Optionally use convex hull of mesh shapes

[osrf-migration]

Original report (archived issue) by Steve Peters (Bitbucket: Steven Peters, GitHub: scpeters).

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There are computational advantages to collision detection using convex meshes. It would be useful for users who carefully construct their own convex meshes to be able to declare that they are convex. Then the collision engine can make smarter choices.

@erwincoumans @hsu

See also issue about gazebo-bullet concave mesh support for commentary on the challenges of real-time decomposition of concave meshes to convex. Using a flag will be computationally faster.

[scpeters]

If we don't want to impact runtime performance, we could add the flag and put the responsibility on users to use it correctly. We could supply an offline verification program to check that meshes declared as convex actually are

[iche033]

I like the idea of using a flag to explicitly indicate that we want to decompose / or simplify the mesh.

One idea is to use a new attribute, simplify (open to suggestion), in <mesh>:

<collision name="my_collision">
  <geometry>
    <mesh simplify="convex">
      <uri>path_to_complex_mesh</uri>
    </mesh>
  </geometry>
</collision>

Ways to simplify a mesh:

• convex_hull - decomposes the mesh to one or multiple simple convex meshes. This can be done by the physics engine if available (e.g. bullet's btConvexHullShape) or use other libraries for decomposition, e.g. https://github.com/kmammou/v-hacd
• bounding_box - Most simple option - just use the object's bounding box as the collision.
• simple_shapes - decomposes to a set of simple shapes (instead of simple convex meshes)

[scpeters]

a //mesh/@optimization attribute has been added in #1382