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How to detect collision with invisible walls in Scratch platformers

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PD

PlatformerDev_Alex

Posted on March 12, 2023 • Intermediate

🚧 How to create invisible walls in platformers?

Hi everyone! I’m working on a platformer game and I want to add invisible walls to create boundaries and secret areas. I’ve tried using the ghost effect to make walls invisible, but I’m having trouble with collision detection.

The walls are invisible now, but the player just passes through them instead of colliding. How can I make them act like normal walls while staying completely invisible?

Any help with the collision detection code would be greatly appreciated! 🎮

CM

CollisionMaster_Pro

Replied 4 minutes later • ⭐ Best Answer

Great question @PlatformerDev_Alex! Invisible walls are a fantastic game mechanic. Here are multiple methods to implement them:

🔍 Invisible Wall Detection Methods

Here’s how different collision detection approaches work:

flowchart TD A[🎮 Player Movement] --> B{Collision Method?} B -->|Ghost Effect Method| C[👻 Set Ghost to 100%] B -->|Pen-Based Method| D[🖊️ Draw with Pen] B -->|Coordinate Method| E[📐 Use X/Y Coordinates] C --> F[Use Touching Block] D --> G[Calculate Geometry] E --> H[Check Position Ranges] F --> I{Touching Wall?} G --> I H --> I I -->|Yes| J[🚫 Block Movement] I -->|No| K[✅ Allow Movement] J --> L[Reverse Last Move] K --> M[Continue Game] L --> N[🎯 Wall Collision!] style A fill:#e1f5fe style C fill:#f3e5f5 style D fill:#e8f5e8 style E fill:#fff3e0 style N fill:#fce4ec

👻 Method 1: Ghost Effect (Recommended)

The simplest and most effective method:

    // In your invisible wall sprite
when flag clicked
set [ghost v] effect to [100]  // Completely invisible
forever
// Wall stays in position
go to x: [200] y: [0]  // Set wall position
end

// In your player sprite
when flag clicked
forever
if <key [right arrow v] pressed?> then
change x by [5]
if <touching [Invisible Wall v]?> then
change x by [-5]  // Reverse movement
// Optional: play sound effect
play sound [bump v]
end
end

if <key [left arrow v] pressed?> then
change x by [-5]
if <touching [Invisible Wall v]?> then
change x by [5]  // Reverse movement
end
end
end

🎨 Method 2: Custom Costume Approach

For more control over wall appearance:

    // Create a wall sprite with transparent costume
// In the wall sprite
when flag clicked
switch costume to [transparent wall v]  // Invisible costume
show  // Sprite is visible but costume is transparent

// Alternative: Use ghost effect with slight visibility
set [ghost v] effect to [99]  // Almost invisible (1% visible)
// This helps with debugging - you can still see the wall faintly

📐 Method 3: Coordinate-Based Detection

For complex wall shapes or when you need precise control:

    // Define invisible wall boundaries
when flag clicked
set [wall left v] to [180]
set [wall right v] to [220]
set [wall top v] to [100]
set [wall bottom v] to [-100]

// In player movement code
define check invisible walls
if <<(x position) > (wall left)> and <(x position) < (wall right)>> then
if <<(y position) > (wall bottom)> and <(y position) < (wall top)>> then
// Player is inside wall area - push them out
if <(previous x) < (wall left)> then
set x to (wall left)
else
set x to (wall right)
end
end
end

🖊️ Method 4: Pen-Based Collision (Advanced)

For when you want walls drawn by pen to be invisible:

    // Create invisible pen walls
when flag clicked
pen up
set pen color to [#000000]  // Black color
set pen size to [10]

// Draw invisible wall (don't actually draw, just track coordinates)
go to x: [200] y: [100]
pen down
go to x: [200] y: [-100]
pen up

// Collision detection using color sensing
define check pen collision
if <touching color [#000000]?> then
// Move player away from wall
change x by [-5]
end

🚀 Advanced Features

Enhance your invisible walls with these features:

    // One-way invisible walls
define check one way wall
if <touching [One Way Wall v]?> then
if <(x velocity) > [0]> then  // Moving right
change x by [(x velocity) * [-1]]  // Block movement
end
// Allow movement in other directions
end

// Invisible walls with sound effects
define wall collision effect
if <touching [Invisible Wall v]?> then
play sound [wall hit v]
// Optional: screen shake effect
repeat [3]
change x by [2]
wait [0.05] seconds
change x by [-2]
wait [0.05] seconds
end
end

// Debug mode to show invisible walls
when [space v] key pressed
if <(debug mode) = [on]> then
broadcast [show walls v]
else
broadcast [hide walls v]
end

// In wall sprites
when I receive [show walls v]
set [ghost v] effect to [50]  // Semi-transparent

when I receive [hide walls v]
set [ghost v] effect to [100]  // Invisible

💡 Pro Tips

  • Ghost effect 100% vs 99%: Both work for collision detection, but 100% is completely invisible
  • Layer management: Put invisible walls on a separate layer for organization
  • Debug mode: Always include a way to temporarily show walls for testing
  • Performance: Use simple rectangular walls when possible for better performance
  • Player feedback: Add subtle effects (sound, screen shake) when hitting invisible walls

Hope this comprehensive guide helps you implement invisible walls perfectly! Let me know if you need clarification on any method! 🎮

GE

GameEngine_Sarah

Replied 20 minutes later

@CollisionMaster_Pro excellent explanation! I want to add a crucial point about performance:

⚡ Performance Optimization:

When using multiple invisible walls, consider grouping them into a single sprite with multiple costumes or using a more efficient detection system:

    // Instead of many wall sprites, use one sprite with regions
define check all walls
// Check multiple wall regions in one sprite
if <<touching color [#FF0000]?> or <touching color [#00FF00]?>> then
// Different colors for different wall types
change x by [-5]
end

This reduces the number of collision checks and improves game performance! 🚀

PD

PlatformerDev_Alex

Replied 1 hour later

@CollisionMaster_Pro @GameEngine_Sarah Thank you both so much! 🎉

The ghost effect method worked perfectly! I used ghost effect 100% and the touching blocks still detect collision flawlessly. My invisible walls are now working exactly as intended.

The debug mode tip was especially helpful - being able to toggle wall visibility made testing so much easier. My platformer now has some cool secret areas! 🕵️‍♂️

VB

Vibelf_Community

Pinned Message • Moderator

🚀 Master Advanced Platformer Development

Great discussion on invisible walls! For those building sophisticated platformer games, our community can help you with:

  • 🎮 Advanced collision systems
  • 🏃‍♂️ Complex player movement mechanics
  • 🗺️ Multi-level world design
  • ⚡ Performance optimization techniques

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