#atom

Creating realistic physical behaviors and interactions in game environments

Core Idea: Game physics implementation involves simulating physical behaviors like gravity, collision detection, momentum, and object interactions to create believable and interactive virtual environments.

Key Elements

Core Concepts

• Rigid Body Dynamics: Simulating solid objects that don't deform
• Collision Detection: Identifying when objects intersect
• Collision Response: Calculating how objects react after collision
• Forces: Applying gravity, friction, and other physical forces
• Constraints: Limiting object movement based on physical rules
• Optimization: Balancing accuracy with performance requirements

Implementation Approaches

• Physics Libraries: Using existing solutions like Box2D, Matter.js, or Bullet Physics
• Custom Physics: Building simplified physics systems for specific game requirements
• Hybrid Approaches: Combining libraries with custom solutions for specific behaviors
• Fixed Timestep: Using consistent time steps to ensure stable simulation
• Spatial Partitioning: Optimizing collision checks by dividing space into regions

Common Components

• Gravity System: Simulating downward acceleration
• Collision System: Detecting and resolving object intersections
• Raycasting: Detecting objects along a line for selection or sensing
• Character Controllers: Specialized physics handling for player characters
• Joint Systems: Connecting objects with physical constraints

Implementation Methods

Basic Gravity and Collision

// Simple gravity and ground collision in JavaScript
function updatePlayerPhysics(player, deltaTime) {
  // Apply gravity
  player.velocity.y += GRAVITY * deltaTime;
  
  // Update position based on velocity
  player.position.y += player.velocity.y * deltaTime;
  player.position.x += player.velocity.x * deltaTime;
  
  // Check for ground collision
  const groundLevel = 0;
  if (player.position.y <= groundLevel) {
    player.position.y = groundLevel;
    player.velocity.y = 0;
    player.onGround = true;
  } else {
    player.onGround = false;
  }
}

AABB Collision Detection

// Axis-Aligned Bounding Box collision detection
function checkAABBCollision(objectA, objectB) {
  return (
    objectA.position.x < objectB.position.x + objectB.width &&
    objectA.position.x + objectA.width > objectB.position.x &&
    objectA.position.y < objectB.position.y + objectB.height &&
    objectA.position.y + objectA.height > objectB.position.y
  );
}

function resolveCollision(player, block) {
  // Calculate overlap on each axis
  const overlapX = Math.min(
    player.position.x + player.width - block.position.x,
    block.position.x + block.width - player.position.x
  );
  
  const overlapY = Math.min(
    player.position.y + player.height - block.position.y,
    block.position.y + block.height - player.position.y
  );
  
  // Resolve along axis with smallest overlap
  if (overlapX < overlapY) {
    if (player.position.x < block.position.x) {
      player.position.x -= overlapX;
    } else {
      player.position.x += overlapX;
    }
    player.velocity.x = 0;
  } else {
    if (player.position.y < block.position.y) {
      player.position.y -= overlapY;
      player.velocity.y = 0;
      player.onGround = true;
    } else {
      player.position.y += overlapY;
      player.velocity.y = 0;
    }
  }
}

Raycasting for Object Detection

// Simple raycast function
function raycast(origin, direction, maxDistance, objects) {
  let closestHit = null;
  let closestDistance = maxDistance;
  
  // Normalize direction vector
  const magnitude = Math.sqrt(direction.x * direction.x + direction.y * direction.y + direction.z * direction.z);
  const normalizedDir = {
    x: direction.x / magnitude,
    y: direction.y / magnitude,
    z: direction.z / magnitude
  };
  
  // Check each object for intersection
  for (const object of objects) {
    // Simplified box intersection test
    const t1 = (object.minX - origin.x) / normalizedDir.x;
    const t2 = (object.maxX - origin.x) / normalizedDir.x;
    const t3 = (object.minY - origin.y) / normalizedDir.y;
    const t4 = (object.maxY - origin.y) / normalizedDir.y;
    const t5 = (object.minZ - origin.z) / normalizedDir.z;
    const t6 = (object.maxZ - origin.z) / normalizedDir.z;
    
    const tmin = Math.max(Math.max(Math.min(t1, t2), Math.min(t3, t4)), Math.min(t5, t6));
    const tmax = Math.min(Math.min(Math.max(t1, t2), Math.max(t3, t4)), Math.max(t5, t6));
    
    // Ray misses the box
    if (tmax < 0 || tmin > tmax) continue;
    
    // Hit is beyond max distance
    if (tmin > maxDistance) continue;
    
    // We found a closer hit
    if (tmin < closestDistance) {
      closestDistance = tmin;
      closestHit = {
        object: object,
        distance: tmin,
        point: {
          x: origin.x + normalizedDir.x * tmin,
          y: origin.y + normalizedDir.y * tmin,
          z: origin.z + normalizedDir.z * tmin
        }
      };
    }
  }
  
  return closestHit;
}

Jump Mechanics

function handleJump(player, jumpForce) {
  if (player.onGround) {
    player.velocity.y = jumpForce;
    player.onGround = false;
  }
}

Minecraft-Style Block Physics

Block-Based Collision System

// Efficient grid-based collision for block worlds
function checkBlockCollisions(player, world) {
  // Get blocks that could possibly collide with the player
  const minBlockX = Math.floor(player.position.x - player.width/2);
  const maxBlockX = Math.floor(player.position.x + player.width/2);
  const minBlockY = Math.floor(player.position.y - player.height/2);
  const maxBlockY = Math.floor(player.position.y + player.height/2);
  const minBlockZ = Math.floor(player.position.z - player.width/2);
  const maxBlockZ = Math.floor(player.position.z + player.width/2);
  
  player.onGround = false;
  
  // Check each potential block
  for (let x = minBlockX; x <= maxBlockX; x++) {
    for (let y = minBlockY; y <= maxBlockY; y++) {
      for (let z = minBlockZ; z <= maxBlockZ; z++) {
        if (world.hasBlockAt(x, y, z)) {
          const block = {
            position: { x, y, z },
            width: 1,
            height: 1,
            depth: 1
          };
          
          if (checkAABBCollision3D(player, block)) {
            resolveCollision3D(player, block);
            
            // If we're standing on top of a block, mark as grounded
            if (player.position.y === block.position.y + block.height) {
              player.onGround = true;
            }
          }
        }
      }
    }
  }
}

Block Breaking Physics

function breakBlock(world, position) {
  // Remove the block from the world
  const block = world.getBlockAt(position.x, position.y, position.z);
  
  if (block) {
    // Remove from world data structure
    world.removeBlockAt(position.x, position.y, position.z);
    
    // Check if any blocks above should fall (simplified gravity)
    checkBlockGravity(world, position.x, position.y + 1, position.z);
  }
}

function checkBlockGravity(world, x, y, z) {
  // If there's a block at this position
  if (world.hasBlockAt(x, y, z)) {
    // If there's no block below
    if (!world.hasBlockAt(x, y - 1, z)) {
      // Move this block down
      const block = world.getBlockAt(x, y, z);
      world.removeBlockAt(x, y, z);
      world.addBlockAt(x, y - 1, z, block);
      
      // Check the block that was above this one
      checkBlockGravity(world, x, y + 1, z);
    }
  }
}

Optimization Techniques

Spatial Partitioning

• Grid-Based: Divide world into uniform cells for quick lookup
• Quadtree/Octree: Hierarchical space division for variable density
• Sweep and Prune: Sort objects along axes to quickly eliminate collision possibilities

Performance Strategies

• Sleep States: Disable physics for inactive objects
• LOD Physics: Simplify physics for distant objects
• Approximation: Use simpler collision shapes for complex objects
• Chunked Updates: Process physics in sections over multiple frames
• Prioritization: Focus computation on player-nearby areas

Common Challenges and Solutions

• Tunneling: Fast-moving objects passing through thin objects

  • Solution: Continuous collision detection or smaller time steps

• Jittering: Objects rapidly bouncing when stacked

  • Solution: Implement resting contact constraints or slight damping

• Stacking Stability: Ensuring objects can properly stack

  • Solution: Solve constraints simultaneously rather than sequentially

• Performance Scaling: Maintaining framerate with many physics objects

  • Solution: Spatial partitioning, sleep states, and simplified physics for distant objects

• Fixed Timestep: Ensuring physics stability with variable framerate

  • Solution: Implement a fixed timestep physics loop with interpolation for rendering

Connections

• Related Concepts: Collision Detection Algorithms (technique), Game Loop Implementation (framework), Spatial Partitioning (optimization)
• Broader Context: Game Engine Architecture (field), Computational Physics (discipline)
• Applications: Minecraft Clone Architecture (implementation example), Character Controller Design (specific use)
• Components: Raycasting Systems (supporting technique), Rigid Body Dynamics (theoretical foundation)

References

1. "Game Physics Engine Development" by Ian Millington
2. "Real-Time Collision Detection" by Christer Ericson
3. Open source physics implementations in popular game engines

#game-physics #collision-detection #simulation #game-development #rigid-body-dynamics

Connections:

Sources:

• From: notJust․dev - Vibe Coding a 3D GAME in React Native and ThreeJS (with AI)