Selective Per-Instance Horizontal Flip for Triangular Grid

Beginners
1

Hi everyone,

2024-11-26 21_10_33-Repeating geometric triangular grid Royalty Free Vector - Brave
2024-11-26 21_10_33-Repeating geometric triangular grid Royalty Free Vector - Brave1202×827 88.8 KB

I’m working on a grid of triangles in TouchDesigner, where each triangle is instanced at points generated from a grid. My goal is to flip the triangles horizontally at every other point, based on their position in the grid. Specifically:

  1. The grid is structured into rows of 60 points.
  2. Every other point in a row (e.g., points 1, 3, 5, …) needs to have a horizontally flipped triangle.
  3. Every other row alternates this pattern (e.g., rows 0, 2, 4 start with unflipped, rows 1, 3, 5 start with flipped).

I’ve already:

  • Grouped points into two groups (GroupA and GroupB) based on the alternating pattern.
  • Fed the grid points into a Geometry COMP for instancing but can’t apply the flip correctly on a per-instance basis.

The main issue:

  • When I use a Transform SOP to flip, it applies the transformation to all points in the group as a whole, not on a per-point basis.

Is there a way to assign a custom attribute (scaleX) or another approach to dynamically control the horizontal flip for each triangle instance? I am trying to avoid creating a grid that it too irregular because I am driving other Instance values via a an input video.

Any guidance on correctly setting up the Attribute Create SOP, or another efficient solution, would be greatly appreciated!

Thanks in advance for your help!

2

Hello,
Using the index of each vertex, you can
– made a pattern with the right length, alterning rotation angle and used in the rotation OP
– use a geometry shader (or perhaps a vertex shader) to rotate each instance based on instance ID
Not on my computer to propose an example :frowning: