[Houdini] Introduction to Procedural Modeling – Voronoi Fracture and UV Mesh Unfold

Introduction

In this article, I will explain how to place cobblestones on a plate polygon using Houdini.

If you use a square plate polygon, it will become a square cobblestone floor like this.

 

If you use a star shaped plate polygon, it will become a star shaped cobblestone floor like this.

What You Can Learn from This Article

・How to use Houdini to place cobblestones on a floor

・How to unfold a UV mesh using Houdini

The Previous Article

Directions to Create a Cobblestone Floor

Prepare a Plate Polygon (Grid Node)

First, we need to prepare a plate polygon which we want to add cobblestones to.

I will use a Grid node (square plate polygon) for this tutorial.

 

Split the Plate (Voronoi Fracture)

Next, we will split the plate using an algorithm called Voronoi tessellation.

I will not explain the details of Voronoi tessellation in this article, but dividing a plate as in the image below is called Voronoi tessellation.

Prepare a Center Point for the Split (Scatter Node)

In order to divide a plate, we need to use a point cloud as a center point for the split.

We will use Scatter node to create a point cloud.

 

Using a Point Cloud for Voronoi Fracture (Voronoi Fracture Node)

Next, we will use a Voronoi Fracture node to split the plate.

Attach the plate polygon (Grid node) to the left of the Voronoi Fracture node, and the point cloud (Scatter node) to the right side of the Voronoi Fracture node.

 

The plate has been divided, but it does not represent cobblestones yet.

Additional Info: Display Wires

Wires can be displayed by pressing the Shift + W keys while selecting in Scene view.

By pressing it once more, they will turn invisible.

Rounding the Stones (Resample Node)

 

Attach a Resample node to the Voronoi Fracture, and resample the divided parts.

Apply the resample result again to round up the stones.

 

Thicken the Stone (PolyExtrude node)

Attach the PolyExtrude node to the Resample node in order to thicken the stones.

 

Unfold UV Mesh (UV Texture Node)

Lastly, unfold the UV mesh.

Attach the UV Quick Shade node and display the UV mesh as in the image below.

This completes the process to make a cobblestone floor.

 

OBJ File Export (ROP Geometry Node)

Use the ROP Geometry node to export as an OBJ file.

Enter the obj file path for the Output File, and click the Save to Disk button to export as an obj file.

If you import the OBJ file into a Unity scene, it will look like the image shown below.

Organize Materials

When imported to Unity, the material of the OBJ file is divided into two.

We can prevent this by setting up a Group within Houdini.

 

If you check the Voronoi Fracture node from previous steps, the group settings are active so we need to deactivate them.

Uncheck the Interior Group and Exterior Group option.

 

If you export as an OBJ file with these options, only one default material will exist.

How to Upload a Prefab from Unity to STYLY

In order to learn how to upload your created prefab to STYLY, refer to the article below.

Extra: Create a Round Floor

We used a Grid node to create a square cobblestone floor, but if you replace the Grid node with a Circle node, the result will be a circular cobblestone floor.

The normal direction of the Circle node is opposite of that of the Grid node, so I used the Reverse node to flip the direction.

 

Extra 2: Create a Star-Shaped Floor

I will explain how to create a star-shaped floor as seen in the image below.

How to Create a Star-Shaped Floor

You can create a star shape by using the Circle node to create a regular decagon with smaller vertices.

 

Circle Node Settings (Create a Regular Decagon)

Change the Division of the Circle node to 10, and the shape will be transformed into a regular decagon.

 

 

Group by Range Node Settings (Select Even Vertices)

Apply group1 to the even vertices.

 

Transform Node Settings (Making the Selected Even Vertices Smaller)

Use the Transform node and change the even vertices to a 0.5 scale.

 

Completed Star-Shaped Floor

By turning the UV Texture node Display flag on, a star-shaped cobblestone floor as in the image below will appear.