Procedural Fence Asset in Houdini

May 20, 2019

Houdini Procedural Fence Asset

Vimeo - Intro to Procedural Modeling in Houdini: Making a Fence Asset

By: trzanko

Notes: Projecting Curve down onto surface - make sure curve is entirely above surface first - done by transforming this up in y an amount equal to the bounding box of the terrain - can use Ray node - used wrangle - VEXpression to project curve onto terrain: vector rayd = {0, -100, 0}; vector hitP, hitUVW; int hitPrim = intersect(1, @P, rayd, hitP, hitUVW); @P = hitP; - this has every point fire a ray downward and determines where this ray intersects the terrain, and then sets that point's position to the intersection point Create Orthos - used a Polyframe node - turned off the Normal Name and reassigned the Tangent Name to "N" - this made all the point normals basically follow allong the curve - use VEXpression to direct normal vectors - used wrangle: - VEXpression: vector up = {0, 1, 0}; v@side = normalize(cross(up, @N)); v@up = normalize(cross(@N, v@side)); - Seeing as this did two cross products in a row, I this sets v@side directly perpendicular to the curve (in plane) then v@up creates a vector perpendicular to all of this, including the plane (so this creates a vector that is up from the line) Created the Posts - simple boxes where we polyextruded the top with a bit of an inset Copy Posts to Terrain - Used simple copyToPoints with our post and points along the terrain - this placed their centers at the curve location however, so they were buried half way underground - to fix this, we added another attribute wrangle before the copyToPoints where we moved the points along their v@up vector a distance equal to half of an offsetDistance - the offsetDistance channel then referenced the box sizey so it was always half of the height of the box - this positioned the posts directly onto the surface Starting Fence Links Simple Spread - Made 3 new copies of our offsetDistance wrangle node - the general offset to center the posts went into the first copy - this copy offset was used for the link locations - this copy then went into both of the remaining offset copies - one of these final offset copies had an inverse relative reference to the other's offset - these were merged - this merge with the combined offsets created a spread, where changing the offset of the one offset corresponded to a reverse offset of the other Creating Separate Staggered Lines - put all of the points of the link lines into a group called cut - used polycut node to turn all of these small line segments between the points into individual prims - used an attribute wrangle with modulus 2 function to basically remove every other primitive - we then used a copy of this setup but with the opposite modulus (when equal to 1 instead of 0) to delete the opposite segments - these were then combined with an offset to give an overall controllable pair of segment groups - this entire setup was then copied to create a second set of links all together Parameterization - Using the offset attribute wrangle we created in several different locations lets us control several dimensions of the fence links - overall distance of links from the ground - distance between the two sets of links - spread distance within a link set itself Creating Links - used a small grid as the base object - used Sweep node to place these all along the link points - used a Polyfill (the polycap they used must be deprecated) to fill in the ends of the links Extra Polish - to make the fence links feel less identical, they added a varied horizontal offset to them - this was done by using another copy of the offset wrangle created, but changing the v@up to v@side - they then added a dir (direction) vector, which used another mod 2 function, but fit the result between -1 and 1 - this was also applied to the offset, so the links would alternate offset directions with each link