River Rapids - 3D Voxel Animation Learning Example

This guide walks you through how to generate a looping 3D voxel animation of river rapids using SpatialStudio. The script creates a flowing river with turbulent water, foam, and dynamic currents 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 winding river with:
- Flowing blue water with depth variations
- White foam and bubbles on the surface
- Rocky riverbed and banks
- Turbulent rapids with splashing effects
Animates the water flow for 8 seconds at 30 FPS
Outputs the file river_rapids.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).
River path The river follows a curved path through the scene using sine waves for natural meandering.
Water flow Blue voxels represent water with varying opacity based on depth, animated with flowing motion.
Rapids and foam White and light blue voxels create turbulent areas where water crashes over rocks.
Riverbed Brown and gray voxels form the rocky bottom and banks of the river.
Animation loop A normalized time variable t cycles from 0 → 2π, creating seamless water flow and foam movement.
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 river_rapids.py and run:

python river_rapids.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/river_rapids.splv"

# River settings
RIVER_WIDTH = 20
RIVER_DEPTH = 15
RAPID_COUNT = 6
FOAM_DENSITY = 0.3

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_river_center(z, t):
    """Calculate the meandering river centerline"""
    flow_offset = t * 10  # Water flows along Z axis
    meander = np.sin((z + flow_offset) * 0.1) * 15
    return CENTER_X + int(meander)

def generate_riverbed(volume, t):
    """Create the rocky riverbed and banks"""
    rock_colors = [(101, 67, 33), (139, 69, 19), (160, 82, 45), (105, 105, 105)]
    
    for z in range(SIZE):
        river_center = get_river_center(z, t)
        
        for x in range(max(0, river_center - RIVER_WIDTH), 
                      min(SIZE, river_center + RIVER_WIDTH)):
            # Distance from river center
            dist_from_center = abs(x - river_center)
            
            # Create riverbed depth
            bed_depth = max(1, RIVER_DEPTH - int(dist_from_center * 0.8))
            noise = int(np.sin(x * 0.3 + z * 0.2 + t) * 2)
            bed_y = CENTER_Y - bed_depth + noise
            
            # Add rocks and sediment
            for y in range(max(0, bed_y - 5), bed_y + 1):
                rock_color = rock_colors[int((x + z + y) * 0.7) % len(rock_colors)]
                add_voxel(volume, x, y, z, rock_color)

def generate_water_flow(volume, t):
    """Create flowing water with depth-based opacity"""
    water_blue = (30, 144, 255)
    deep_blue = (0, 100, 200)
    
    for z in range(SIZE):
        river_center = get_river_center(z, t)
        flow_noise = np.sin(z * 0.2 + t * 3) * 2
        
        for x in range(max(0, river_center - RIVER_WIDTH + 2), 
                      min(SIZE, river_center + RIVER_WIDTH - 2)):
            dist_from_center = abs(x - river_center)
            
            # Water depth varies across river width
            water_depth = max(2, RIVER_DEPTH - int(dist_from_center * 0.6))
            surface_y = CENTER_Y + int(flow_noise)
            
            for y in range(max(0, surface_y - water_depth), surface_y + 1):
                depth_ratio = (surface_y - y) / water_depth
                
                # Deeper water is darker
                if depth_ratio > 0.7:
                    color = water_blue
                    alpha = min(255, int(180 + depth_ratio * 75))
                else:
                    color = deep_blue
                    alpha = min(255, int(200 + depth_ratio * 55))
                
                # Add flow turbulence
                turbulence = np.sin(x * 0.4 + z * 0.3 + t * 4 + y * 0.5)
                if turbulence > 0.3:
                    add_voxel(volume, x, y, z, color, alpha)

def generate_rapids_and_foam(volume, t):
    """Create white water rapids and foam"""
    foam_white = (255, 255, 255)
    foam_blue = (173, 216, 230)
    
    # Create rapids at specific locations
    for rapid_id in range(RAPID_COUNT):
        rapid_z = int((rapid_id / RAPID_COUNT) * SIZE)
        river_center = get_river_center(rapid_z, t)
        
        # Rapids area
        rapid_size = 8 + int(np.sin(rapid_id + t * 2) * 3)
        
        for dz in range(-rapid_size, rapid_size + 1):
            for dx in range(-rapid_size//2, rapid_size//2 + 1):
                z_pos = rapid_z + dz
                x_pos = river_center + dx
                
                if 0 <= z_pos < SIZE and 0 <= x_pos < SIZE:
                    # Create foam with random distribution
                    foam_intensity = np.sin(x_pos * 0.5 + z_pos * 0.3 + t * 5 + rapid_id)
                    foam_height = np.sin(x_pos * 0.2 + z_pos * 0.4 + t * 3)
                    
                    if foam_intensity > 0.2:
                        base_y = CENTER_Y + int(foam_height * 3)
                        
                        # Spray and foam above water
                        for dy in range(0, 4):
                            y_pos = base_y + dy
                            if 0 <= y_pos < SIZE:
                                spray_chance = np.sin(x_pos + z_pos + t * 6 + dy * 0.8)
                                
                                if spray_chance > 0.5:
                                    color = foam_white if dy > 1 else foam_blue
                                    alpha = max(100, int(255 - dy * 50))
                                    add_voxel(volume, x_pos, y_pos, z_pos, color, alpha)

def generate_surface_details(volume, t):
    """Add surface ripples and small foam patches"""
    light_foam = (240, 248, 255)
    
    for z in range(0, SIZE, 3):
        river_center = get_river_center(z, t)
        
        for x in range(max(0, river_center - RIVER_WIDTH + 5), 
                      min(SIZE, river_center + RIVER_WIDTH - 5)):
            
            # Surface ripples
            ripple = np.sin(x * 0.8 + z * 0.6 + t * 4) * np.cos(x * 0.3 + t * 3)
            
            if ripple > 0.6:
                surface_y = CENTER_Y + int(np.sin(z * 0.2 + t * 3) * 2)
                if 0 <= surface_y < SIZE - 1:
                    add_voxel(volume, x, surface_y + 1, z, light_foam, 180)

def generate_scene(volume, t):
    """Generate the complete river rapids scene"""
    generate_riverbed(volume, t)
    generate_water_flow(volume, t)
    generate_rapids_and_foam(volume, t)
    generate_surface_details(volume, 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 river rapids"):
    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 RIVER_WIDTH to create narrower or wider rivers
Change RAPID_COUNT to add more turbulent areas
Modify the rock_colors array for different riverbed materials
Add fish or debris by creating new voxel objects that flow with the current
Experiment with FOAM_DENSITY to control how much white water appears
Create waterfalls by adding vertical drops in the riverbed

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River Rapids - 3D Voxel Animation Learning Example

What this script does

How it works (simplified)