# Houdini polyline

If you're coming from a Maya background, you might wonder what the fuss is about. You might be extra puzzled when people talk about points vs primitives prims for shortand even more puzzled when verticies verts are thrown into discussion too. What's the deal? Nearly everything in Houdini directly assumes you're working with points, just think in those terms, everything should work.

A point in Houdini is close to the mathematical definition of a point; it's a location in space, with no associated area or dimension or connectivity. At it's most basic, a point will store its position P. If you're coming from Maya, a point is equivalent to a particle; a standalone position in space. Unlike maya, which keeps particles hidden inside a particleShape node, Houdini treats points as first class citizens.

Furthermore, a point can and often will store extra attributes, like colour and velocity, and even some attributes that don't make sense in a mathematical context, like normal and scale.

How can a dimensionless point have a normal? Or area? The answer is that while a Houdini point derives from a mathematical point, we're not mathematicians damnit, we can do whatever the hell we want!

For example, you have points representing a spray of water, and you want to render them. In a mathematically pure sense of a point, this makes no sense, they're infinitely small, invisible things.

**MCVersus Vista (Houdini-Clarisse-Terragen) - Procedural modeling**

For Houdini and Mantra, they treat points as spheres with a radius of 0. If you have a pscale attribute, it uses that as a radius instead. If you have v, it will use that as a velocity vector, Cd for colour etc Again relating back to maya, the particle comparison holds true.

Yes particles are infinitely small, unless you have scalePP, and a dimensionless point can't possibly have colour, unless of course you've defined rgbPP, etc There's many ways to create a point or points. The add sop is probably the easiest way, tick the toggle next to the first field, and there you go, a point:. The add sop can also be used to convert any poly, nurbs or curve back into points, by using the 'delete geometry but keep the points' toggle:.

Some of the basic geometry sops box, and grid for example have an option to make points directly. For the others, just use the add 'delete geometry but keep the points' trick. Other sops that make unconnected points are scattergenerate pointspoints from volumeand probably several others I'm yet to discover Maya folk usually bristle at all this, wondering what's wrong with vertices, isn't this all semantics?

The answer is that by ensuring most of Houdini's tools are compatible with points, it means you're guaranteed everything works with everything. Maya has many low-level components vertices, curve cv's, particles, lattice points, cluster handles, subdiv points etcbut that means that a tool designed to work with verts may not work with curve cvs or particles. In Houdini, if its a point, it can be manipulated as a point, regardless of how it was created. To setup one of these sails, they have 4 hooks and some stretchy material.

They take the material and attach it to each hook, forming a large flat shape:. While those guys might call all those things 'pole-top', 'sail corner, 'sail', here's where this too-long analogy kicks back into houdini land, and you gasp in delight:. Note that while the outer corners have a 1-to-1 relationship 1 point controls 1 vertexthe inner points 1 and 4 each control 2 vertices.

Once this relationship of points-to-verts-to-prims is setup, wherever the points move, the verts and prims of course move too. It follows then that while you'll frequently manipulate points, and you'll occasionally work with prims in the sailcloth analogy, you might paint one red and one blueyou rarely work directly with vertices. Their main purpose is to bind prims to points, once that is done, you can mostly ignore them.Did you ever wonder how to create polygons and polylines through code in Houdini.

But you have to know some things about the way Houdini organizes and stores geometry in memory. In this tutorial Manuel will walk you through the process of creating geometry with VEX in a wrangle.

Restify exampleUpdate from Vimeo by Zybrand Jacobs: Great tutorials guys! Its probably worth adding that you are creating 2 overlapping primitives between near points. That should half the primitives but still look the same. Hello, thank you very much for your lessons! Could you tell us in your lessons about render in Houdini? Thanks, really useful!

Is there a way to animate that building up?

Not just edges poping, but really drawing the connections? Of course. A simple hint could be to try the carve SOP on the generated geo. But before doing so you have to get rid of the duplicate connections this setup generates.

This is a little more complicated. Stuff for another tutorial…. Thank you. I mapped the uvs of the geo to the range 0 to 1 in x and used this value to drive an Octane gradient for the colors. Worked quite well. Any advice?

### CREATING GEOMETRY WITH VEX

I managed to get it to show up only after putting it through a wireframe node which makes the viewport very laggy so if there is a more efficient way of doing it I would love to know!Did you ever wonder how to create polygons and polylines through code in Houdini. But you have to know some things about the way Houdini organizes and stores geometry in memory. In this tutorial Manuel will walk you through the process of creating geometry with VEX in a wrangle. Its probably worth adding that you are creating 2 overlapping primitives between near points.

That should half the primitives but still look the same. More from Manuel Casasola Merkle. I feel like Houdini is going to the top of my list of 3D tools. Done a ton of interactive coding and 3D coding outside of the usual DCC packages, so this really speaks to me.

Muchas Gracias! Forgot your password? The basic sequence of geo creation is the following: Create the points with addpoint Create an empty primitive to later store the connectivity information Add as many vertices as you like with addvertex to the primitive Update the point references, these vertices are storing Update from Vimeo by Zybrand Jacobs: "Great tutorials guys!

Houdini Geometry VEX. If you enter anything in this field your comment will be treated as spam. Choose language.Vein growth has been pretty popular recently.

Most setups rely on rather intricate techniques such as Space Colonization. Download Project File. This method creates a lot of overlapping polylines.

Is this a side-effect of it being a clean and simple process? My exported geo ended up being several GBs. Thus the paths needed to form all the connections end up using parts of the same paths to get to the individual end points, similar in a highway network where the big cross country highways are the biggest and most frequented roads. A very simple yet not perfect technique to get rid of most of the overlaps would be to drop down a fuse SOP after the carve SOP. Really enjoying this tut!

What am I missing? You always make so fantastic renderings to teaser your tutorials. Did you make these renderings within Houdini or did you use another software? It may be a noobish an slow resolution, but for getting the lines moving trough the volume. This separates every prim.

After making some tests with the groups nodes, I still have the Warning: No start points are specified. Someone could me help with this one? This will include all the points from point 0 to point N I am trying to replicate it on an entire word but it only works on the first letter?

What am I doing wrong or what do I have to do to make it work? Thank you for amazing tutorials.Accessing geometry attributes and info. Accessing attributes on other inputs. Troubleshooting error messages. These VEX expressions run on each element point, particle, edge, primitive, voxel, depending on the node type passing through the node.

Platformio stm32 exampleThe code can read the values of node parameters and geometry attributes, and set special variables to change values in the input geometry. For performance reasons, Houdini is moving toward doing ad-hoc geometry modifications with VEX operating on attributes, rather than HScript expressions operating on local variables and external channel references. Using VEX and attributes has major performance benefits over HScript expressions and local variables. It runs faster and automatically supports threading and parallel computation.

Since technical work in Houdini often revolves around attributes, this can actually make VEX expressions a lot simpler than the equivalent HScript expressions. Passing information down the network on attributes is inherently friendlier to parallel processing than using external references on later nodes to data on earlier nodes. As users work on ever-larger and more complex geometry, threading and parallel processing become more and more important to get acceptable performance.

This simple fact is the reason why VEX will only become more widely used to replace HScript expressions for ad-hoc geometry manipulation. See the list of VEX functions.

VEX has a concept of "contexts". Some functions are only available in certain contexts for example, functions for accessing geometry information in the SOP context. In VEX, trigonometry functions such as sin and cos use radians, not degrees. Vector attributes are handled as v.

This can be unexpected, like in the force example, where you may have expected all components of the force to be randomized equally by id. Use a float cast to force it scalar. To get the internal ID of a parameter, hover over the parameter name in the parameter editor. The tooltip will show Parameter: id.Create a polygon or polyline without any points. You can then add vertices to the primitive with addvertex.

Make sure to add at least one vertex to the created primitive. You can use these numbers with setvertexattrib to set attributes on the vertices, however they may not be the final numbers of the vertices.

If the primitive was created, but any points were invalid, the corresponding vertex numbers in the array will be These signatures overwrite the primnum variable with the new primitive number instead of returning it. A handle to the geometry to write to. Currently the only valid value is 0 or geoselfwhich means the current geometry in a node. This argument may be used in the future to allow writing to other geometries. Sphere, circle, tube, metaball, or metasuperquadric primitive.

Require exactly 1 point. You cannot add vertices to these primitives. Packed Alembic or packed disk primitive. A primitive number for the created primitive, or -1 if the point could not be created. You can use the return value with setprimattrib to set attributes on the new point, however it may not be the final number of the point.

Returns number of elements where an integer or string attribute has a certain value. Copies the value of a geometry attribute into a variable and returns a success flag.

Best header for 2zzInterpolates the value of an attribute at a certain parametric u, v position and copies it into a variable. Returns position derivative on a primitive at a certain parametric u, v position. Returns one of the set of unique values across all values for an int or string attribute. Returns the set of unique values across all values for an int or string attribute. Interpolates the value of an attribute at certain UV coordinates using a UV attribute.

Returns the albedo percentage of reflected light for a bsdf given the outgoing light direction. Returns an anisotropic volumetric BSDF, which can scatter light forward or backward.

Returns the value of a CHOP local transform channel at the specified sample and evaluation time. Returns 1 if the edge specified by the point pair is in the group specified by the string.

### Points and Verts and Prims

This function computes the intersection of the specified ray with the geometry in uv space. Returns the linear vertex number of the next vertex sharing a point with a given vertex. Returns the linear vertex number of the previous vertex sharing a point with a given vertex. Returns 1 if the point specified by the point number is in the group specified by the string. Returns 1 if the primitive specified by the primitive number is in the group specified by the string.

Returns 1 if the vertex specified by the vertex number is in the group specified by the string. Returns the point into which the vertex following the destination vertex of a half-edge in its primitive is wired. Returns the vertex following the destination vertex of a half-edge in its primitive. Returns the point into which the vertex that precedes the source vertex of a half-edge in its primitive is wired.This node works like the Wireframe nodebut this node creates more complex tube geometry from curves, with smoother bends and intersections than Wireframe, especially for L-systems.

The Wireframe node creates transition surfaces where the original curve branches.

Ros inverse kinematicsYou can disable end caps using a workaround. First, add an attribute wrangle between the input curve and the Polywire node with the following snippet:.

Then, in the Polywire node, set Smooth points to isinterior. Prevent Joint Buckling scales up the intersection points so that they lie on the intersection of two tubes, rather than a width sized sphere. This can cause the points to be scaled past the first segment of the tube, however, causing buckling. This parameter allows you to change on a point level what the maximum scale applied to the points is. If the expression evaluates to a non-zero value for a point, the generated tube is smooth and connected through that point.

If the expression is zero, the corresponding segment is disconnected. A value of zero will leave ends uncapped. This is the number of divisions in the circle which is to be swept over the polygon. It can vary on a point basis.

Gm38 gas maskThe number of segments to divide each edge of the polygon into. These are how far into the segment to make the first circle and how far towards the end to keep going. Both values are in the rangewhere 0 is the start and 1 the end.

These are segment specific values. This toggle when set will scale the intersection point of edges to avoid a collapse when sharp turns are made. Toggles whether vertex textures are generated for the geometry. For best texturing of branch points, the points of the wire should be ordered so the "important" side has least point number.

For example, in a Y branch, the bottom of the Y should have the smallest point numbers. A per segment parameter which cycles how far around the tube the seam is placed. The seam is always snapped to the nearest polygon edge. If enabled, the up vector at each joint is set to the specified value. This will result in twisting of the branches.

PolywireModel Example for PolyWire geometry node. This example demonstrates how the Polywire SOP builds polygonal geometry based on a polygonal frame, and how the parameters can be customized with local variables.

Adaptive Prune. Agent Clip. Agent Clip Properties.

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