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< Wiki Index

Houdini

⭐ I also have saved some useful snippets as gists

Third party Tools

A rough list of some free, some paid, useful HDAs and tool sets

Other blogs/tutorials

Misc

Rescale camera

For example a camera from Maya needs to be rescaled from meters to cm for houdini This could have adverse effects, in mantra for example (maybe no longer) scaling the actual camera object by 0.01 the exposure is also scaled, so instead you can just fetch and blend

image

Sequence offset from frame 1 to 1001

padzero(4, $F4-1000)

Get max attribute

A good way (showed to me by Mark J) to get the maximum value of a specific attribute is to use attribute promote SOP and promote to detail based on maximum

image

Attach to deforming geo

Use extract transform and transform pieces SOPs to 'stick' additional geometry to somewhere on a deforming geo. The setup can be confusing but it works like this:

Extract Transform wants:

  • input 1: rest point
  • input 2: deformed/animated point

Transform Pieces wants:

  • input 1: geo to deform IN situ of rest point
  • input 2: extracted transform point

image

Rotate camera 360 in 100 frames

as an expression

fit(@Frame, 1001, 1101, 0, 360)

Frame Sequence translate from frame 1 to 1001

In camera background for example

$JOB/MySequence.`padzero(4, $F4-1000)`.jpg

Rigging

Just watch these Sidefx tutorials by Michael Goldfarb

✔️ Watch on youtube instead of vimeo, better player, supports resuming.

HDAs

The SideFX rigging tutorials have lots of useful tips on how to create, and manage HDAs

Turn on asset definitions toolbar

assettoolbar

Turning on the asset definitions toolbar is useful for to see the version of a HDA in your scene (toolbar appears at top of parameters window) Assets Toolbar > Asset Manager... > Configuration tab > Asset Bar switch dropdown menu to 'Display Menu of All Definitions' Enable asset bar to show versions

Param Callbacks

This is detailed in the help, but briefly:

  • On a param's 'Callback Script' setting, add callback code like
hou.pwd().hm().my_function(kwargs)
  • Then in the scripts tab, add a PythonModule
  • Then add the function with kwargs argument
    • If the param was a menu for example, script_value0 returns the item selected in the dropdown
def my_function(kwargs):
    this_node = kwargs['node']
    selection_value = kwargs['script_value0']

Script action

If there is a cog button to press such as this example from the deadline submitter node, you can acccess the python module in the HDA like this: image

It's useful to pass kwargs along too

kwargs['node'].hdaModule().myfunction(kwargs)

Set HDA node look and settings

To set a HDA's initial look, add a OnCreated python script in scripts tab. The following code sets the shape as 'clipped_left' and to some blueish colour.

kwargs['node'].setUserData('nodeshape', 'clipped_left')
kwargs['node'].setColor(hou.Color(0.175, 0.3, 0.35))

If it is a material, it is useful to set the material flag

kwargs['node'].setMaterialFlag(True)

Camera

Set focus from object (null), this expression gets distance between origins of two objects

vlength(vtorigin(".","../focus"))

Retopo

Cloth

Python

Print a list of all materials attributes assigned on a selected node. Made this as I wanted a list to be able to pick materials to override in a redshift proxy!

for n in hou.selectedNodes():
    g = n.geometry()
    a = g.findPrimAttrib('shop_materialpath')
    
    materials = a.strings()
     
    for m in materials:
        print(m)

Check if in UI mode, ie. disable popups or enable things only when rendering

hou.isUIAvailable()

Create null objects from transform SOPs. This can be useful to re-create transforms at object level instead of 'deforming' geometry which is much heavier.

def nulls_from_x():
    for node in hou.selectedNodes():
        print(node.name())
        t = node.parmTuple('t').eval()
        r = node.parmTuple('r').eval()
        s = node.parmTuple('s').eval()
        scale = node.parm('scale').eval()

        new_null = hou.node('obj/').createNode('null')
        new_null.parmTuple('t').set(t)
        new_null.parmTuple('r').set(r)
        new_null.parmTuple('s').set(s)
        new_null.parm('scale').set(scale)

VEX

General useful vex wrangle examples

// get nearest point index of second input
int np = nearpoint(1, @P);

// get that point's position
vector np_pos = point(1, 'P', np);

// measure distance
float dist = distance(@P, np_pos);

// normalise distance
dist = fit(dist, ch('in_min'), ch('in_max'), ch('out_min'), ch('out_max'));

// remap with ramp
dist = chramp('remap', dist);

// set attribute
f@dist = dist;

get centroid

// get centroid
vector min, max;
getbbox(min, max);
vector centroid = (min+max)/2;

Create random direction vector in cone

vector axis = {0, 1, 0};
vector2 u = rand(@class);
vector direction = sample_direction_cone(axis, radians(ch("angle")), u);

Add point on each prim

On a prim wrangle!

addpoint(0, @P);
removeprim(0, @primnum, 1);

image

Rotate packed prims

image

int posprim;
vector param_uv;
float maxdist = 1;
float dist = xyzdist(1, @P, posprim, param_uv, maxdist);

// if you needed to store the position / primuv
i@posprim = posprim;
v@param_uv = param_uv;

float dist_ramped = chramp('distance', dist);

// create angle from dist ramp
float angle = chf('angle') * dist_ramped;

// get current packed transform
matrix packed_transform = getpackedtransform(0, @primnum);

// matrix to transform by
matrix transform = ident();
rotate(transform, radians(angle), normalize(chv('axis')));

// set transform
setpackedtransform(0, @primnum, transform * packed_transform);

Rotate packed prims 2 (test)

Based on [[http://www.tokeru.com/cgwiki/?title=Houdini#Transform_packed_prims_with_instance_attributes|cgwiki]]! in a primitive wrangle sop

// instead of creating a new transform, use the current one
//matrix3 m = ident();
matrix3 m = primintrinsic(0, "transform", @primnum);

float angle = @Time*10;

// rotate around up
vector axis = {0,1,0};
// vector axis = primintrinsic(0, "transform", @primnum);

// rotate
rotate(m, angle, axis);

// set the attribute
setprimintrinsic(0, "transform", @primnum, m);

Redshift

Not well documented, how to enable console log

# Toggle Redshift console log
hou.hscript("Redshift_setLogLevel -L 5")

# Set log level
hou.hscript("Redshift_switchConsoleLog")

RBD

Cache points only

Useful big save on caching to disk is just saving the points from a RBD solver. But this often doesn't work how you would expect.

This example works, had problems with using the rbd input or configure geo, but the first frame of the solver works fine - inside the rbd solver SOP it is actually using transform pieces for the first output... image