3D Voxel Animation: Candle

This guide walks you through how to generate a looping 3D voxel animation of a candle using SpatialStudio. The script creates a realistic candle with a flickering flame and melting wax that dances 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 1 animated candle with:
- A cylindrical wax body that appears to melt
- A dynamic flickering flame
- Glowing light effects around the flame
- Realistic wax drip animations
Animates the flame flickering naturally for 8 seconds at 30 FPS
Outputs the file candle.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).
Candle body The candle is drawn as a cylinder with subtle variations to simulate melting wax texture.
Flame animation The flame uses sine waves and noise functions to create realistic flickering motion.
Glow effects Orange and yellow voxels are layered around the flame to simulate light emission.
Wax drips Animated dripping effects are added to the sides of the candle for realism.
Animation loop A normalized time variable t cycles from 0 → 2π, ensuring the flame flicker 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 candle.py and run:

python candle.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/candle.splv"

# Candle settings
CANDLE_HEIGHT = 40
CANDLE_RADIUS = 8
FLAME_HEIGHT = 15
WICK_HEIGHT = 3

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_candle_body(volume, cx, cy, cz, t):
    wax_color = (255, 248, 220)  # Cream color
    
    for y in range(CANDLE_HEIGHT):
        current_y = cy - CANDLE_HEIGHT//2 + y
        # Add slight melting effect
        melt_factor = max(0, 1.0 - (CANDLE_HEIGHT - y) / CANDLE_HEIGHT * 0.3)
        current_radius = CANDLE_RADIUS + int(melt_factor * 2 * np.sin(t + y * 0.1))
        
        for dx in range(-current_radius, current_radius + 1):
            for dz in range(-current_radius, current_radius + 1):
                distance = np.sqrt(dx*dx + dz*dz)
                if distance <= current_radius:
                    # Add texture variation
                    brightness = 0.9 + 0.1 * np.sin(dx * 0.3 + dz * 0.3 + t * 0.2)
                    final_color = tuple(int(c * brightness) for c in wax_color)
                    add_voxel(volume, cx + dx, current_y, cz + dz, final_color)

def generate_wax_drips(volume, cx, cy, cz, t):
    drip_color = (245, 238, 200)  # Slightly darker wax
    
    # Generate several drip streams
    for i in range(4):
        angle = (i / 4) * 2 * np.pi + t * 0.1
        drip_x = cx + int((CANDLE_RADIUS + 1) * np.cos(angle))
        drip_z = cz + int((CANDLE_RADIUS + 1) * np.sin(angle))
        
        # Animated drip length
        drip_length = int(8 + 4 * np.sin(t * 1.5 + i))
        start_y = cy + CANDLE_HEIGHT//2 - 5
        
        for j in range(drip_length):
            drip_y = start_y - j
            if j > 3:  # Make drips get thinner
                offset = int((j - 3) * 0.3)
                if np.random.random() > 0.7:  # Sparse drips
                    add_voxel(volume, drip_x, drip_y, drip_z, drip_color)

def generate_wick(volume, cx, cy, cz, t):
    wick_color = (101, 67, 33)  # Dark brown
    wick_base_y = cy + CANDLE_HEIGHT//2
    
    for i in range(WICK_HEIGHT):
        wick_y = wick_base_y + i
        # Add slight sway to the wick
        sway = int(np.sin(t * 3 + i * 0.5) * 0.5)
        add_voxel(volume, cx + sway, wick_y, cz, wick_color)

def generate_flame(volume, cx, cy, cz, t):
    flame_base_y = cy + CANDLE_HEIGHT//2 + WICK_HEIGHT
    
    # Flame colors from hot (white/yellow) to cool (red/orange)
    flame_colors = [
        (255, 255, 255),  # White hot center
        (255, 255, 100),  # Bright yellow
        (255, 200, 50),   # Yellow-orange
        (255, 150, 0),    # Orange
        (255, 100, 0),    # Red-orange
        (200, 50, 0),     # Red
    ]
    
    for y in range(FLAME_HEIGHT):
        flame_y = flame_base_y + y
        progress = y / FLAME_HEIGHT
        
        # Flame gets narrower and more turbulent as it rises
        base_width = max(1, int((1 - progress) * 4))
        flicker_intensity = progress * 2
        
        # Add flickering using multiple sine waves
        flicker = np.sin(t * 5 + y * 0.3) * flicker_intensity
        flicker += np.sin(t * 3.7 + y * 0.5) * flicker_intensity * 0.5
        flicker += np.sin(t * 7.1 + y * 0.1) * flicker_intensity * 0.3
        
        flame_width = max(1, int(base_width + flicker))
        
        # Choose color based on height and intensity
        color_index = min(len(flame_colors) - 1, int(progress * len(flame_colors)))
        flame_color = flame_colors[color_index]
        
        for dx in range(-flame_width, flame_width + 1):
            for dz in range(-flame_width, flame_width + 1):
                distance = np.sqrt(dx*dx + dz*dz)
                if distance <= flame_width:
                    # Add randomness for flame texture
                    if np.random.random() > 0.3:
                        flame_x = cx + dx + int(np.sin(t * 2 + y * 0.2) * 0.5)
                        flame_z = cz + dz
                        add_voxel(volume, flame_x, flame_y, flame_z, flame_color)

def generate_glow_effects(volume, cx, cy, cz, t):
    glow_color = (255, 200, 100)  # Warm glow
    flame_center_y = cy + CANDLE_HEIGHT//2 + WICK_HEIGHT + FLAME_HEIGHT//2
    
    glow_radius = int(12 + 2 * np.sin(t * 2))
    
    for dx in range(-glow_radius, glow_radius + 1):
        for dy in range(-glow_radius//2, glow_radius//2 + 1):
            for dz in range(-glow_radius, glow_radius + 1):
                distance = np.sqrt(dx*dx + dy*dy*2 + dz*dz)  # Flatten vertically
                if distance <= glow_radius:
                    # Check if voxel is empty (don't overwrite existing voxels)
                    vx, vy, vz = cx + dx, flame_center_y + dy, cz + dz
                    if (0 <= vx < SIZE and 0 <= vy < SIZE and 0 <= vz < SIZE and
                        volume[vx, vy, vz, 3] == 0):
                        # Fade glow based on distance
                        intensity = max(0, 1 - distance / glow_radius)
                        if intensity > 0.1 and np.random.random() > 0.8:
                            alpha_color = tuple(int(c * intensity * 0.3) for c in glow_color)
                            volume[vx, vy, vz, :3] = alpha_color
                            volume[vx, vy, vz, 3] = int(255 * intensity * 0.2)

def generate_scene(volume, t):
    generate_candle_body(volume, CENTER_X, CENTER_Y, CENTER_Z, t)
    generate_wax_drips(volume, CENTER_X, CENTER_Y, CENTER_Z, t)
    generate_wick(volume, CENTER_X, CENTER_Y, CENTER_Z, t)
    generate_glow_effects(volume, CENTER_X, CENTER_Y, CENTER_Z, t)
    generate_flame(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 candle"):
    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 FLAME_HEIGHT to make the flame taller or shorter.
Change flame_colors to create different colored flames (blue, green, etc.).
Modify CANDLE_RADIUS to make thicker or thinner candles.
Add multiple candles by calling the generation functions with different positions.
Experiment with flicker_intensity for more or less dramatic flame movement.

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