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Detecting sprite proximity and range in Scratch

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PA

ProximityDev_Alex

Posted on January 26, 2024 • Intermediate

📏 Need help with sprite distance detection

I’m working on a game where I need to detect when one sprite gets close to another sprite within a certain range or radius. Think like:

  • Enemy AI that activates when player gets close
  • Collectible items that glow when player approaches
  • Proximity-based interactions and triggers
  • Safe zones and danger zones

I’ve been trying to figure out the math and logic, but I’m getting confused with the distance calculations. How do I create an invisible “detection circle” around a sprite? 🤔

Any help with the scripting would be amazing!

DD

DistanceDetector_Sam

Replied 3 hours later • ⭐ Best Answer

Perfect question @ProximityDev_Alex! Distance detection is super useful for game mechanics. Let me show you several methods from simple to advanced:

📐 Understanding Distance Detection

Here’s how proximity detection works conceptually:

flowchart TD A[🎯 Sprite A Position] --> B[Calculate Distance] C[🎮 Sprite B Position] --> B B --> D{Distance < Range?} D -->|Yes| E[✅ Within Range] D -->|No| F[❌ Too Far] E --> G[Trigger Action] F --> H[No Action] G --> I[Examples:] I --> J[• Enemy attacks<br/>• Item glows<br/>• Sound plays<br/>• UI appears] B --> K[Distance Methods] K --> L[Built-in: distance to] K --> M[Custom: Pythagorean theorem] style A fill:#e1f5fe style C fill:#e1f5fe style E fill:#e8f5e8 style F fill:#ffebee style L fill:#fff3e0 style M fill:#f3e5f5

🚀 Method 1: Simple Built-in Distance

The easiest way using Scratch’s built-in distance block:

    when flag clicked
set [detection range v] to [100]  // Adjust this value

forever
if <(distance to [target sprite v]) < (detection range)> then
say [Target detected!] for [1] seconds
// Add your proximity actions here
else
say [Scanning...] for [1] seconds
end
end

⚡ Method 2: Multiple Range Zones

Create different behaviors for different distances:

    when flag clicked
set [close range v] to [50]
set [medium range v] to [100]
set [far range v] to [150]

forever
set [distance to target v] to (distance to [player v])

if <(distance to target) < (close range)> then
set [alert level v] to [HIGH]
say [DANGER! Too close!] for [1] seconds
set [color v] effect to [25]  // Red tint
else
if <(distance to target) < (medium range)> then
set [alert level v] to [MEDIUM]
say [Player nearby...] for [1] seconds
set [color v] effect to [0]  // Normal color
else
if <(distance to target) < (far range)> then
set [alert level v] to [LOW]
say [Player detected] for [1] seconds
set [brightness v] effect to [10]  // Slight glow
else
set [alert level v] to [NONE]
clear graphic effects
end
end
end
end

🧮 Method 3: Custom Distance Calculation

For when you need more control or want to understand the math:

    when flag clicked
forever
// Get positions of both sprites
set [target x v] to ([x position v] of [target sprite v])
set [target y v] to ([y position v] of [target sprite v])
set [my x v] to (x position)
set [my y v] to (y position)

// Calculate distance using Pythagorean theorem
set [x difference v] to ((target x) - (my x))
set [y difference v] to ((target y) - (my y))

// Distance = sqrt(x² + y²)
set [distance squared v] to (((x difference) * (x difference)) + ((y difference) * (y difference)))
set [actual distance v] to ([sqrt v] of (distance squared))

// Check if within range
if <(actual distance) < [75]> then
broadcast [proximity detected v]
end
end

🎯 Method 4: Optimized Performance Version

For games with many sprites - avoids expensive square root calculation:

    when flag clicked
set [range v] to [80]
set [range squared v] to ((range) * (range))  // Pre-calculate

forever
// Skip square root by comparing squared distances
set [x diff v] to (([x position v] of [player v]) - (x position))
set [y diff v] to (([y position v] of [player v]) - (y position))
set [distance squared v] to (((x diff) * (x diff)) + ((y diff) * (y diff)))

if <(distance squared) < (range squared)> then
// Player is within range!
set [ghost v] effect to [0]  // Make visible
point towards [player v]
else
set [ghost v] effect to [50]  // Make semi-transparent
end
end

🎮 Practical Applications

💡 Use Cases:
• Enemy AI: Activate when player approaches
• Collectibles: Glow or animate when nearby
• NPCs: Start dialogue when player is close
• Triggers: Open doors, play sounds, change scenes
• Power-ups: Auto-collect when in range

Start with Method 1 for simplicity, then upgrade to Method 2 for more complex behaviors! 🎯

PA

ProximityDev_Alex

Replied 1 hour later

@DistanceDetector_Sam This is exactly what I needed! 🎉

The multiple range zones approach is perfect for my enemy AI system. I love how you explained both the simple method and the optimized version. The performance tip about avoiding square root is really clever!

My game feels so much more interactive now. Thank you! 🙏

AI

AIExpert_Jordan

Replied 2 hours later

Great solutions! 🤖 Here are some advanced tips for AI behavior with proximity detection:

    // Smart AI that remembers player location
when flag clicked
set [last seen x v] to [0]
set [last seen y v] to [0]
set [search mode v] to [false]

forever
if <(distance to [player v]) < [120]> then
// Player detected - update last known position
set [last seen x v] to ([x position v] of [player v])
set [last seen y v] to ([y position v] of [player v])
set [search mode v] to [false]

// Direct pursuit
point towards [player v]
move [3] steps
else
if <(search mode) = [false]> then
// Lost player - go to last known position
set [search mode v] to [true]
end

// Move towards last known position
point in direction (([atan v] of ((last seen y) - (y position)) / ((last seen x) - (x position))) * [180] / [3.14159])
move [1] steps
end
end
  • 🎯 Line of sight: Combine distance with raycast detection
  • 🔊 Audio cues: Different sounds for different ranges
  • ⏱️ Reaction delays: Add realistic response times
  • 🧠 Memory systems: AI remembers where it last saw the player

Distance detection is the foundation of great AI! 🌟

VB

Vibelf_Community

Pinned Message • Moderator

🚀 Master Advanced Collision & Detection Systems!

Excellent discussion on proximity detection! For those looking to create even more sophisticated interaction systems, our experts can help with:

  • 🎯 Advanced collision detection algorithms
  • 🤖 Complex AI behavior systems
  • ⚡ Performance optimization for many sprites
  • 🌐 Multi-layered detection zones

📚 Related Detection Topics

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