First shot at implementing acacia trees

this is mostly working, but due to some issue with leaf decay, the edges of the larger canopy will decay within minutes.

I don't know why this is yet, but it's likely some incorrect implementation of Leaves causing the problem.

In addition, the secondary branch of acacia may generate next to the base block of the trunk, which I've never observed to happen in vanilla. This has a 2% chance of occurring, so I haven't been able to rule it out yet, but it probably shouldn't happen.

src/world/generator/object/AcaciaTree.php

@@ -0,0 +1,132 @@
+<?php
+
+/*
+ *
+ *  ____            _        _   __  __ _                  __  __ ____
+ * |  _ \ ___   ___| | _____| |_|  \/  (_)_ __   ___      |  \/  |  _ \
+ * | |_) / _ \ / __| |/ / _ \ __| |\/| | | '_ \ / _ \_____| |\/| | |_) |
+ * |  __/ (_) | (__|   <  __/ |_| |  | | | | | |  __/_____| |  | |  __/
+ * |_|   \___/ \___|_|\_\___|\__|_|  |_|_|_| |_|\___|     |_|  |_|_|
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * @author PocketMine Team
+ * @link http://www.pocketmine.net/
+ *
+ *
+ */
+
+declare(strict_types=1);
+
+namespace pocketmine\world\generator\object;
+
+use pocketmine\block\VanillaBlocks;
+use pocketmine\math\Facing;
+use pocketmine\math\Vector3;
+use pocketmine\utils\Random;
+use pocketmine\world\BlockTransaction;
+use function abs;
+use function array_rand;
+
+final class AcaciaTree extends Tree{
+	private const MIN_HEIGHT = 5;
+
+	private ?Vector3 $mainBranchTip = null;
+	private ?Vector3 $secondBranchTip = null;
+
+	public function __construct(){
+		parent::__construct(
+			VanillaBlocks::ACACIA_LOG(),
+			VanillaBlocks::ACACIA_LEAVES(),
+			0 //we don't use this anyway - everything is overridden
+		);
+	}
+
+	protected function generateTrunkHeight(Random $random) : int{
+		//50% chance of 2 extra blocks, 33% chance 1 or 3, 17% chance 0 or 4
+		return self::MIN_HEIGHT + $random->nextRange(0, 2) + $random->nextRange(0, 2);
+	}
+
+	protected function placeTrunk(int $x, int $y, int $z, Random $random, int $trunkHeight, BlockTransaction $transaction) : void{
+		// The base dirt block
+		$transaction->addBlockAt($x, $y - 1, $z, VanillaBlocks::DIRT());
+
+		$firstBranchHeight = $trunkHeight - 1 - $random->nextRange(0, 3);
+
+		for($yy = 0; $yy <= $firstBranchHeight; ++$yy){
+			$transaction->addBlockAt($x, $y + $yy, $z, $this->trunkBlock);
+		}
+
+		$mainBranchFacing = Facing::HORIZONTAL[array_rand(Facing::HORIZONTAL)];
+
+		//this branch may grow a second trunk if the diagonal length is less than the max length
+		$this->mainBranchTip = $this->placeBranch(
+			$transaction,
+			new Vector3($x, $y + $firstBranchHeight, $z),
+			$mainBranchFacing,
+			$random->nextRange(1, 3),
+			$trunkHeight - $firstBranchHeight
+		);
+
+		$secondBranchFacing = Facing::HORIZONTAL[array_rand(Facing::HORIZONTAL)];
+		if($secondBranchFacing !== $mainBranchFacing){
+			$secondBranchLength = $random->nextRange(1, 3);
+			$this->secondBranchTip = $this->placeBranch(
+				$transaction,
+				new Vector3($x, $y + ($firstBranchHeight - $random->nextRange(0, 1)), $z),
+				$secondBranchFacing,
+				$secondBranchLength,
+				$secondBranchLength //the secondary branch may not form a second trunk
+			);
+		}
+	}
+
+	protected function placeBranch(BlockTransaction $transaction, Vector3 $start, int $branchFacing, int $maxDiagonal, int $length) : Vector3{
+		$diagonalPlaced = 0;
+
+		$nextBlockPos = $start;
+		for($yy = 0; $yy < $length; $yy++){
+			$nextBlockPos = $nextBlockPos->up();
+			if($diagonalPlaced < $maxDiagonal){
+				$nextBlockPos = $nextBlockPos->getSide($branchFacing);
+				$diagonalPlaced++;
+			}
+			$transaction->addBlock($nextBlockPos, $this->trunkBlock);
+		}
+
+		return $nextBlockPos;
+	}
+
+	protected function placeCanopyLayer(BlockTransaction $transaction, Vector3 $center, int $radius, int $maxTaxicabDistance) : void{
+		$centerX = $center->getFloorX();
+		$centerY = $center->getFloorY();
+		$centerZ = $center->getFloorZ();
+
+		for($x = $centerX - $radius; $x <= $centerX + $radius; ++$x){
+			for($z = $centerZ - $radius; $z <= $centerZ + $radius; ++$z){
+				if(
+					abs($x - $centerX) + abs($z - $centerZ) <= $maxTaxicabDistance &&
+					$transaction->fetchBlockAt($x, $centerY, $z)->canBeReplaced()
+				){
+					$transaction->addBlockAt($x, $centerY, $z, $this->leafBlock);
+				}
+			}
+		}
+	}
+
+	protected function placeCanopy(int $x, int $y, int $z, Random $random, BlockTransaction $transaction) : void{
+		$mainBranchTip = $this->mainBranchTip;
+		if($mainBranchTip !== null){
+			$this->placeCanopyLayer($transaction, $mainBranchTip, radius: 3, maxTaxicabDistance: 5);
+			$this->placeCanopyLayer($transaction, $mainBranchTip->up(), radius: 2, maxTaxicabDistance: 2);
+		}
+		$secondBranchTip = $this->secondBranchTip;
+		if($secondBranchTip !== null){
+			$this->placeCanopyLayer($transaction, $secondBranchTip, radius: 2, maxTaxicabDistance: 3);
+			$this->placeCanopyLayer($transaction, $secondBranchTip->up(), radius: 1, maxTaxicabDistance: 2);
+		}
+	}
+}

src/world/generator/object/TreeFactory.php

@@ -49,6 +49,8 @@ final class TreeFactory{
 			}else{*/
 
 			//}
+		}elseif($type->equals(TreeType::ACACIA())){
+			return new AcaciaTree();
 		}
 		return null;
 	}