Alessio Quaglino
4c8ffb44bf
SdfLib returns the sum of the distance from a given point to the bounding box and a saved minimum distance from the surface over the whole box boundary. This underestimates the true distance and can cause spurious contacts and jittering. This CL performs a box projection of points outside the bounding box and adds the distance of the original point from the box to the distance of the projected point to the surface. This overestimates the true distance and avoids spurious collisions. PiperOrigin-RevId: 586701933 Change-Id: I22eecb9757fa22359440156ef6433135648fa3ff
Signed distance function (SDF) plugins
These are first-party plugins that implement implicit geometries using SDFs. They can be applied to geoms and meshes (in the asset section). Sample models can be found in this folder.
Bolt
Implemented in bolt.cc. Example usage in nutbolt.xml.
This plugin implements a bolt with a hexagonal head, similar to https://www.shadertoy.com/view/XtffzX.
Parameters:
radius[m]: bolt radius (default0.26).
Bowl
Implemented in bowl.cc. Example usage in bowl.xml.
The plugin implements a cut hollow sphere from https://www.shadertoy.com/view/7tVXRt.
Parameters:
height[m]: location of the cut plane (default0.4).radius[m]: radius of the sphere (default1).thickness[m]: thickness of the bowl (default0.02).
Gear
Implemented in gear.cc. Example usage in gear.xml.
The plugin implements a 3D extrusion of the 2D gear geometry from https://www.shadertoy.com/view/3lG3WR.
Parameters:
alpha[m]: initial angle of rotation of the gear (default0).diameter[m]: gear diameter (default2.8).teeth[]: number of teeth (default25).
Nut
Implemented in nut.cc. Example usage in nutbolt.xml.
This plugin implements a hexagonal nut identical to the bolt head from https://www.shadertoy.com/view/XtffzX.
Parameters:
radius[m]: nut radius (default0.26).
Torus
Implemented in torus.cc. Example usage in torus.xml.
This plugin implements a torus.
Parameters:
radius1[m]: major radius (default0.35).radius1[m]: minor radius (default0.15).
How to make your own SDF
Create your MySDF.h and MySDF.cc files in the SDF folder, where this README is located. Implement your SDF using the
following interface:
struct MySDFAttribute {
static constexpr int nattribute =
/* insert the number of attributes */;
static constexpr char const* names[nattribute] =
/* an array of attributes with the same order as the attribute array in your SDF class */;
static constexpr mjtNum defaults[nattribute] =
/* an array of default values for your attributes */;
};
class MySDF {
public:
// creates a new MySDF instance or returns null on failure.
static std::optional<MySDF> Create(const mjModel* m, mjData* d, int instance);
MySDF(MySDF&&) = default;
~MySDF() = default;
// functions that return the SDF and its gradient at a query point
mjtNum Distance(const mjtNum point[3]) const;
void Gradient(mjtNum grad[3], const mjtNum point[3]) const;
// a call to this needs to be added to register.cc
static void RegisterPlugin();
// an array of attributes with the same order as in the struct above
mjtNum attribute[MySDFAttribute::nattribute];
private:
Torus(const mjModel* m, mjData* d, int instance);
};