[sldev] Optimus Prim vs. Megatrim: "The Big Prim Problem"

[Harold Brown]

One of the biggest uses for the Mega Prims is for buildings... not
vehicles.   Would a flag to specify "this item is havok4 static" be
possible?  Or even "This prim is larger then 54x54x54 and must be havok4
static"  and then don't allow scripted movement?

On 10/17/07, Kelly Linden <kelly at lindenlab.com> wrote:
>
> Callum Lerwick wrote:
>
> On Wed, 2007-10-17 at 10:18 -0700, Kelly Linden wrote:
>
>
>  You need to perform collision detection on megaprims. The fact that the
> megaprim itself is not physical however should prevent the need to merge
> "simulation islands" in the physics engine, which was previously cited
> as a major performance concern.
>
>
>
> This last bit is not true.  Large prims, even if they are "static",
> still effect the simulation islands.
>
>
> You're being unclear. Yes they "affect" them, that's the whole point. My
> point is, say you have a long, nonphysical horizontal 2x4, with an SI on
> each end:
>
>    SI                                     SI
> --------------------------------------------------
>
> While both SI's are interacting with the same stick, since the stick
> itself is non-physical, there should be no need to merge the two SIs.
>
> If your physics engine is doing so, then your physics engine's early
> culling sucks^H^H^H^H^H is less than optimal. :P
>
> Note that the long 2x4 doesn't even have to be "megaprim" size.
>
> Considering the AWG, the last thing we need to be doing is letting low
> level implementation detail dictate arbitrary limitations upon the upper
> layers. If you do so, you end up with crap like IMAP.
>
>
> I did not mean to be unclear, sorry.
>
> In havok4 no simulation island is smaller than the pieces in it that are
> colliding.  In havok4 no simulation island contains any partial pieces (ie
> only one end of the stick).  In havok4 the stick itself must be entirely
> contained in a simulation island.  In havok4 the creation of simulation
> islands is dynamic and handled entirely by havok4 - SL does not dictate what
> the simulation islands are and they can change based on content.
>
> Truly havok-static objects are not part of the simulation islands, but SL
> static objects are not havok-static, they are key framed.  Havok-static
> objects are assumed to never (or extremely rarely) change or move and as
> such it is costly to manipulate them (change their shape, position etc) or
> change them to or from 'static'.  If you consider most havok uses (standard
> games) this makes a lot of sense for the majority of the content (deformable
> terrain and structures are relatively new).  It is harder in SL where
> *every* havok body can potentially change or move.  It might be possible to
> make some prims truly static, such as mega prims, but given the costs
> associated with moving or changing them there might need to be restrictions
> particularly for what LSL scripts can do to them.  This path has not yet
> been thoroughly investigated.
>
>  - Kelly
>
>
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