3D Voxel Rainbow Animation Tutorial

This guide walks you through how to generate a looping 3D voxel animation of a rainbow using SpatialStudio. The script creates a vibrant rainbow arc that shimmers and glows 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 rainbow arc with:
- 7 colored bands (red, orange, yellow, green, blue, indigo, violet)
- Smooth color transitions and gradients
- Shimmering light effects
- Gentle swaying motion
Animates the rainbow for 8 seconds at 30 FPS
Outputs the file rainbow.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).
Rainbow arc The rainbow is drawn as a series of concentric arcs, each representing a different color band.
Color bands Seven distinct color layers create the classic rainbow spectrum (ROYGBIV).
Shimmer effects Animated brightness variations and sparkle effects make the rainbow appear magical.
Animation loop A normalized time variable t cycles from 0 → 2π, creating smooth swaying and shimmering motions.
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 rainbow.py and run:

python rainbow.py

Full Script

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

# Scene setup
SIZE, FPS, SECONDS = 128, 30, 8
FRAMES = FPS * SECONDS
CENTER_X = CENTER_Y = CENTER_Z = SIZE // 2
OUT_PATH = "../outputs/rainbow.splv"

# Rainbow settings
RAINBOW_RADIUS = 45
RAINBOW_THICKNESS = 4
BAND_COUNT = 7

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

def get_rainbow_color(band_index):
    colors = [
        (255, 0, 0),    # Red
        (255, 165, 0),  # Orange
        (255, 255, 0),  # Yellow
        (0, 255, 0),    # Green
        (0, 0, 255),    # Blue
        (75, 0, 130),   # Indigo
        (148, 0, 211)   # Violet
    ]
    return colors[band_index % len(colors)]

def generate_rainbow_arc(volume, cx, cy, cz, t):
    sway = np.sin(t * 0.8) * 3
    
    for band in range(BAND_COUNT):
        base_radius = RAINBOW_RADIUS - (band * RAINBOW_THICKNESS)
        color = get_rainbow_color(band)
        
        # Create arc from 0 to π (half circle)
        for angle_step in range(180):
            angle = np.radians(angle_step)
            
            for thickness in range(RAINBOW_THICKNESS):
                radius = base_radius + thickness
                
                # Calculate arc position
                x = int(cx + radius * np.cos(angle) + sway)
                y = int(cy - radius * np.sin(angle) * 0.7)  # Flatten slightly
                z = cz
                
                # Add depth to the rainbow
                for depth in range(-2, 3):
                    # Shimmer effect
                    shimmer = np.sin(t * 3 + angle * 2 + band * 0.5) * 0.3 + 0.7
                    brightness = max(0.4, shimmer)
                    
                    final_color = tuple(int(c * brightness) for c in color)
                    add_voxel(volume, x, y, z + depth, final_color)

def generate_sparkles(volume, cx, cy, cz, t):
    sparkle_color = (255, 255, 255)
    
    # Generate moving sparkles around the rainbow
    for i in range(15):
        # Create pseudo-random but consistent sparkle positions
        seed_x = np.sin(i * 1.7 + t * 2.1) * RAINBOW_RADIUS * 0.8
        seed_y = np.cos(i * 2.3 + t * 1.8) * RAINBOW_RADIUS * 0.4
        seed_z = np.sin(i * 3.1 + t * 2.5) * 8
        
        x = int(cx + seed_x)
        y = int(cy - abs(seed_y))  # Keep sparkles above ground
        z = int(cz + seed_z)
        
        # Sparkle intensity varies over time
        intensity = (np.sin(t * 4 + i * 0.8) + 1) * 0.5
        
        if intensity > 0.7:  # Only show bright sparkles
            alpha = int(255 * intensity)
            add_voxel(volume, x, y, z, sparkle_color, alpha)
            
            # Add small cross pattern for sparkle effect
            add_voxel(volume, x+1, y, z, sparkle_color, alpha//2)
            add_voxel(volume, x-1, y, z, sparkle_color, alpha//2)
            add_voxel(volume, x, y+1, z, sparkle_color, alpha//2)
            add_voxel(volume, x, y-1, z, sparkle_color, alpha//2)

def generate_glow_effect(volume, cx, cy, cz, t):
    # Add a subtle glow beneath the rainbow
    glow_intensity = (np.sin(t * 1.5) + 1) * 0.3 + 0.2
    
    for i in range(RAINBOW_RADIUS * 2):
        for j in range(20):
            x = cx - RAINBOW_RADIUS + i
            y = cy + 10 + j
            z = cz
            
            if 0 <= x < SIZE and 0 <= y < SIZE:
                # Create soft gradient
                distance_from_center = abs(x - cx) / RAINBOW_RADIUS
                vertical_fade = (20 - j) / 20
                
                if distance_from_center <= 1.0:
                    alpha = int(50 * glow_intensity * (1 - distance_from_center) * vertical_fade)
                    glow_color = (255, 255, 200)  # Soft yellow glow
                    
                    if alpha > 10:
                        add_voxel(volume, x, y, z, glow_color, alpha)

def generate_scene(volume, t):
    generate_rainbow_arc(volume, CENTER_X, CENTER_Y, CENTER_Z, t)
    generate_sparkles(volume, CENTER_X, CENTER_Y, CENTER_Z, t)
    generate_glow_effect(volume, CENTER_X, CENTER_Y, CENTER_Z, t)

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

for frame in tqdm(range(FRAMES), desc="Generating rainbow"):
    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 RAINBOW_RADIUS to make the rainbow larger or smaller
Change BAND_COUNT to create more or fewer color bands
Modify the colors array to create a custom color spectrum
Add + int(t*10) to the Y position to make the rainbow rise and fall
Experiment with the sparkle count by changing the range in generate_sparkles()
Try different shimmer patterns by modifying the sine wave parameters

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