Keep players above support blocks that grow into their hitbox

index.js

@@ -203,8 +203,25 @@ function Physics (mcData, world) {
     }
 
     let playerBB = getPlayerBB(pos)
-    const queryBB = playerBB.clone().extend(dx, dy, dz)
-    const surroundingBBs = getSurroundingBBs(world, queryBB)
+    let queryBB = playerBB.clone().extend(dx, dy, dz)
+    let surroundingBBs = getSurroundingBBs(world, queryBB)
+    if (entity.onGround) {
+      let supportGrowth = 0
+      for (const blockBB of surroundingBBs) {
+        const overlap = blockBB.maxY - playerBB.minY
+        if (blockBB.minY < playerBB.minY && blockBB.intersects(playerBB) && overlap > 0 && overlap <= physics.stepHeight) {
+          supportGrowth = Math.max(supportGrowth, overlap)
+        }
+      }
+      if (supportGrowth > 0) {
+        const liftedBB = playerBB.clone().offset(0, supportGrowth, 0)
+        if (!surroundingBBs.some(blockBB => blockBB.intersects(liftedBB))) {
+          playerBB = liftedBB
+          queryBB = playerBB.clone().extend(dx, dy, dz)
+          surroundingBBs = getSurroundingBBs(world, queryBB)
+        }
+      }
+    }
     const oldBB = playerBB.clone()
 
     for (const blockBB of surroundingBBs) {

test/bedrock.test.js

@@ -0,0 +1,145 @@
+/* eslint-env mocha */
+
+const assert = require('assert')
+const { Physics } = require('prismarine-physics')
+const { Vec3 } = require('vec3')
+
+const cases = [
+  { version: '1.17.1', original: 'farmland', replacement: 'dirt' },
+  { version: 'bedrock_1.17.40', original: 'farmland', replacement: 'dirt' },
+  { version: 'bedrock_1.19.1', original: 'mud', replacement: 'clay' }
+]
+
+function createWorld (Block, replacement) {
+  return {
+    getBlock (position) {
+      const name = position.equals(new Vec3(0, 60, 0)) ? replacement : 'air'
+      const block = Block.fromStateId(Block.fromProperties(name, {}).stateId, 0)
+      block.position = position.clone()
+      return block
+    }
+  }
+}
+
+function createEntity (position, overrides = {}) {
+  return {
+    pos: position,
+    vel: new Vec3(0, 0, 0),
+    onGround: true,
+    isInWater: false,
+    isInLava: false,
+    isInWeb: false,
+    isCollidedHorizontally: false,
+    isCollidedVertically: false,
+    elytraFlying: false,
+    elytraEquipped: false,
+    jumpTicks: 0,
+    jumpQueued: false,
+    fireworkRocketDuration: 0,
+    attributes: {},
+    yaw: 0,
+    pitch: 0,
+    control: {
+      forward: false,
+      back: false,
+      left: false,
+      right: false,
+      jump: false,
+      sprint: false,
+      sneak: false
+    },
+    jumpBoost: 0,
+    speed: 0,
+    slowness: 0,
+    dolphinsGrace: 0,
+    slowFalling: 0,
+    levitation: 0,
+    depthStrider: 0,
+    ...overrides
+  }
+}
+
+for (const { version, original, replacement } of cases) {
+  describe(`${original} replaced with ${replacement} on ${version}`, () => {
+    it('moves a grounded player onto the new collision surface', () => {
+      const mcData = require('minecraft-data')(version)
+      const Block = require('prismarine-block')(version)
+      const originalBlock = Block.fromStateId(mcData.blocksByName[original].defaultState, 0)
+      const originalHeight = Math.max(...originalBlock.shapes.map(shape => shape[4]))
+      const world = createWorld(Block, replacement)
+      const entity = createEntity(new Vec3(0.5, 60 + originalHeight, 0.5))
+
+      const physics = Physics(mcData, world)
+      physics.simulatePlayer(entity, world)
+      assert.strictEqual(entity.pos.y, 61)
+      physics.simulatePlayer(entity, world)
+
+      assert.strictEqual(entity.pos.y, 61)
+      assert.strictEqual(entity.onGround, true)
+    })
+  })
+}
+
+describe('support-growth collision guards', () => {
+  const version = 'bedrock_1.17.40'
+  const mcData = require('minecraft-data')(version)
+  const Block = require('prismarine-block')(version)
+  const physics = Physics(mcData, createWorld(Block, 'dirt'))
+  const farmlandHeight = Math.max(...Block.fromStateId(mcData.blocksByName.farmland.defaultState, 0).shapes.map(shape => shape[4]))
+
+  it('does not lift an airborne player out of an overlapping block', () => {
+    const world = createWorld(Block, 'dirt')
+    const entity = createEntity(new Vec3(0.5, 60 + farmlandHeight, 0.5), { onGround: false })
+    physics.simulatePlayer(entity, world)
+    assert.ok(entity.pos.y < 61)
+  })
+
+  it('does not lift through growth taller than the configured step height', () => {
+    const world = createWorld(Block, 'dirt')
+    const carpetHeight = Math.max(...Block.fromStateId(mcData.blocksByName.carpet.defaultState, 0).shapes.map(shape => shape[4]))
+    const entity = createEntity(new Vec3(0.5, 60 + carpetHeight, 0.5))
+    physics.simulatePlayer(entity, world)
+    assert.ok(entity.pos.y < 61)
+  })
+
+  it('does not move a player already standing on a full block', () => {
+    const world = createWorld(Block, 'dirt')
+    const entity = createEntity(new Vec3(0.5, 61, 0.5))
+    physics.simulatePlayer(entity, world)
+    assert.strictEqual(entity.pos.y, 61)
+  })
+
+  it('does not lift a player into a low ceiling', () => {
+    const world = {
+      getBlock (position) {
+        let shapes = []
+        if (position.equals(new Vec3(0, 60, 0))) shapes = [[0, 0, 0, 1, 1, 1]]
+        if (position.equals(new Vec3(0, 62, 0))) shapes = [[0, 0.5, 0, 1, 1, 1]]
+        return { position: position.clone(), shapes, type: 0 }
+      }
+    }
+    const entity = createEntity(new Vec3(0.5, 60.5, 0.5))
+
+    physics.simulatePlayer(entity, world)
+
+    assert.ok(entity.pos.y < 61)
+  })
+
+  it('keeps horizontal movement while lifting onto the replacement surface', () => {
+    const world = createWorld(Block, 'dirt')
+    const entity = createEntity(new Vec3(0.5, 60 + farmlandHeight, 0.5), {
+      control: {
+        forward: true,
+        back: false,
+        left: false,
+        right: false,
+        jump: false,
+        sprint: false,
+        sneak: false
+      }
+    })
+    physics.simulatePlayer(entity, world)
+    assert.strictEqual(entity.pos.y, 61)
+    assert.notStrictEqual(entity.pos.z, 0.5)
+  })
+})