topology onto a single-
texture domain. These are the two main advantages of the original Ptex method
that we preserve in our adaptation.
The drawbacks of packed Ptex relative to conventional texture atlasing are
additional runtime computation, additional texture filtering expense, and changes
in asset production. The main change in asset production is that our method cur-
 
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