# Build a convex hull from a given mesh in Bullet

According to this tutorial, a convex hull is the most accurate shape one can build from a mesh? I have two questions regarding this:

1. How do I build a convex hull from a given, complex mesh in Bullet?
2. Should this be done offline? How do most people do this? (that is, create a collision shape from a mesh in games)

You can do it using btConvexHullShape, calling the addPoint method. But that's usually not what you want. You should manually make a much much simpler collision mesh in your 3D modeling tool. Collision meshes don't have to be detailed. Use only a few triangles.
A good way to create an accurate representation is to use a compound shape (btCompoundShape) made of convex shapes since working with concave shapes directly is cumbersome. Here I explain how to export .bullet files from Blender which can then be imported in Bullet using btBulletWorldImporter http://xissburg.com/post/export-bullet-from-blender/