See the paper, Ptex: Per-Face Texture Mapping for Production Rendering, Brent Burley and Dylan Lacewell, Eurographics Symposium on Rendering 2008.

View the slides from the Eurographics presentation as Powerpoint or pdf.

Watch a YouTube video, demonstrating the Ptex painting workflow.
Note: the application shown in the video is not part of the Ptex open source package.

Ptex uses a custom file format that is designed specifically for efficient rendering. A Ptex file can store an arbitrary number of textures along with mipmaps and adjacency data used for filtering across face boundaries.

• Ptex File Format Specification
• Adjacency data
• Triangle textures
• Standard meta data keys

The Ptex API is written in C++ and can peform file I/O, caching, and filtering needed for rendering.
See the Ptex API docs for details.

PTEX SOFTWARE
Copyright 2018 Disney Enterprises, Inc. All rights reserved

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

• Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
• Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
• The names "Disney", "Walt Disney Pictures", "Walt Disney Animation Studios" or the names of its contributors may NOT be used to endorse or promote products derived from this software without specific prior written permission from Walt Disney Pictures.

Disclaimer: THIS SOFTWARE IS PROVIDED BY WALT DISNEY PICTURES AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, NONINFRINGEMENT AND TITLE ARE DISCLAIMED. IN NO EVENT SHALL WALT DISNEY PICTURES, THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND BASED ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.