Chapter 6: Enemy and Collisions

Technical requirements

Understanding collisions in 2D games

node2d.go, add GetWorldPosition

collision.go, CollisionCircle and overlap test

Struct and constructor

Overlap test

collisionMask.go, layers and collision filtering

Layer constants

CollisionMask struct

CanCollideWith and GetIdentity

collider.go, Node2D with collision

Struct Collider

SetOnCollide

Getters and CanCollideWith

collisionManager.go, CheckCollision

Where the manager lives

Struct, registration, and NewCollider

CollisionManager struct

NewCollisionManager

AddCollider

NewCollider

Registration in Player and Enemy

How many pairs per frame?

Why j = i + 1 (no duplicate pairs)

Sampling each collider once per outer step

Scene graph vs collider slice, two parallel structures

When to call CheckCollision

Timeline, the frame contact happens

CheckCollision

circleSample, cached circle geometry

sampleCircle, read centre and radius from a collider

pairWantsCollision, layer mask filter

samplesOverlap, narrow-phase circle test

notifyPair, invoke callbacks

checkColliderPair, one unordered pair end-to-end

CheckCollision, pair loops only

Cost per pair (unchanged behaviour)

Chapter 7 note, combineCollisionIDs

What the manager does not do

O(n²) loop and when to optimise

Debugging CheckCollision

spawnEnemyFarFrom, enemy spawn for infinite map

Why spawning is different on an infinite map

Distance choice: 200 pixels

Struct and constant

spawnEnemyFarFrom and NewEnemyFarFromPlayer

game.go, setup and logic

Imports

Constants

Paths and layers

Game struct

NewGame, engine, textures, input

NewGame, tileset and tilemap

NewGame, player

NewGame, enemy

NewGame, camera and callback

Update, gameOver and player movement

Update, enemy AI and collisions

Draw, engine draw and HUD overlay

HUD, the GAME OVER overlay

Running the chapter

go.mod, dependencies

Summary