Physics objects can't quite touch each other?

I just started working on a new physics based project, and I noticed that the physics objects, when pressed against each other, don't quite touch, as if there's an invisible 1 pixel wide force-field separating them. It doesn't appear to be a rendering issue, as when I set the layout zoom to 4x, the gap increases proportionally, becoming about 4 screen pixels wide.

In older projects physics collisions appeared perfectly accurate up to 10x zoom, much less 1x.

I don't recall ever seeing this happen in any prior projects.

I now can't get precise collisions to work in any new projects.

Is there something that changed in the physics behavior, or is there a setting that might help?

Any thoughts or suggestions welcome.

maybe your collision polygon is slightly off...

or maybe try the old Box2d web physics engine instead of the newer asm.js (or give Chipmunk Physics a try)

Thanks for the reply AllanR,

I double checked the polygons but they were just bounding squares around objects that are squares. The individual vertices are all at integer coords, so I don't think the polygons are off. Likewise if I actually just set all the objects to bounding box collision mode (rather than polygons) I get the same gap.

Setting the collision mode to circles seems to produce the nearly perfect collisions I recall from older projects, but unfortunately, my objects are not all circles, so that's not really a long-term solution.

The "web" version of Box2d does seem to be quite a bit better with a gap about 1/4th or less than the size of the "asm.js" version.

It almost seems like the collision poly lines themselves have some kind of line-thickness.