Vector Victor - This is confusing me

Hi everyone, recently I saw the setVelocity() option for vehicles and i thought "lets set the y value positive and make flying things!"

Believe it or not, it worked. Then I got to thinking... hey this could be a mode of transport around my server. So I got out my java compiler and started writing.

Anyways, after a few hours of digging around the interwebs for formulas and coding, I got something that compiled (yay) and made sense (yay) but didn't work (booo).

So I'm posting my code for everyone to take a look at and tell me what I'm doing wrong.

Theres a command /ft (for fly test) and it takes <x1> <z1> <x2> <z2>. You should set x1 and z1 to your current coordinates and x2 z2 to your destination. I have no idea how to work in y values, so those are just a random value for now.

Also, there are some random debug statements

Anyways, please help ;(

Code:

package net.serenity.flight;

import java.io.File;
import java.util.HashMap;
import java.io.File;
import java.util.logging.Logger;
import java.util.HashSet;
import java.util.Set;
import java.util.Arrays;
import java.lang.Math;
import org.bukkit.command.Command;
import org.bukkit.command.CommandSender;
import org.bukkit.entity.Player;
import org.bukkit.Server;
import org.bukkit.event.Event.Priority;
import org.bukkit.event.Event;
import org.bukkit.plugin.PluginDescriptionFile;
import org.bukkit.plugin.PluginLoader;
import org.bukkit.plugin.java.JavaPlugin;
import org.bukkit.plugin.PluginManager;
import org.bukkit.util.Vector;

/**
 * Flight WIP
 *
 * @author MonsieurApple
 */
public class Flight extends JavaPlugin {

    protected static final Logger log = Logger.getLogger("Minecraft");

    public void onDisable()
    {
        PluginDescriptionFile pdfFile = this.getDescription();
           log.info( pdfFile.getName() + " version " + pdfFile.getVersion() + " is disabled!" );
    }

    public void onEnable()
    {
        PluginDescriptionFile pdfFile = this.getDescription();
        log.info( pdfFile.getName() + " version " + pdfFile.getVersion() + " is enabled!" );
    }

    @Override
    public boolean onCommand(CommandSender sender, Command command, String commandLabel, String[] args){
        String commandName = command.getName();
        Player player;
        Integer x1 = Integer.valueOf(args[0]);
        Integer z1 = Integer.valueOf(args[1]);
        Integer x2 = Integer.valueOf(args[2]);
        Integer z2 = Integer.valueOf(args[3]);

        if (sender instanceof Player)
        {
            player = (Player) sender;
        }
        else
        {
            return false;
        }

        player.sendMessage(" X1: " + args[0] + " Z1: " + args[1] + " X2: " + args[2] + " Z2: " + args[3]);

        float d2d = Distance(new Vector(x1, 0, z1), new Vector(x2, 0, z2));
        player.sendMessage("Our distance is:" + String.valueOf(d2d));
        float distanceFinal = (float)Math.sqrt(Math.pow((double)d2d, 2.0) + Math.pow((double)(0), 2.0));
        player.sendMessage("Our distance is:" + String.valueOf(distanceFinal));
        Vector vector1 = new Vector(x1, 0, z1);
        float heading = Heading(new Vector(x2, 0, z2), new Vector(x1, 0, z1));
        player.sendMessage("Our new heading is " + String.valueOf(heading));
        Vector reposition = Reposition(vector1, heading, distanceFinal);
        // OMG!
        player.sendMessage("X: " + String.valueOf(reposition.getX()) + " Z: " + String.valueOf(reposition.getZ()));
        player.getVehicle().setVelocity(reposition);

        return true;
    }

    public static float Distance(Vector Pos1, Vector Pos2)
    {
        return (float)Math.sqrt(Math.pow((double)(Pos2.getX() - Pos1.getX()), 2.0) + Math.pow((double)(Pos2.getZ() - Pos1.getZ()), 2.0));
    }

    public static Vector Reposition(Vector Pos, float Ang, float Hyp)
    {
        float r = (float)Math.toRadians(Ang);
        float a = (float)(Math.sin(r)) * Hyp;
        float b = (float)(Math.cos(r)) * Hyp;
        return new Vector((double)(Pos.getX() + b), 3, (double)(Pos.getZ() + a));
    }

    public static float Heading(Vector Origin, Vector Dest)
    {
        double ang = (double)Math.atan2((Dest.getZ() - Origin.getZ()), (Dest.getX() - Origin.getX()));
        return (float)Math.toDegrees(ang);
    }
}

 

There is a built in vector method to compute the distance between two vectors. vector.distance(vector v).

Anyway, what do you mean by "doesn't work"?

 

Well I fly places but never to the right place and sometimes in the opposite direction

Also, a good proof that theres something wrong in my logic is /ft 1 1 1 1 (which should not move at all, same position) shoots me somewhere >.<
[MERGETIME="1299651765"][/MERGETIME]
Ok I changed the first part of the Reposition function to
float r = Ang * (float)Math.PI / 180.0f;
and it works a little more reliably, but not perfectly.
[MERGETIME="1299651855"][/MERGETIME]
Something is up. /ft 0 0 10 10 gives me -10 x and z

/ft 10 10 20 20 gives me 0 x 0 z!?
[MERGETIME="1299684584"][/MERGETIME]
Well I know someone that is good with 3D space and could probably figure this out. I'll email him later today.

 

Are you just trying to get the player to move in a particular direction?

That should just be

Code:

// Assumes that targetLoc is the location of the target

double speed = 0.1; // whatever

Location loc = player.getLocation();

Vector target = new Vector(targetLoc.getX(), targetLoc.getY(), targetLoc.getZ());

Vector velocity = target.clone().subtract(new Vector(loc.getX(), loc.getY(), loc.getZ()));

velocity.multiply(speed/velocity.length());

player.setVelocity(velocity);

This doesn't take into account gravity though.

In theory, that could be taken into account. (assuming gravity is known )

 

I'll have to test that

As for gravity, it's explained here http://www.minecraftforum.net/viewtopic.php?f=3&t=167836&p=2413341
[MERGETIME="1299772994"][/MERGETIME]
Tested: all it managed to do was smack me around the world

 

However, did it send you in the right direction ?

 

Sometimes, sometimes not.

 

Unless there is a coding error if the target is above the player, it should work If the target is below they there could be a problem with being pushed into the ground.

 

On a separate note, it turns out there is a limit on how high of a velocity you can set. I'll investigate more tomorrow when I'm not half falling asleep.

 

Yep. Found that myself. Even though the data is stored as doubles, I believe Notch treats them like Floats, and it overflows when Floats overflow.

 

Line 825-835? https://github.com/Bukkit/CraftBukkit/blob/master/src/main/java/net/minecraft/server/Entity.java

 

Actually, I find this most damning:

Code:

        if (Math.abs(this.motX) > 10.0D) {
             this.motX = 0.0D;
         }
         if (Math.abs(this.motY) > 10.0D) {
             this.motY = 0.0D;
         }
          if (Math.abs(this.motZ) > 10.0D) {
             this.motZ = 0.0D;
         }

 

Isn't that what lines 825-835 are?

 

This worked wonderfully for me. Check it out in action in my two new pstones, Sky Bouncer and Launch Pad. They have a couple of added twists. The vertical height of the jump is determined by the vertical aim of the player, and they can be redstone activated.

http://forums.bukkit.org/threads/se...-sky-bouncer-and-launch-pad-pstones-556.1034/