Implement proper liquids

MiniBlocks.playground/Sources/Component/PlayerControlComponent.swift

@@ -134,11 +134,16 @@ class PlayerControlComponent: GKComponent {
         // Running into terrain pushes the player back, causing them to 'slide' along the block.
         // For more info, look up 'AABB sliding collision response'.
         let feetPos = position
+        let headPos = feetPos + Vec3(y: 1)
         var finalVelocity = requestedVelocity
         var iterations = 0
 
         if gameMode.enablesGravityAndCollisions {
-            while let hit = worldNode?.hitTestWithSegment(from: SCNVector3(feetPos), to: SCNVector3(feetPos + finalVelocity)).first, iterations < maxCollisionIterations {
+            while iterations < maxCollisionIterations {
+                let hit = [feetPos, headPos]
+                    .flatMap { worldNode?.hitTestWithSegment(from: SCNVector3($0), to: SCNVector3($0 + finalVelocity)) ?? [] }
+                    .first { !(world?.block(at: BlockPos3(rounding: $0.node.position))?.type.isLiquid ?? false) }
+                guard let hit = hit else { break }
                 let normal = Vec3(hit.worldNormal)
                 let repulsion = normal * abs(finalVelocity.dot(normal))
                 finalVelocity += repulsion

MiniBlocks.playground/Sources/Component/PlayerGravityComponent.swift

@@ -3,7 +3,9 @@ import SceneKit
 
 /// Accelerates the associated node downwards (i.e. in negative-y direction).
 class PlayerGravityComponent: GKComponent {
-    var acceleration: Double = -0.4
+    private let baseAcceleration: Double = -0.4
+    private let submergedFactor: Double = 0.5
+
     private var throttler = Throttler(interval: 0.1)
 
     private var world: World? {
@@ -31,10 +33,18 @@ class PlayerGravityComponent: GKComponent {
             var velocity = playerInfo!.velocity
 
             let y = position.y
-            let yBound = world.height(below: BlockPos3(rounding: position)).map { $0 + 1 }
+            let blockPos = BlockPos3(rounding: position)
+            let yBound = world.height(below: blockPos, includeLiquids: false).map { $0 + 1 }
 
+            let isSubmerged = world.block(at: blockPos)?.type.isLiquid ?? false
             let willBeOnGround = !playerInfo!.leavesGround && yBound.map { y + velocity.y <= Double($0) } ?? false
 
+            var acceleration = baseAcceleration
+
+            if isSubmerged {
+                acceleration *= submergedFactor
+            }
+
             if willBeOnGround {
                 velocity.y = 0
                 if !playerInfo!.isOnGround {

MiniBlocks.playground/Sources/Model/Strip.swift

@@ -14,9 +14,9 @@ struct Strip: Hashable, Codable, Sequence {
         set { blocks[y] = newValue }
     }
 
-    func block(below y: Int?) -> (y: Int, Block)? {
+    func block(below y: Int?, includeLiquids: Bool = true) -> (y: Int, Block)? {
         blocks
-            .filter { $0.key <= (y ?? .max) }
+            .filter { $0.key <= (y ?? .max) && (includeLiquids || !$0.value.type.isLiquid) }
             .max { $0.key < $1.key }
             .map { (y: $0.key, block: $0.value) }
     }

MiniBlocks.playground/Sources/Model/World.swift

@@ -59,8 +59,8 @@ struct World: Codable, Sequence {
     }
 
     /// Fetches the height below the given position. O(n) where n is the number of blocks in the strip at the given (x, z) coordinates.
-    func height(below pos: BlockPos3) -> Int? {
-        self[pos.asVec2].block(below: pos.y)?.y
+    func height(below pos: BlockPos3, includeLiquids: Bool = true) -> Int? {
+        self[pos.asVec2].block(below: pos.y, includeLiquids: includeLiquids)?.y
     }
 
     /// Fetches the block at the given position. O(1).