xatlas
A cleaned up version of thekla_atlas.
Mesh charting, parameterization and atlas packing. Suitable for generating unique texture coordinates for baking lightmaps.
Screenshots
Example - Cesium Milk Truck
| Viewer | Random packing | Brute force packing |
|---|---|---|
 |
 |
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Example - Godot Third Person Shooter demo
Graphite/Geogram
Changes from thekla_atlas
- Smaller code size - from about 18 KLOC to 10 KLOC
- Easier to integrate and build - a single source/header file pair instead of around 120 files and 10 directories.
- Atlas resolution option for outputting multiple atlases.
- Flexible data description API for input meshes.
- Better tolerance of bad input geometry. Zero length edges and zero area faces are ignored.
- Support for packing multiple atlases/parameterizations into a single atlas.
How to use
Generate an atlas (simple API)
- Create an empty atlas with
xatlas::Create. - Add one or more meshes with
xatlas::AddMesh. - Call
xatlas::Generate. Meshes are segmented into charts, which are parameterized and packed into an atlas.
The xatlas::Atlas instance created in the first step now contains the result: each input mesh added by xatlas::AddMesh has a corresponding new mesh with a UV channel. New meshes have more vertices (the UV channel adds seams), but the same number of indices.
Cleanup with xatlas::Destroy.
Generate an atlas (tools/editor integration API)
Instead of calling xatlas::Generate, the following functions can be called in sequence:
xatlas::ComputeCharts: meshes are segmented into charts.xatlas::ParameterizeCharts: charts are flattened into 2D parameterizations.xatlas::PackCharts: charts are packed into one or more atlases.
All of these functions take a progress callback. Return false to cancel.
You can call any of these functions multiple times, followed by the proceeding functions, to re-generate the atlas. E.g. calling xatlas::PackCharts multiple times to tweak options like unit to texel scale and resolution.
See the viewer for example code.
Pack multiple atlases into a single atlas
- Create an empty atlas with
xatlas::Create. - Add one or more meshes with
xatlas::AddUvMesh. - Call
xatlas::PackCharts.
TODO
- Segmentation: improve chart merging by using similar metrics to chart growing
- Segmentation/Parameterization: detect geometry with zero Gaussian curvature (e.g. a cylinder) and unwrap as a single chart
- Viewer: better lightmap baking
- Viewer: chart picking in scene and texture views
Technical information / related publications
Ignacio Castaño's blog post on thekla_atlas
P. Sander, J. Snyder, S. Gortler, and H. Hoppe. Texture Mapping Progressive Meshes
K. Hormann, B. Lévy, and A. Sheffer. Mesh Parameterization: Theory and Practice
P. Sander, Z. Wood, S. Gortler, J. Snyder, and H. Hoppe. Multi-Chart Geometry Images
D. Julius, V. Kraevoy, and A. Sheffer. D-Charts: Quasi-Developable Mesh Segmentation
B. Lévy, S. Petitjean, N. Ray, and J. Maillot. Least Squares Conformal Maps for Automatic Texture Atlas Generation
O. Sorkine, D. Cohen-Or, R. Goldenthal, and D. Lischinski. Bounded-distortion Piecewise Mesh Parameterization
Y. O’Donnell. Precomputed Global Illumination in Frostbite
Used by
Lightmaps - An OpenGL sample demonstrating path traced lightmap baking on the CPU with Embree
Related projects
Microsoft's UVAtlas - isochart texture atlasing.
simpleuv - Automatic UV Unwrapping Library for Dust3D.
Ministry of Flat - Commercial automated UV unwrapper.
Lightmapper - Hemicube based lightmap baking. The example model texture coordinates were generated by thekla_atlas.
aobaker - Ambient occlusion baking. Uses thekla_atlas.
seamoptimizer - A C/C++ single-file library that minimizes the hard transition errors of disjoint edges in lightmaps.
Models used
Gazebo model by Teh_Bucket