Session APIs - Managing Your Scene

Overview

Vuer provides a set of intuitive APIs for managing your 3D scene dynamically. Understanding when to use each API is crucial for building efficient, interactive applications.

This guide covers the six core session APIs:

session.set - Initialize the scene
session.upsert - Update or insert elements
session.update - Update existing elements only
session.add - Add new elements
session.remove - Remove elements
session.till - Wait for client events

Quick Reference

API	Purpose	Behavior if element exists	Behavior if element missing
`session.set`	Initialize root scene	N/A (replaces entire scene)	N/A (creates new scene)
`session.upsert`	Ensure element exists	Updates it	Creates it
`session.update`	Modify existing only	Updates it	Does nothing (NOOP)
`session.add`	Add new elements	Error/duplicate	Creates it
`session.remove`	Delete elements	Removes it	Does nothing
`session.till`	Wait for event	N/A	Waits until received

1. session.set - Initialize the Scene

Purpose: Set up the root scene structure. This should be called once at the beginning of your session.

When to use:

At the start of your session to initialize the scene
When you need to completely replace the entire scene structure

Accepts: Only Scene or DefaultScene objects

python

from vuer import Vuer, VuerSession
from vuer.schemas import DefaultScene, Box, Sphere

app = Vuer()

@app.spawn(start=True)
async def main(session: VuerSession):
    # Initialize the scene once
    session.set @ DefaultScene(
        Box(key="box-1", args=[1, 1, 1], position=[0, 0, 0]),
        Sphere(key="sphere-1", args=[0.5], position=[2, 0, 0]),
    )

    await session.forever()

2. session.upsert - Update or Insert (Most Common)

Purpose: Ensure an element with a specific key exists with the given properties. If it exists, update it; if not, create it.

When to use:

When you want to guarantee an element exists (most common use case)
For dynamic, real-time updates where you don't know if the element was created yet
When building interactive applications with frequent updates

Behavior:

If element with the key exists → updates it
If element doesn't exist → inserts it as new

python

@app.spawn(start=True)
async def main(session: VuerSession):
    # Initialize scene
    session.set @ DefaultScene()

    # Upsert elements - creates them if they don't exist
    session.upsert @ Box(
        key="dynamic-box",
        args=[1, 1, 1],
        position=[0, 0, 0],
        color="red"
    )

    # Later, update the same box (or create if removed)
    await session.sleep(1)
    session.upsert @ Box(
        key="dynamic-box",
        position=[2, 0, 0],  # Moved to new position
        color="blue"         # Changed color
    )

    await session.forever()

Advanced: Targeting specific parents

python

# Upsert into a specific parent node
session.upsert(
    Box(key="child-box", args=[0.5, 0.5, 0.5]),
    to="parent-group-key"
)

# Upsert multiple elements at once
session.upsert @ [
    Box(key="box-1", position=[0, 0, 0]),
    Sphere(key="sphere-1", position=[2, 0, 0]),
    Cylinder(key="cyl-1", position=[4, 0, 0])
]

3. session.update - Update Existing Only

Purpose: Modify existing elements without creating new ones. Safe for conditional updates.

When to use:

When you want to update elements but not create them if they don't exist
For defensive programming where you want to avoid accidental creation
When you're unsure if an element exists

Behavior:

If element exists → updates it
If element doesn't exist → does nothing (NOOP)

python

@app.spawn(start=True)
async def main(session: VuerSession):
    # Initialize with a box
    session.set @ DefaultScene(
        Box(key="my-box", args=[1, 1, 1], position=[0, 0, 0])
    )

    # This updates the existing box
    session.update @ Box(key="my-box", color="blue")  # ✅ Works

    # This does nothing because "other-box" doesn't exist
    session.update @ Box(key="other-box", color="red")  # ❌ NOOP (no error)

    await session.forever()

Real-world example: Safe property updates

python

# Only update position if the robot model has been loaded
session.update @ Urdf(
    key="robot",
    position=new_position,
    jointValues=new_joint_values
)
# If robot isn't loaded yet, this won't create a duplicate or error

4. session.add - Add New Elements

Purpose: Explicitly add new elements to the scene. Assumes the element doesn't already exist.

When to use:

When you're certain the element doesn't exist yet
For one-time additions where you control the lifecycle
When you want explicit "add" semantics in your code

Behavior:

If element doesn't exist → adds it
If element exists → behavior depends on implementation (may create duplicate or error)

python

@app.spawn(start=True)
async def main(session: VuerSession):
    # Initialize scene
    session.set @ DefaultScene()

    # Add new elements explicitly
    session.add @ Box(
        key="new-box",
        args=[1, 1, 1],
        position=[0, 0, 0]
    )

    # Add to specific parent
    session.add(
        Sphere(key="child-sphere", args=[0.3]),
        to="new-box"  # Add as child of the box
    )

    await session.forever()

Adding multiple elements:

python

# Add multiple elements at once
session.add @ [
    Box(key="box-1", position=[0, 0, 0]),
    Box(key="box-2", position=[2, 0, 0]),
    Box(key="box-3", position=[4, 0, 0])
]

5. session.remove - Delete Elements

Purpose: Remove elements from the scene by their keys.

When to use:

When you need to delete specific elements
For cleanup operations
To remove temporary visualizations

Behavior:

Removes elements matching the provided key(s)
Safe to call even if elements don't exist

python

@app.spawn(start=True)
async def main(session: VuerSession):
    # Initialize scene with multiple boxes
    session.set @ DefaultScene(
        Box(key="box-1", position=[0, 0, 0]),
        Box(key="box-2", position=[2, 0, 0]),
        Box(key="box-3", position=[4, 0, 0])
    )

    # Remove a single element
    await session.sleep(1)
    session.remove @ "box-1"

    # Remove multiple elements
    await session.sleep(1)
    session.remove @ ["box-2", "box-3"]

    await session.forever()

Practical example: Toggle visualization

python

async def toggle_grid(session: VuerSession, visible: bool):
    if visible:
        session.upsert @ Grid(key="main-grid")
    else:
        session.remove @ "main-grid"

Common Patterns

Pattern 1: Initialize then Update

The most common pattern: use set once, then upsert for updates.

python

@app.spawn(start=True)
async def main(session: VuerSession):
    # 1. Initialize scene once
    session.set @ DefaultScene(
        Box(key="robot-base", args=[1, 0.5, 1])
    )

    # 2. Continuously update elements
    for i in range(100):
        session.upsert @ Box(
            key="robot-base",
            position=[i * 0.1, 0, 0]  # Move along x-axis
        )
        await session.sleep(0.1)

Pattern 2: Dynamic Element Management

Add and remove elements dynamically based on application state.

python

@app.spawn(start=True)
async def main(session: VuerSession):
    session.set @ DefaultScene()

    active_markers = set()

    # Add markers as they appear
    for i, position in enumerate(detected_positions):
        key = f"marker-{i}"
        session.add @ Sphere(
            key=key,
            args=[0.1],
            position=position
        )
        active_markers.add(key)

    # Remove old markers
    for key in old_markers:
        session.remove @ key
        active_markers.discard(key)

Pattern 3: Efficient Batch Updates

Update multiple elements efficiently.

python

# Update multiple objects in one call
session.upsert @ [
    Box(key="box-1", position=positions[0]),
    Box(key="box-2", position=positions[1]),
    Box(key="box-3", position=positions[2]),
    Box(key="box-4", position=positions[3])
]

Pattern 4: Safe Updates with Fallback

Use update for conditional changes, upsert when you need guarantees.

python

# Try to update existing camera
session.update @ PerspectiveCamera(
    key="main-camera",
    position=[5, 5, 5]
)

# If camera might not exist, use upsert instead
session.upsert @ PerspectiveCamera(
    key="main-camera",
    position=[5, 5, 5],
    makeDefault=True
)

Performance Considerations

Efficient Updates

❌ Inefficient: Rebuilding entire scene

python

# Bad: rebuilding scene every frame
for frame in frames:
    session.set @ DefaultScene(
        Box(key="animated-box", position=frame.position),
        Sphere(key="static-sphere", position=[0, 0, 0]),
        # ... many other static elements
    )

✅ Efficient: Updating only what changed

python

# Good: initialize once, update only animated elements
session.set @ DefaultScene(
    Box(key="animated-box", position=[0, 0, 0]),
    Sphere(key="static-sphere", position=[0, 0, 0]),
    # ... other static elements
)

for frame in frames:
    session.upsert @ Box(
        key="animated-box",
        position=frame.position  # Only update position
    )

Batch Operations

When updating multiple elements, batch them into a single operation:

python

# Better: batch update
session.upsert @ [
    Box(key=f"box-{i}", position=[i, 0, 0])
    for i in range(10)
]

# Less efficient: individual updates
for i in range(10):
    session.upsert @ Box(key=f"box-{i}", position=[i, 0, 0])

Summary

Decision Tree:

Setting up initial scene? → Use session.set
Need element to exist with specific properties? → Use session.upsert ⭐ (most common)
Only update if exists, otherwise skip? → Use session.update
Adding definitely new elements? → Use session.add
Removing elements? → Use session.remove
Need to wait for a client event? → Use session.till

Most Common Usage:

python

@app.spawn(start=True)
async def main(session: VuerSession):
    # Step 0: Identify client type (optional)
    e = await session.till("INIT")
    print(f"Client: {e.value.get('client')}")

    # Step 1: Initialize scene (once)
    session.set @ DefaultScene()

    # Step 2: Add/update elements dynamically (many times)
    while True:
        session.upsert @ Box(
            key="animated-box",
            position=compute_position(),
            rotation=compute_rotation()
        )
        await session.sleep(0.016)  # ~60 FPS

6. session.till - Wait for Client Events

Purpose: Wait for and receive a specific event type from the client. This is useful for awaiting events like INIT to identify the client type.

When to use:

When you need to wait for a specific event before proceeding
To identify client type (browser vs Python client) on connection
For handshake or initialization sequences

Behavior:

Registers a one-time handler for the specified event type
Returns the event when received
Optionally times out if event doesn't arrive

python

@app.spawn(start=True)
async def main(session: VuerSession):
    # Wait for the INIT event from the client
    e = await session.till("INIT")

    # Check if it's a Python client or browser
    client = e.value.get('client')

    if client == 'python':
        print("Python client connected!")
        print(f"  Platform: {e.value.get('platform')}")
        print(f"  Python: {e.value.get('pythonVersion')}")
    else:
        # Browser client
        print(f"Browser connected!")
        print(f"  User Agent: {e.value.get('userAgent')}")
        print(f"  Screen: {e.value.get('screenWidth')}x{e.value.get('screenHeight')}")

    session.set @ DefaultScene()
    await session.forever()

With timeout:

python

import asyncio

@app.spawn(start=True)
async def main(session: VuerSession):
    try:
        # Wait up to 5 seconds for INIT
        e = await session.till("INIT", timeout=5.0)
        print(f"Client connected: {e.value.get('clientType')}")
    except asyncio.TimeoutError:
        print("No INIT received within 5 seconds")

    await session.forever()

Client Info (INIT Event Value):

Common fields (both clients):

client — "browser" or "python"
clientVersion — library version
timezone — IANA format, e.g., "America/Los_Angeles"
timezoneOffset — minutes from UTC

Python clients send:

python

{
    "client": "python",
    "clientVersion": "0.1.x",
    "pythonVersion": "3.11.13",
    "platform": "Darwin",
    "platformVersion": "24.2.0",
    "machine": "arm64",
    "timezone": "America/Los_Angeles",
    "timezoneOffset": 480
}

Browser clients send:

python

{
    "client": "browser",
    "clientVersion": "0.0.97",
    "userAgent": "Mozilla/5.0...",
    "screenWidth": 2560,
    "screenHeight": 1440,
    "devicePixelRatio": 2,
    "timezone": "America/Los_Angeles",
    "timezoneOffset": 480
}

Session APIs - Managing Your Scene

Overview

Quick Reference

1. session.set - Initialize the Scene

2. session.upsert - Update or Insert (Most Common)

3. session.update - Update Existing Only

4. session.add - Add New Elements

5. session.remove - Delete Elements

Common Patterns

Pattern 1: Initialize then Update

Pattern 2: Dynamic Element Management

Pattern 3: Efficient Batch Updates

Pattern 4: Safe Updates with Fallback

Performance Considerations

Efficient Updates

Batch Operations

Summary

6. session.till - Wait for Client Events

See Also