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My platform game so far - Need help with slope detection

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PG

PlatformGameDev

Posted on July 17, 2025 • Intermediate

🎮 Platformer slope detection challenge

Hey everyone! I’m working on a platform game and I’ve got the basic movement working fine using a standard platformer tutorial. However, I’m running into a major issue: my character can’t go up slopes! 😅

The current collision system works perfectly for flat surfaces and walls, but when the character encounters a slope, they just get stuck against it instead of smoothly climbing up.

I’ve tried modifying the collision detection code to handle slopes, but I can’t seem to get it working properly. The character either:

  • Gets stuck at the bottom of slopes
  • Clips through the slope geometry
  • Moves too jerkily when trying to climb

Has anyone successfully implemented smooth slope detection in their platformer? I’d really appreciate some guidance on how to modify the collision system to handle angled surfaces! 🤔

PE

PlatformerExpert_N8

Replied 1 day later • ⭐ Best Answer

Great question @PlatformGameDev! Slope detection is one of the trickier aspects of platformer physics, but once you understand the concept, it becomes much more manageable.

🧠 Understanding Slope Detection Logic

The key insight is this: when your character hits a wall, you should check if moving slightly upward would resolve the collision. If it does, then you’re hitting a slope that can be climbed!

flowchart TD A[🏃 Player moves horizontally] --> B[Check for wall collision] B --> C{Collision detected?} C -->|No| D[✅ Continue movement] C -->|Yes| E[Try moving up 1 pixel] E --> F[Check collision again] F --> G{Still colliding?} G -->|No| H[✅ Climb slope - stay at higher Y] G -->|Yes| I[❌ Hit wall - stop horizontal movement] style A fill:#e1f5fe style H fill:#e8f5e8 style I fill:#ffebee style E fill:#fff3e0

🔧 Step 1: Basic Collision Detection Function

First, make sure you have a solid collision detection system:

    define Check Solid
set [Solid v] to [0]
if <touching [Walls v] ?> then
set [Solid v] to [1]
end

define Move X (amount)
change [X v] by (amount)
Check Solid
if <(Solid) = [1]> then
change [X v] by ((0) - (amount))
end

🏔️ Step 2: Enhanced Slope-Aware Movement

Now here’s the magic - modify your horizontal movement to include slope detection:

    define Change X By (X)
// Move in small increments for precise collision
repeat ([ceiling v] of ([abs v] of (X)::operators)::operators)
// Move one pixel at a time in the direction we want to go
change [X v] by ((X) / ([abs v] of (X)::operators))

// Check if we hit something
Check Solid

if <(Solid) > [0]> then
// We hit a wall! Try to climb up (slope detection)
change [Y v] by (1)
Check Solid

if <(Solid) = [0]> then
// Success! We can climb this slope
// Stay at the higher Y position and continue
else
// Can't climb - this is a real wall
// Undo both the X and Y movement
change [X v] by ((0) - ((X) / ([abs v] of (X)::operators)))
change [Y v] by (-1)
stop [this script v]
end
end
end

⚡ Step 3: Optimized Version with Better Physics

For even smoother movement, here’s an enhanced version:

    define Advanced Move X (X)
set [original Y v] to (Y)
set [steps v] to ([ceiling v] of ([abs v] of (X)::operators))
set [step size v] to ((X) / (steps))

repeat (steps)
change [X v] by (step size)
Check Solid

if <(Solid) > [0]> then
// Try climbing up to 8 pixels (adjustable slope steepness)
set [climb attempts v] to [0]
repeat until <<(Solid) = [0]> or <(climb attempts) > [8]>>
change [Y v] by (1)
change [climb attempts v] by (1)
Check Solid
end

if <(Solid) > [0]> then
// Couldn't climb - hit a wall
change [X v] by ((0) - (step size))
set [Y v] to (original Y)
stop [this script v]
end
end
end

🎯 Step 4: Slope Descent (Going Down Slopes)

Don’t forget about going down slopes smoothly:

    define Check Slope Descent
// Only check if we're on the ground
if <(Y velocity) = [0]> then
// Look ahead to see if there's ground below
change [X v] by (1) // Look one pixel ahead
change [Y v] by (-1) // Look one pixel down
Check Solid

if <(Solid) = [0]> then
// No ground ahead - we might be at a slope edge
change [Y v] by (-7) // Check up to 8 pixels down
Check Solid

if <(Solid) > [0]> then
// Found ground below - stick to it
repeat until <(Solid) = [0]>
change [Y v] by (1)
Check Solid
end
change [Y v] by (-1) // Back up one pixel to be on solid ground
else
// No ground found - we're at a cliff edge
change [Y v] by (8) // Reset Y position
end
else
change [Y v] by (1) // Reset Y position
end

change [X v] by (-1) // Reset X position
end

🚀 Step 5: Complete Integration

Put it all together in your main movement script:

    when flag clicked
set [X velocity v] to [0]
set [Y velocity v] to [0]
set [on ground v] to [0]

forever
// Handle input
if <key [right arrow v] pressed?> then
set [X velocity v] to [5]
end
if <key [left arrow v] pressed?> then
set [X velocity v] to [-5]
end

// Apply horizontal movement with slope detection
if <not <(X velocity) = [0]>> then
Advanced Move X (X velocity)
set [X velocity v] to ((X velocity) * (0.8)) // Friction
end

// Apply gravity and vertical movement
change [Y velocity v] by (-0.8) // Gravity
Move Y (Y velocity)

// Check for slope descent when moving horizontally
if <not <(X velocity) = [0]>> then
Check Slope Descent
end

// Update position
go to x: (X) y: (Y)
end

💡 Pro Tips for Perfect Slope Physics

  • Slope steepness limit: Adjust the maximum climb height (8 pixels in the example) to control how steep slopes can be
  • Smooth movement: Use fractional velocities and pixel-by-pixel movement for the smoothest experience
  • Ground detection: Always check if the player is on the ground before applying slope descent
  • Performance: Consider using a “ground sensor” sprite positioned slightly below the player for more efficient ground detection

This system will give you smooth slope climbing and descent that feels natural and responsive! The key is the step-by-step collision checking combined with the upward movement attempt. 🎮

PG

PlatformGameDev

Replied 2 hours later

@PlatformerExpert_N8 This is absolutely perfect! 🤩 The step-by-step explanation makes so much sense now!

I implemented the basic version first and it works like a charm - my character can now smoothly climb slopes without getting stuck. The pixel-by-pixel movement approach was the key insight I was missing.

The advanced version with the climb attempts limit is brilliant too - it lets me control exactly how steep the slopes can be. Thanks for the detailed breakdown and the pro tips! My platformer feels so much more polished now! 🎉

CS

CollisionSpecialist

Replied 3 hours later

Excellent solution @PlatformerExpert_N8! 👏 I’d like to add one more optimization for anyone implementing this:

For even better performance, you can use a “ground sensor” approach:

    // Create a separate sprite called 'Ground Sensor'
when flag clicked
forever
go to x: ([x position v] of [Player v]) y: (([y position v] of [Player v]) - (20))

if <touching [Walls v] ?> then
broadcast [on ground v]
else
broadcast [in air v]
end
end

This reduces the number of collision checks and makes the slope detection even more reliable! 🎯

VB

Vibelf_Community

Pinned Message • Moderator

🎮 Master Advanced Platformer Development

Fantastic discussion on slope detection and collision systems! For developers ready to create professional-quality platformers with advanced physics, our expert tutors can help you master:

  • 🏔️ Advanced collision detection and slope physics
  • ⚡ Performance optimization for complex movement systems
  • 🎯 Precise hitbox and sensor-based detection
  • 🚀 Advanced platformer mechanics (wall jumping, ledge grabbing, etc.)

📚 Related Platformer Topics

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