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In this guide, we will take a look at the groom­ing tools in­tro­duced in Hou­dini’s 16.5 to quickly lay down the flow of the hair’s guide curves. This way, we can achieve a de­tailed and re­al­is­tic look to gain a fur­ther un­der­stand­ing of its pro­ce­dural work­flow and or­gan­ise our lay­out for ef­fi­ciency. We’ll also ex­am­ine al­ter­na­tive ways of cre­at­ing in­tri­cate cus­tom shading through Hou­dini’s own pro­gram­ming lan­guage VEX to al­low com­plete con­trol of the amount of colours and blend­ing pat­tern through­out each hair strand with­out the use of shaders; this method is com­pat­i­ble with tex­ture maps, too. Ad­di­tion­ally, we will go through the steps for caching col­li­sions us­ing VDB vol­umes and new op­tions to iso­late sec­tions of in­di­vid­ual strands of hair us­ing dif­fer­ent pa­ram­e­ters. Spe­cial thanks to Tighe Rzankowski for his as­sis­tance with VEX script­ing. 01

Add fur by den­sity at­tribute The groom was cre­ated through Guide Groom ob­ject’s skin at­tribute; it works by paint­ing in­ter­ac­tively on the mesh a mask where the guides will be gen­er­ated. 02

Groom pro­ce­du­rally The ad­van­tage of Hou­dini’s pro­ce­dural work­flow is the abil­ity to go back up­stream to ap­ply changes any­time, be it the ini­tial mesh or any ad­just­ments to the groom­ing tools them­selves. The Guide Groom ob­ject sets down the ini­tial guides that will be later sim­u­lated. The Hair­gen ob­ject de­pends on these curves

as its func­tion is to gen­er­ate the hair on ren­der time and most of the de­tailed styling hap­pens here. Frizz, Clump­ing and Bend tools were the most used. 03

Use Curve Ad­vect This new node in­tro­duced in Hou­dini 16.5 works sim­i­larly to Ini­tial­ize Guides node; it can be used to set down the gen­eral di­rec­tion of the hair. How­ever, it also of­fers the abil­ity to draw curves di­rectly on the geom­e­try to spec­ify the flow of the groom guides into unique paths. In the Taran­tula groom, it was ex­tremely help­ful as the Curve Ad­vect node de­fined the di­rec­tion of each leg’s hair as they spread out­wards from the body. 04

Re­move over­lap­ping hair The Guide Groom SOP node of­fers dif­fer­ent brush tools such as Length Ad­just and Sur­face Brush. In this case, Cut was per­fect for delet­ing the guides go­ing into the eye sock­ets and other spots where hair shouldn’t gen­er­ate.

05 Utilise Guide Col­lide VDB To be cer­tain the curves are not in­ter­sect­ing into the skin geom­e­try, create a Guide Col­lide VDB node at the end of the chain in­side the Guide Groom or Hair­gen sub­net­work. The curves can be ei­ther off­set or pushed away from the skin sur­face – the lat­ter al­lows you to iso­late a sec­tion of each curve such as the seg­ments closer to the root. 06

Work with Groom Merge An­other new fea­ture is the Groom Merge node, which al­lows you to work on dif­fer­ent iso­lated groom ob­jects. In the Taran­tula project, the hair is sep­a­rated by dif­fer­ent body parts such as the ab­domen, legs, ster­num and mouth. Af­ter the Guide Groom’s curves are styled, Groom Merge al­lows the user to com­bine these dif­fer­ent sys­tems into one sin­gle set of guides that is ready to be de­formed and sim­u­lated. Ad­di­tion­ally, Groom Merge cre­ates groups that the Hair­gen will be able to pick up to blend the guides be­tween each other to create smooth tran­si­tions. 07

Cache Col­li­sions It is pos­si­ble to work with the Guide Groom’s rest skin VDB set­tings as the de­fault From Skin Geom­e­try. How­ever, to man­age faster ren­der­ing speed, it’s al­ways best to cache out the VDB vol­umes be­fore­hand. You would need to do so for the T-pose and an­i­mated mesh sep­a­rately. To achieve this, sim­ply use a VDB From Poly­gons node con­nected to a File­cache node. Keep in mind that this works best on a mesh that doesn’t have any open holes, so be sure to cap any gaps! 08

Use Point Color as dif­fuse To ap­ply cus­tomised colour pat­terns to the groom, paint di­rectly on your base mesh us­ing a Paint node. Since it’s de­pen­dent on the amount of points that ex­ist within the geom­e­try to store the Cd at­tribute, you may wish to sub­di­vide be­fore­hand. To trans­fer the Cd at­tribute, it’s best to cache out your painted geom­e­try per frame through a File Cache node, then load the BGEO as a File node within the Hair­gen ob­ject and use an At­tribute Trans­fer node to copy the painted Cd at­tribute. Keep in mind the cached BGEO must match the cor­re­spond­ing de­form­ing mesh, so it can’t be the static T-pose geom­e­try you started your groom with. If you painted your T-pose mesh first, just copy and paste the Paint node be­low your de­form­ing mesh.

09 Load tex­ture maps in­side Hair­gen Create an At­tribute Wran­gle and con­nect the wire that cor­re­sponds to the HAIRS SOP up top to the first in­put. next, plug in a cached BGEO file of the mesh into the sec­ond in­put – this is to trans­fer the uv at­tribute di­rectly to the hair. The Vex­pres­sion that you need to type down is shown on this step’s im­age. Af­ter­wards, place an At­tribute From Map node right un­der­neath and set your tex­ture path ac­cord­ingly. In this ex­am­ple, a tiger pat­tern was used for clar­ity. 10

Cus­tom root and tip blends This method re­quires a Point Wran­gle node and VEX. The ad­van­tage of blend­ing through these is the com­plete con­trol of the dif­fuse colour along the strands with­out de­pend­ing on the hair shader. Ei­ther a mesh that was painted us­ing a Paint node may be used, or the Cd at­tribute from a tex­ture file that is fed di­rectly into the hair­gen – or any com­bi­na­tion of both. On the im­age you can see the setup and the Vex­pres­sion needed to be able to do cus­tom blend­ing. In this ex­am­ple, three colours were used for clar­ity: ma­genta for the roots, or­ange for the tip and lastly for the blend be­tween the two the Point Color that was di­rectly painted on the Taran­tula mesh. In­side the Hair­gen ob­ject, create an At­tribute Re­name (set from Cd to root­d­if­fuse­c­olor) and a new At­tribute Create node (set name to tipdif­fuse­c­olor and size to 3 – the first three val­ues at the bot­tom of the pa­ram­e­ter box will de­ter­mine what colour the tip of the hair will be). Both At­tribute Re­name and Create plug into the sec­ond and third in­put of a point at­tribute wran­gle re­spec­tively. 11

Mask sin­gle hairs The Guide Mask node is very help­ful to drive the mask with var­i­ous types of noise, hair length or even sin­gle out ran­domly scat­tered strands. The abil­ity to group them al­lows you to make them be af­fected by var­i­ous Guide Pro­cesses such as Frizz, Clump­ing or even by Color. For the ab­domen a length mask was used to group the long­est hairs. 12

Depth pass On the Ex­tra Im­age Planes tab on your Mantra ROP, you can create a new im­age plane by click­ing the plus but­ton and set­ting the VEX Vari­able to Pz. The sam­ple fil­ter Clos­est to Sur­face and pixel fil­ter set to Ob­ject With Most Cov­er­age proved to ren­der a re­li­able and ar­ti­fact-free Depth pass.

To man­age faster ren­der­ing speed, it’s al­ways best to cache out the VDB vol­umes be­fore­hand













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