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How to create realistic sprite bounce physics based on collision direction

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PG

PhysicsGamer_Alex

Posted on January 24, 2024 • Advanced

⚽ Realistic bounce physics help needed

Hey everyone! I’m working on a physics-based game (think Pong meets Breakout) where I need sprites to bounce off surfaces realistically. Right now I’m just using “turn 180 degrees” but that looks terrible and unrealistic! 😅

I need help creating a system where:

  • Sprites bounce at realistic angles based on their approach direction
  • The bounce angle depends on the surface they hit (horizontal vs vertical walls)
  • Velocity is preserved but direction changes properly
  • It works like real physics - like a ball bouncing off a wall

I’ve seen games where the ball bounces perfectly based on physics laws, but I can’t figure out how to implement this in Scratch. The math behind reflection angles is confusing me!

Any help with the collision detection and angle calculations would be amazing! 🙏

PE

PhysicsEngine_Pro

Replied 3 hours later • ⭐ Best Answer

Excellent question @PhysicsGamer_Alex! Realistic bouncing is all about understanding reflection physics. Here’s a complete system:

⚡ Physics Bounce System Flow

Here’s how realistic bouncing works:

flowchart TD A[🎯 Collision Detected] --> B[Get Approach Direction] B --> C[Determine Surface Type] C --> D{Horizontal Surface?} C --> E{Vertical Surface?} D -->|Yes| F[Flip Y Velocity] E -->|Yes| G[Flip X Velocity] F --> H[Calculate New Direction] G --> H H --> I[Apply Bounce Damping] I --> J[Update Sprite Direction] J --> K[Move Away from Surface] K --> L[Continue Movement] style A fill:#e1f5fe style F fill:#e8f5e8 style G fill:#fff3e0 style H fill:#f3e5f5 style L fill:#fce4ec

🔧 Step 1: Velocity-Based Movement System

First, set up a proper velocity system instead of simple movement:

    when flag clicked
set [x velocity v] to [5]
set [y velocity v] to [3]
set [speed v] to [1]
set [bounce damping v] to [0.9]

forever
// Move based on velocity
change x by ((x velocity) * (speed))
change y by ((y velocity) * (speed))

// Check for collisions
check collisions
end

⚽ Step 2: Smart Collision Detection

Detect which side of an object was hit:

    define check collisions
if <touching [Wall v]?> then
// Move back to find collision point
change x by (((x velocity) * (speed)) * [-1])
change y by (((y velocity) * (speed)) * [-1])

// Test each direction to find collision side
change x by ((x velocity) * (speed))
if <touching [Wall v]?> then
// Hit vertical surface
change x by (((x velocity) * (speed)) * [-1])
set [x velocity v] to ((x velocity) * [-1])
bounce horizontal
else
change y by ((y velocity) * (speed))
if <touching [Wall v]?> then
// Hit horizontal surface
change y by (((y velocity) * (speed)) * [-1])
set [y velocity v] to ((y velocity) * [-1])
bounce vertical
end
end
end

🎯 Step 3: Realistic Bounce Calculations

Implement proper physics-based bouncing:

    // Horizontal surface bounce (floor/ceiling)
define bounce vertical
// Flip Y velocity, keep X velocity
set [y velocity v] to ((y velocity) * [-1] * (bounce damping))
set [x velocity v] to ((x velocity) * (bounce damping))

// Add slight randomness for realism
change [x velocity v] by (pick random [-0.5] [0.5])

// Play bounce sound
play sound [bounce v]

// Visual effect
create clone of [bounce effect v]

// Horizontal surface bounce (walls)
define bounce horizontal
// Flip X velocity, keep Y velocity
set [x velocity v] to ((x velocity) * [-1] * (bounce damping))
set [y velocity v] to ((y velocity) * (bounce damping))

// Add slight randomness
change [y velocity v] by (pick random [-0.5] [0.5])

// Effects
play sound [bounce v]
create clone of [bounce effect v]

🚀 Step 4: Advanced Angle-Based Bouncing

For more complex surfaces with different angles:

    // Advanced bounce with surface angles
define bounce off surface (surface angle)
// Get current direction
set [current direction v] to (direction)

// Calculate reflection angle
// Reflection formula: new_angle = 2 * surface_angle - old_angle
set [new direction v] to (((2) * (surface angle)) - (current direction))

// Apply the new direction
point in direction (new direction)

// Reduce speed slightly for realism
set [speed v] to ((speed) * (bounce damping))

// Convert direction back to velocity components
set [x velocity v] to ((cos of (new direction)) * (speed))
set [y velocity v] to ((sin of (new direction)) * (speed))

💎 Step 5: Complete Bouncing Ball Example

Here’s a complete implementation for a bouncing ball:

    // Main ball physics loop
when flag clicked
go to x: [0] y: [0]
set [x velocity v] to [6]
set [y velocity v] to [4]
set [gravity v] to [-0.2]
set [bounce damping v] to [0.85]

forever
// Apply gravity
change [y velocity v] by (gravity)

// Move
change x by (x velocity)
change y by (y velocity)

// Bounce off edges
if <(x position) > [230]> then
set x to [230]
set [x velocity v] to ((x velocity) * [-1] * (bounce damping))
end

if <(x position) < [-230]> then
set x to [-230]
set [x velocity v] to ((x velocity) * [-1] * (bounce damping))
end

if <(y position) > [170]> then
set y to [170]
set [y velocity v] to ((y velocity) * [-1] * (bounce damping))
end

if <(y position) < [-170]> then
set y to [-170]
set [y velocity v] to ((y velocity) * [-1] * (bounce damping))
// Add extra bounce for floor
if <(y velocity) > [-2]> then
set [y velocity v] to [-2]
end
end

// Stop if moving too slowly
if <<((x velocity) * (x velocity)) + ((y velocity) * (y velocity))> < [0.1]> then
set [x velocity v] to [0]
set [y velocity v] to [0]
end
end

🎮 Step 6: Paddle/Player Interaction

For games like Pong, add player influence on bounce:

    // Enhanced paddle bounce
define bounce off paddle
// Get relative hit position (-1 to 1)
set [hit position v] to (((x position) - (paddle x)) / [50])

// Influence bounce angle based on hit position
set [angle influence v] to ((hit position) * [30])

// Calculate new direction
set [base angle v] to [90]
set [new angle v] to ((base angle) + (angle influence))

// Apply new direction with speed boost
point in direction (new angle)
set [speed v] to ((speed) * [1.1])

// Convert to velocity
set [x velocity v] to ((cos of (new angle)) * (speed))
set [y velocity v] to ((sin of (new angle)) * (speed))

💡 Pro Physics Tips

  • Energy conservation: Use damping (0.8-0.95) to simulate energy loss
  • Minimum velocity: Stop objects when they’re moving too slowly
  • Surface materials: Different surfaces can have different bounce factors
  • Spin effects: Add rotation to influence bounce direction
  • Air resistance: Gradually reduce velocity over time

This system creates realistic, physics-based bouncing that feels natural and responsive! 🎯

PG

PhysicsGamer_Alex

Replied 2 hours later

@PhysicsEngine_Pro This is absolutely incredible! 🤯 The physics explanation is perfect!

I implemented the basic version and the difference is night and day! One question - how do I handle corner collisions where the sprite might hit two surfaces at once?

CD

CollisionDetective_Sam

Replied 45 minutes later

@PhysicsGamer_Alex Great question about corner collisions! Here’s how to handle them:

    // Corner collision detection
define handle corner collision
// Check if hitting both X and Y surfaces
set [x collision v] to [false]
set [y collision v] to [false]

// Test X movement
change x by (x velocity)
if <touching [Wall v]?> then
set [x collision v] to [true]
change x by ((x velocity) * [-1])
end

// Test Y movement
change y by (y velocity)
if <touching [Wall v]?> then
set [y collision v] to [true]
change y by ((y velocity) * [-1])
end

// Handle collision type
if <<(x collision) = [true]> and <(y collision) = [true]>> then
// Corner hit - reverse both velocities
set [x velocity v] to ((x velocity) * [-1] * (bounce damping))
set [y velocity v] to ((y velocity) * [-1] * (bounce damping))
else
if <(x collision) = [true]> then
set [x velocity v] to ((x velocity) * [-1] * (bounce damping))
end
if <(y collision) = [true]> then
set [y velocity v] to ((y velocity) * [-1] * (bounce damping))
end
end

This prevents sprites from getting stuck in corners! 💪

VB

Vibelf_Community

Pinned Message • Moderator

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