# Techniques ## Readings * ## Transferring attributes * Using `attribtransfer` eg. P, Cd * Using Pointwrangle Get attributes from second input in wrangle node \[[src](https://www.sidefx.com/forum/topic/54084/)] 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](https://www.deborahrfowler.com/HoudiniResources/Overview-Looping.html), 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 * ### 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))\` ![](/files/-MY-vJ1pLS80lPgzo8GQ) ### **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 pack**ed** geo * add `unpack` ## Texturing ### Random color ovveride ```c // rand bw color rand(@ptnum), rand(@ptnum), rand(@ptnum) // rand RGB rand(@ptnum) , rand(@ptnum+25), rand(@ptnum+10) ``` ## Multi-image texturing * [Texture Override](https://www.deborahrfowler.com/HoudiniResources/HoudiniTipsAndTricksRender.html), Deborah Fowler * [Light Instancing](https://www.deborahrfowler.com/HoudiniResources/Lights-Instanced.html), 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 Ove`r`rides` 1. Parameter: **basecolor\_texture** 2. Use any of these expressions: ```c // 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/](https://forums.odforce.net/topic/29212-texture-on-copy-based-on-luminance-value/?do=findComment\&comment=165461) ## Texturing & UV ### Best practice for assigning materials * Texturing prim faces with the same image using groups: * polygon sop > `uvproject` * `uvquickshade` ## Recursive subdivision Space partitioning algorithm ### Tutorials: * [Loops & VEX: Artistic Quadtrees](https://youtu.be/uN8Kxxvpkzc), Entagma * [Spiral Pattern Generation Tutorial - Houdini + Cinema4D](https://www.youtube.com/watch?v=ZHgzif3iIzY), Roman Pillai ## Unsorted VEX notes ### Torus wrangle node example ```c // 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 ```c if(@P.x>ch('threshold') + .5 * (noise(@P * 5)* 2 - 1)){ removepoints(@ptnum) } ``` * Sphere > Scatter > delete by threshold for pos.x * particlefluid surace --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.nosleepcreative.com/dev/archive/vex/techniques.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.