Export particles from Houdini to Maya using Alembic and Arnold ONLY

hello everybody I would like to show you a new way to export particles from uini to Maya because when I read all the comments uh to the part one and the part two uh many people have issue with uh bifrost so I find another wife with Arnold so here we go I've got a simulation a grain simulation uh in inini simple simulation for on few frame and explode in wet sand up the grain with the color something interesting here is there bright on the top and and darker in in in in the bottom uh because the sand is wet under uh the surface so I've got the ground with the same um difference color darker in in the bottom and and brighter in the in the surface and to have a better integration I just add a scatter and normally um we used to make a mesh of the simulation but here for the purpose we will export the grain so the first thing we have to do as usual is to scale up uh the particles in Maya uh the units are in centim and in udini the units are in Mets as you noticed we can't see anything because this P scale is different so I tried uh to scale up the P scale but I didn't arrive to um modify it and and to use it I I will I will dip a little bit in in in the setup to to find a way to to export this P scale we will reset the P scale into my so here is I just remove all the all the the attribute I just keep the color and the ID the P the piscal and the V and the piscal I think I can I can remove it um here's I use my ID uh I set my ID here my my my ID attribute which is ID in fact I don't use ID attribute because there's some issue when you set ID a custom ID attribute in the in the input of the valance server because the valance Ser use ID attribut so it can make some strange behavior of your grain and the same in Maya you can't uh reuse attribute so I export that you have to make a sequence of file not one alumic with all the simulation so uh we have to use dollar F4 as usual to have a sequence of anomic and it's lighter and it's better and you have to do that to use in rde after that I just export the ground with the scale again and I promote the color from point to vertex because in Maya as you know Maya understand vertex and not point so I export only one alumic for that and I will use a classic method to import into uh into Maya and the last one is a skatter I use um on the ground it's simply skatter and the same I just scale up and Export one frame grind s from IBC here we go we are in Mya now so so I've got a simple scene with two light area light from my main lighting and sky from the environment so first of all import to ground with the usual method cach alic cach import alic buff and take the ground ABC import so I've got my ground as you notice there's a color Into My Scene It export the CD color uh in vertex uh remember we just promote here the color to point to vertex so uh it's in the view it's a good sign because uh it means that the information is in the mesh if I want to use it in Arnold I have to make some few thing the first things to do is to go to the shape and and the shape is named promote because I didn't set the string path in UDD so it's not a problem go to arold tab export and you have to check export vertex color it means that Arnold can read the information the color information on the vertex so now in the uh ipers shade I will create AI standard shaders surface I usual okay nothing to change I can put the specular to zero I don't want specular and as in the previous um tutorial we have to use uh AI data user color and then we put the name of the attribute C D and just plug to the bass color of the object select the object assign the material and now if I render you noticed I've got the color as you can see we have darker in the bottom and some issue here but no problem with the glame okay okay let's stop the render now we have to import uh the ground particle for that we'll not use cash because as you know an in Maya cannot import particles so I will use anal standing tool standing tool is very useful I just click standing I've got the standing here I will rame it now gr ground ground r Nam okay and I will check the ground skater here load and we've got the the skto when I render I've got nothing I will add the ground here rename it round Geo Okay add it and as you noticed there's a bounding box and it's uh a good thing when you see B because it means there some information the problem with this methods that you cannot have a preview with particles but when we you runer you will have something but now we have nothing why because the piscal is not at the good size as you remember we just scale uh the um the object to fit to Maya units and now uh we don't you we don't scale the piscal it doesn't work uh for the moment so we are to change it when you import the thing you can see here we've got the hierarchy of what is inside the alumic the standing and we see here we've got the particle and now we can have some attributes on this particle so I will click on ADD assignment point and let's select radius here I can put radius one for example and now when I render it I've got my particles let's zoom in to see the particles if I decide to change to have bigger particles we can you can have bigger particles so it works now how can I shade it because uh there's a color it's uniform color on gra but I want this color to in my May so let's back into let's go back into my hper shade up thank you I think we can use the same in fact yes we can use the same so so I will assign uh the uh Shadow to the standing uh there's two way to do that the first one is to assign the shadow directly to the standing but there's another way um to do that and is to assign on the object here and I can do add assignment Shader and it had a Shader uh fi where you can put Shader why is this is interesting because in the in the alumic you can export many things in the same Al here I've got only particles but if I want to export a geometry too I can assign different shadow in say inside the same standing the same alic so I prefer to use this method so I will assign this to the shadow so the same it will take the color and put into my B color and let's render and as you can see I've got the color now it works let's zoom in a bit and you can see my partic are color great so now we have to import oh I will unhide my ground um let's import as a simulation so the same we will create another standing here I will name it grade Sim I will check I got the folder with all my Alum bit one pair frame so I select the first one okay you can notice we've got a bounding box appearing when I do so so the first thing to do is to use f name because uh there's a sequence of anomic so you needs to load uh all the sequence uh don't worry about that sometimes the path is not updated but when I reselect the object the path is okay the same we've got the uh particle here but for example when I select the ground as you can see when I move the timeline the boning box is changing size so it's a very good sign because it it means that it works it can read all the AL all the sequence we will do exactly the same for this one we will add Point radius put that to one for example and we will add a Shader and we will reassign the shadow here and now if I move a bit into my simulation render as you can see we've got the particle and if you can you can notice the motion B working too that's great uh export the V and understand the V inside um the particles so I can uh remove the Mion blur Mion blur just to have a better look into my viewport p and it works let's wait for my computer to runer it works quite good when I change the timeline it updates the render and the simulation and I've got all my grain I think my lighting is a bit too high but I will perhaps try to uh reduce the are real light or to hide it I will hide it yes it's better so it works let's stop the rendering I will show you a little trick we can be very useful to use custom attribute from udini to Maya though for that I will just create another uh Shad up so let's create AI standard surfice the same and we use quite the same meod we use the AI user data integer because as you remember here I've got an attribute my ID which is an integer and is an ID so let's go back to Maya let's put my ID and here I will put uh AI random node for example you can use if you want not this one but you can use a custom float attribute to put into a ramp something like that to remap the color for example but here I will put a render to color because the output I want a color and connect the output to the seed so each particle have a different number on my ID attribute and it will shange the color for each particle and connect it into the Bas color now now I go back to the grain Sim and send the shedow here okay and now when I render as you can see we've got different color for each particles could be very useful uh we can for example set the a random to gray scale so now we've got only gray scale attribute and we can do you know a multiply with the color for example so I will stop the rendering and add AI [Music] um data user data I need to color to get back the color CD and perhaps multiply a I multiply the color with the random color the random gray skate color and um I can put into my base color so I will show you I will put a switch a I switch to show you with and without can take this one and put without is the input one and with the mix in the input two go to B color so here when I render this one I've got nothing change all the particle have exactly the same color and when I put to one so I've got a mix and as you can see we've got some variation added onto the color so it can be very useful uh especially on the end of the simulation where all the grain are in the ground you can add slightly different and for that we can because I think this one are too black so I can perhaps add the AI color correct AI color correct it's not very easy when you come from uh udini because in udini you can use to make space in in the tab menu and here it there's no space so it's a little bit confusing okay let's put the color input here and there and perhaps if I push this not too far I can add a clamp to avoid that a a clamp so I would just have a strict color from zero to one so I can change the color and perhaps uh I don't know uh bring up the exposure to 02 or 05 and so I will not have the the black the black one here I've got little variation if I switch to zero you can see there variation on my grain and here we go and I repeat the method is working with motion blur okay A bit easier to render but it's very interesting uh if I go I will just stop the r now and go to I think there's a tab here andic setting here we've got the velocity scale we go back to previous frame okay I've got a lot of mushion bre here okay and if I want to reduce sub Mission Blur by half and you can can see I will have less motion bar on my particle so it works stting is very useful because it's very light into the viewport uh when you import mesh you can have a preview Point preview or wireframe of your mesh inside but in particles with particle you've got no preview so don't be confused about that um just check as you can see my my Bing box is is is too little here but when I move the timeline it changed so it means it works uh it's a little bit confusing because you don't have anything into the viewport but it's very useful because when you've got very huge St uh it's very useful to export for example uh your building sorry uh into standing and reimport new s so it will be very very light and as you notice when when we when you push the Rend button it start immediately so it's it's very useful for that okay so thank you for watching and I will show you perhaps to import export from Maya have a good time byebye

Channel: Thomas Renault

Views: 2,525

Keywords: Houdini, Maya, alembic, particles, Arnold

Id: 8QsmIjeSzlE

Length: 18min 8sec (1088 seconds)

Published: Fri Dec 29 2023