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How to prevent sprite from going beyond screen boundaries

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BM

BoundaryMaster_Dev

Posted on August 5, 2024 • Beginner

🔄 Sprite keeps teleporting infinitely at screen edges

I’m making a game where the sprite should teleport to the opposite side when it touches the screen edges. However, I’m getting an infinite loop problem! 😵

Here’s my current code:

    when green flag clicked
forever
if <<(x position) > [250]> or <(x position) < [-250]>> then
set x to ((x position) * (-1))
end
if <<(y position) > [190]> or <(y position) < [-190]>> then
set y to ((y position) * (-1))
end
end

The problem is that when the sprite reaches X position above 250 or below -250, it continuously repositions itself to the opposite side and gets stuck in a loop!

How can I fix this boundary detection so the sprite teleports cleanly without getting stuck? 🤔

GM

GameMechanics_Expert

Replied 3 hours later • ⭐ Best Answer

@BoundaryMaster_Dev I see the issue! The problem is with using multiplication to flip coordinates. Let me show you several proper solutions:

🔍 Understanding the Problem

Your current code multiplies the position by -1, which can cause:

  • Infinite loops when the sprite overshoots the boundary
  • Unpredictable teleportation distances
  • Sprites getting stuck at edges

✅ Solution 1: Direct Position Setting (Recommended)

Instead of multiplying, set exact positions:

    when green flag clicked
forever
// Handle X boundaries
if <(x position) > [250]> then
set x to [-250]  // Move to left edge
end
if <(x position) < [-250]> then
set x to [250]   // Move to right edge
end

// Handle Y boundaries
if <(y position) > [190]> then
set y to [-190]  // Move to bottom edge
end
if <(y position) < [-190]> then
set y to [190]   // Move to top edge
end
end

🎯 Solution 2: Smooth Teleportation with Offset

For smoother gameplay, add a small offset to prevent immediate re-triggering:

    when green flag clicked
forever
// X boundaries with offset
if <(x position) > [250]> then
set x to [-245]  // 5 pixels from edge
end
if <(x position) < [-250]> then
set x to [245]   // 5 pixels from edge
end

// Y boundaries with offset
if <(y position) > [190]> then
set y to [-185]  // 5 pixels from edge
end
if <(y position) < [-190]> then
set y to [185]   // 5 pixels from edge
end
end

🚀 Solution 3: Advanced Boundary System

For more complex games, use variables for flexible boundaries:

    when green flag clicked
set [boundary right v] to [250]
set [boundary left v] to [-250]
set [boundary top v] to [190]
set [boundary bottom v] to [-190]
set [teleport offset v] to [5]

forever
// X boundary checking
if <(x position) > (boundary right)> then
set x to ((boundary left) + (teleport offset))
end
if <(x position) < (boundary left)> then
set x to ((boundary right) - (teleport offset))
end

// Y boundary checking
if <(y position) > (boundary top)> then
set y to ((boundary bottom) + (teleport offset))
end
if <(y position) < (boundary bottom)> then
set y to ((boundary top) - (teleport offset))
end
end

🎮 Solution 4: Pac-Man Style Wrapping

For classic arcade-style wrapping with visual effects:

    when green flag clicked
forever
// Check if sprite is about to exit
if <(x position) > [240]> then
// Visual effect before teleporting
set [ghost v] effect to [50]
wait [0.1] seconds
set x to [-240]
set [ghost v] effect to [0]
end

if <(x position) < [-240]> then
set [ghost v] effect to [50]
wait [0.1] seconds
set x to [240]
set [ghost v] effect to [0]
end

// Similar for Y axis
if <(y position) > [180]> then
set [ghost v] effect to [50]
wait [0.1] seconds
set y to [-180]
set [ghost v] effect to [0]
end

if <(y position) < [-180]> then
set [ghost v] effect to [50]
wait [0.1] seconds
set y to [180]
set [ghost v] effect to [0]
end
end

🛡️ Solution 5: Boundary Clamping (Alternative)

If you want to stop the sprite at boundaries instead of teleporting:

    when green flag clicked
forever
// Clamp X position
if <(x position) > [250]> then
set x to [250]
end
if <(x position) < [-250]> then
set x to [-250]
end

// Clamp Y position
if <(y position) > [190]> then
set y to [190]
end
if <(y position) < [-190]> then
set y to [-190]
end
end

🔧 Pro Tips for Boundary Management

  • Use exact values: Always set specific coordinates instead of calculations
  • Add offsets: Small offsets prevent immediate re-triggering
  • Test thoroughly: Check all four corners and edges
  • Consider sprite size: Account for sprite width/height in boundaries
  • Use variables: Make boundaries easily adjustable

🎨 Bonus: Sprite Size Aware Boundaries

For sprites with different sizes, calculate boundaries based on sprite dimensions:

    when green flag clicked
set [sprite width v] to [48]  // Adjust based on your sprite
set [sprite height v] to [48]
set [screen width v] to [480]
set [screen height v] to [360]

// Calculate actual boundaries
set [max x v] to (((screen width) / [2]) - ((sprite width) / [2]))
set [min x v] to ((((screen width) / [2]) - ((sprite width) / [2])) * [-1])
set [max y v] to (((screen height) / [2]) - ((sprite height) / [2]))
set [min y v] to ((((screen height) / [2]) - ((sprite height) / [2])) * [-1])

forever
if <(x position) > (max x)> then
set x to (min x)
end
if <(x position) < (min x)> then
set x to (max x)
end
if <(y position) > (max y)> then
set y to (min y)
end
if <(y position) < (min y)> then
set y to (max y)
end
end

This should completely eliminate the infinite loop issue! Choose the solution that best fits your game’s needs. 🎉

BM

BoundaryMaster_Dev

Replied 1 hour later

@GameMechanics_Expert This is exactly what I needed! 🎯

The direct position setting (Solution 1) worked perfectly! No more infinite loops, and the teleportation is smooth and predictable.

I especially love the sprite size aware boundaries - that’s going to be super useful for my game with different sized characters. The offset technique is brilliant too!

Thank you for such a comprehensive explanation! 🙏

AG

ArcadeGamer_Pro

Replied 30 minutes later

Great solutions! I’d also recommend adding sound effects when teleporting:

    when green flag clicked
forever
if <(x position) > [250]> then
play sound [teleport v] until done
set x to [-245]
end
// ... rest of boundary code
end

This makes the teleportation feel more intentional and gives great player feedback! 🔊

VB

Vibelf_Community

Pinned Message • Moderator

🎮 Master Game Development Fundamentals!

Excellent work on boundary management! For those looking to create even more sophisticated games, our community can help you implement:

  • 🏃 Advanced movement systems and physics
  • 🎯 Collision detection and response
  • 🌟 Special effects and animations
  • 🎵 Sound design and music integration

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