Techniques

Proceduralism

Readings

• https://www.deborahrfowler.com/HoudiniResources/HoudiniOverview.html

Transferring attributes

• Using attribtransfer eg. P, Cd

• Using Pointwrangle Get attributes from second input in wrangle node [src]

If you want to get an attribute (lets say color) from a specific point number (lets say 123456) from input 2, you can use

@Cd = point(1, 'Cd', 123456);

If you have the same number of points on both inputs and you want to get an attribute from the corresponding point on input 2 you can use this shortcut

@Cd = v@opinput1_Cd;

Where the number 1 describes the input port.

Ah, you want the number of points on input 1?

@number_of_points_on_input_1 = npoints(1)

Copy stamping & Looping

• Looping, Deborah Fowler

There are three ways of manipulating and copying points

1. Copy Stamp with Expressions - good for quick prototyping

2. Copy to Points with a SOP eg. circle

3. Copy to Points with pointwrangle and VEX

Point generation

1. Using VEX

2. Using line to create points > point to change the position eg. Creating circle of points

Orient objects or profiles to a curve

Using polyframe

Instancing = packed geo & copypoints

Tutorials

• https://vimeo.com/207724703

Lights

• Instance - similar to copytopoints to grid

  • Select Instance object

  • Place points or geo inside network

  • Point Instancing: Fast-point for geometry, full point instancing for lights

Random geometries

• Pros: faster processing and work with render engines

• Reveal instance in viewport via Display Opetion > Geometry > Instancing

1. create mmultiple objects: demo1, demo2, demo3

2. attribcreate -

   1. string , name: "instance", String: /obj/demo1

   2. /obj/demo`round(fit01(rand(@ptnum),1,2))`

Random geometry with copytoPoints

• Attach an attribute called "variant" to each geometry

1. geometry eg. object_merge > pointWrangle - i@variant =1;

Generating a random integer value for each point

• grid> attribrandomize - scale > point wrangle

int(rint@variant = fit01(rand(@ptnum),0,2));

• Retrieve the random variable values by listing "variant" in the Piece Attrbute from copytopoints

• transform using target point orientation

• Setting the object to faceup: pointwrangle: @N = {1,0,0};

Unpacking

• Arnold renderer does not accept packed geo

• add unpack

Texturing

Random color ovveride

// rand bw color
rand(@ptnum), rand(@ptnum), rand(@ptnum)
// rand RGB
rand(@ptnum) , rand(@ptnum+25), rand(@ptnum+10)

Multi-image texturing

• Texture Override, Deborah Fowler
• Light Instancing, Deborah Fowler

Using copy stamp and expressions

Prerequisite: You must use an image sequence; eg. all files are named: image_04.jpg

1. Assign a material SOP and input a principle shader to target object

2. Activate Overrides use Local overrides and merge Overrides

   1. Parameter: basecolor_texture

   2. Use any of these expressions:

// using frame number
$HIP/textures/image_$F2.png

// random image from concatenating strings
$HIP/textures/image_`padzero(2,ceil(fit01(rand(@ptnum),0,7)))`.png
$HIP/tex/`image_floor(fit01(rand(@primnum),0,90))`.png

// Use all of your sequence frames: 
$HIP/tex/`image_@primnum%90`.jpg

• 90 is an arbituary value ; you can use your total image sequence frames

• the backticks ` allows use to add an expression into the string

• This technique is similar to copyStamp; we are referencing primnumber and adding an different image for each.

Texture override

CopyPacked geo

• grid with uvproject1

• expression in material node (point attrib)

CopyUnpacked

• stamp input

• material

Method: based on frame number

1. copy stamp

2. material

   1. parameter: basecolor_texture

   2. type: string value

3. String value:

Based on UV

Pros: good for seamless tiling eg. brick tesselattion

1. grid > uvproject > group > material

Based on luminance value

• https://forums.odforce.net/topic/29212-texture-on-copy-based-on-luminance-value/

Texturing & UV

Best practice for assigning materials

• Texturing prim faces with the same image using groups: https://www.deborahrfowler.com/HoudiniResources/Overview-UVs.html
• polygon sop > uvproject

  • uvquickshade

Recursive subdivision

Space partitioning algorithm

Tutorials:

• Loops & VEX: Artistic Quadtrees, Entagma
• Spiral Pattern Generation Tutorial - Houdini + Cinema4D, Roman Pillai

Unsorted VEX notes

Torus wrangle node example

// bbox equivalent 
@Cd.r = relbbox(0,@P).x;
@Cd.g = relbbox(0,@P).y;
@Cd.b = relbbox(0,@P).z;

• Using facet to make unique points;

Simulating bubble popping with scatter

if(@P.x>ch('threshold') + .5 * (noise(@P * 5)* 2 - 1)){
    removepoints(@ptnum)
}

• Sphere > Scatter > delete by threshold for pos.x

• particlefluid surace