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How to sync projectiles in multiplayer Scratch games using cloud variables

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MD

MultiplayerDev_Alex

Posted on January 24, 2024 • Advanced

🕷️ Need help syncing projectiles in my multiplayer spider game

Hey everyone! I’m working on a multiplayer game where players are spider-cats that shoot webs at each other. I’ve got the basic multiplayer movement working using cloud variables, but I’m struggling with making the web projectiles visible to all players.

The challenges I’m facing:

  • Already using 8/10 cloud variables for player positions
  • Need to sync web position, direction, and shooter ID
  • Cloud variables only support numbers, not text
  • Can only update one cloud variable per frame to avoid lag
  • Need efficient data encoding to fit multiple values in one variable

I’m using Griffpatch’s cloud player system but need to extend it for projectiles. Any help with optimized cloud variable usage would be amazing! 🎯

CN

CloudNetworking_Pro

Replied 4 hours later • ⭐ Best Answer

Excellent question @MultiplayerDev_Alex! Syncing projectiles efficiently requires smart data encoding and prediction algorithms. Here’s a comprehensive solution:

🌐 Multiplayer Projectile Architecture

Here’s how an optimized projectile sync system works:

flowchart TD A[🎮 Player Shoots] --> B[📊 Encode Projectile Data] B --> C[☁️ Send to Cloud] C --> D[📡 Other Players Receive] D --> E[🔍 Decode Data] E --> F[🎯 Predict Trajectory] F --> G[🎨 Render Projectile] B --> H[📦 Data Encoding] H --> I[🔢 Player ID (2 digits)] I --> J[📍 Start X (3 digits)] J --> K[📍 Start Y (3 digits)] K --> L[🧭 Direction (3 digits)] L --> M[⚡ Speed (2 digits)] M --> N[⏰ Timestamp (4 digits)] N --> O[📋 Combined: 17-digit number] O --> C E --> P[🔄 Reverse Encoding] P --> Q[📍 Extract Position] Q --> R[🧭 Extract Direction] R --> S[⚡ Extract Speed] S --> T[⏰ Extract Timestamp] T --> U[🎯 Calculate Current Position] U --> V[📊 Apply Physics] V --> W[🎨 Update Visual] W --> X[🔍 Check Collisions] X --> Y{Hit Target?} Y -->|Yes| Z[💥 Show Impact] Y -->|No| AA{Out of Bounds?} AA -->|Yes| BB[🗑️ Remove Projectile] AA -->|No| CC[⏭️ Next Frame] CC --> U Z --> DD[🎵 Play Sound] DD --> EE[📊 Update Score] EE --> BB style A fill:#e1f5fe style B fill:#c8e6c9 style F fill:#fff3e0 style U fill:#f3e5f5 style Z fill:#ffebee

🔧 Step 1: Data Encoding System

First, create an efficient encoding system for projectile data:

    // Encode projectile data into single number
define encode projectile (player id) (start x) (start y) (direction) (speed)
set [encoded data v] to [0]

// Player ID (2 digits: 01-99)
change [encoded data v] by ((player id) * [100000000000000000])

// Start X position (3 digits: 000-480, offset by +240)
change [encoded data v] by (((start x) + [240]) * [100000000000000])

// Start Y position (3 digits: 000-360, offset by +180)
change [encoded data v] by (((start y) + [180]) * [100000000000])

// Direction (3 digits: 000-360)
change [encoded data v] by ((direction) * [100000000])

// Speed (2 digits: 01-99)
change [encoded data v] by ((speed) * [1000000])

// Timestamp (6 digits: current time mod 1000000)
change [encoded data v] by ((timer) mod [1000000])

report (encoded data)

🔍 Step 2: Data Decoding System

Create the reverse process to extract data:

    // Decode projectile data from single number
define decode projectile (encoded data)
set [temp data v] to (encoded data)

// Extract player ID
set [decoded player id v] to ((temp data) / [100000000000000000])
set [decoded player id v] to (round (decoded player id))
change [temp data v] by (0 - ((decoded player id) * [100000000000000000]))

// Extract start X
set [decoded start x v] to ((temp data) / [100000000000000])
set [decoded start x v] to ((round (decoded start x)) - [240])
change [temp data v] by (0 - (((decoded start x) + [240]) * [100000000000000]))

// Extract start Y
set [decoded start y v] to ((temp data) / [100000000000])
set [decoded start y v] to ((round (decoded start y)) - [180])
change [temp data v] by (0 - (((decoded start y) + [180]) * [100000000000]))

// Extract direction
set [decoded direction v] to ((temp data) / [100000000])
set [decoded direction v] to (round (decoded direction))
change [temp data v] by (0 - ((decoded direction) * [100000000]))

// Extract speed
set [decoded speed v] to ((temp data) / [1000000])
set [decoded speed v] to (round (decoded speed))
change [temp data v] by (0 - ((decoded speed) * [1000000]))

// Extract timestamp
set [decoded timestamp v] to (temp data)

🚀 Step 3: Projectile Shooting System

Implement the shooting mechanism with cloud sync:

    // When player shoots
when [space v] key pressed
if <(can shoot) = [true]> then
set [can shoot v] to [false]

// Calculate projectile data
set [shoot x v] to (x position)
set [shoot y v] to (y position)
set [shoot direction v] to (direction)
set [shoot speed v] to [15]

// Encode and send to cloud
encode projectile (my player id) (shoot x) (shoot y) (shoot direction) (shoot speed)
set [☁ projectile data v] to (encoded data)

// Create local projectile
create clone of [web projectile v]

// Cooldown timer
wait [0.5] seconds
set [can shoot v] to [true]
end

🎯 Step 4: Projectile Prediction System

Create predictive rendering for smooth gameplay:

    // Projectile clone behavior
when I start as a clone
decode projectile (☁ projectile data)

// Skip if it's my own projectile (already rendered locally)
if <(decoded player id) = (my player id)> then
delete this clone
end

// Calculate time elapsed since shot
set [time elapsed v] to ((timer) - (decoded timestamp))
if <(time elapsed) < [0]> then
change [time elapsed v] by [1000000]
end

// Predict current position
set [current x v] to (decoded start x)
set [current y v] to (decoded start y)
point in direction (decoded direction)

// Move to predicted position
repeat (time elapsed)
move (decoded speed) steps
if <<touching [edge v]?> or <touching color [#000000]?>> then
delete this clone
end
end

// Continue normal movement
forever
move (decoded speed) steps
if <<touching [edge v]?> or <touching color [#000000]?>> then
delete this clone
end

// Check collision with players
if <touching [player v]?> then
broadcast [projectile hit v]
delete this clone
end
end

⚡ Step 5: Optimized Cloud Management

Manage cloud variables efficiently:

    // Cloud variable manager
when flag clicked
forever
// Only update one cloud variable per frame
if <(cloud update queue) > [0]> then
if <(cloud update type) = [projectile]> then
set [☁ projectile data v] to (pending projectile data)
set [cloud update queue v] to [0]
end
end

// Check for new projectile data
if <not <(☁ projectile data) = (last projectile data)>> then
set [last projectile data v] to (☁ projectile data)
if <(☁ projectile data) > [0]> then
broadcast [new projectile v]
end
end
end

// Queue projectile update
define queue projectile update (data)
set [pending projectile data v] to (data)
set [cloud update type v] to [projectile]
set [cloud update queue v] to [1]

🎨 Step 6: Visual Effects and Polish

Add professional visual effects:

    // Projectile trail effect
when I start as a clone
set [ghost v] effect to [0]
forever
create clone of [trail particle v]
wait [0.05] seconds
end

// Trail particle
when I start as a clone
set size to [50] %
repeat [20]
change [ghost v] effect by [5]
change size by [-2]
end
delete this clone

// Impact effect
when I receive [projectile hit v]
repeat [10]
create clone of [impact particle v]
end
play sound [web hit v]

🚀 Step 7: Advanced Features

Add these enhancements for professional multiplayer:

Lag Compensation:

    // Compensate for network lag
define compensate lag (ping time)
set [lag compensation v] to ((ping time) / [1000])
move ((decoded speed) * (lag compensation)) steps

Collision Prediction:

    // Predict collision before it happens
define predict collision
set [future x v] to ((x position) + ((decoded speed) * [3]))
set [future y v] to ((y position) + ((decoded speed) * [3]))
if <(distance to [player v]) < [30]> then
broadcast [incoming projectile v]
end

This system efficiently syncs projectiles using minimal cloud variables while maintaining smooth gameplay! 🕷️✨

MD

MultiplayerDev_Alex

Replied 2 hours later

@CloudNetworking_Pro This is absolutely incredible! 🤯 The data encoding system is genius!

I implemented the basic version and it works perfectly. The predictive rendering makes the projectiles look smooth even with network lag. The 17-digit encoding fits all the data I need in just one cloud variable!

One question - how would I handle multiple projectiles being shot at the same time by different players?

QM

QueueMaster_Sam

Replied 45 minutes later

@MultiplayerDev_Alex Great question! Here’s how to handle multiple simultaneous projectiles:

    // Projectile queue system
when flag clicked
set [projectile queue v] to []
forever
if <(length of [projectile queue v]) > [0]> then
set [current projectile v] to (item [1] of [projectile queue v])
delete [1] of [projectile queue v]

// Process this projectile
decode projectile (current projectile)
create clone of [web projectile v]

wait [0.1] seconds // Small delay between processing
end
end

// When receiving new projectile data
when I receive [new projectile v]
add (☁ projectile data) to [projectile queue v]

This queues multiple projectiles and processes them sequentially! 🎯

VB

Vibelf_Community

Pinned Message • Moderator

🚀 Master Multiplayer Game Development

Amazing discussion on projectile synchronization! For those wanting to create even more advanced multiplayer systems, our experts can help you build:

  • 🌐 Real-time chat systems
  • 🏆 Leaderboards and rankings
  • 🎮 Lobby and matchmaking
  • ⚡ Lag compensation algorithms
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