Alessio Quaglino
0995af83f9
Fixes #2182. PiperOrigin-RevId: 690980373 Change-Id: Ifc94f928e9cfbdbef3cb6f11ad4bffed542bf49a
118 lines
3.7 KiB
Markdown
118 lines
3.7 KiB
Markdown
<h1>
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<a href="#"><img alt="MuJoCo" src="../../banner.png" width="100%"/></a>
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</h1>
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## Signed distance function (SDF) plugins
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These are first-party plugins that implement implicit geometries using SDFs. They can be applied to **geoms** and
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**meshes** (in the **asset** section). Sample models can be found in [this folder](../../model/plugin/sdf/).
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### Bolt
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Implemented in [bolt.cc](bolt.cc). Example usage in [nutbolt.xml](../../model/plugin/sdf/nutbolt.xml).
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This plugin implements a bolt with a hexagonal head, similar to https://www.shadertoy.com/view/XtffzX.
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Parameters:
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- `radius` [m]: bolt radius (default `0.26`).
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### Bowl
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Implemented in [bowl.cc](bowl.cc). Example usage in [bowl.xml](../../model/plugin/sdf/bowl.xml).
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The plugin implements a cut hollow sphere from https://www.shadertoy.com/view/7tVXRt.
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Parameters:
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- `height` [m]: location of the cut plane (default `0.4`).
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- `radius` [m]: radius of the sphere (default `1`).
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- `thickness` [m]: thickness of the bowl (default `0.02`).
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### Gear
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Implemented in [gear.cc](gear.cc). Example usage in [gear.xml](../../model/plugin/sdf/gear.xml).
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The plugin implements a 3D extrusion of the 2D gear geometry from https://www.shadertoy.com/view/3lG3WR.
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Parameters:
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- `alpha` [m]: initial angle of rotation of the gear (default `0`).
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- `diameter` [m]: gear diameter (default `2.8`).
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- `teeth` []: number of teeth (default `25`).
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### Nut
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Implemented in [nut.cc](nut.cc). Example usage in [nutbolt.xml](../../model/plugin/sdf/nutbolt.xml).
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This plugin implements a hexagonal nut identical to the bolt head from https://www.shadertoy.com/view/XtffzX.
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Parameters:
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- `radius` [m]: nut radius (default `0.26`).
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### Torus
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Implemented in [torus.cc](torus.cc). Example usage in [torus.xml](../../model/plugin/sdf/torus.xml).
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This plugin implements a torus.
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Parameters:
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- `radius1` [m]: major radius (default `0.35`).
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- `radius1` [m]: minor radius (default `0.15`).
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### SdfLib
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Implemented in [sdflib.cc](sdflib.cc). Example usage in [cow.xml](../../model/plugin/sdf/cow.xml).
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This plugin uses the library [SdfLib](https://github.com/UPC-ViRVIG/SdfLib) to compute a voxel-based approximation of a
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user-specified mesh. The mesh can be arbitrary and not necessarily convex. This offers an alternative to
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convex-decomposed meshes. The performance is likely to be slower than that of analytic SDFs, since a cubic
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approximation has to be evaluated on the convex grid. However, the SDF generation is done automatically, simplifying the
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task of creating an SDF, which can be difficult for complex shapes.
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### How to make your own SDF
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Create your `MySDF.h` and `MySDF.cc` files in the SDF folder, where this README is located. Implement your SDF using the
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following interface:
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```
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struct MySDFAttribute {
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static constexpr int nattribute =
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/* insert the number of attributes */;
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static constexpr char const* names[nattribute] =
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/* an array of attributes with the same order as the attribute array in your SDF class */;
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static constexpr mjtNum defaults[nattribute] =
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/* an array of default values for your attributes */;
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};
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class MySDF {
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public:
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// creates a new MySDF instance or returns null on failure.
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static std::optional<MySDF> Create(const mjModel* m, mjData* d, int instance);
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MySDF(MySDF&&) = default;
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~MySDF() = default;
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// functions that return the SDF and its gradient at a query point
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mjtNum Distance(const mjtNum point[3]) const;
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void Gradient(mjtNum grad[3], const mjtNum point[3]) const;
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// a call to this needs to be added to register.cc
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static void RegisterPlugin();
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// an array of attributes with the same order as in the struct above
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mjtNum attribute[MySDFAttribute::nattribute];
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private:
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MySDF(const mjModel* m, mjData* d, int instance);
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};
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```
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