What Is Important to Understand When First Learning 3D in Houdini?

3D Points in Houdini – Understanding Geometry

Houdini uses points and attributes. Houdini also has primitives, which are single polygons with at least three points. Houdini also uses vertexes, but we will get more into that later. Primitives can’t exist without points. Points have an attribute that Houdini calls Position.

If we look at the picture below we can see a sphere with the point numbers turned on. The important thing to see here is at the top of the sphere. This is point “0” and it is a single point. Okay, why is this so important?

Looking at Point Numbers on geometry in Houdini

What Is The Difference Between 3D Points and 3D Vertexes in Houdini, and Why Do We Care?

Attributes define all sorts of properties in Houdini. We can also make our own attributes. We can name our attributes almost whatever we want. When we look at the sphere example we can see that we have 266 points. The points have the attribute “position”. The attribute “position” is a vector that defines where each point is in space. The “position” vector has three values, X, Y, and Z. Each of these three values are “float” values. In Houdini, we need to understand what is a vector and what is a float.  A vector is a collection of at least two float values. A float is a number with a decimal place. 1.0 is a float, as is 2.089. We differentiate between numbers that have decimals and numbers that don’t. 1.0 is a float and 1 is an integer. I am always surprised how many new students do not know this.

So now we understand that “position” is an attribute that defines the shape of a piece of geometry will be. Houdini has several reserved attributes that define a piece of geometry. These are Normals, Color, UVW, and others. For a piece of  3D geometry to be renderable, we need at least, Position, Normals, and UVs.

Looking at Vertexes on geometry in Houdini

Why Do We Have Point Normals and Vertex Normals?

This is a concept that confuses many of my students. It is an easy concept but remembering to actually set the right attribute is the problem I see the most. Point Normals define a direction that will use to do something. Usually, this will be copying an item to a group of points. Vertex

Normals are for rendering and how our geometry will render. We use the terms “Hard” Normals and “Soft” Normals. Hard Normals mean a very faceted rendering surface. Soft Normals means a smooth shaded surface. We can see this in the following picture. Here we use the same sphere, with two different normal settings.

Understanding 3D Geometry in Houdini

The difference between hard and soft normals for shading

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Jordan Halsey | www.jordanhalsey.com