# 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))\` ![](https://2289002225-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-Lgx0HTP5iKvQQwXUStq%2F-MY-U-zqTtN_w5Eoobdt%2F-MY-vJ1pLS80lPgzo8GQ%2Fimage.png?alt=media\&token=5dd935ec-72cd-4484-b646-1a839835624a) ### **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