Fish Swimming Animation

This guide walks you through how to generate a looping 3D voxel animation of fish using SpatialStudio. The script creates colorful fish that swim, glide, and move their fins 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
Spawns 6 fish, each with:
- An elliptical voxel body with scales
- Animated fins and tail
- Eyes that follow their swimming direction
Animates them swimming in circular patterns for 8 seconds at 30 FPS
Outputs the file fish.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).
Fish body Fish are drawn as elongated ellipsoids with procedural scale patterns for realistic texture.
Fins and tail Each fish gets animated pectoral fins and a tail that wave naturally as they swim.
Eyes Small black voxels with white highlights are positioned on each side of the fish head.
Animation loop A normalized time variable t cycles from 0 → 2π, creating smooth swimming motions and fin 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 fish.py and run:

python fish.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/fish.splv"

# Fish settings
FISH_COUNT = 6
FISH_LENGTH = 12
FISH_HEIGHT = 6
FISH_WIDTH = 4

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 generate_fish_body(volume, cx, cy, cz, color, direction, t):
    # Create elliptical fish body with scales
    for dx in range(-FISH_LENGTH//2, FISH_LENGTH//2 + 1):
        for dy in range(-FISH_HEIGHT//2, FISH_HEIGHT//2 + 1):
            for dz in range(-FISH_WIDTH//2, FISH_WIDTH//2 + 1):
                # Ellipsoid equation
                ellipse_val = (dx*dx)/(FISH_LENGTH//2)**2 + (dy*dy)/(FISH_HEIGHT//2)**2 + (dz*dz)/(FISH_WIDTH//2)**2
                if ellipse_val <= 1.0:
                    # Add scale pattern
                    scale_pattern = np.sin(dx * 0.5) * np.sin(dy * 0.7) * 0.2
                    brightness = 1.0 + scale_pattern
                    final_color = tuple(min(255, int(c * brightness)) for c in color)
                    
                    # Rotate based on swimming direction
                    rx = int(cx + dx * np.cos(direction) - dz * np.sin(direction))
                    ry = cy + dy
                    rz = int(cz + dx * np.sin(direction) + dz * np.cos(direction))
                    add_voxel(volume, rx, ry, rz, final_color)

def generate_fins(volume, cx, cy, cz, direction, t, fin_color):
    # Animated pectoral fins
    fin_wave = np.sin(t * 4.0) * 0.3
    fin_size = 3
    
    # Left fin
    for i in range(fin_size):
        fx = cx + int((2 + i) * np.cos(direction + np.pi/2 + fin_wave))
        fy = cy - 1
        fz = cz + int((2 + i) * np.sin(direction + np.pi/2 + fin_wave))
        add_voxel(volume, fx, fy, fz, fin_color)
    
    # Right fin
    for i in range(fin_size):
        fx = cx + int((2 + i) * np.cos(direction - np.pi/2 - fin_wave))
        fy = cy - 1
        fz = cz + int((2 + i) * np.sin(direction - np.pi/2 - fin_wave))
        add_voxel(volume, fx, fy, fz, fin_color)

def generate_tail(volume, cx, cy, cz, direction, t, tail_color):
    # Animated tail
    tail_wave = np.sin(t * 5.0) * 0.4
    tail_length = 4
    
    for i in range(1, tail_length + 1):
        # Tail gets wider as it goes back
        tail_spread = i // 2
        tail_x = cx - int((FISH_LENGTH//2 + i) * np.cos(direction))
        tail_z = cz - int((FISH_LENGTH//2 + i) * np.sin(direction))
        
        # Main tail spine
        add_voxel(volume, tail_x, cy, tail_z, tail_color)
        
        # Tail spread (top and bottom)
        if i > 1:
            sway = int(tail_wave * i * 0.5)
            add_voxel(volume, tail_x + sway, cy + tail_spread, tail_z, tail_color)
            add_voxel(volume, tail_x + sway, cy - tail_spread, tail_z, tail_color)

def generate_eyes(volume, cx, cy, cz, direction):
    # Eye positions on sides of head
    eye_offset = 2
    eye_x = cx + int(eye_offset * np.cos(direction))
    eye_z = cz + int(eye_offset * np.sin(direction))
    
    # Left eye
    left_eye_x = eye_x + int(np.cos(direction + np.pi/2))
    left_eye_z = eye_z + int(np.sin(direction + np.pi/2))
    add_voxel(volume, left_eye_x, cy + 1, left_eye_z, (0, 0, 0))
    add_voxel(volume, left_eye_x, cy + 2, left_eye_z, (255, 255, 255))
    
    # Right eye
    right_eye_x = eye_x + int(np.cos(direction - np.pi/2))
    right_eye_z = eye_z + int(np.sin(direction - np.pi/2))
    add_voxel(volume, right_eye_x, cy + 1, right_eye_z, (0, 0, 0))
    add_voxel(volume, right_eye_x, cy + 2, right_eye_z, (255, 255, 255))

def generate_school(volume, t):
    fish_colors = [
        (255, 140, 0),    # Orange
        (30, 144, 255),   # Dodger Blue
        (255, 69, 0),     # Red Orange
        (50, 205, 50),    # Lime Green
        (255, 20, 147),   # Deep Pink
        (138, 43, 226),   # Blue Violet
    ]
    
    for i in range(FISH_COUNT):
        # Each fish swims in its own circular pattern
        base_angle = (i / FISH_COUNT) * 2 * np.pi
        swim_radius = 25 + 10 * np.sin(i * 0.7)
        
        # Swimming motion
        angle = base_angle + t * 0.5 + i * 0.3
        x = CENTER_X + int(swim_radius * np.cos(angle))
        z = CENTER_Z + int(swim_radius * np.sin(angle))
        y = CENTER_Y + int(8 * np.sin(t * 0.8 + i * 0.5))  # Vertical bobbing
        
        # Swimming direction
        direction = angle + np.pi/2
        
        color = fish_colors[i % len(fish_colors)]
        fin_color = tuple(max(20, c - 50) for c in color)  # Darker fins
        
        # Generate fish parts
        generate_fish_body(volume, x, y, z, color, direction, t)
        generate_fins(volume, x, y, z, direction, t, fin_color)
        generate_tail(volume, x, y, z, direction, t, fin_color)
        generate_eyes(volume, x, y, z, direction)

def generate_bubbles(volume, t):
    # Add some floating bubbles for atmosphere
    bubble_color = (200, 230, 255)
    for i in range(15):
        bubble_x = CENTER_X + int(20 * np.sin(t * 0.3 + i))
        bubble_y = int((CENTER_Y - 40 + (t * 10 + i * 8) % 80))  # Rising bubbles
        bubble_z = CENTER_Z + int(15 * np.cos(t * 0.4 + i * 0.7))
        
        # Small bubble (1-2 voxels)
        add_voxel(volume, bubble_x, bubble_y, bubble_z, bubble_color)
        if i % 3 == 0:  # Some bigger bubbles
            add_voxel(volume, bubble_x + 1, bubble_y, bubble_z, bubble_color)

def generate_scene(volume, t):
    generate_school(volume, t)
    generate_bubbles(volume, t)

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

for frame in tqdm(range(FRAMES), desc="Generating fish"):
    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

Change FISH_COUNT to create a larger or smaller school.
Modify fish_colors to use different color schemes.
Adjust swim_radius to make fish swim in tighter or wider circles.
Add seaweed or coral by creating vertical structures with add_voxel().
Experiment with different swimming patterns by changing the angle calculations.

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