TouchDesigner Tutorial: Working with SOPs

This tutorial covers Surface Operators (SOPs) in TouchDesigner - the operator family for creating and manipulating 3D geometry.

What Are SOPs?

SOPs (Surface Operators) are TouchDesigner’s operator family for working with 3D content. They can read, create, and modify:

• 3D points and polygons
• Lines and curves
• Particle surfaces
• Spheres and metaballs

Like all TouchDesigner operators, SOPs work within procedural pipelines. This means changes to your SOP networks immediately impact your final result - a core concept that makes TouchDesigner powerful for real-time creative work.

Basic SOP Workflow: Copy SOP

The tutorial demonstrates a fundamental workflow using the Copy SOP:

1. Create a Rectangle SOP - Use Tab to open the operator create dialog and add a rectangle
2. Add a Copy SOP - Right-click on the rectangle’s output and add a copy operator
3. Set number of copies - Increase copies to 10
4. Apply transformations - Set translate X to 1.25 to space copies along the X axis

Each copy is translated by the specified amount, creating a row of rectangles. You can also apply rotation (e.g., rotation Z) to spin each primitive on its axis.

Viewer Navigation

To examine your 3D geometry, activate the viewer with the A key:

• Left mouse button - Tumble (rotate) the view
• Right mouse button - Pan the view
• Middle mouse button - Zoom
• H key - Home the view (reset to default position)

You can also middle-mouse drag on parameters to interactively adjust values while seeing real-time results.

Template-Based Copying

The Copy SOP has a powerful second input for template-based copying:

1. Create a Rectangle SOP (set size to 0.1 x 0.1)
2. Create a Circle SOP
3. Add a Copy SOP
4. Connect the rectangle to input 1, circle to input 2

This places a copy of the first input at each vertex of the second input. Changing the circle’s divisions immediately affects how many copies appear - demonstrating the procedural nature of TouchDesigner.

Display Options for Debugging

Right-click inside an active viewer and select “Display Options” to see:

• Vertex positions
• Vertex number counts
• Normals (useful for understanding orientation and lighting)
• XYZ coordinates for each point

This information is invaluable when debugging geometry or understanding how operators transform your data.

Sweep SOP Workflow

The Sweep SOP creates geometry by sweeping a profile along a backbone:

1. Create a Rectangle SOP (the profile)
2. Create a Circle SOP set to “Open” arc type, ending at 180 degrees (the backbone)
3. Add a Sweep SOP
4. Connect rectangle to input 1, circle to input 2

Initial parameters to adjust:

• Scale: Set to 0.25 for a smaller profile
• Twist: Set to 5 for a spiral effect
• Output page: Enable “Skin” to create a continuous surface

Creating Low-Poly Geometry

To achieve a faceted, low-poly look:

1. Add a Convert SOP after your sweep to convert to polygons
2. Add a Facet SOP with:
   • “Unique Points” enabled
   • “Compute Normals” enabled

This creates distinct faces with hard edges rather than smooth shading.

Key Takeaways

1. SOPs are procedural - Changes anywhere in your network propagate to the final result
2. Use the A key to activate viewers and examine geometry in 3D
3. Copy SOP can use a second input as a template for placing copies at vertices
4. Sweep SOP creates geometry by sweeping profiles along paths
5. Display Options help you understand vertex positions, normals, and point data
6. Convert and Facet SOPs are essential for controlling polygon output and normals