Spring Animation - 3D Voxel Learning Example

This guide walks you through how to generate a looping 3D voxel animation of a spring using SpatialStudio. The script creates a colorful metallic spring that bounces, compresses, and extends inside a cubic 3D space, then saves the animation to a .splv file.

What this script does

Creates a 3D scene of size 128×128×128
Generates a metallic spring with:
- Helical coil structure made of connected voxel segments
- Realistic compression and extension motion
- Metallic sheen with highlights and shadows
- Dynamic bounce animation
Animates the spring compressing and extending for 6 seconds at 30 FPS
Outputs the file spring.splv that you can play in your viewer

How it works (simplified)

Voxel volume Each frame is a 3D grid filled with RGBA values (SIZE × SIZE × SIZE × 4).
Helical geometry The spring is constructed using parametric equations that create a 3D helix with varying pitch.
Compression animation The spring's height and coil spacing change over time using sine waves to create realistic bouncing motion.
Metallic appearance Multiple shades of gray and silver create depth, with white highlights simulating metal reflections.
Animation loop A normalized time variable t cycles from 0 → 2π, making the compression and extension loop smoothly.
Encoding Frames are passed into splv.Encoder, which writes them into the .splv video file.

Try it yourself

Install requirements first:

pip install spatialstudio numpy tqdm

Then copy this script into spring.py and run:

python spring.py

Full Script

import numpy as np
from spatialstudio import splv
from tqdm import tqdm

# Scene setup
SIZE, FPS, SECONDS = 128, 30, 6
FRAMES = FPS * SECONDS
CENTER_X = CENTER_Y = CENTER_Z = SIZE // 2
OUT_PATH = "../outputs/spring.splv"

# Spring settings
SPRING_RADIUS = 15
SPRING_HEIGHT_BASE = 50
COIL_THICKNESS = 3
COIL_COUNT = 8

def add_voxel(volume, x, y, z, color):
    if 0 <= x < SIZE and 0 <= y < SIZE and 0 <= z < SIZE:
        volume[x, y, z, :3] = color
        volume[x, y, z, 3] = 255

def get_spring_colors():
    return {
        'base': (120, 120, 120),      # Base metal color
        'dark': (80, 80, 80),         # Shadow areas
        'bright': (180, 180, 180),    # Lit areas
        'highlight': (255, 255, 255)  # Metallic shine
    }

def generate_spring_coil(volume, cx, cy, cz, compression_factor, t):
    colors = get_spring_colors()
    
    # Calculate spring height with compression
    current_height = SPRING_HEIGHT_BASE * compression_factor
    
    # Generate points along the helical path
    steps = int(COIL_COUNT * 50)  # Points per full spring
    
    for i in range(steps):
        # Parametric helix equations
        theta = (i / steps) * COIL_COUNT * 2 * np.pi
        height_progress = i / steps
        
        # Spring position along helix
        x = cx + SPRING_RADIUS * np.cos(theta)
        z = cz + SPRING_RADIUS * np.sin(theta)
        y = cy - current_height/2 + height_progress * current_height
        
        # Add thickness to the coil
        for dx in range(-COIL_THICKNESS, COIL_THICKNESS+1):
            for dy in range(-COIL_THICKNESS//2, COIL_THICKNESS//2+1):
                for dz in range(-COIL_THICKNESS, COIL_THICKNESS+1):
                    if dx*dx + dy*dy + dz*dz <= COIL_THICKNESS*COIL_THICKNESS:
                        # Calculate lighting based on position
                        light_factor = (np.cos(theta) + 1) / 2  # Simple lighting
                        
                        # Choose color based on lighting and position
                        if light_factor > 0.8:
                            color = colors['highlight']
                        elif light_factor > 0.6:
                            color = colors['bright']
                        elif light_factor > 0.3:
                            color = colors['base']
                        else:
                            color = colors['dark']
                        
                        final_x = int(x + dx)
                        final_y = int(y + dy)
                        final_z = int(z + dz)
                        
                        add_voxel(volume, final_x, final_y, final_z, color)

def generate_spring_ends(volume, cx, cy, cz, compression_factor, t):
    """Generate flat end caps for the spring"""
    colors = get_spring_colors()
    current_height = SPRING_HEIGHT_BASE * compression_factor
    
    # Top and bottom end positions
    top_y = int(cy + current_height/2)
    bottom_y = int(cy - current_height/2)
    
    # Draw circular end caps
    for dx in range(-SPRING_RADIUS-2, SPRING_RADIUS+3):
        for dz in range(-SPRING_RADIUS-2, SPRING_RADIUS+3):
            distance = np.sqrt(dx*dx + dz*dz)
            if distance <= SPRING_RADIUS + 2:
                # Add end caps with some thickness
                for dy in range(-1, 2):
                    if distance < SPRING_RADIUS - 2:
                        color = colors['base']
                    else:
                        color = colors['dark']
                    
                    add_voxel(volume, cx+dx, top_y+dy, cz+dz, color)
                    add_voxel(volume, cx+dx, bottom_y+dy, cz+dz, color)

def generate_scene(volume, t):
    # Create bouncing compression effect
    # Spring compresses and extends in a realistic bouncing motion
    base_compression = 0.7 + 0.3 * np.sin(t * 3.0)  # Main bounce
    secondary_bounce = 0.05 * np.sin(t * 12.0)      # Secondary oscillation
    compression_factor = base_compression + secondary_bounce
    
    # Clamp compression to reasonable values
    compression_factor = max(0.4, min(1.2, compression_factor))
    
    # Generate the spring
    generate_spring_coil(volume, CENTER_X, CENTER_Y, CENTER_Z, compression_factor, t)
    generate_spring_ends(volume, CENTER_X, CENTER_Y, CENTER_Z, compression_factor, t)
    
    # Add some floating particles for effect (optional)
    generate_bounce_particles(volume, CENTER_X, CENTER_Y, CENTER_Z, compression_factor, t)

def generate_bounce_particles(volume, cx, cy, cz, compression_factor, t):
    """Add small particles that bounce off the spring"""
    colors = get_spring_colors()
    
    # Only show particles when spring is highly compressed
    if compression_factor < 0.6:
        particle_count = 5
        for i in range(particle_count):
            angle = (i / particle_count) * 2 * np.pi + t * 2
            radius = 25 + 10 * np.sin(t * 4 + i)
            
            px = cx + int(radius * np.cos(angle))
            pz = cz + int(radius * np.sin(angle))
            py = cy + int(20 * np.sin(t * 6 + i * 0.5))
            
            # Small particle
            for dx in range(-1, 2):
                for dy in range(-1, 2):
                    for dz in range(-1, 2):
                        if dx*dx + dy*dy + dz*dz <= 1:
                            add_voxel(volume, px+dx, py+dy, pz+dz, colors['bright'])

# Initialize encoder
enc = splv.Encoder(SIZE, SIZE, SIZE, framerate=FPS, outputPath=OUT_PATH, motionVectors="off")

# Generate animation frames
for frame in tqdm(range(FRAMES), desc="Generating spring"):
    volume = np.zeros((SIZE, SIZE, SIZE, 4), dtype=np.uint8)
    t = (frame / FRAMES) * 2*np.pi
    generate_scene(volume, t)
    enc.encode(splv.Frame(volume, lrAxis="x", udAxis="y", fbAxis="z"))

enc.finish()
print(f"Created {OUT_PATH}")

Next steps

Adjust COIL_COUNT to create springs with more or fewer coils
Modify the compression_factor calculation for different bounce patterns
Change the metallic colors in get_spring_colors() for gold, copper, or other materials
Add + int(t*10) to the Y position to make the spring bounce vertically through space
Experiment with SPRING_RADIUS and COIL_THICKNESS for different spring proportions

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