houdini-vex-programming

houdini-vex-programming

Version: 1.1.0 Last Updated: 2026-10-09 Dependencies: Houdini 20+

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CRITICAL: MANDATORY FIRST STEP

ALWAYS understand VEX execution context:

// Check what you're operating on
// Point Wrangle: Runs once per point (@ptnum)
// Primitive Wrangle: Runs once per primitive (@primnum)
// Detail Wrangle: Runs once for entire geometry
// Vertex Wrangle: Runs once per vertex (@vtxnum)

// Print current element (helps debug)
printf("Processing element: %d\n", @ptnum);  // In point wrangle

Why Critical:

• Context Matters: Wrong wrangle type = unexpected results or errors
• Performance: Running on points vs primitives has different costs
• Attribute Access: Some attributes only available in specific contexts (e.g., @vtxnum in vertex wrangle)

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QUICK START

Most Common Use Case: Attribute Manipulation

Goal: Modify point positions or attributes using VEX

Step 1: Create Wrangle Node

Create Point Wrangle node in SOP network
Connect input geometry

Step 2: Write VEX Code

// Example: Move points up based on X position
@P.y += @P.x * 0.5;

// Add color attribute
@Cd = {1.0, 0.0, 0.0};  // Red color

// Create custom attribute
f@custom_scale = fit(@P.y, -5, 5, 0.5, 2.0);

Step 3: Verify Output

// Debug: Print values for first 10 points
if (@ptnum < 10) {
    printf("Point %d: P=%v, scale=%f\n", @ptnum, @P, f@custom_scale);
}

Step 4: Check Geometry Spreadsheet

Open Geometry Spreadsheet (RMB on node -> Spreadsheet)
Verify new attributes exist: custom_scale, Cd
Check values are in expected range

Expected Output:

Points moved vertically based on X
All points have red color (Cd = 1,0,0)
custom_scale attribute ranges from 0.5 to 2.0

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STANDARD WORKFLOWS

Workflow 1: Noise and Procedural Deformation

Use When: Creating organic variation, terrain, or animated effects

Steps:

1. Basic Noise Pattern

   // Point Wrangle
   
   // Simple noise displacement
   vector noise_pos = @P * chf("frequency");
   float noise_val = noise(noise_pos);
   @P += @N * noise_val * chf("amplitude");
   

   Why: Displaces points along normals using Perlin noise