implement crawling

server/block/cube/bbox.go

@@ -282,3 +282,26 @@ func (box BBox) ZOffset(nearby BBox, deltaZ float64) float64 {
 	}
 	return deltaZ
 }
+
+// Corners returns slice of all hitbox corners
+func (box BBox) Corners() []mgl64.Vec3 {
+	min := box.min
+	max := box.max
+	xyZ := mgl64.Vec3{min[0], min[1], max[2]}
+	xYz := mgl64.Vec3{min[0], max[1], min[2]}
+	xYZ := mgl64.Vec3{min[0], max[1], max[2]}
+	XYz := mgl64.Vec3{max[0], max[1], min[2]}
+	XyZ := mgl64.Vec3{max[0], min[1], max[2]}
+	Xyz := mgl64.Vec3{max[0], min[1], min[2]}
+	return []mgl64.Vec3{min, max, xyZ, xYz, xYZ, XYz, XyZ, Xyz}
+}
+
+// Mul performs a scalar multiplication for min, max points of BBox
+func (box BBox) Mul(val float64) BBox {
+	return BBox{min: box.min.Mul(val), max: box.max.Mul(val)}
+}
+
+// Volume calculates Volume of the BBox
+func (box BBox) Volume() float64 {
+	return box.Height() * box.Length() * box.Width()
+}

server/player/player.go

@@ -63,7 +63,7 @@ type Player struct {
 	armour                   *inventory.Armour
 	heldSlot                 *atomic.Uint32
 
-	sneaking, sprinting, swimming, gliding, flying,
+	sneaking, sprinting, swimming, gliding, crawling, flying,
 	invisible, immobile, onGround, usingItem atomic.Bool
 	usingSince atomic.Int64
 
@@ -951,7 +951,7 @@ func (p *Player) Respawn() {
 // particles show up under the feet. The player will only start sprinting if its food level is high enough.
 // If the player is sneaking when calling StartSprinting, it is stopped from sneaking.
 func (p *Player) StartSprinting() {
-	if !p.hunger.canSprint() && p.GameMode().AllowsTakingDamage() {
+	if !p.hunger.canSprint() && p.GameMode().AllowsTakingDamage() || p.crawling.Load() {
 		return
 	}
 	ctx := event.C()
@@ -1044,6 +1044,37 @@ func (p *Player) StopSwimming() {
 	p.updateState()
 }
 
+// StartCrawling makes the player start crawling if it is not currently doing so. If the player is sneaking
+// while StartCrawling is called, the sneaking is stopped.
+func (p *Player) StartCrawling() {
+	var isAir bool
+	for _, corner := range p.Type().BBox(p).Translate(p.Position()).Corners() {
+		_, isAir = p.World().Block(cube.PosFromVec3(corner).Add(cube.Pos{0, 1, 0})).(block.Air)
+		if !isAir {
+			break
+		}
+	}
+
+	if !isAir && !p.crawling.CompareAndSwap(false, true) {
+		return
+	}
+	p.StopSneaking()
+	p.updateState()
+}
+
+// StopCrawling makes the player stop crawling if it is currently doing so.
+func (p *Player) StopCrawling() {
+	if !p.crawling.CompareAndSwap(true, false) {
+		return
+	}
+	p.updateState()
+}
+
+// Crawling checks if the player is currently crawling.
+func (p *Player) Crawling() bool {
+	return p.crawling.Load()
+}
+
 // StartGliding makes the player start gliding if it is not currently doing so.
 func (p *Player) StartGliding() {
 	if !p.gliding.CompareAndSwap(false, true) {
@@ -2615,12 +2646,16 @@ func (p *Player) OnGround() bool {
 	return p.onGround.Load()
 }
 
-// EyeHeight returns the eye height of the player: 1.62, or 0.52 if the player is swimming.
+// EyeHeight returns the eye height of the player.
 func (p *Player) EyeHeight() float64 {
-	if p.swimming.Load() {
+	switch {
+	case p.swimming.Load() || p.crawling.Load():
 		return 0.52
+	case p.sneaking.Load():
+		return 1.26
+	default:
+		return 1.62
 	}
-	return 1.62
 }
 
 // PlaySound plays a world.Sound that only this Player can hear. Unlike World.PlaySound, it is not broadcast

server/player/type.go

@@ -14,10 +14,10 @@ func (Type) BBox(e world.Entity) cube.BBox {
 	p := e.(*Player)
 	s := p.Scale()
 	switch {
+	case p.Gliding(), p.Swimming(), p.Crawling():
+		return cube.Box(-0.3*s, 0, -0.3*s, 0.3*s, 0.6*s, 0.3*s)
 	case p.Sneaking():
 		return cube.Box(-0.3*s, 0, -0.3*s, 0.3*s, 1.5*s, 0.3*s)
-	case p.Gliding(), p.Swimming():
-		return cube.Box(-0.3*s, 0, -0.3*s, 0.3*s, 0.6*s, 0.3*s)
 	default:
 		return cube.Box(-0.3*s, 0, -0.3*s, 0.3*s, 1.8*s, 0.3*s)
 	}

server/session/controllable.go

@@ -69,6 +69,9 @@ type Controllable interface {
 	StartSwimming()
 	Swimming() bool
 	StopSwimming()
+	StartCrawling()
+	Crawling() bool
+	StopCrawling()
 	StartFlying()
 	Flying() bool
 	StopFlying()

server/session/entity_metadata.go

@@ -50,6 +50,9 @@ func (s *Session) addSpecificMetadata(e any, m protocol.EntityMetadata) {
 	if sw, ok := e.(swimmer); ok && sw.Swimming() {
 		m.SetFlag(protocol.EntityDataKeyFlags, protocol.EntityDataFlagSwimming)
 	}
+	if cr, ok := e.(crawler); ok && cr.Crawling() {
+		m.SetFlag(protocol.EntityDataKeyFlags, protocol.EntityDataFlagCrawling)
+	}
 	if gl, ok := e.(glider); ok && gl.Gliding() {
 		m.SetFlag(protocol.EntityDataKeyFlags, protocol.EntityDataFlagGliding)
 	}
@@ -178,6 +181,10 @@ type swimmer interface {
 	Swimming() bool
 }
 
+type crawler interface {
+	Crawling() bool
+}
+
 type glider interface {
 	Gliding() bool
 }

server/session/handler_player_auth_input.go

@@ -122,6 +122,12 @@ func (h PlayerAuthInputHandler) handleInputFlags(flags uint64, s *Session) {
 	if flags&packet.InputFlagStartJumping != 0 {
 		s.c.Jump()
 	}
+	if flags&packet.InputFlagStartCrawling != 0 {
+		s.c.StartCrawling()
+	}
+	if flags&packet.InputFlagStopCrawling != 0 {
+		s.c.StopCrawling()
+	}
 	if flags&packet.InputFlagMissedSwing != 0 {
 		s.swingingArm.Store(true)
 		defer s.swingingArm.Store(false)