[Opensim-dev] Negative z values

[Melanie]

I have never seen a Z < 0 build. I see lots of problems that may be
possible with this, but I think that quite beautiful and interesting
builds could make use of this and would support keeping it. The
change in the viewer is recent and likely trivial to undo.

- Melanie

On 25/04/2014 00:32, Justin Clark-Casey wrote:
> Hi folks.  Historically, whether by accident or design, OpenSimulator has allowed negative Z values for terrain, objects 
> and avatars (e.g. <130, 50, -45>.  I have seen people use this facility to build fully underwater or partially 
> underwater structures (e.g. oil rigs, sunken ships, etc.) which are conceptually far below the water line without having 
> to set that water line at a level that may be way above that of surrounding regions.
> 
> However, at least on Singularity 1.8.5 on Linux, fog effects do not work properly when z < 0, where all view distances 
> have very high fog no matter what the fog settings.  This may be a recent change - I remember fog working properly at 
> negative z values in the past, though the fog issue still occurred past a certain -ve z.  There may be other issues of 
> which I'm not aware.  Arguably, these are not bugs since the Linden Grid does not allow z < 0 (though one could make the 
> same argument for var regions, etc.).
> 
> With in-world testing of current development code, BulletSim appears to have a hard-coded check where I can't move my 
> avatar below z == 2 whether terrain is z < 0 or not (this should probably at least be fixed so z = 0 is possible).  ODE 
> has allowed and still allows the avatar to descend to negative depths.
> 
> One argument is that in the light of such bugs, it would be better to consistently enforce z >= 0 and require people 
> with -z builds to either move them and the water level up using OpenSimulator commands (e.g. "translate scene") or never 
> update their OpenSimulator installation.
> 
> However, I think there is a real value in keeping the -ve z ability.  It allows people to extend deep water builds 
> without having to adjust any neighbouring sims for consistency (which they may not have control over).  I'm sure it's 
> possible to address the viewer-side issues.  OpenSimulator could have an allow-negative-z flag which is false by default 
> to make it explicit that using -ve z may have issues at this time.  I accept this is a more complicated solution than 
> enforcing z == 0, though enforcing z == 0 will also requires many changes to the current code where bounds are not checked.
> 
> If my experience is unusual and -z builds are very rare then there's more of a case for enforcing z >= 0.
> 
> Thoughts?
>