beginner question: convex hull shapes gaps

[karloscampus]

hi everyone,

at first, sorry for my bad english.. ;/

i am going to create some 2d-convex hulls (currently just 2d boxes), which are going to fall on a btplanerplaneShape (at pos y: -10, everything in 2d space).
everything works great, except somehow there is a gap, when the boxes has fallen on the ground, then i look at the exact coordinates. in detail, then a box has the hull ((-2,-2),(-2,2),(2,2),(2,-2)) somehow the middle of the box is not at -8 but instead at about -8.02. so a little bit taller then expected. the gap accumulates continuously, then i stack more then one box on each other.

so what is the problem?

thanks a lot,

karloscampus

[Erwin Coumans]

If you are using the btConvex2dShape, it might be because of the collision margin. In general it is best not to change the margin or set it to zero, it might create stability issues.

There is a way to shrink the convex hull, so it matches the graphics geometry. I don't have a link handy right now.
Thanks,
Erwin