Pamela Galli Posted March 12, 2015 Share Posted March 12, 2015 So I discovered that this mesh arched-opening wall in my house was set to convex hull, which means no one could walk through the arched opening. This is a 1 LI wall, when set to convex hull, which I have used in several other houses -- the only difference being that this one I added a material to and reuploaded. Also in the other houses the arch was Convex Hull, not prim.So I change the wall to Prim and bam, it goes to Lost & Found. It will not re rez because "the region is full". I rez an older copy . Set the wall to Prim again and notice the house went from 261 LI to over 8000 just before vanishing!So now I have the wall set to none. I tried setting the unlinked wall to prim, went to 8000. But WHY on earth would this wall add 8000 LI??? ETA I would really like some Linden to explain this, but no clue how to go about it -- make a JIRA? I have made plenty of JIRAs but not sure this is the right course for this. ETA: I corrected some things I disovered when Drongle came out to look at it. ETA: Drongle suggested I make one small change in the mesh, upload it not as triangles, and analyze on upload, which I am in the process of doing now. Link to comment Share on other sites More sharing options...
Drongle McMahon Posted March 12, 2015 Share Posted March 12, 2015 The wall was an example of a phenomenon that can happen with triangle-based physics shapes made from one or two completely flat shapes. For some unknown reason, the physics weight can become enormous, and it often depends on the order of triangles in the dae file. It also gets a bit smaller as the two planes are stretched further apart. Adding another face at right angles, connecting the tw sides of the wall in this case, can bring the weight down to the expected range. However, in this case there is a round arch with 16 segments. Consequently there are manu small triangles, and the physics weight stays quite high, whether triangle based or hull based (Analyzed). Trying to simplify the Analyzed shape doesn't seem to work without closing the archway. So I think this is one of those cases where you have to make a special physics mesh with simpler geometry. Here are the meshes I tried out with an arch with similar geometry. Top row is LOD meshes (third one used in lowest 2 slots). Bottom is two meshes for triangle-based shapes, without and then with the extra connecting face, then a mesh for a hull-based shape. With these three physics shapes, the physics weights/LI were 14.6/15, 0.5/1, 1.8/2. So this arch had the high physics weight problem, but much less than Pamella's, and it was solved by the extra face. With that solution, it was better than the hull-based shape, but that all depends on the size (here 8x8x0.52) and will not always be the case. Link to comment Share on other sites More sharing options...
Pamela Galli Posted March 13, 2015 Author Share Posted March 13, 2015 Thank you Drongle -- I really appreciate your help with this! All I really need is a couple of blocks on the side panels, dont even need the top arched part. I will try that now. ETA: Down to 7. Not good. Link to comment Share on other sites More sharing options...
Jenni Darkwatch Posted March 13, 2015 Share Posted March 13, 2015 I've made a few arched doorways and have seen that issue before - my solution was always pretty drastic, but in the end it was workable: I made the physics mesh a simple door shape (i.e. no arch on top, just a horizontal block) and it always rendered with physics weight well below 1 LI even for fairly big arches. Granted, not 100% accurate but it's really not noticeable since most people walk through those arches and never hit the top anyway. Link to comment Share on other sites More sharing options...
Pamela Galli Posted March 13, 2015 Author Share Posted March 13, 2015 I made just a couple of plain blocks for the sides -- still 7 LI. Since my build already had 256 pieces, I had to find a place to reduce the # by one, and then I just put a regular prim inside the wall. They can still walk through the wall on the other side, but it is in a corner. If/when someone complains I can tell them how to put a block inside that wall, tho they cant link it. (I am always tempted to tell ppl who dont want to walk through walls, to stop trying.) Link to comment Share on other sites More sharing options...
Drongle McMahon Posted March 13, 2015 Share Posted March 13, 2015 Yes. In a hull-based (that is Analyzed) shape, a simple stretched cube has a physics weight of 0.36. So this simple arch will be 1.08, which appears in "More info" as 1.1, but is rounded down to 1 for LI. So any arch using this would have LI of 1 unkess the download weight made it higher. Make sure the boxes don't overlap and use "Solid" before "Analyze" on the physics tab. It should say 24 vertices and 3 hulls. Hull based shapes don't change weight with size. So the size doesn't matter, while for triangle-based shapes it does. Also, it can be as thin as you like and the hole will stay open, while a triangle-based shape has to be 0.5m or thicker or the hole will be blocked (by the server - it doesn't show on the physics shape view). So the hull-based shape is probably the better general-purpose solution. Link to comment Share on other sites More sharing options...
Aquila Kytori Posted March 15, 2015 Share Posted March 15, 2015 Hi Drongle I hadn't heard about that "adding another face at right angles" to reduce Physics weight on those meshes with the unexpected very high physics weights. So I have now tried it out on two separate occasions with the same mesh Arch and got similar results. All my uploads were using non analyzed Physics and when set to Physics Shape Type: Prim worked as expected. I uploaded my mesh Arch 4 times, First using Phys 1, a physics mesh created from a copy of the High LOD mesh and then removing edges with the dissolve function in Blender and deleting the faces joining the front and back sides of the wall. Second using Phys 2, a copy of Phys 1 and then adding a plane to join the two sides. Third using Phys 3, a copy of Phys 1 then selecting all the vertices of one side and scaling them down to zero in the Y axis ( S Y 0 ) to insure they were all lying perfectly on the same plane. (one of the things you mentioned to do in a thread a long time ago now) Each time the Download weight was 0.6. For the mesh using Phys 1 the physics weight was 11908 (note the other day when i tried this the Physics weight was over 16000). Using Phys 2 the Physics weight was 8.7 and Phys 3 was 0.5. You will see from the image above that even though I set the Physics Shape Type to prim they still looked as if they were convex hull when Show Physics was enabled. (The physical openings in the archway were working ok) So after a bit more experimenting I finally got an arch which showed the Physics correctly, Arch 4. Arch 4 was achieved by selecting all the vertices of one side of the wall in the High LOD mesh and scaling to zero in the Y axis, then repeating for the other side of the wall. Then repeated for the other 2 LOD meshes and then uploaded using the Phys 3 mesh for Physics. So the visual mesh can effect how the Physics mesh looks ! ? And to Pamela, In future when this happens you could also try the S Y 0 thing in Blender to your physics mesh before uploading. Link to comment Share on other sites More sharing options...
Pamela Galli Posted March 15, 2015 Author Share Posted March 15, 2015 Thanks Aquila, it would not have occurred to me that each side was not already 0 on Y! Link to comment Share on other sites More sharing options...
Drongle McMahon Posted March 15, 2015 Share Posted March 15, 2015 Yes. I remember that now. In fact having one vertex out of the plane by an amount much smaller than the smallest number that can ve represented in the 16-bit upload format could produce the ridiculous physics weight thing in some cases. That was beyond mmy understanding because the rounding to 16-bit values bshould have made them identical to the perfectly flat case, in the uploaded data. Perfect flattening is certainly a better solution if it works, because it doesn't add triangles. Did you try changing the wall thickness? That had a big effect on my high weights too. I'm afraid I just decided triangle physcics weights were irredemably mind-boggling. Playing with this arch, I also noticed the physics shape display showing CH instead of triangle-based shapes, although I could still walk throght the arch - so it's the display and not the physics that's wrong for some reason. I think this is new, as I never noticed it before. Link to comment Share on other sites More sharing options...
Aquila Kytori Posted March 15, 2015 Share Posted March 15, 2015 Drongle McMahon wrote: Did you try changing the wall thickness? That had a big effect on my high weights too. I'm afraid I just decided triangle physcics weights were irredemably mind-boggling. Yes, with the same results as last time : Multiplying the wall thickness by 2 will half the Physics weight. Multiplying by 4 the thickness will divide the physics weight by 4 etc Also gives the same results with the wall that uses the physics mesh with the extra plane at right angles. double the thicknes will half the Physic cost. Link to comment Share on other sites More sharing options...
Pamela Galli Posted March 16, 2015 Author Share Posted March 16, 2015 This whole thread shows that we have entered the Twilight Zone. How is anybody supposed to know this stuff??? Link to comment Share on other sites More sharing options...
ChinRey Posted March 16, 2015 Share Posted March 16, 2015 Pamela Galli wrote: How is anybody supposed to know this stuff??? Oh, that's easy. Just read every single post Drongle and Aquila have posted in this forum! :matte-motes-wink: Link to comment Share on other sites More sharing options...
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