Second Life Physics Shape Changing When Uploading
20 hours agone, EnCore Mayne said:
however have no thought where information technology's stated that changing the convex hull to prim explodes the Land Affect.
i take a means to go to empathize the unknown and far besides inconsistent physics tingy. i'g using Firestorm exclusively, only needed to switch to the lab'due south viewer cause the Starlight skin (and my font tweaks) doesn't show me whatsoever model information. so far i've tweaked the model numerous times in response to the results the uploader gives me. were i not in the beta grid, i'd be broke, and so there's that....
unfortunately, once i call up i've got it all together and upload to the main grid, the numbers don't jive. if i re-create a mesh, the LI jumps. i switch betwixt prim and convex hull and sometimes the LI changes, other times not. i really don't get how a flat plane can be 10LI when a similar vertical plane is 1.
oh, and what'due south an Analysis button? and why does it price extra Lindens if i invoke information technology? and what practise all these damned colours hateful. could someone point me to where the Lab rats inform the citizenry of their magical tools?
Overall land bear on is defined by the larger of the three components download/streaming, physics and server. At upload server volition Always be 0.5* the number of links in the linkset/group, the download cost is defined by a published algorithm and will friction match that shown in the uploader.
I have a blog post from many years back that dissects the streaming cost, information technology is non for the faint hearted though, this is not in an attempt to make anyone feel stupid but an attempt to explain a specific algorithm that is used within second life, and to become some way to explaining why it was divers in those terms. http://beqsother.blogspot.com/2016/07/the-truth-near-mesh-streaming.html this discussion gets more technical once more equally it spills over into https://beqsother.blogspot.com/2016/07/blender-mesh-data-deep-dive.htm
As that blog illustrates the download cost is indirectly related to the number of triangles. but volition vary depending on how well the pinch software is able to squeeze the mesh data.
So.... putting download price to one side that leaves the states with physics.
The physics cost shown in the uploader has always (until the newest firestorm) shown the convex hull cost of the mesh. But there are a few subtleties that demand to be teased out here.
The convex hull physics shape is mandatory. it must be present for the mesh asset to be uploadable. Information technology is created by the viewer on your behalf and uses the bachelor LOD models to exercise this. A convex hull is single surface that wraps your object, I tend to liken it to what we brits call "Cling Film".
Much like the wrap above it follows the outline of the object bridging whatever concave areas. An farthermost example would be a mixing bowl with wrap stretched over it, the top would be flat.
For the convex hull in Second Life the viewer has to be able to produce this shape using no more than 256 vertices. If it cannot manage this then y'all will go one of those magical MAV_BLOCKING_MISSING errors that we all beloved. The missing block being the mandatory physics data.
We can also provide a user-defined physics shape, and this can exist presented in one of 2 forms, a low poly mesh, or a set of up to 256 convex hulls. Both start from a user model.
If you select a user mesh shape, past specifying one of the LOD models or uploading your own custom mesh, then by default the Mesh physics is computed. Mesh Physics cost is defined by an algorithm that is not published then we cannot reverse engineer the results (not without a lot of work at least), however, it is based on the number and the area of the triangles that comprise the specified model. In general, the smaller the surface area the larger the cost with long thin triangles being more than heavily penalised than small equilaterals. The price of the physics being inversely related to the area of the triangles is what leads to the extreme physics issues (and the "sparse wall" cap) associated with small mesh items. These are discussed in https://beqsother.blogspot.com/2016/07/when-is-door-not-door-and-other-things.html. The final side-consequence of using a mesh model for physics is the "degenerate triangle". Another one of our lovely MAV errors, degenerate triangles are triangles that are and then sparse that the uploader only rejected them and refuses to accept the model for upload until you ready them. and so new Firestorm uploader highlights these improve than previous viewers but in about cases when you run across this error information technology should set an alarm bell in your caput telling yous that your physics mesh is likewise circuitous and it is fourth dimension to rethink.
To avert the scalability concerns and remove the degenerate triangle problem you tin utilize the Analyse Mesh function. The analyse function takes the user mesh model specified for physics and tries i of a number of selectable algorithms to decompose the shape into a series of convex hulls. As earlier the maximum number of vertices in a hull is 256 and the maximum number of hulls (per mesh particular in the link set) is as well 256. The accuse for an analysed physics shape is derived from the number of hulls and (I call up) the number of vertices of those hulls. This tin can lead it a very expensive physics shape, but the resultant shape has a stock-still toll no affair what scale and does not get affected past the "thin wall" limit thus making it ideal for build components that may be resized. analysing an arbitrary shape and working out how best to present that in physics is a complex task and your results will be far improve if you leave big heavy hints for the code, one common way of doing this is to represent a physics mesh equally a series of detached cubes with a small gap effectually them. The hull analysis is and so able to wrap each of those in a prissy convex hull and give a stable, predictable shape.
The real upshot with physics costs has e'er been that it is largely guesswork. You don't know for certain (unless you've got plenty feel to think information technology out for yourself) what the cost of setting physics to prim will exist when you get the detail in world. The new Firestorm mesh uploader (coming to the SL viewer real soon) provides y'all with information that yous were never given before. In a new panel on the upload screen it volition bear witness yous the toll of the convex hull alongside the cost of either the mesh or the analysed physics.
The following very contrived example shows a fox sculpt that is about 7000 triangles (I'm just learning to sculpt don't shoot me for my creative skills) it is large scale (6m high and 5m long)
Fullscreen version: https://i.gyazo.com/ef67b31b06f132b0e4148a3b31835caa.mp4
- I go with the defaults and see a convex hull cost of 7.2 LI
- I use the generated LOW LOD for the physics without analysing and the cost is 45.7 LI based on the 436 triangles that contain that LOD at that scale) Annotation that if I were to alter the scale to exist smaller (which is likely once in earth - nobody wants a 6m play a joke on) the physics cost would escalate.
- I use the analyse function with high-quality setting selected to requite a better lucifer to the shape. This gives us 73 hulls at a toll of 43.2 LI
- We finally select a user-defined mesh.
- At just 48 triangles, this gives a physics cost of 5.2, and note also that the convex (base of operations) hull has reduced to 3.1 because information technology is existence calculated from the user-defined mesh model at present.
- Finally, we analyse this and go 7 hulls at a cost of 2.four LI
It is worth noting too that the algorithms that perform the decomposition appear to have an element of randomisation to them. Equally a result, yous can get small differences in costs each time you repeat the process. As this code is unavailable to us outside the lab, there is not much more than to be said on that. It may be that the randomisation is non in the decomposition but in the fact we are using the GLOD generated LOD models which are known to employ a random seed and thus give varying results.
I hope that this helps explain things somewhat. The high-level concept is simple enough to sympathize just it is not a simple process to understand if you lot are focussing on the details. At that place are many nuances and various "tricks" that people try, but this summary I call up has covered almost aspects.
Beq
Edited by Beq Janus
added gif preview of video
Source: https://community.secondlife.com/forums/topic/432047-mesh-upload/
0 Response to "Second Life Physics Shape Changing When Uploading"
Post a Comment