Add gravity and player-seeking AI to zombies

internal/network/handler.go

@@ -44,6 +44,8 @@ func (h *handler) serve() {
 	defer cancel() // stops the streamer when the read loop ends
 	h.ctx = ctx
 
+	defer h.srv.RemovePlayerPosition(h.conn.Profile.Name)
+
 	for {
 		pkt, err := h.conn.ReadPacket()
 		if err != nil {

internal/network/play.go

@@ -48,7 +48,8 @@ func (h *handler) beginPlay() error {
 
 // onPlayerMove recenters the streamer when the player crosses into a new chunk.
 // It is a non-blocking push; the read loop never waits on generation.
-func (h *handler) onPlayerMove(x, z float64) error {
+func (h *handler) onPlayerMove(x, y, z float64) error {
+	h.srv.SetPlayerPosition(h.conn.Profile.Name, x, y, z)
 	cx := int32(int64(math.Floor(x)) >> 4)
 	cz := int32(int64(math.Floor(z)) >> 4)
 	if h.streamer != nil {
@@ -230,14 +231,15 @@ func (h *handler) handlePlay(pkt protocol.Packet) error {
 		if err != nil {
 			return err
 		}
-		if _, err := r.Float64(); err != nil { // feet Y, unused for streaming
+		y, err := r.Float64() // feet Y
+		if err != nil {
 			return err
 		}
 		z, err := r.Float64()
 		if err != nil {
 			return err
 		}
-		return h.onPlayerMove(x, z)
+		return h.onPlayerMove(x, y, z)
 
 	case protocol.PlayPlayerAction:
 		return h.handlePlayerAction(pkt)

internal/server/server.go

@@ -4,6 +4,7 @@ package server
 
 import (
 	"encoding/json"
+	"sync"
 
 	"regionio/internal/protocol"
 	"regionio/internal/world"
@@ -55,6 +56,9 @@ type Server struct {
 	chunks   *world.Cache
 	store    *world.Store // nil when persistence is disabled
 	entities *world.EntityManager
+
+	// playerPos tracks the last known position of each player by name.
+	playerPos sync.Map // map[string][3]float64
 }
 
 // New constructs a Server from cfg. When cfg.WorldDir is set, the world is
@@ -89,6 +93,33 @@ func (s *Server) Chunks() *world.Cache { return s.chunks }
 // Entities returns the shared entity manager.
 func (s *Server) Entities() *world.EntityManager { return s.entities }
 
+// SetPlayerPosition updates the tracked position of a player.
+func (s *Server) SetPlayerPosition(name string, x, y, z float64) {
+	s.playerPos.Store(name, [3]float64{x, y, z})
+}
+
+// RemovePlayerPosition removes a player from tracking.
+func (s *Server) RemovePlayerPosition(name string) {
+	s.playerPos.Delete(name)
+}
+
+// NearestPlayer returns the position of the nearest player to (x, y, z).
+// Returns false if no players are online.
+func (s *Server) NearestPlayer(x, y, z float64) (pos [3]float64, ok bool) {
+	minDist := float64(-1)
+	s.playerPos.Range(func(key, value any) bool {
+		p := value.([3]float64)
+		dist := (p[0]-x)*(p[0]-x) + (p[1]-y)*(p[1]-y) + (p[2]-z)*(p[2]-z)
+		if minDist < 0 || dist < minDist {
+			minDist = dist
+			pos = p
+			ok = true
+		}
+		return true
+	})
+	return
+}
+
 // Store returns the on-disk world store, or nil if persistence is disabled.
 func (s *Server) Store() *world.Store { return s.store }
 

internal/server/spawner.go

@@ -1,6 +1,7 @@
 package server
 
 import (
+	"math"
 	"math/rand"
 	"time"
 
@@ -20,12 +21,46 @@ func (s *Server) entityTickLoop() {
 	for range ticker.C {
 		all := s.entities.All()
 		for _, e := range all {
-			// Basic random wandering
+			// Apply gravity
+			yBelow := int(e.Y - 0.1) // slightly below the entity
+			blockBelow := s.chunks.GetBlock(int(e.X), yBelow, int(e.Z))
+			
+			if blockBelow == world.StateAir || blockBelow == world.StateWater { // Air or Water
+				e.VelocityY -= 80 // gravity acceleration
+				if e.VelocityY < -3000 {
+					e.VelocityY = -3000 // terminal velocity
+				}
+			} else {
+				e.VelocityY = 0
+				e.Y = float64(yBelow + 1)
+				
+				// Basic random wandering or player tracking when on ground
+				pos, ok := s.NearestPlayer(e.X, e.Y, e.Z)
+				
+				if ok && e.TypeName == "minecraft:zombie" {
+					// Zombies move towards the player
+					dx := pos[0] - e.X
+					dz := pos[2] - e.Z
+					dist := math.Sqrt(dx*dx + dz*dz)
+					if dist > 1.0 && dist < 32.0 {
+						e.X += (dx / dist) * 0.15
+						e.Z += (dz / dist) * 0.15
+						// Simple yaw calculation
+						e.Yaw = float32(math.Atan2(-dx, dz) * (180 / math.Pi))
+					}
+				} else {
+					// Random wander
 					e.X += (rand.Float64() - 0.5) * 0.2
 					e.Z += (rand.Float64() - 0.5) * 0.2
 					e.Yaw += float32((rand.Float64() - 0.5) * 10.0)
 				}
 			}
+			
+			if e.VelocityY != 0 {
+				e.Y += float64(e.VelocityY) / 8000.0
+			}
+		}
+	}
 }
 
 func (s *Server) mobSpawnLoop() {

internal/world/cache.go

@@ -187,6 +187,18 @@ func (c *Cache) Frame(cx, cz int32) []byte {
 	return frame
 }
 
+// GetBlock returns the block state at world coordinates (x, y, z).
+// It loads or generates the chunk if necessary.
+func (c *Cache) GetBlock(x, y, z int) uint16 {
+	if y < MinY || y >= MinY+WorldHeight {
+		return 0 // StateAir
+	}
+	cx := int32(x >> 4)
+	cz := int32(z >> 4)
+	ch := c.chunkAt(cx, cz)
+	return ch.GetBlock(x, y, z)
+}
+
 // SetBlock changes the block at world coordinates (x, y, z), invalidating the
 // affected chunk's cached frame and marking it dirty for autosave. It reports
 // whether a chunk was actually touched (false if y is out of range).