Houdini Engine Tips! - Using Vellum for Cloth in Unity 2021.1

howdy guys indiepixel here in this video we're going to walk through how to set up an hda so that we can take advantage of using vellum inside of our hta's inside of unity and inside of unreal so i'm just going to cover the unity side of things but we're going to look at how to make it so we can assign collisions to our cloth objects and how to set up pin points for our object as well as go over some reduction stuff and just the whole workflow in general so let's take a look at how to get all this stuff set up inside of houdini and unity all right so the first thing we're going to do is we are going to create a new geometry note i'm just going to give this a name of ip vellum cloth something like that and we're going to right click on it and say create digital asset and i'm going to go and set up my namespace so you just put the cones like so and then at the end you just do the version number same way then you can also give it a different label if you want down here i tend to go and capitalize these things there you go and then we want to go and save it into our project so in this case it's my hip directory and so uh i'm going to name this folder hda and i'm just going to save it right there for now say accept and we're going to destroy all spare parameters i'm going to go to the version number and put in 1.0 and in the parameters i just want to go and hide everything because we want to go and set up our own custom ui so i'm just going to set those guys to invisible hit accept and just make sure i save the node type and we now have our hda so now let's put in the meat of the actual hda i'm going to double click it to dive inside and for this demonstration i'm going to just set up a simple grid you could actually feed in any sort of mesh that you want but in this case i'm just going to make a simple grid here and we'll default it to 10 by 10 so let's actually add that to our type property so just right click on the hda right here just go to type properties and we can just go then and do an alt middle mouse click on the label here for the size to promote it to our hda up there there we go now your defaults you might want to pay attention to uh you might want to set that to just one for the minimum size and maybe you know 50 for the max this is a simulation so you know you could get quite a bit of geometry created from this particular technique system so you want to keep all this stuff in mind so the defaults are tenant and that's good cool so i'm just going to say apply and accept with our grid done we need to apply some uvs first so it's a good idea to do that just so you know you have the uvs now if you want to just verify that your projection plane because we are using the orthographic setup here if you want to verify that in the scene you just want to go and select the node and then hit enter in the scene view over here and you can see that our plane is perfectly oriented correctly and we can do a spacebar five on the keyboard and to go into the uv view just to also verify that we actually have uvs then do a spacebar one just to go backwards just one if you're already out of um or in camera mode all right so now we've got uvs i'm going to do a remesh so let's drop down that remesh node and really we're just doing this because if the villain solver likes to work these triangles you just get more realistic cloth look out of it so the one thing that's really important here is the size this allows you to change the resolution of the simulation so we should probably promote that so i'm just going to go to my type properties again and i'm just going to do another alt middle mouse click there to promote it to my type properties up here so i can tweak this stuff inside of unity also inside of unreal for using the unreal engine as well and so i'm just going to leave the labels and all this stuff set up by default for now you can tweak it all later i really just want to cover the technique here all right so with that all set up we now have our grid so i'm just going to drop down a volume configure cloth i'm just going to wire that in like so and all the defaults will be fine for now as well and then we're going to go and get the solver so we just want the vellum solver i'm just going to mouse over the guy to auto hook up those lines there there we go so now we have a vellum solver in here so i'm just going to hit play just to verify that it's moving yep there you go and it's actually got some pins there that's pretty weird um all right so let's go now and set this up for the houdini engine so i need to actually drop down a time shift node here to control the solver because inside of the houdini engine we don't have a timeline right there's no timeline and so this time shift node allows you to push time forward and backwards which then triggers the vellum solver to run inside of the houdini engine so all we need to do is expose this frame value to our type properties so i'm just going to open up type properties here and just do an alt middle mouse click and now we have our frame one thing you should take note of is just lock this at one because if you get zero frames it just removes all the geometry from the hda alright hit apply and accept all right you can also leave that open if you don't want to have to constantly be doing that and then finally we're going to drop down a vellum post so let's do a volume post process this just smooths things out for you we'll set the subdivision to loop you can also put up the blur a little bit as well or just promote these parameters to your hda alright then i'm just going to drop down that output node here and there we go so now we have a really basic vellum set up for our hda so let's go and test this out now inside of unity first thing always remember right click on your hd and save it so let's go and test this out in unity now okay so what i did is i open up the folder location of where my hda is and i'm just going to drag and drop it into unity over here into my hda folder wherever you want to save these guys and i'm just going to pull this guy off screen and now i just want to drag and drop this into the level you can put it into the hierarchy you can put it in the scene view it doesn't really matter all right so you get your grid and we don't really have a lot of parameters yet but you can see over here in the inspector i can grab this guy there we go all right so what we can do is go and change the size so we can do something like 4x4 and we can change the overall target size so to see that we just go to a shaded wireframe there and we go to something like 0.5 you can see we've got really big triangles if we do like 0.05 we get really tiny triangles so you get more resolution out of it which gives you a better solve so i'm going to leave it at point 2 just to start here and if i were to increase the frames now to something like 20 and let the houdini engine run you can see that our cloth piece is all the way below the floor here and that's because we're not colliding with anything yet so what we need to do is we need to go back to our hda and add some collision properties to our system so in order to do the collision basically we need a way to actually import geometry that we set up inside of our unity scene into our hda here and to do that we use object merge nodes this object margin node allows us to basically fetch or you know go and find geometry that the user is assigned and so to set this up what we need to do is we need to set this to into this object for the transform option the reason being is that this will import the location of the objects in the unity scene into houdini here so it's all relative basically which is what we want so i'm just going to wire this into the third input here on the vellum cloth node which is for collision and so now whatever we assign inside of unity we'll collide with our cloth solver there and so i'm going to actually name this i'm going to call this get collision and we need to promote this object one parameter up to our hda so let's go and do that i'm going to go to my type properties and i'm going to put in a separator for this you can also use folders or organize this stuff however you want and then i'm just going to do a middle mouse click and uh alt on the keyboard to promote my parameter up to the hda up here and i'm just going to call this collision input like so we'll call this collision input just to make it clear inside the editor and hit apply and accept so now we'll be able to assign collisions to our vellum solver inside of the houdini engine which is super cool and to finish this up i am just going to right click on the hda and say save node type and then let's hop back into unity and test that out okay so to get those changes back here inside of unity that i made to the hda i'm going to go and right click on my hda here inside of unity and i'm going to say show in explorer let me go to the location where i've been working on the hda so this is a different hda than the one that is actually inside the project now you could be working on these particular hdas i tend to keep them separate just as backup all right so i'm just going to copy this and i'm going to paste it and replace it there so now it's all imported or re-imported so all you need to do is go and select the vellum cloth and hit a rebuild on it and what that does is it basically updates the internal hda all the nodes and stuff to the latest version that we just updated all right and you can notice that we get this new collision input over here in the inspector well this allows us to go and assign any geometry any static mesh from the scene to our hda and what will happen is the vellum cloth solver actually interact with those pieces of geometry so in this case i want to add all these cubes that i set up here just to act as like cardboard boxes or something like that and so i'm going to go to the hda here and say add selection and then i want to go and turn on roots only so i can select just these grouped bits of game objects here and i'm going to turn on collision objects hit accept and those are all the objects that i actually want to collide with and in this case i do want to add one more so you can actually go and add a separate slot and in this case i want to go and drag and drop the ground into this right here so what we need to do now is actually go back to frame one right and then sim to something like let's do like 50. and see what happens so now we're running the vellum solver it's just that you don't get a real-time update or anything like that so it's just skipping the frame 50 but it's got to go and cook all that stuff so you can see that our cloth is kind of bundling up over there so i'm gonna go and set this to one but you know it's actually kind of a pain to constantly go and toggle this back to one than having to set the sim time again so it'd be nice to actually be able to trigger that and you can actually do that inside of the hda by promoting the resimulate button so let's go and take a look at that all right so i'm going to go up here and i'm going to go and expose the type properties and we really just need to go to the vellum solver here then go and promote this reset button right here so i'm just going to alt middle mouse click and that puts it right there so let's actually move it up with these other values here and let's actually put a separator between these two guys so we have all simulation stuff then we have size stuff and then our inputs all right so hit apply and accept and then just make sure you save it and now we can go and update our version inside of unity so let's copy our new hda or the updated version and paste it over the old one over here i'm going to jump back into unity and hit a rebuild on the hda and you'll notice now we have a reset simulation button which is great so i can leave this now at something let's say like 40. and when i want to update the simulation i can just hit the reset simulation button and it'll re-cook so let's go now and just move this and then just say reset simulation let it cook for a little bit and there you go so now we're starting to fold but you'll notice that we're getting quite chunky results here and that's just because of our target size so let's set this down to something like 0.1 and hit reset simulation and there you go so now we're starting to get something a little more realistic let's turn off our wireframe just so we can see this yeah starting to look pretty cool so there's a couple more things i want to do and i have an example already set up here let me actually turn this guy over off over here and turn on the previous version here so i want to be able to go and pin certain sides of my cloth like if i want to tie up this tarp or something like that well i can also go and assign spheres in this case i use spheres you can assign any geometry you want to use as a pinning point and hook it up to the hda so that way we can control the look of our cloth here much easier all right so let's go now and take a look at that inside of houdini in order to pin geometry on vellum cloth you need to go to the pinpoints group right here so this particular parameter right here is actually looking for a group of points to pin all right so if you hit this drop down you'll notice there's no groups i haven't set anything up so we need to set up that group right so i'm going to go and drag these guys up here and drop down a group node and the way i want to do this is i want to allow the user to assign any piece of geometry to select an area of the cloth to pin all right i just find that to be a good way to let users interact with the cloth and just really art direct it all right so i'm just going to drop down an object merge note that again this is going to import geometry that the user assigned so i'm going to call this get pins there we go and we need to set this to into this object as well and then we need to promote this object one parameter so let's go up to our type properties up here and i'm going to create another separator and this will all be for pins so i'm just going to do an alt middle mouse click there and we'll call this pin inputs and i do like to keep these lowercase so pin inputs and pin inputs for the label and everything else is fine hit apply and now in the group node here we need to set the group name first that's very important so we'll just do pin and we're going to change this from the base group to keeping bounding regions now this only works with points so we need to convert the group type to points there and then we need to change this to the bounding object so the bounding objects are going to be all those spheres or cubes or whatever you assign to this object merge node and i'm going to feed that into that first input of the vellum constraints node and inside of that volume constraints node i'm going to go and select that pin group alright so that will allow us to then go and pin the parts of the cloth so let's hit accept everything looks good there i'm going to go and save my hda by right clicking on it saying save node and then let's jump back into unity and take a look so i went ahead already and did a rebuild and updated it everything looks to be fine so what we need to do is go and create a new empty game object i'm going to call this my pins and underneath that i'm going to create a sphere to act as my pin group or the object that i want to use is my pin group so i'm going to call this pin01 and let's go now and i'm going to scale it down quite considerably and we're going to then move this over here and to make this a little bit easier on myself let's go up to the vellum cloth hda and i'm going to set the frame back to one just so i can see where it's starting from that'll help a lot not also i'm going to assign a material i made for this guy a bright red material just so i can see it easily i'm going to call it pin matte i'm going to use pin mat there and let's now go and put this into position like on one of these corners here so let's make this a little bit bigger just make it easier on myself there we go so let's do both these corners over here i'm going to go drag it there and then do a control d and move it over here and these two are going to act by pin points you need to make sure that it intersects it just so it has some points to select all right and then on our hda here let's go and assign those two guys again you can just go and get your pin group so i'm going to go and add selection turn on my roots only and go and find pins up here say yeah accept and then we can go and resimulate so let's set this back up to oh let's do 50 this time and let that cook and there we go voila we're now pinning our stuff so you can even go and add a third one in the middle there so let's do that and let's make sure we go and grab our group again so i'm just going to go like so and hit accept and let's just remove the original one there and let's do a rebuild or i could hit reset simulation and there you go so now we've got all three so you can go and pin it wherever you want pretty cool stuff so the last couple things i want to do is i want to make sure that we get a material assigned to this and then i want to be able to reduce the polycount because you're going to want to go and increase the polycount on these things i tend to go to something like .05 for these and then do reset simulation you'll end up with quite a bit of geometry and so i want to be able to probably reduce that here inside of the editor and so once this is done we're going to take a look at how to set that up all right so the first thing i want to do is just assign the material which is pretty easy you just drop down a wrangle note here and go call this unity material and i want to make it so that you can assign whatever material you want especially for something like lots you might be swapping out cloth materials quite a bit so to do this you say s at unity underscore material is equal to chs and the name of the property so when you say chs you're making a string channel so a parameter that'll exist down here and i'm going to call this material call whatever you want it's really just the internal name for this particular parameter all right and so then we need to promote that to our hda so go into the type properties here and i think i'm going to put it at the top right because that is you can just drag and drop it as well that is um all the kind of the base parameters over there all right so that is all set up let's make sure we set that to the primitives as well it'll still work on points i'd usually just put it on primitives all right so the last thing i want to do is go and probably reduce so let's drop a poly reduce node in here and we are going to set this to by default let's say 50 and i want the user to be able to switch this on and off as need be because it is a heavy operation so might as well let them run the vellum solver without the poly reduce it'll just make the hda go faster and then when they're ready to reduce it let them reduce it with a switch note so they can just toggle between the two different states so switch reduce and now i need to promote two parameters from here one on the toggle so oral and the switch node here so to do that you can just drag and drop this down here and i think i'm going to put it up here and put a separator between this so it makes it easy to see and we're going to call this the reduce toggle and we'll call this reduce with the question mark and then we'll convert the type of the parameter from integer over to a toggle just so it shows up as a checkbox in unity and then we want to give them control over the amount to reduce so in this case i'm just going to promote the percent to keep for now you can use you know the other settings as well for now i'm just going to say 50 is the default so if you go to the channels tab that'll be where your default is and then this is your range so you hit apply and accept and then make sure to put the display flag on the output and right click on the hda save to node and let's take a look inside of unity and after rebuilding i get my new options here so we have our reduce option here so i can go and turn this on and then set this to oh i don't know let's do like 20 let's see there we go so now we're getting a lot less polys which is perfect we can go lower and see what happens here so you can really stretch that let's set this to shaded and it looks pretty much the same so the other new feature here is the material so the way this works is you've got to go over to the material you want and right click on it and say copy path and then paste it into the option here and hit enter and that will set it up so because we set up uvs this will work i went through and basically made these materials inside of a qixel mixer and just kind of blended a few things together as a mixture of tarp and custom layers which is some noise on top of it and just kind of blended with the bottom tarp material same with all the other stuff here so nothing here is really all that fancy so anyways that is how you set up vellum inside of houdini engine for unity now the really only differences between uh unity and unreal for this they both basically work the same way as you need to set up in this case for this hda the material assignment needs to be set to the s at unreal material attribute inside of houdini so just keep that a note if you are using unreal this totally works in unreal too i have tested it myself so thanks so much guys see you soon