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I've created a HIP that reproduces the problem in a more manageable way UPRES.hip

https://ibb.co/Y2N8z8B Made a grid to use its points as your particle sources connected a pop net to it In the pop net i mainly edited the POP Source Source Tab: changed geometry source to "use first Context Geometry" to use grid points as sources Birth Tab: Crank your "Const Birth Rate" a little up and change the "Jitter Birth Time" to negative. This made the points fall a little more unperfect Attributes Tab: "Initial Velocity" gets setted to Set innitial v and than adjust the variance slightly of x and z. The points will not fall straight downward but a little left and right. i added an additonal nodes like "popinteract" to get them a bit together if they are close or add some forces to mak their movement a little more random like a small "pop wind" or so Outside the Popnet i added some additional nodes so the points get geometry. added a "attributeadjustfloat" with a operation as "set initial" and Pattern Type as "Random" with Min/Max values to my likeing (this randomly changed the size of the "droplets") added a "vdb from particles" node with quiet a small point radius and smaller voxel size. added a convert vdb and set it to polygon to get the final geometry. https://ibb.co/TPxDzsr      

I watched Paul Esteves' Hive froma few days ago, and followed his example for inflating a cushion using pressure constraints. I wanted to understand how to control pressure with animated antributes. I can't get his VEX code to work, and I can't understand why it doesn't, but worse I don't understand why it would if it did!  (It doesn't vary the pressure across the geometry). He's setting a mask attrib on the main geo, then referencing this on input 3 of a Geometry Wrangle in the solver set to the ConstraintGeometry stream. Here's the code, with my atribute inserts for saving out the varibales so I can try to see what's happening in the spreadsheet. int pt = primpoint(0, @primnum, 0); i@mpt = pt; float falloff = point(2, "mops_falloff", pt); f@mask = falloff; falloff = fit01(falloff, chf("min"), chf("max")); f@restlength = f@restlengthorig * falloff; The code is using primpoint() to get the point number of the first vertex of each constraint prim, storing it in pt and multiplying this with the mops_falloff mask and saving it to @restlength of the pstretch group (named in the Pressure constraint SOP). But when I inspect @mpt ('mpt' so it's next to 'mask' in the spreadsheet), its all zeros. 'That would explain why it's not working' I think... iiuc though, the pressure contraint is just a single polyline, 1 prim, connecting many points stored in an array (@pts) and so has just one restlength attribute. So I don't see how this code could write the differnt masked values as there's only a single entry for it. I must be misunderstandning something but cannot figure out what. See grab. Here's the part of the vid with the code in a Geometry Wrangle in the Vellum Solver:    

A noob grains upres question here…   I created a massive fracturing grains sim with Vellum at a low-ish resolution, and I'm using the grains' velocities to drive smaller dumber particles.   When using the POP Advect by Volume, the particles are pushed around correctly as expected, but when they exist the Velocity field they slow down dramatically almost to a halt. This is because I am using "Treat as Wind" with very high "Air Resistance" values, to counteract the Gravity force. How can I sample the Density of the same volume, and use that to influence the "Air Resistance"? This way the core of the volume will stick to the Velocity, and as we get further away from the core, the Velocity will have less and less influence, with gravity taking over...   I spent hours on this yesterday, trying to find a way to bring the volume Density into the DOPNet as a sort of falloff for the POP Advect by Volume node…   I even tried transferring the volume density to the Grain source points in SOPs as a float value, hoping I could hook strength data out of them that way, but again, just not luck at all!   I’m aware this must be incredibly simple to do, but I just cannot figure it out at all. There doesn’t seem to be any kind of masking options available in the nodes I’m using. One kind Facebook user on the Houdini Artists group told me this VEXpression could be pasted into the POP Advect by Volume node: @airresistance *= fit(length(volumevelocity), 0, value, 0, 1); value = the speed value where you want the resistance to be full.     However, this is not referencing density, and so far, isn't working anyway - but I get the idea.... Can anyone advise on the best steps to do this?

Amazing! Thank you!