So I decided it was time to engage in some building and set myself out a new Mesh path, a Mesh path is something that is very straight forward to build in a program such as Blender, it’s also very straight forward to UV Map, so if you’re thinking Mesh is just too complicated, I advise you to start with something straight forward like this. I’m not going to go through the process here, but I am going to go through why making a Mesh object have a physics shape of prim, rather than Convex Hull, can help things work nicely.
Now by default, Mesh will take on the physics shape of Convex Hull. There are many good reason for this, which I’m not going to discuss. However as we can see, my Mesh path is currently Convex Hull:
However there’s a problem, when I walk along my new funky Mesh path, I sink into the ground at the edges. At one end of my path are some steps, I actually end up falling down behind them, on the main path, you just sink slightly at the edges. Am I doing something wrong? Maybe, but after delving into the murky world of the official forums, being pointed at the Jira and getting some assistance from the ever helpful Drongle McMahon, I decided to change the physics shape to Prim and suddenly, it all works as expected!
I posted my query to the Mesh creation forum, where Drongle promptly pointed me in the direction of the Jira, this is why being able to read Jira issues is bloody handy. Jira VWR-28416 explains an issue whereby Convex Hull doesn’t seem to fill the full boundaries, but switching to prim does. Indeed you can get a concept of this by going to the develop menu/render metadata/ Physics Shapes:
Now everything will look a bit funky, like you’ve had too many pints and decided it was a good idea to start on the Aftershock, but you can see the issue:
Note the green line across my path, that’s where I’m sinking into the ground. So I engage in a bit of jiggery pokery and change the physics shape of my path to prim.
Now I check my Render Metadata/Physics Shapes again, watch and be amazed:
Note there’s no green line across my path anymore, indeed if I now walk along the path, I no longer sink into the ground at the edges, basically everything is now working as expected. The green you can see is the grass from the sim terrain, which we can ignore.
Hold on though, are there any implications in case of land impact and costs for this? Well using such a basic shape, the answer seems to be no.
Above are my weights and details whilst I have a physics shape of prim, let’s change that to Convex Hull and compare:
They are identical, of course this may have been due to some borkiness, or rebaking region oddness, but I think it’s just the way it is. Indeed if I link two of my path objects together, I end up with a Mesh cost saving of two equalling one, they only count for a score of one in Land Impact:
As you can see, two prims, but the land impact score is only one. Indeed I can go further and join another two paths, to give me four prims with a land impact score of two:
So a simple Mesh shape, gives me the land impact savings I want, but to make it work physically, I’m having to change my item to physics shape prim. My basic testing here suggests, that’s not going to cause any harm. Now it could be that I’m doing something extremely silly, but there does appear to be a bug with how Convex Hull shapes work in terms of physics, indeed I reported my own issue regarding the build/copy tools not playing nicely when you have a physics shape of Convex Hull. Jira SH-2948 exemplifies that issue.
However the good news seems to be, with basic shapes anyway, a physics shape of prim won’t hurt you. Hurrah!