BauSystem2.0/BauSystem_Main/src/de/steamwar/bausystem/utils/RayTraceUtils.java

/*
 * This file is a part of the SteamWar software.
 *
 * Copyright (C) 2022  SteamWar.de-Serverteam
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

package de.steamwar.bausystem.utils;

import de.steamwar.entity.REntity;
import lombok.Data;
import lombok.experimental.UtilityClass;
import org.bukkit.FluidCollisionMode;
import org.bukkit.GameMode;
import org.bukkit.Location;
import org.bukkit.block.Block;
import org.bukkit.block.BlockFace;
import org.bukkit.entity.Player;
import org.bukkit.util.RayTraceResult;
import org.bukkit.util.Vector;

import java.util.List;

@UtilityClass
public class RayTraceUtils {

    public static RRayTraceResult traceREntity(Player player, Location to, List<REntity> entityList) {
        if (player.getGameMode() == GameMode.SPECTATOR) {
            return null;
        }

        Location startPos = to.clone().add(0.0, player.getEyeHeight(), 0.0);
        Vector direction = to.getDirection();
        RayTraceResult blocks = player.getWorld().rayTraceBlocks(startPos, direction, 10.0, FluidCollisionMode.NEVER, true);

        REntity nearestHitEntity = null;
        RRayTraceResult nearestHitResult = null;
        double nearestDistanceSq = Double.MAX_VALUE;
        for (REntity entity: entityList) {
            if (!isOccluded(startPos.toVector(), direction, new Vector(entity.getX(), entity.getY() + 0.5, entity.getZ()))) continue;
            double distanceSq = new Vector(entity.getX(), entity.getY() + 0.5, entity.getZ()).distanceSquared(startPos.toVector());
            if (distanceSq > 100.0) continue;
            if (distanceSq < nearestDistanceSq) {
                nearestHitEntity = entity;
                nearestHitResult = new RRayTraceResult(new Vector(entity.getX(), entity.getY() + 0.5, entity.getZ()), null, null, entity);
                nearestDistanceSq = distanceSq;
            }
        }
        RRayTraceResult entities = nearestHitEntity == null ? null : new RRayTraceResult(nearestHitResult.getHitPosition(), nearestHitResult.getHitBlock(), nearestHitResult.getHitBlockFace(), nearestHitEntity);

        if (blocks == null) {
            return entities;
        } else if (entities == null) {
            return RRayTraceResult.fromRayTraceResult(blocks);
        } else {
            Vector startVec = startPos.toVector();
            double blockHitDistance = startVec.distance(blocks.getHitPosition());
            double entityHitDistanceSquared = startVec.distanceSquared(entities.getHitPosition());
            return entityHitDistanceSquared < blockHitDistance * blockHitDistance ? entities : RRayTraceResult.fromRayTraceResult(blocks);
        }
    }

    @Data
    public static class RRayTraceResult {
        private final Vector hitPosition;
        private final Block hitBlock;
        private final BlockFace hitBlockFace;
        private final REntity hitEntity;

        public static RRayTraceResult fromRayTraceResult(RayTraceResult rayTraceResult) {
            return new RRayTraceResult(rayTraceResult.getHitPosition(), rayTraceResult.getHitBlock(), rayTraceResult.getHitBlockFace(), null);
        }
    }

    public static boolean isOccluded(Vector a, Vector n, Vector b) {
        // a = Head pos, n = View direction (normalized), b = entity center
        // https://en.wikipedia.org/wiki/Distance_from_a_point_to_a_line#Vector_formulation

        double abX = b.getX() - a.getX();
        double abY = b.getY() - a.getY();
        double abZ = b.getZ() - a.getZ();
        double lambda = abX * n.getX() + abY * n.getY() + abZ * n.getZ();
        double distX = abX - n.getX() * lambda;
        double distY = abY - n.getY() * lambda;
        double distZ = abZ - n.getZ() * lambda;
        return Math.abs(distX) < 0.5 && Math.abs(distY) < 0.5 && Math.abs(distZ) < 0.5;
    }
}