Quote - hi bagginsbill,

just a quicky at sunrise after breakfast.

1. did you really use the hires square or just a simple one? The latter is far too low on vert/poly density to do any reasonable sim testing. Hires cloth against lores cube is exactly what cloth room was made for, originally, so all defaults only should do fine.

I specifically and intentionally used the one-sided square. After so much effort on reverse-engineering the material room nodes, I am convinced that if I don't understand how a simple scenario works in isolation, however contrived and useless it may be for real work, I have no hope of understanding a larger system of components interacting with each other. As an example, I never would have discovered how transparency and specularity interact with each other in the material room if I had not done precise measurements of specularity without any transparency, and transparency without any specularity. There are some surprising cases in the material room where .5 * 1 = .7. Similarly, my discovery of how to get at the W coordinate (of the U/V/W texture coordinate system) for dynamic hair was based on absurd and useless test cases that had no value in actually shading hair, but revealed a ton of information about how the hair node works. I now control the Hair node like nobody has ever done before.

The importance of these contrived and over-simplified scenarios, such as a single clothified quad falling on a box, is to verify hypotheses, allowing me to make accurate predictions of cause and effect. Then when applied to real use, I do not have to wonder at which of 20 factors is the cause of unexpected results.

In this case, I was trying to understand this: We have an expectation that enabling the additional collision options will do something. We assume we know what "object vertex against cloth polygon" means, but without testing that assumption, we can't explain to Nanette why turning all of them on still results in the skirt passing through the knees.

My single square test did something very similar in some cases, and not in others. Since I am able to reproduce the problem with even a single polygon, it stands to reason that the solution will likely be revealed by manipulating that single polygon and its cloth settings. I have the benefit, as well, of a simulation that finishes in .2 seconds, allowing me to do hundreds of trials in an hour instead of just a few trials.

Quote - 2) preview has a problem handling the sim result detailts well. See nanettes post, and other threads. Don't know why, yet.

Right - that's why I mentioned it. Until I said it, nobody else had. My point was not that I have an answer to why, nor do I need one. The important thing to know from the single poly case is that you cannot trust what you see in preview. Don't even bother posting preview screen shots to show a poke through problem. The preview is somewhat irrelevant. Always show a rendered version of the problem.

And, related to making the rendered geometry visible to each other in test cases, it's a good idea to use some standardized materials that are designed specifically to make contours easy to see - perhaps even some false-color ones would be in order. I'm developing these to share so we can all better understand what we're looking at. Frankly, the semi-transparent and textured skirt Nanette shows is very difficult for me to see what sort of mis-folding is happening there.

Quote - general: you're in reality, aka the Poser understanding of it. If you drop cloth from a height, airstreams will take effect, especially at the edges, then creep inward. Air layers will make it hover just above the table, and make it slip at low table-to-cloth sheer resistance. Think about clothing the table, in the garden, at a quite summer day, and you warp the cloth from the second floor down. What happens? Think rough wood versus smooth plastic for the table, makes a difference. So: zero the airdamping to get rid of (most of) this effect.

Right - I did set the air damping to zero. In fact, I set everything to make the square very rigid and super heavy at first. It fell pretty flat. Later, still with no air damping, I managed to get it to fold up, not because of air damping, but because the detection of intersections between the clothified square and the box were not behaving in a way that would be classified as "reality". Specifically I saw a slight bend that should not be there, and then I did things to accentuate that anomalous bending until it was truly absurd. I would post what I did, but I forgot how I did it after so many trials. In this early stage, I'm pretty much just creating questions, not answers - questions that we didn't even know to ask.

Example: The top of the box is a regular grid of square polygons. At the time when the cloth square strikes it, it is very close to flat and all of the box polys are well inside the square. Why did some "catch" and others not?

Quote - Poser will not let you reach real zero BTW, as one cannot have no air resistance in real life.

I'm not disputing that (yet) but I have to ask how you know that assertion to be true? And I would like us to be really careful (instead of careless) about what is meant by 0! We all know that .000001 is not zero and if that is the lower bound it is accurate to say the air damping cannot be zero. But is it relevant? Is it measurable? (In my work-place, every statement we make and act on must be clear, accurate, relevant, and measurable.) If the minimum air damping is such that it alters the position or velocities by one part in a trillion, then that's certainly not something to argue is the cause of a major folding in half of the quad. It's not relevant if the non-zero true value is unmeasurable.

I would like to see an experiment done in which the falling cloth time is demonstrated to be other than the solution to 1/2 a t^2 = H, where a is acceleration of gravity, t is time, and H is initial height. If you can show me that the expected fall time is off by a measurable amount even when air damping is set to 0, then I'll believe that it cannot be set close enough to 0 to be able to exclude that factor from consideration when performing an experiment.

Quote - Increasing cloth density makes it jeans like instead of thin linnen (the default values). You know from life what to expect.

That's an interesting statement, but here's my counter. I "expect" that when I set up a single polygon 10.25 inches on a side that weights 50 Kg, has the maximum possible stiffness (fold resistance, stretch resistance, etc.) and I set air damping to 0, that it does not fold up at all. That is not what happened.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)