[其它] A Space-efficient and Hardware-friendly Implementation of Ptex

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发表于 2012-1-5 08:46:51 |只看该作者 |倒序浏览

Abstract

We introduce a method to pack Ptex per-face texture data that

is both space-efficient and hardware-friendly. Recently presented

real-time implementations of Ptex have been wasteful with space

and required a storage cost many times higher than the size of the

original texture data. Our method packs multiple levels of Ptex

data together, and requires only around 8% increase in storage for

our test textures. Additionally, because of efficient data packing,

our method wastes less space than a typical texture atlas, which requires

buffer regions to be added between the separate charts within

the texture.

CR Categories: I.3.7 [Computer Graphics]: Three-dimensional

Graphics and Realism—Texture;

Keywords: real-time graphics, texturing

1 Introduction and Background

Texture mapping is an integral part of real-time graphics applications,

and in a typical application such as a video game, each art asset

will have one or more UV-sets paired with the texture data. Unfortunately,

handling the UV-sets introduces several complications.

First, the actual creation of the UV-map is an art unto itself because

most automatic generation methods do not create maps with

high enough quality. Often, an artist will have to modify the generated

UV-maps by hand, which is a labor-intensive task, to get the

desired look. Additionally, small local changes to a UV-map can

cause drastic, non-local effects on rendered images. For instance,

increasing the effective sampling density in one region of the UVmap

will necessarily affect the sampling density in the rest of the

UV-map. Finally, seams in the UV-map add additional complexity

to UV-map creation when using tessellation due to the difficulty in

preventing cracks.

A texture atlas is a common way to pack a model’s surface data into

a single texture; an example is shown in Image 1(b). As can be seen

in this image, there are a large number of unused ***ls - in this texture,

only 63% of the ***ls store actual surface data. Additionally,

colors can bleed from one piece to another in the down-sampled

mip-map levels when the pieces are too close together in the atlas,

and a texture atlas does not give the artist fine control over the

creation of the mip-map.

Ptex [Burley and Lacewell 2008], a UV-less per-face texturing

method, solves many of the issues with traditional texture mapping,

and is becoming widely used in the film industry. The need to assign

UV-maps is completely eliminated with Ptex, and resolution

can be varied independently for each face.

The basic idea of Ptex is to store a small texture, including its mipmap

chain, for each face of the model along with the adjacency information

for each face. Using the adjacency information, seamless

interpolation can be handled at***n time by searching through the

neighboring faces when necessary. Because multiple digital content

creation applications natively support Ptex, it is an attractive

technique to modify for real time use because it can be integrated

into existing art pipelines relatively easily