3D Voxel Animation Tutorial: Black Hole

This guide walks you through how to generate a looping 3D voxel animation of a black hole using SpatialStudio. The script creates a mesmerizing black hole with swirling matter, particle streams, and gravitational distortion effects 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 black hole with:
- A dark central void with event horizon
- Swirling accretion disk with hot plasma colors
- Particle streams being pulled into the gravity well
- Distortion effects around the event horizon
Animates the gravitational pull and rotation for 8 seconds at 30 FPS
Outputs the file blackhole.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).
Event horizon The center contains a dark sphere that represents the black hole's event horizon.
Accretion disk Hot matter spirals around the black hole in a flattened disk, with colors ranging from deep red to bright white based on temperature and distance.
Particle streams Individual particles are drawn as they get pulled toward the black hole, creating dynamic trails.
Gravitational effects Matter appears to stretch and distort as it approaches the event horizon, simulating gravitational lensing.
Animation loop A normalized time variable t cycles from 0 → 2π, ensuring the rotation and particle motion loops 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 blackhole.py and run:

python blackhole.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/blackhole.splv"

# Black hole settings
EVENT_HORIZON_RADIUS = 8
ACCRETION_DISK_INNER = 12
ACCRETION_DISK_OUTER = 45
PARTICLE_COUNT = 150

def add_voxel(volume, x, y, z, color, alpha=255):
    if 0 <= x < SIZE and 0 <= y < SIZE and 0 <= z < SIZE:
        # Blend with existing color if there's already something there
        existing_alpha = volume[x, y, z, 3] / 255.0
        new_alpha = alpha / 255.0
        blend_factor = new_alpha * (1 - existing_alpha)
        
        for i in range(3):
            volume[x, y, z, i] = int(volume[x, y, z, i] * existing_alpha + color[i] * blend_factor)
        volume[x, y, z, 3] = min(255, int((existing_alpha + new_alpha) * 255))

def generate_event_horizon(volume, cx, cy, cz, t):
    # Create the dark center with subtle distortion
    horizon_color = (20, 5, 30)  # Very dark purple
    
    for dx in range(-EVENT_HORIZON_RADIUS-2, EVENT_HORIZON_RADIUS+3):
        for dy in range(-EVENT_HORIZON_RADIUS-2, EVENT_HORIZON_RADIUS+3):
            for dz in range(-EVENT_HORIZON_RADIUS-2, EVENT_HORIZON_RADIUS+3):
                dist = np.sqrt(dx*dx + dy*dy + dz*dz)
                if dist <= EVENT_HORIZON_RADIUS:
                    # Add subtle distortion effect
                    distortion = np.sin(t * 3 + dist * 0.5) * 0.3
                    if dist <= EVENT_HORIZON_RADIUS + distortion:
                        intensity = max(0, 1 - dist / EVENT_HORIZON_RADIUS)
                        color = tuple(int(c * intensity * 0.3) for c in horizon_color)
                        add_voxel(volume, cx+dx, cy+dy, cz+dz, color)

def get_temperature_color(temperature):
    # Temperature-based color mapping for hot plasma
    if temperature < 0.3:
        # Dark red
        return (int(80 * temperature / 0.3), 0, 0)
    elif temperature < 0.6:
        # Red to orange
        t = (temperature - 0.3) / 0.3
        return (80 + int(175 * t), int(50 * t), 0)
    elif temperature < 0.8:
        # Orange to yellow
        t = (temperature - 0.6) / 0.2
        return (255, 50 + int(155 * t), int(50 * t))
    else:
        # Yellow to white (hottest)
        t = (temperature - 0.8) / 0.2
        return (255, 205 + int(50 * t), 50 + int(205 * t))

def generate_accretion_disk(volume, cx, cy, cz, t):
    for dx in range(-ACCRETION_DISK_OUTER-5, ACCRETION_DISK_OUTER+6):
        for dz in range(-ACCRETION_DISK_OUTER-5, ACCRETION_DISK_OUTER+6):
            for dy in range(-8, 9):  # Flattened disk
                radius = np.sqrt(dx*dx + dz*dz)
                
                if ACCRETION_DISK_INNER <= radius <= ACCRETION_DISK_OUTER:
                    # Calculate spiral position
                    angle = np.arctan2(dz, dx)
                    spiral_angle = angle + t * 2.0 - radius * 0.08
                    
                    # Create spiral arms
                    spiral_intensity = (np.sin(spiral_angle * 3) + 1) * 0.5
                    
                    # Height falloff for disk shape
                    height_falloff = np.exp(-abs(dy) * 0.3)
                    
                    # Distance-based temperature and density
                    temp_factor = 1.0 / (1 + (radius - ACCRETION_DISK_INNER) * 0.02)
                    density = spiral_intensity * height_falloff * temp_factor
                    
                    if density > 0.1:  # Only draw if dense enough
                        # Add turbulence
                        turbulence = np.sin(dx*0.2 + dz*0.15 + t*4) * 0.1
                        temperature = temp_factor + turbulence
                        
                        color = get_temperature_color(temperature)
                        alpha = min(255, int(density * 180))
                        
                        add_voxel(volume, cx+dx, cy+dy, cz+dz, color, alpha)

def generate_particle_streams(volume, cx, cy, cz, t):
    particle_color = (255, 200, 100)  # Bright yellow-orange
    
    for i in range(PARTICLE_COUNT):
        # Each particle follows a unique spiral path
        particle_phase = (i / PARTICLE_COUNT) * 2 * np.pi
        
        # Particle's journey from outer edge to event horizon
        progress = (t * 0.5 + particle_phase) % (2 * np.pi)
        journey = progress / (2 * np.pi)
        
        # Start from outer disk, spiral inward
        start_radius = ACCRETION_DISK_OUTER + 10
        current_radius = start_radius * (1 - journey * 0.8)
        
        if current_radius > EVENT_HORIZON_RADIUS + 2:
            angle = particle_phase + progress * 5  # Spiral motion
            
            # Particle position
            px = int(current_radius * np.cos(angle))
            pz = int(current_radius * np.sin(angle))
            py = int(np.sin(progress * 4 + particle_phase) * 4)  # Vertical oscillation
            
            # Intensity based on proximity to black hole
            intensity = min(1.0, 2.0 / (1 + current_radius * 0.05))
            color = tuple(int(c * intensity) for c in particle_color)
            alpha = int(intensity * 200)
            
            add_voxel(volume, cx+px, cy+py, cz+pz, color, alpha)
            
            # Add particle trail
            for trail in range(1, 4):
                trail_angle = angle - trail * 0.1
                trail_px = int(current_radius * np.cos(trail_angle))
                trail_pz = int(current_radius * np.sin(trail_angle))
                trail_alpha = alpha // (trail + 1)
                trail_color = tuple(c // (trail + 1) for c in color)
                add_voxel(volume, cx+trail_px, cy+py, cz+trail_pz, trail_color, trail_alpha)

def generate_gravitational_lensing(volume, cx, cy, cz, t):
    # Add bright spots around the event horizon to simulate lensing effects
    lensing_color = (150, 150, 255)  # Blue-white light
    
    for i in range(8):
        angle = (i / 8) * 2 * np.pi + t * 1.5
        radius = EVENT_HORIZON_RADIUS + 4
        
        lx = int(radius * np.cos(angle))
        lz = int(radius * np.sin(angle))
        ly = int(np.sin(t * 2 + i) * 2)
        
        intensity = (np.sin(t * 3 + i * 0.5) + 1) * 0.5
        color = tuple(int(c * intensity * 0.7) for c in lensing_color)
        alpha = int(intensity * 150)
        
        # Add multiple voxels for a glowing effect
        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, cx+lx+dx, cy+ly+dy, cz+lz+dz, color, alpha//2)

def generate_scene(volume, t):
    generate_accretion_disk(volume, CENTER_X, CENTER_Y, CENTER_Z, t)
    generate_particle_streams(volume, CENTER_X, CENTER_Y, CENTER_Z, t)
    generate_gravitational_lensing(volume, CENTER_X, CENTER_Y, CENTER_Z, t)
    generate_event_horizon(volume, CENTER_X, CENTER_Y, CENTER_Z, t)

# 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 black hole"):
    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 EVENT_HORIZON_RADIUS to create larger or smaller black holes
Modify PARTICLE_COUNT to increase the density of matter streams
Change the temperature color mapping in get_temperature_color() for different plasma effects
Experiment with ACCRETION_DISK_OUTER to create more expansive disks
Add pulsing effects by modulating the intensity with sine waves over time

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3D Voxel Animation Tutorial: Black Hole

What this script does

How it works (simplified)