Collision detection system

collision/types.go

@@ -0,0 +1,87 @@
+package collision
+
+type Point struct {
+	X float64
+	Y float64
+}
+
+type Polygon struct {
+	Points []Point
+}
+
+type ObjectType int
+
+const (
+	Hero ObjectType = 1 << iota
+	Zombie
+)
+
+type Collidable interface {
+	CollisionShape() Polygon
+	HandleCollisionEvent(other Collidable)
+	CollisionObjectType() ObjectType
+}
+
+// Helper function to calculate the dot product of two points
+func dot(p1, p2 Point) float64 {
+	return p1.X*p2.X + p1.Y*p2.Y
+}
+
+// Helper function to get the normal of the edge between two points
+func edgeNormal(p1, p2 Point) Point {
+	return Point{X: p2.Y - p1.Y, Y: p1.X - p2.X}
+}
+
+// Project a polygon onto an axis and return the min and max projections
+func projectPolygon(axis Point, polygon Polygon) (float64, float64) {
+	min := dot(axis, polygon.Points[0])
+	max := min
+	for _, p := range polygon.Points[1:] {
+		projection := dot(axis, p)
+		if projection < min {
+			min = projection
+		}
+		if projection > max {
+			max = projection
+		}
+	}
+	return min, max
+}
+
+// Check if two projections on an axis overlap
+func overlap(minA, maxA, minB, maxB float64) bool {
+	if minA > maxB || minB > maxA {
+		return false
+	}
+	return true
+}
+
+// Overlaps checks if two polygons overlap using the Separating Axis Theorem
+func (p Polygon) Overlaps(p2 Polygon) bool {
+	if len(p.Points) == 0 || len(p2.Points) == 0 {
+		return false
+	}
+	for i := 0; i < len(p.Points); i++ {
+		next := (i + 1) % len(p.Points)
+		axis := edgeNormal(p.Points[i], p.Points[next])
+		minA, maxA := projectPolygon(axis, p)
+		minB, maxB := projectPolygon(axis, p2)
+
+		if !overlap(minA, maxA, minB, maxB) {
+			return false
+		}
+	}
+
+	for i := 0; i < len(p2.Points); i++ {
+		next := (i + 1) % len(p2.Points)
+		axis := edgeNormal(p2.Points[i], p2.Points[next])
+		minA, maxA := projectPolygon(axis, p)
+		minB, maxB := projectPolygon(axis, p2)
+
+		if !overlap(minA, maxA, minB, maxB) {
+			return false
+		}
+	}
+
+	return true
+}

collision/world.go

@@ -0,0 +1,32 @@
+package collision
+
+type World struct {
+	Entities []Collidable
+}
+
+func (w *World) AddEntity(e Collidable) {
+	w.Entities = append(w.Entities, e)
+}
+
+func (w *World) RemoveEntity(e Collidable) {
+	for i, entity := range w.Entities {
+		if entity == e {
+			w.Entities = append(w.Entities[:i], w.Entities[i+1:]...)
+		}
+	}
+}
+
+func (w *World) NotifyAboutCollisions() {
+	for i, entity := range w.Entities {
+		for _, other := range w.Entities[i+1:] {
+			if entity.CollisionShape().Overlaps(other.CollisionShape()) {
+				entity.HandleCollisionEvent(other)
+				other.HandleCollisionEvent(entity)
+			}
+		}
+	}
+}
+
+func NewWorld() *World {
+	return &World{}
+}

hero/hero.go

@@ -3,6 +3,7 @@ package hero
 import (
 	"bytes"
 	"github.com/hajimehoshi/ebiten/v2"
+	"gitlab.com/kbr4/9heroja/collision"
 	"gitlab.com/kbr4/9heroja/configuration"
 	"gitlab.com/kbr4/9heroja/resources"
 	"image"
@@ -23,9 +24,11 @@ type Hero struct {
 	direction configuration.Direction
 	IsWalking bool
 	Health    int // Health as a percentage (0-100)
+	X         float64
+	Y         float64
 }
 
-type spritePosition struct {
+type spriteFramePosition struct {
 	x int
 	y int
 }
@@ -34,8 +37,8 @@ func (h *Hero) DrawHero(screen *ebiten.Image) {
 
 	// set movement positions to be hashmap of sprite positions for each direction
 
-	movementPositions := map[configuration.Direction][]spritePosition{}
-	movementPositions[configuration.North] = []spritePosition{
+	movementPositions := map[configuration.Direction][]spriteFramePosition{}
+	movementPositions[configuration.North] = []spriteFramePosition{
 		{0, 166},
 		{33, 166},
 		{66, 166},
@@ -45,7 +48,7 @@ func (h *Hero) DrawHero(screen *ebiten.Image) {
 		{66, 166},
 		{33, 166},
 	}
-	movementPositions[configuration.NorthEast] = []spritePosition{
+	movementPositions[configuration.NorthEast] = []spriteFramePosition{
 		{168, 0},
 		{201, 0},
 		{0, 33},
@@ -56,7 +59,7 @@ func (h *Hero) DrawHero(screen *ebiten.Image) {
 		{201, 0},
 	}
 
-	movementPositions[configuration.East] = []spritePosition{
+	movementPositions[configuration.East] = []spriteFramePosition{
 		{132, 99},
 		{165, 99},
 		{198, 99},
@@ -67,7 +70,7 @@ func (h *Hero) DrawHero(screen *ebiten.Image) {
 		{165, 99},
 	}
 
-	movementPositions[configuration.SouthEast] = []spritePosition{
+	movementPositions[configuration.SouthEast] = []spriteFramePosition{
 		{33, 66},
 		{66, 66},
 		{99, 66},
@@ -78,7 +81,7 @@ func (h *Hero) DrawHero(screen *ebiten.Image) {
 		{66, 66},
 	}
 
-	movementPositions[configuration.South] = []spritePosition{
+	movementPositions[configuration.South] = []spriteFramePosition{
 		{66, 132},
 		{0, 99},
 		{33, 99},
@@ -89,7 +92,7 @@ func (h *Hero) DrawHero(screen *ebiten.Image) {
 		{0, 99},
 	}
 
-	movementPositions[configuration.SouthWest] = []spritePosition{
+	movementPositions[configuration.SouthWest] = []spriteFramePosition{
 		{99, 33},
 		{33, 0},
 		{66, 0},
@@ -100,7 +103,7 @@ func (h *Hero) DrawHero(screen *ebiten.Image) {
 		{33, 0},
 	}
 
-	movementPositions[configuration.West] = []spritePosition{
+	movementPositions[configuration.West] = []spriteFramePosition{
 		{198, 66},
 		{99, 132},
 		{132, 132},
@@ -111,7 +114,7 @@ func (h *Hero) DrawHero(screen *ebiten.Image) {
 		{99, 132},
 	}
 
-	movementPositions[configuration.NorthWest] = []spritePosition{
+	movementPositions[configuration.NorthWest] = []spriteFramePosition{
 		{0, 0},
 		{132, 33},
 		{165, 33},
@@ -129,7 +132,9 @@ func (h *Hero) DrawHero(screen *ebiten.Image) {
 
 	// ground
 	op.GeoM.Reset()
-	op.GeoM.Translate(float64(screenWidth/2-16), float64(screenHeight/2-16))
+	h.X = float64(screenWidth/2 - 16)
+	h.Y = float64(screenHeight/2 - 16)
+	op.GeoM.Translate(h.X, h.Y)
 	//op.GeoM.Translate(float64(i*tileSize-floorMod(g.cameraX, tileSize)),
 	//		float64((ny-1)*tileSize-floorMod(g.cameraY, tileSize)))
 
@@ -138,8 +143,8 @@ func (h *Hero) DrawHero(screen *ebiten.Image) {
 	// Drawing the dynamic health bar below the hero
 	maxHealthBarWidth := resources.HeroTileSize // Maximum width of the health bar (same as the character width)
 	healthBarHeight := 5                        // Height of the health bar
-	healthBarX := float64(screenWidth/2 - 16)   // Align with the hero
-	healthBarY := float64(screenHeight/2 + 20)  // Position below the hero
+	healthBarX := float64(h.X)                  // Align with the hero
+	healthBarY := float64(h.Y + 37)             // Position below the hero
 
 	// Calculate the current width of the health bar based on the hero's health
 	currentHealthBarWidth := int(float64(maxHealthBarWidth) * (float64(h.Health) / 100.0))
@@ -180,7 +185,7 @@ func NewHero() *Hero {
 	hero := &Hero{
 		step:      0,
 		IsWalking: false,
-		Health:    33,
+		Health:    100,
 	}
 
 	go func() {
@@ -217,3 +222,29 @@ func (h *Hero) Stop() {
 	walkTicker.Stop()
 	h.IsWalking = false
 }
+
+func (h *Hero) CollisionShape() collision.Polygon {
+	return collision.Polygon{
+		Points: []collision.Point{
+			{X: h.X, Y: h.Y},
+			{X: h.X + 33, Y: h.Y},
+			{X: h.X + 33, Y: h.Y + 33},
+			{X: h.X, Y: h.Y + 33},
+		},
+	}
+}
+
+func (h *Hero) CollisionObjectType() collision.ObjectType {
+	return collision.Hero
+}
+
+func (h *Hero) HandleCollisionEvent(other collision.Collidable) {
+	coll := other.CollisionObjectType()
+	switch coll {
+	case collision.Zombie:
+		h.Health -= 25
+		if h.Health <= 0 {
+			h.Health = 10
+		}
+	}
+}

main.go

@@ -3,6 +3,7 @@ package main
 import (
 	"github.com/hajimehoshi/ebiten/v2"
 	"github.com/hajimehoshi/ebiten/v2/inpututil"
+	"gitlab.com/kbr4/9heroja/collision"
 	"gitlab.com/kbr4/9heroja/configuration"
 	"gitlab.com/kbr4/9heroja/hero"
 	"gitlab.com/kbr4/9heroja/input"
@@ -51,6 +52,7 @@ type Game struct {
 	hero    *hero.Hero
 	terrain *terrain.Terrain
 	zombies []*zombie.Zombie
+	world   *collision.World
 }
 
 func (g *Game) Update() error {
@@ -63,17 +65,18 @@ func (g *Game) Update() error {
 		g.terrain.Move()
 		g.hero.Walk()
 	}
+	g.world.NotifyAboutCollisions()
 	return nil
 }
 
 func (g *Game) Draw(screen *ebiten.Image) {
 	g.terrain.DrawTerrain(screen)
-	g.hero.DrawHero(screen)
 	for _, z := range g.zombies {
 		z.OffsetX = g.terrain.PositionX
 		z.OffsetY = g.terrain.PositionY
 		z.DrawZombie(screen)
 	}
+	g.hero.DrawHero(screen)
 }
 
 func (g *Game) Layout(outsideWidth, outsideHeight int) (screenWidth, screenHeight int) {
@@ -86,10 +89,12 @@ var GameInstance *Game
 func init() {
 
 	GameInstance = &Game{}
+	GameInstance.world = collision.NewWorld()
 	GameInstance.control = &input.Keyboard{}
 	GameInstance.hero = hero.NewHero()
 	GameInstance.zombies = []*zombie.Zombie{zombie.NewZombie(), zombie.NewZombie(), zombie.NewZombie(), zombie.NewZombie(), zombie.NewZombie()}
 
+	GameInstance.world.AddEntity(GameInstance.hero)
 	// put zombies in random places on the screen but not too close to the hero or each other
 	for _, z := range GameInstance.zombies {
 		z.X = float64(configuration.Random(50, screenWidth-50))
@@ -99,6 +104,7 @@ func init() {
 			z.Y = float64(configuration.Random(0, screenHeight))
 		}
 		z.Walk()
+		GameInstance.world.AddEntity(z)
 	}
 
 	GameInstance.terrain = terrain.NewTerrain()

zombie/zombie.go

@@ -3,6 +3,7 @@ package zombie
 import (
 	"bytes"
 	"github.com/hajimehoshi/ebiten/v2"
+	"gitlab.com/kbr4/9heroja/collision"
 	"gitlab.com/kbr4/9heroja/configuration"
 	"gitlab.com/kbr4/9heroja/resources"
 	"image"
@@ -25,6 +26,7 @@ type Zombie struct {
 	Y         float64
 	OffsetX   float64
 	OffsetY   float64
+	IsDead    bool
 }
 
 type spritePosition struct {
@@ -57,7 +59,10 @@ func (z *Zombie) DrawZombie(screen *ebiten.Image) {
 	op.GeoM.Reset()
 	op.GeoM.Translate(z.X+z.OffsetX, z.Y+z.OffsetY)
 	op.GeoM.Scale(1, 1)
-
+	// Apply red tint if the zombie is dead
+	if z.IsDead {
+		op.ColorScale.Scale(1, 0, 0, 1) // Scale the red channel up, green and blue down.
+	}
 	screen.DrawImage(zombieImage.SubImage(image.Rect(p.x+1, p.y, p.x+resources.ZombieTileSize, p.y+resources.HeroTileSize)).(*ebiten.Image), op)
 }
 
@@ -73,23 +78,26 @@ func init() {
 }
 
 func NewZombie() *Zombie {
-	hero := &Zombie{
+	zombie := &Zombie{
 		step:      0,
 		IsWalking: false,
+		IsDead:    false,
 	}
 
 	go func() {
 		for {
 			select {
 			case <-walkTicker.C:
-				hero.step++
-				if hero.step > 3 {
-					hero.step = 0
+				if zombie.IsWalking {
+					zombie.step++
+					if zombie.step > 3 {
+						zombie.step = 0
+					}
 				}
 			}
 		}
 	}()
-	return hero
+	return zombie
 }
 
 func (z *Zombie) Walk() {
@@ -109,6 +117,36 @@ func (z *Zombie) ChangeDirection(d configuration.Direction) {
 
 func (z *Zombie) Stop() {
 	z.step = 2
-	walkTicker.Stop()
 	z.IsWalking = false
 }
+
+func (z *Zombie) CollisionShape() collision.Polygon {
+	if !z.IsDead {
+		return collision.Polygon{
+			Points: []collision.Point{
+				{X: z.X + z.OffsetX, Y: z.Y + z.OffsetY},
+				{X: z.X + z.OffsetX + 32, Y: z.Y + z.OffsetY},
+				{X: z.X + z.OffsetX + 32, Y: z.Y + z.OffsetY + 32},
+				{X: z.X + z.OffsetX, Y: z.Y + z.OffsetY + 32},
+			},
+		}
+	} else {
+		return collision.Polygon{
+			Points: []collision.Point{},
+		}
+	}
+}
+
+func (z *Zombie) CollisionObjectType() collision.ObjectType {
+	return collision.Zombie
+}
+
+func (z *Zombie) HandleCollisionEvent(other collision.Collidable) {
+	coll := other.CollisionObjectType()
+	switch coll {
+	case collision.Hero:
+		z.Stop()
+		z.IsDead = true
+
+	}
+}