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How to Add Collision and Gravity to Your First Platformer

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PA

PlatformerDev_Alex

Posted on July 23, 2025 • Intermediate

🎮 Need help with collision and gravity for my first platformer

Hey everyone! I’m trying to create my first platformer game but I’m struggling with the physics. My character keeps going through walls and there’s no gravity system. I need help with:

  • Wall collision detection (so character can’t walk through walls)
  • Floor collision (so character stands on platforms)
  • Gravity system (so character falls when not on ground)
  • Smooth movement that feels good to play

I’ve tried some code but nothing is working properly. Any help would be amazing! 🙏

PE

PhysicsExpert_Mario

Replied 1 hour later • ⭐ Best Answer

Great question @PlatformerDev_Alex! Platformer physics can be tricky at first, but once you understand the system, it becomes much easier. Here’s a complete collision and gravity system:

🏗️ Platformer Physics System Flow

Here’s how a proper platformer physics system works:

flowchart TD A[🎮 Game Loop Start] --> B[Handle Input] B --> C[Apply Horizontal Movement] C --> D[Check Wall Collision] D -->|Collision Found| E[Push Out of Wall] D -->|No Collision| F[Apply Gravity] E --> F F --> G[Apply Vertical Movement] G --> H[Check Floor/Ceiling Collision] H -->|Floor Hit| I[Land on Ground] H -->|Ceiling Hit| J[Stop Upward Movement] H -->|No Collision| K[Continue Falling] I --> L[Reset Gravity] J --> M[Set Gravity to 0] K --> N[Increase Fall Speed] L --> O[Update Sprite Position] M --> O N --> O O --> P[Check Game State] P --> A style A fill:#e1f5fe style D fill:#fff3e0 style H fill:#f3e5f5 style O fill:#e8f5e8

🔧 Step 1: Set Up Variables

First, create these variables for your physics system:

    when flag clicked
set [x velocity v] to [0]
set [y velocity v] to [0]
set [gravity v] to [-0.8]
set [jump power v] to [15]
set [move speed v] to [5]
set [on ground v] to [false]

🏃 Step 2: Main Physics Loop

Create the main game loop that handles all physics:

    when flag clicked
forever
// Handle horizontal input
set [x velocity v] to [0]
if <key (right arrow v) pressed?> then
set [x velocity v] to (move speed)
end
if <key (left arrow v) pressed?> then
set [x velocity v] to (0 - (move speed))
end

// Apply horizontal movement
change x by (x velocity)
check horizontal collision

// Apply gravity and vertical movement
if <(on ground) = [false]> then
change [y velocity v] by (gravity)
end

// Handle jumping
if <<key (space v) pressed?> and <(on ground) = [true]>> then
set [y velocity v] to (jump power)
set [on ground v] to [false]
end

// Apply vertical movement
change y by (y velocity)
check vertical collision
end

🧱 Step 3: Horizontal Collision Detection

Create a custom block for wall collision:

    define check horizontal collision
if <touching (Walls v)?> then
if <(x velocity) > [0]> then
// Moving right, push left
repeat until <not <touching (Walls v)?>>
change x by [-1]
end
else
// Moving left, push right
repeat until <not <touching (Walls v)?>>
change x by [1]
end
end
end

⬇️ Step 4: Vertical Collision Detection

Create vertical collision detection for floors and ceilings:

    define check vertical collision
set [on ground v] to [false]

if <touching (Floors v)?> then
if <(y velocity) < [0]> then
// Falling down, hit floor
repeat until <not <touching (Floors v)?>>
change y by [1]
end
set [y velocity v] to [0]
set [on ground v] to [true]
else
// Moving up, hit ceiling
repeat until <not <touching (Floors v)?>>
change y by [-1]
end
set [y velocity v] to [0]
end
end

🎯 Step 5: Advanced Collision (Optional)

For more precise collision, use pixel-perfect detection:

    // More precise collision detection
define precise horizontal collision
set [collision found v] to [false]
repeat (abs (x velocity))
if <(x velocity) > [0]> then
change x by [1]
else
change x by [-1]
end

if <touching (Walls v)?> then
if <(x velocity) > [0]> then
change x by [-1]
else
change x by [1]
end
set [collision found v] to [true]
stop [this script v]
end
end

🚀 Step 6: Enhanced Movement Features

Add some polish to make movement feel better:

Coyote Time (grace period for jumping):

    // Allow jumping shortly after leaving ground
when flag clicked
set [coyote timer v] to [0]

forever
if <(on ground) = [true]> then
set [coyote timer v] to [6]  // 6 frames of grace
else
if <(coyote timer) > [0]> then
change [coyote timer v] by [-1]
end
end
end

// Modified jump check
if <<key (space v) pressed?> and <(coyote timer) > [0]>> then
set [y velocity v] to (jump power)
set [on ground v] to [false]
set [coyote timer v] to [0]
end

Variable Jump Height:

    // Allow shorter jumps by releasing space early
when flag clicked
forever
if <<not <key (space v) pressed?>> and <(y velocity) > [5]>> then
set [y velocity v] to [5]  // Cut jump short
end
end

This system will give you smooth, responsive platformer physics! The key is separating horizontal and vertical movement and handling each collision type properly. 🎮✨

PA

PlatformerDev_Alex

Replied 2 hours later

@PhysicsExpert_Mario This is incredible! Thank you so much! 🎉

The collision system works perfectly now and my character feels so much better to control. One question - how can I add slopes and ramps to my platformer? Right now it only works with flat surfaces.

ST

SlopeTeacher_Ben

Replied 1 hour later

@PlatformerDev_Alex Great question! Slopes are more advanced but here’s a basic approach:

    // Slope detection and movement
define check for slopes
if <touching (Slopes v)?> then
// Move up slightly to see if we can walk on slope
change y by [2]
if <not <touching (Slopes v)?>> then
// We can walk on this slope
set [on ground v] to [true]
set [y velocity v] to [0]
else
// Too steep, treat as wall
change y by [-2]
end
end

For more complex slope physics, you’ll need to calculate angles and adjust movement vectors accordingly. It’s quite advanced but very rewarding! 🏔️

VB

Vibelf_Community

Pinned Message • Moderator

🎮 Ready to Build Amazing Platformers?

Excellent discussion everyone! For those looking to create even more advanced platformer games, our community can help you implement:

  • 🏃 Advanced movement mechanics (wall jumping, dashing)
  • 🎯 Enemy AI and behavior systems
  • 🗺️ Level design and progression systems
  • ⚡ Special abilities and power-ups

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