PIPE­LINE TECH­NIQUES: es­sen­tial Houdini tips for the new user

Tyler Bay’s friendly begin­ner’s guide

3D Artist - - CONTENTS -

Houdini is one of the most im­pres­sive, well-built 3D ap­pli­ca­tions on the mar­ket, and there’s noth­ing else quite like it. When some­body men­tions Houdini the first thing that might come to mind is in­cred­i­ble VFX! Pro­ce­dural work­flows!

And… it’s also per­haps an ap­pli­ca­tion that’s su­per in­tim­i­dat­ing and al­most im­pos­si­ble to learn at first. For many peo­ple, Houdini looks like some­thing that’s a bit too out-of-reach or tech­ni­cal, but in my opin­ion, it’s ac­tu­ally quite easy to use once you get past some of the ba­sics. When I set out to cre­ate the Houdini For The New Artist course I wanted to make Houdini as friendly as pos­si­ble to the artist, build some­thing that looks awe­some, and of­fer a way to even­tu­ally reach harder con­cepts with a foun­da­tion of skills and knowl­edge set in the right place. Let’s take a quick look at how that can hap­pen with this tu­to­rial. The goal here is to cre­ate a trans­for­ma­tion ef­fect that turns a dark-mar­bled dragon into gold by us­ing a com­bi­na­tion of par­ti­cles and cus­tom shaders.

Also, as a side note, be sure to check out the File­silo as you’ll find ex­tra re­sources, such as a Houdini cheat­sheet, de­signed specif­i­cally with the new user in mind.

01 Pre­pare the scanned model The first step in this process is to pre­pare the dragon model. When work­ing with scanned mod­els, it’s im­por­tant to re­duce the poly-count so that our scene doesn’t get too slow. To do this, we can use the Poly-re­duce node and set the tar­get poly-count to 100,000. On top of that, we’re also able to paint ar­eas that will con­tain a higher con­cen­tra­tion of those 100,000 along the face to pre­serve some of the im­por­tant, fine de­tails where it mat­ters.

02 Tex­ture in Sub­stance Since the ty­pol­ogy is dense and tri­an­gu­lated, the best way to ap­ply UVS is by se­lect­ing mis­cel­la­neous sec­tions of the mesh and un­fold­ing them. In order to do this, you can ei­ther se­lect the faces man­u­ally or use the Auto-uv node that can be found within the game-dev toolset. Next, go into Sub­stance Pain­ter, here I utilised Sub­stance Source for the base mar­ble ma­te­rial along with the gold and then I baked out all the usual sig­nal maps like oc­clu­sion, edges and so on. Af­ter adding some dirt, ox­i­da­tion and other de­tails, I also made a mask that will be used to con­trol where the par­ti­cles will even­tu­ally spawn.

03 Ap­ply the tex­ture maps To bring all this back into Houdini, you can set the ex­port style within sub­stance to Metal­lic/rough­ness along with switch­ing the Nor­mal map style to Opengl. This setup works well with Houdini’s prin­ci­pled shader, and all the maps just get read di­rectly into the ma­te­rial pa­ram­e­ters.

This setup works well with Houdini’s prin­ci­pled shader, and all the maps just get read di­rectly into the ma­te­rial pa­ram­e­ters

04 Set the key light Next is light­ing! The first thing I start with is an over­cast, blue-coloured HDR that’s set to a low ex­po­sure. By do­ing this, my goal is to al­low the light val­ues to hover just above black. This adds de­tail to the shad­owed ar­eas and gives us a base to work off of. Af­ter that, I be­gin set­ting the key light.

When adding this, I try to imag­ine what the light is do­ing to the per­son­al­ity of the face. I could make the dragon feel heroic or men­ac­ing just by the an­gle, so I went for a heroic feel by set­ting it to the top-left po­si­tion.

05 Add rims, fills and ‘skim­mers’ Once the key light is in place, I move on by adding other sorts of light such as rim lights, fills and some­thing I like to call ‘skim­mers’. Rims help de­fine the sil­hou­ette. Fills help in re­cov­er­ing form that gets lost in dark ar­eas and ‘skim­mers’ skim the sur­face to pick up the small de­tails that can be found along the sur­face.

06 Ap­ply in­ter­est­ing forces On top of this, ex­tra forces get added to the Solver to help con­trol the gen­eral be­haviour along with adding break-up and vari­a­tion.

For this, I added a Wind Force to help give a wavy be­haviour along with some noise that pushed th­ese par­ti­cles in var­i­ous direc­tions.

07 Us­ing noise to mask gold Once the DOP net­work is set up, the next step is to cre­ate a cus­tom shader that will blend be­tween the dark mar­ble and gold ma­te­ri­als. To do this, first cre­ate the two prin­ci­pled ma­te­ri­als in­de­pen­dently from each other. Af­ter this, you can sim­ply blend the two by us­ing a Layer Mix node.

To make this work though, the Layer Mix needs a way to read the sur­face of the ge­om­e­try and ei­ther say ‘yes, this is gold’ or ‘no, this is not gold’. We can tell the Layer Mix this in­for­ma­tion by us­ing at­tributes.

08 Use at­tributes for more con­trol An at­tribute is ba­si­cally like a piece of in­for­ma­tion that gets at­tached to our ge­om­e­try, and in Houdini, set­ting and cre­at­ing your own cus­tom at­tributes is re­ally easy. For this gold ef­fect, I used a noise to as­sign a Yes value of 1 or a No value of 0 along the sur­face of the ge­om­e­try. As the noise an­i­mates over time, so too does the lo­ca­tion of the gold vs mar­ble, and I can plug in all that in­for­ma­tion with a cus­tom at­tribute into the Layer Mix node in order to make ev­ery­thing work. I also used this at­tribute to pre­vent par­ti­cles from spawn­ing wher­ever there was gold.

To do this, first cre­ate the two prin­ci­pled ma­te­ri­als in­de­pen­dently from each other. Af­ter this, you can sim­ply blend the two by us­ing a Layer Mix node. To make this work though, the Layer Mix needs a way to read the sur­face of the ge­om­e­try and ei­ther say ‘yes, this is gold’ or ‘no, this is not gold’

09 Sep­a­rate el­e­ments for ren­der­ing For ren­der­ing, I sep­a­rated out each part of our scene – the dragon, back­drop, par­ti­cles and even the light that gets gen­er­ated from the par­ti­cles, into sep­a­rate ren­ders.

The idea be­hind this is to op­ti­mise ren­der set­tings for each el­e­ment in­di­vid­u­ally and then even­tu­ally bring them back to­gether in comp.

10 De-grain spe­cific passes An­other cool thing you can do with Houdini be­sides sep­a­rat­ing out scene el­e­ments, is adding ren­der passes.

Dur­ing comp, we can use th­ese ex­tra ren­der passes to re-build the fi­nal image, and along the way, de-grain spe­cific passes that ap­pear too noisy. The cool thing about ap­ply­ing the de-grain ef­fect to spe­cific passes is that this also min­imises the neg­a­tive im­pact of the de-grain oper­a­tion. The end re­sult looks much cleaner this way.

11 Com­pos­ite the fi­nal ad­just­ments Last, but not least, all the fi­nal com­posit­ing ad­just­ments are made. I can con­trol the in­ten­sity of the lights even af­ter things have been ren­dered, add a lit­tle bit of glow to the par­ti­cles, and also fix any ar­eas along the high­lights that may have been get­ting too bright. The end re­sult is what you see here!

Tyler Bay tylerbay3d.comBioTyler Bay is a 3D artist who free­lances and teaches on­line cour­ses. Past pro­jects in­clude Pixar’s Coco along with the Houdini For The New Artist cour­ses at cg­cir­cuit.com.

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