Top Tricks for Houdini 17

Dis­cover how to up­grade your phys­i­cal sim­u­la­tions with the lat­est re­lease from sidefx

3D Artist - - CONTENTS -

Bril­liant tech­niques for mas­ter­ing the lat­est ver­sion of Sidefx’s soft­ware

Ban­shee, the lat­est ver­sion of Houdini from Sidefx, may just be the most pow­er­ful re­lease of the phys­i­cal sim­u­la­tion tool yet. New to Houdini 17 are a host of key fea­tures in­clud­ing a new Vel­lum multi-solver for cre­at­ing fast cloth, as well as hair, soft bod­ies and grains. Ma­te­rial-based de­struc­tion tools also make it sim­pler to set up de­struc­tion and art di­rect too. Other new tools like Soft Con­straints, Con­vex De­com­po­si­tion will help pre­frac­ture ma­te­ri­als in­clud­ing con­crete, glass and wood while build­ing con­straint net­works au­to­mat­i­cally to tie ev­ery­thing to­gether. An­other ad­di­tion is that of new UV tools which au­to­mat­i­cally seam and pro­vide ac­cu­rate flat­ten­ing, al­low­ing for a fully pro­ce­dural work­flow.

The White­wa­ter Solver is also now more or­ganic, re­al­is­tic and foamy with an ac­cu­rate re­la­tion­ship to the source FLIP sim­u­la­tion. Ter­rain now also in­cludes up­dated, ad­vanced ero­sion tools that pro­vide more con­trol over de­tails such as flu­vial lines, river banks and de­bris. Hi­er­ar­chi­cal Scat­ter­ing now makes place­ment of el­e­ments more ef­fi­cient, too.

Other fea­tures in­clude Re­time SOP for stretch­ing or slow­ing sim­u­lated data with ef­fec­tive interpolation and blend op­tions to cre­ate clean and re­al­is­tic re­sults, a Poly­draw tool for in­ter­ac­tive mod­el­ling, a new an­i­ma­tor friendly time­line for char­ac­ter an­i­ma­tion and a new GITF im­porter and ex­porter (based on feed­back from the gamedev com­mu­nity), a 3ds Max plugin, a Unity v2.0 plugin and im­prove­ments to the Maya and Un­real En­gine 4 plug­ins. So what are you wait­ing for? Dive in to Houdini 17 Ban­shee now!

VEL­LUM SUBSTEPS VS CON­STRAINT IT­ER­A­TIONS

Each Sub­step runs a given num­ber of Con­straint It­er­a­tions. A quick way to gauge how many are needed per step is to make a rough es­ti­mate of how many edges ex­ist across the ge­om­e­try. For fast mov­ing cloth and col­li­sions, in­creased Substeps would be best. For all else, in­creased Con­straint It­er­a­tions would be cheaper. Sara Abril rascón Espinoza

PAN­ELLING SHIRT

The main shape con­sists of sep­a­rate curves that were fused, so each seg­ment can be grouped and re­sam­pled in­de­pen­dently. Pla­nar Patch from Curves con­verts the sil­hou­ette into a tri­an­gu­lated mesh. An­other curve can be placed in­side the sil­hou­ette to ‘guide’ the topol­ogy flow or cre­ate straight lines in­side the gen­er­ated mesh. Sara Abril rascón Espinoza

LONG HAIR

Self Col­li­sions can be dis­abled for op­ti­mi­sa­tion and Glue can be used in its place. This cre­ates a net­work of con­straints on the guide’s points that prop­a­gates to nearby curves, mim­ick­ing clump­ing. Hairs can de­tach by en­abling Break­ing. On the solver, each Glue con­straint’s stress ra­tio can be vi­su­alised, which is help­ful to see! Sara Abril rascón Espinoza

SHORT HAIR

To pre­vent hair fall­ing flat against the scalp and los­ing vol­ume, a ramp can be used through a wran­gle to cre­ate a soft falloff, con­trol­ling bend stiff­ness from root to tip. An­other ramp was used to drive Glue and At­tach to Ge­om­e­try con­straints, so that roots hold shape with­out stiff­en­ing the tips. Sara Abril rascón Espinoza

MA­TE­RIAL-BASED FRAC­TUR­ING RIGID BODY PAINT NODE

The Rigid Body Paint Node stores the val­ues of the painted ar­eas by cre­at­ing its own float at­tribute, which can be later trans­ferred to the RBD Ma­te­rial Frac­ture SOP to cre­ate scat­ter points. Ar­eas with dense paint will frag­ment into more pieces.

Ad­di­tion­ally, us­ing this (vs Paint SOP) will al­low you to keep the painted ar­eas even if you change the res­o­lu­tion of the ge­om­e­try. Sun­deep Mukala

SOFT CON­STRAINT

In a de­fault soft con­straint setup, you have stiff­ness and damp­ing ra­tio. When the con­straint’s an­gle is higher than the given

de­gree (an­gle) value, the con­straints switch and tend to break .hav­ing more res­o­lu­tion to the frac­ture re­sults in more flex­i­bil­ity, such as with bend­ing for ex­am­ple. Sun­deep Mukala

UVS UV AUTOSEAM

UV Autoseam will try to find the op­ti­mal seams on your mesh, based on cur­va­ture. You can then plug the re­sult­ing seam se­lec­tion into a UV Flat­ten to un­wrap and start lay­ing our your UVS. Fianna Wong

UV FLAT­TEN

In ad­di­tion to un­wrap­ping UVS, you can fur­ther edit UV is­lands by us­ing Straighten Edge Loops (for ex­am­ple, on a leather belt) or Rec­tify Groups of Quads (to force as much as pos­si­ble, a uni­form un­wrap of any UV is­land into an evenly scaled and straight­ened quad-filled UV is­land (eg bricks). Fianna Wong

UV LAY­OUT (PACK­ING)

You can now spec­ify ro­ta­tion in­cre­ments for your UV is­land ro­ta­tion it­er­a­tions, and even newer, you can pack UVS to be even tighter by us­ing Stack Iden­ti­cal Is­lands (over­laps same UV is­lands) and if your mesh has sym­me­try, use Match Mir­rored Is­lands for max­i­mum cram (flips and over­laps same UV is­lands). Fianna Wong

UV LAY­OUT (UDIMS)

In­ter­ac­tively as­sign and cre­ate your UDIM tiles by se­lect­ing any UV is­land and typ­ing in the de­sired UDIM tile. Use the over­rides for scal­ing and off­set to pri­ori­tise which UDIM tile or UV is­land re­quires big­ger real es­tate (tex­ture res­o­lu­tion). This is non­de­struc­tive, so ad­just freely as needed. Fianna Wong

WHITE­WA­TER WHITE­WA­TER SOLVER

With the new White­wa­ter Solver, there are a lot of new at­tributes which are very dif­fer­ent from the old solver. Test­ing th­ese new at­tributes on wedge tests is the best way to learn how they work to­gether or by them­selves. Test­ing the same setup on dif­fer­ent scenes is also im­por­tant, be­cause you can see how they work and whether you have the same re­sult or other­wise. igor Zanic

RUN­NING FASTER

Us­ing Opencl can re­ally speed up the sim­u­la­tion times, but due to me­mory lim­i­ta­tion on our GPU, the sim can crash or be­come un­sta­ble. You can run the sim on a smaller re­gion and get re­sults faster than just run­ning the fi­nal sim with­out Opencl. With the new

White­wa­ter Solver, you can get a more nat­u­ral look than be­fore. igor Zanic

SAV­ING TIME

One good thing with the new White­wa­ter Solver is that the re­sult is al­most the same if you were to use low, mid or high res sim­u­la­tion, due to re­pel­lent and stiff­ness at­tributes. So you can re­ally save on main sim times if you have dif­fer­ent an­gles of your cam­era, but you need to main­tain the same foam look. igor Zanic

TER­RAINS HEIGHTFIELD ERODE

Hav­ing tons of con­trols on ero­sion can al­low you to art di­rect the shape of your ter­rain very eas­ily. The ter­rain gen­er­a­tion work­flow in Houdini in­volves start­ing on a low-res­o­lu­tion Heightfield where the ero­sion gives you strong and deep re­sults, which will help you to block out the shape you de­sire. Then, slowly in­crease the res­o­lu­tion with each ero­sion pass to get the fine de­tails that can be seen in real-life ter­rain. Fine de­tails are added later in High Res Ero­sion Passes. ra­jen­dra Khi­rod­kar

HEIGHTFIELD DIS­TORT

We have two dis­tor­tion nodes in Houdini 17: HF Dis­tort By Noise and HF Dis­tort By Layer. Dis­tort by Layer, newly added in Houdini 17, gives you con­trol over warp­ing and dis­tort­ing fea­tures along a vec­tor field. Use the Swirl Mode to sharpen or smooth out the top edges of your ter­rain. Us­ing Dis­tort by Layer just be­fore a High-res Ero­sion will give a very nat­u­ral feath­er­ing to the ero­sion. Dis­tort by Noise gives nat­u­ral re­sults when ap­plied at the very end, usu­ally af­ter the last Ero­sion node on the high­est res­o­lu­tion Heightfield. ra­jen­dra Khi­rod­kar

CHAR­AC­TER IN­TER­AC­TIVE FOLDER TABS

Cmd/ctrl+right-click­ing on a folder tab re­veals a num­ber of ac­tions avail­able to af­fect all chan­nels con­tained within the folder. This makes it easy to per­form com­mon op­er­a­tions on col­lected chan­nels all at once. Cmd/ Ctrl+right-click on a folder tab to: set keyframes on all chan­nels in the folder, cre­ate a chan­nel group from the folder con­tents, and copy and paste chan­nel val­ues. John Mariella

DRIVE BLENDSHAPES WITH POSE SPACE DEFORMATION

You can drive Blendshapes au­to­mat­i­cally by pos­ing your char­ac­ter and sculpt­ing the shapes your char­ac­ter should de­form into when­ever your skele­ton ap­proaches the pose joint an­gles. John Mariella

GITF IN HOUDINI EN­GINE HOUDINI 17 AND GITF

GITF (GL Trans­mis­sion For­mat) is a Json­based open-stan­dard file for­mat for 3D scenes and mod­els. Given its grow­ing pop­u­lar­ity, es­pe­cially in game de­vel­op­ment and in real-time game en­gines, sup­port for both im­port­ing GITF files and ex­port­ing ge­om­e­try in GITF 2.0 for­mat was added to Houdini 17. See­lan Va­math­eva

IM­PORT AND EX­PORT­ING GITF

The Houdini GITF im­porter al­lows for load­ing in scenes with trans­form hi­er­ar­chy or in­di­vid­ual ob­jects, along with their ma­te­ri­als us­ing Prin­ci­pled Shaders and Tex­tures. Sim­i­larly, the GITF ex­porter can ex­port scenes or in­di­vid­ual ob­jects with their ma­te­ri­als and tex­tures. See­lan Va­math­eva

MOD­EL­LING POLY­DRAW

Poly­draw al­lows you to free-hand draw poly­gons in an empty scene. This is use­ful when you need to trace base shapes us­ing blue­prints in or­tho­graphic views.

Within Poly­draw are ad­di­tional tools that al­low you to straighten in­sert edge-loops, split edge, slide along edge, smooth-re­lax, brush move, make cir­cle and more. Fianna Wong

CON­STRUC­TION PLANES

You can quickly set Con­struc­tion Planes to an edge or face, so that you can spec­ify the ori­en­ta­tion and place­ment of ge­om­e­try to align and con­tinue build­ing upon. You can also book­mark up to four dif­fer­ent con­struc­tion planes, to save and jump be­tween, when mod­el­ling. Fianna Wong

RE­TIME SET YOUR RANGE

You have the op­tion of ma­nip­u­lat­ing your an­i­ma­tion by Frame, Time, Speed, Shift Range and Fit Range. Use pre- and post-cy­cle op­tions to loop an­i­ma­tion cy­cles and zigzag if the cy­cle isn’t fully synced. Us­ing the Speed op­tion is a good start­ing point for cre­at­ing fast or slow-mo­tion shots. Liam Hoyle

SET THE INTERPOLATION (SMOOTH­NESS BE­TWEEN FRAMES)

Th­ese pa­ram­e­ters al­low you to con­trol the blend­ing be­tween frames (lin­ear, cu­bic or sub­di­vi­sion) and works best when tack­ling pyro and fluid sim­u­la­tions. To avoid un­wanted pul­sat­ing, and to av­er­age arte­facts be­tween frames, make sure to use the re­sult­ing re­timed and in­ter­po­lated field from the tool. Liam Hoyle

Lion made us­ing Houdini 17

Vel­lum – long hair

UVS – UV Lay

Ma­te­rial-based frac­tur­ing – soft con­straints

Mod­el­ling – align com­po­nents

re­time sop

Ter­rains – Height­fields

Mod­el­ling chan­nels in the view­port

gitf – im­port and Ex­port­ing gitf

Ter­rain – high-res ero­sion pass

char­ac­ter – in­ter­ac­tive folder tabs

Ter­rains – with dis­tort by noise

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