# Convex hull is slowing the game down

For some reason the convex hull bound property is slowing the game down and making in kinda glitchy. I’ve tried box bounds it runs smooth but I would like a more defined bound. Is there anything that can be done in blender or do you think its just because of a slow computer witch is what I’m thinking.

Answer is simple: Convex Hull is more sofisticated than just bound box. Use convex hull only if you must.

Try researching composite bound shapes. They can provide good bounds with good performance.

Convex hull effectively uses most of the mesh polygons to define the bounding shape. Imagine like wrapping your model in wrapping paper or cling film so there are no indentations… that is the convex hull. It doesn’t do indentations, but if your mesh was a ball with 10,000 polygons then it would try to calculate collisions for all polys. Calculating the collisions for each face is very slow.

A simple bound shape such as cube, cylinder, sphere, etc. is usually used. Multiple collision objects that have these basic shapes can be combined to approximate the shape of your model as composite bounds.

Edit: Another approach is to model a simple collision mesh that approximates the shape of your model and then parent the model to this. Your model should be set to “no collision” and “static”. This much simpler convex hull will run much faster. It’s still advised to use basic bounds though since they are mathematically simpler for the physics engine to consider so will still run much faster.

eg. A car could be modeled as a simple mesh with about 16 quads and set to convex hull or could be modeled as two boxes, a longer one for the body and a smaller one for the roof, both set to box bounds. I’ve not checked, but i guess the two boxes might be faster.