TouchDesigner Tutorial: Instancing with TOPs

This tutorial demonstrates how to use Texture Operators (TOPs) for instancing in TouchDesigner. Using TOPs for instancing is particularly helpful when working with hundreds of thousands of instances, as it leverages GPU-based texture data for efficient rendering.

Why Use TOPs for Instancing?

While CHOPs are commonly used for instancing, TOPs offer significant advantages when dealing with massive numbers of instances. Point file data can be loaded directly to the GPU through texture operators, making this approach highly efficient for large-scale visualizations.

Getting Started with Point File In TOP

Loading Point Data

Begin by adding a Point File In TOP to your network. This operator allows you to load point file data directly to the GPU.

Understanding the Channel Layout

By default, the Point File In TOP displays a normalized split view of your point file contents:

• Red Channel - X position data
• Green Channel - Y position data
• Blue Channel - Z position data
• Alpha Channel - Active data (true/false for whether a point exists)

The Active Channel

The Alpha channel’s “active” data is crucial. Point files need to fit inside a square texture, which means some pixels may not contain actual point data. An active value of zero indicates these empty pixels, helping the system know which instances to render.

Setting Up the Basic Workflow

Step 1: Connect to a Null TOP

Connect your Point File In TOP to a Null TOP. You can view the points spatially by:

1. Turning on the viewer active flag for the Null TOP
2. Right-clicking inside the viewer
3. Selecting “Viewer Points”
4. Pressing H to home the view

Step 2: Create Instance Geometry

Set up your instance geometry using SOPs:

1. Add an Add SOP and turn on “Add Points”
2. Connect to a Convert SOP
3. Set the Convert SOP to convert “To Particles Per Point”
4. Connect to a Geometry Component

Step 3: Configure Instancing

On the Geometry component’s Instance page:

1. Turn on the Instancing parameter
2. Set your Null TOP as the translate information source
3. Map the channels correctly:
   • Active - Alpha channel
   • Translate X - Red channel
   • Translate Y - Green channel
   • Translate Z - Blue channel

Visualizing Instances with Materials

To better see your instances, add a Line Material:

1. Open the OP Create dialogue and select Line Material
2. Drag and drop it onto your Geometry component
3. On the Line page, turn off “Draw Lines”
4. On the Point page, turn on “Draw Points”
5. Set near and far colors to the same value (e.g., bright white)
6. Adjust the point size multiplier as needed

Press A to make the Geometry component viewer active, then H to home the view.

Working with Different Point Files

Loading Custom Point Files

You can load different point files (like the banana.ply example) through the file browser in the Point File In TOP. After loading, reassign the channels:

• Red = X position
• Green = Y position
• Blue = Z position

Extracting Additional Data with Point File Select TOP

Point files often contain more information than four channels can hold. Use the Point File Select TOP to extract additional data:

1. Add a Point File Select TOP
2. Drag and drop your point file onto it
3. Select which information to pack into each channel (e.g., RGB and Alpha color values)

Normalizing Color Data

If your color data is in 0-255 range, use a Math TOP to normalize:

1. Connect the Math TOP to your Point File Select TOP
2. On the Range page, set “From Range” as 0 to 255
3. Set “To Range” as 0 to 1
4. Connect to a Null TOP (use Alt+N shortcut)

Applying Color to Instances

On the Geometry component’s Instance 2 page:

1. Find the Color Operator parameter
2. Drag and drop your color Null TOP
3. Map R, G, B, and A channels to the corresponding color parameters

Using Rotation Data

Extracting Normal Vectors

For instances that need to align to surfaces, extract normal data:

1. Add another Point File Select TOP
2. Select NX (Normal X), NY (Normal Y), and NZ (Normal Z) for the RGB channels
3. Connect to a Null TOP

Configuring Rotate To

On the Geometry component’s Instance 2 page:

1. Set the Rotate To OP parameter to your normal data Null TOP
2. Map the channels:
   • Rotate To Vector X = R channel
   • Rotate To Vector Y = G channel
   • Rotate To Vector Z = B channel

This allows instances to correctly align to surfaces, such as distributing circles across a sphere.

Using Different Instance Geometry

Instead of points, you can use any geometry for instances:

1. Create a Circle SOP with a small radius (e.g., 0.06 for X and Y)
2. Right-click on the Circle SOP output and add a Geometry Component
3. Enable instancing and connect your point data Null TOP
4. Map the channels as before

Key Takeaways

1. TOPs for Scale - Use TOPs when working with hundreds of thousands of instances
2. Point File In TOP - Loads point data directly to GPU
3. Active Channel - Alpha channel indicates valid points in square textures
4. Point File Select TOP - Extracts additional data like colors and normals
5. Math TOP - Normalizes data ranges (e.g., 0-255 to 0-1)
6. Rotate To - Uses normal vectors for instance orientation

This tutorial provides a foundation for TOP-based instancing. There are many more ways to drive instances with texture operators, opening up possibilities for complex, large-scale visualizations.