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Implementing Multi-Directional Scrolling with Hitboxes in Scratch

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SM

ScrollMaster_Jake

Posted on January 24, 2024 • Advanced

🌍 Multi-Directional Scrolling Challenge

Hey everyone! My team and I are working on an ambitious game project that needs:

  • 🔄 Smooth multi-directional scrolling (up, down, left, right)
  • 📦 Proper hitbox collision detection that works with scrolling
  • 🎮 Support for both top-down RPG style and side-scrolling platformer mechanics
  • ⚡ Smooth movement with friction and momentum

We’ve seen some amazing examples but can’t figure out how to implement the scrolling system properly. The hitboxes seem to break when the camera moves! 😅

Could someone explain the proper order of implementation? We’re looking for a comprehensive solution that covers both the scrolling mechanics and collision system. Any help would be amazing! 🙏

CS

CameraSystem_Pro

Replied 2 hours later • ⭐ Best Answer

Excellent question @ScrollMaster_Jake! Multi-directional scrolling with hitboxes is definitely advanced territory. Let me break this down into a comprehensive system that you can implement step by step:

🏗️ System Architecture Overview

Here’s how a proper scrolling system with hitboxes works:

flowchart TD A[🎮 Player Input] --> B[Calculate Movement] B --> C[Update Camera Position] C --> D[Move All World Objects] D --> E[Check Collisions] E --> F[Apply Collision Response] F --> G[Update Display] H[🌍 World Coordinates] --> I[Camera Transform] I --> J[Screen Coordinates] K[📦 Hitbox System] --> L[Relative Positioning] L --> M[Collision Detection] M --> N[Response Calculation] style A fill:#e1f5fe style C fill:#f3e5f5 style E fill:#fff3e0 style G fill:#e8f5e8

🎯 Step 1: Camera System Setup

First, create the core camera variables and initialization:

    // Camera system initialization
when flag clicked
set [Camera X v] to [0]
set [Camera Y v] to [0]
set [Player X v] to [0]
set [Player Y v] to [0]
set [X Speed v] to [0]
set [Y Speed v] to [0]
set [Friction v] to [0.8]
set [Speed v] to [1.2]
set [Camera Smoothing v] to [0.1]

🏃‍♂️ Step 2: Smooth Movement System

Implement the movement system with friction and momentum:

    // Player movement with smooth controls
define handle player movement
// Horizontal movement
if <key [right arrow v] pressed?> then
change [X Speed v] by (Speed)
end
if <key [left arrow v] pressed?> then
change [X Speed v] by ((0) - (Speed))
end

// Vertical movement
if <key [up arrow v] pressed?> then
change [Y Speed v] by (Speed)
end
if <key [down arrow v] pressed?> then
change [Y Speed v] by ((0) - (Speed))
end

// Apply friction
set [X Speed v] to ((X Speed) * (Friction))
set [Y Speed v] to ((Y Speed) * (Friction))

// Update player position
change [Player X v] by (X Speed)
change [Player Y v] by (Y Speed)

📹 Step 3: Camera Following System

Create a smooth camera that follows the player:

    // Smooth camera following
define update camera
// Calculate target camera position (center player on screen)
set [Target Camera X v] to ((Player X) - [240])  // Half screen width
set [Target Camera Y v] to ((Player Y) - [180])  // Half screen height

// Smooth camera movement (lerp)
change [Camera X v] by (((Target Camera X) - (Camera X)) * (Camera Smoothing))
change [Camera Y v] by (((Target Camera Y) - (Camera Y)) * (Camera Smoothing))

// Optional: Add camera bounds
if <(Camera X) < [0]> then
set [Camera X v] to [0]
end
if <(Camera Y) < [0]> then
set [Camera Y v] to [0]
end

🌍 Step 4: World Object Positioning

For all world objects (walls, enemies, items), use this positioning system:

    // For each world object sprite
when flag clicked
set [World X v] to [100]  // Object's world position
set [World Y v] to [200]

forever
// Convert world coordinates to screen coordinates
go to x: ((World X) - (Camera X)) y: ((World Y) - (Camera Y))

// Hide if off-screen (optimization)
if <<((World X) - (Camera X)) < [-300]> or <((World X) - (Camera X)) > [540]>> then
hide
else
if <<((World Y) - (Camera Y)) < [-220]> or <((World Y) - (Camera Y)) > [400]>> then
hide
else
show
end
end
end

📦 Step 5: Collision Detection System

Implement collision detection that works with the scrolling system:

    // Collision detection for player
define check collisions
// Store old position
set [Old Player X v] to (Player X)
set [Old Player Y v] to (Player Y)

// Move horizontally and check collision
change [Player X v] by (X Speed)
if <touching [Walls v]?> then
set [Player X v] to (Old Player X)
set [X Speed v] to [0]
end

// Move vertically and check collision
change [Player Y v] by (Y Speed)
if <touching [Walls v]?> then
set [Player Y v] to (Old Player Y)
set [Y Speed v] to [0]
end

// Update player sprite position for collision detection
go to x: ((Player X) - (Camera X)) y: ((Player Y) - (Camera Y))

🔄 Step 6: Main Game Loop

Put it all together in the main game loop:

    // Main game loop
when flag clicked
forever
handle player movement
check collisions
update camera

// Update player sprite visual position
go to x: ((Player X) - (Camera X)) y: ((Player Y) - (Camera Y))

// Broadcast position updates for other systems
broadcast [camera updated v]
end

🎮 Step 7: Advanced Features

Camera Zones (for different areas):

    // Camera boundaries for different zones
define set camera bounds (min x) (max x) (min y) (max y)
if <(Camera X) < (min x)> then
set [Camera X v] to (min x)
end
if <(Camera X) > (max x)> then
set [Camera X v] to (max x)
end
if <(Camera Y) < (min y)> then
set [Camera Y v] to (min y)
end
if <(Camera Y) > (max y)> then
set [Camera Y v] to (max y)
end

Multiple Layer Scrolling (Parallax):

    // For background layers
when I receive [camera updated v]
// Background moves slower for depth effect
go to x: (((World X) - (Camera X)) * [0.5]) y: (((World Y) - (Camera Y)) * [0.5])

// Foreground moves faster
go to x: (((World X) - (Camera X)) * [1.2]) y: (((World Y) - (Camera Y)) * [1.2])

🛠️ Implementation Tips

  1. 🎯 Start Simple: Get basic scrolling working before adding collision
  2. 📊 Use World Coordinates: Always think in world space, convert to screen space for display
  3. 🔄 Separate Systems: Keep movement, camera, and collision as separate functions
  4. ⚡ Optimize: Hide off-screen objects to improve performance
  5. 🧪 Test Incrementally: Add one feature at a time and test thoroughly

The key insight is that everything moves relative to the camera, not the player! The player stays centered while the world moves around them. 🌍

SM

ScrollMaster_Jake

Replied 3 hours later

@CameraSystem_Pro This is absolutely incredible! 🤩 Thank you so much!

The step-by-step breakdown is exactly what we needed. The world coordinates vs screen coordinates concept finally clicked for me. We’re implementing this system now and it’s working beautifully!

One quick question: How do we handle objects that need to interact with the player (like NPCs or collectibles) in this system?

CS

CameraSystem_Pro

Replied 1 hour later

@ScrollMaster_Jake Great question! For interactive objects, use distance-based detection in world coordinates:

    // For NPCs, collectibles, etc.
when flag clicked
set [World X v] to [300]  // NPC world position
set [World Y v] to [400]

forever
// Position sprite on screen
go to x: ((World X) - (Camera X)) y: ((World Y) - (Camera Y))

// Check interaction distance in world coordinates
set [Distance v] to (sqrt (((((Player X) - (World X)) * ((Player X) - (World X))) + (((Player Y) - (World Y)) * ((Player Y) - (World Y))))))

if <(Distance) < [50]> then
// Player is close enough to interact
if <key [space v] pressed?> then
broadcast [talk to npc v]
end
say [Press SPACE to talk]
else
say []
end
end

The key is always using world coordinates for logic, screen coordinates only for display! 🎯

VB

Vibelf_Community

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