Houdini learning

Houdini learning

Center Pivot

// In Pivot Translate in a Transform node

centroid(0,0)
centroid(0,1)
centroid(0,2)

Delete by Connectivity attribute

// In a Delete node, in Group (by example)

@class=7777

Increase Volume Density

// In a volumewrangle

@density *= 10;

Substract any VDB by another VDB

// In a volumewrangle

if (volumesample(1,"surface",@P)<0)@density=0;

//inverse:

if (volumesample(1,"surface",@P)>0)@density=0;

Get bound & centroid

// In a null object

bbox(opinputpath('.',0),D_XSIZE)
bbox(opinputpath('.',0),D_YSIZE)
bbox(opinputpath('.',0),D_ZSIZE)

centroid(opinputpath('.',0),D_X)
centroid(opinputpath('.',0),D_Y)
centroid(opinputpath('.',0),D_Z)

UVs

// In this order : uvautoseam - uvflatten - uvlayout
In uvflatten : Seams = seams

Kill emission on a smoke source after frame 300

if (@Frame>300) @density = 0;

Attribfrommap - Use UDIMs images

// Replace 1001 by <UDIM> and check UDIM Filename Expansion

Attribwrangle - Udim number on primitives attributes

// In a wrangle set on Primitives
vector uv = primuv(0, "uv", @primnum, set(0.5, 0.5, 0));
i@udim = 1001 + int(uv.x) + int(uv.y)*10;

Place at World center, scale et re-transform for export

// In a transform translates
-centroid(0,0) -centroid(0,1) -centroid(0,2)
// In a transform Uniform scale
(bbox("/obj/neigeSol/timeshift1/", D_ZSIZE))/(bbox("/obj/neigeSol/transform_centerWorld/", D_ZSIZE))

// At end, in a transform Uniform scale
1/((bbox("/obj/neigeSol/timeshift1/", D_ZSIZE))/(bbox("/obj/neigeSol/transform_centerWorld/", D_ZSIZE)))

Misc Attr Wrangle expressions

// Delete by color
if (@Cd.x<chf("seuilColor"))removepoint(0,@ptnum);

// Set random pscale
@pscale = fit01(pow(rand(@ptnum), ch("power")), ch("pscale_min"), ch("pscale_max"));

// Udim attr for each Udim
vector uv = primuv(0, "uv", @primnum, set(0.5, 0.5, 0));
i@udim = 1001 + int(uv.x) + int(uv.y)*10;
// Next, with a Delete SOP: Group: @udim=$F - Pattern mode !*

// Set pscale Min/Max
@pscale = fit01(pow(rand(@ptnum), ch("power")), ch("pscale_min"), ch("pscale_max"));

// Remove small parts - In a Foreach connected piece loop
@size = (getbbox_size(0).x+getbbox_size(0).y+getbbox_size(0).z);

if(@size < chf("taille"))
removepoint(geoself(), @ptnum);

// Set @variant integer for Copytopoints (change objects number)
i@variant =floor(rand(@id)*3);

//// Get position difference between two objects, and match animation
// On Rest pose object:
v@fixe = 0;
@fixe.x = getbbox_center(0).x;
@fixe.y = getbbox_center(0).y;
@fixe.z = getbbox_center(0).z;
// On animated object:
v@anim = 0;
@anim.x = getbbox_center(0).x;
@anim.y = getbbox_center(0).y;
@anim.z = getbbox_center(0).z;
// After two previous AttrWrangles:
v@anim_offset = point(0, 'fixe', 1) - point(1, 'anim', 1);
// To match animation:
@P = point(0, "P", @ptnum) + point(1, 'anim_offset', 1);

//// Blend shape through a mask attribute - Posted by Cudarsjanis on Odforce
// Geo with mask attribute in first input, blend shape in second
v@P=lerp(v@P, point(1,'P',@ptnum), f@mask*ch('blend'));

//// Set a fixed normal attribute
v@z = set(0,1,0);

//// Place at world center
v@P -= getbbox_center(0);

Delete small pieces

// As seen on Sidefx forum, posted by paulboiii
// First create a measure SOP, set to per piece

// Then, in an attribwrangle set on primitives
float threshold = chf("Size_Threshold");
if ( f@area < threshold ) removeprim(0,@primnum,1);

Attribute Wrangle - Copy attribute from second input

// With same number of points on both inputs - From Bonsak on Sidefx.com

// Copy P from second input
@P = v@opinput1_P;

Bounding-box - Position Reference color

// As seen on https://houdinihelp.ru/ref/expression_cookbook.html

// In an attribwrangle set on primitives
@Cd.r = relbbox(0,@P).x;
@Cd.g = relbbox(0,@P).y;
@Cd.b = relbbox(0,@P).z;

Group by uv.y

// Thanks to https://vfxbrain.wordpress.com/2019/06/14/vex-snippets-2/

// In an attribwrangle set on points
if(@uv.y<chf("seuil")) @group_base = 1;

Specify attribute value for one point

if (@ptnum == 322) f@mask=1;