Debugging movement/collision code in 2d tile game

Newbie & Debugging Questions
#1

Hello, I’m working on a top down 2d game and am having some problems with collision detection. Here is a basic screenshot.

https://dl.dropboxusercontent.com/u/24222531/game1.png

My issue involves buggy movement. If I spam movement keys near a wall, I can pass through and get stuck. I think my problem may be related to multiple threads, but I am not sure.

I have a text file grid of integers read in for collision, 1 = not passable, 0 = passable. My checkCollision function checks the proposed new player position for a collision, and disallows that movement if there is a tile.

I use a overridden Keymanager classhttp://pastebin.java-gaming.org/b9854254086 to alter Player’s public variables UP, DOWN, LEFT, RIGHT to transfer keyboard to game logic.

Here is the player tick class:


public class Player {
**SNIP SNIP**
public void tick() {
        if (moving) {
            updatePlayerPosition();
        }

        if (sprinting) {
            moveSpeed = SPRINT; // 16
        } else {
            moveSpeed = WALK; // 8
        }

        if (!moving) {
            if (up) {
                moveUp();
            }
            if (down) {
                moveDown();
            }
            if (right) {
                moveRight();
            }
            if (left) {
                moveLeft();
            }

        }

Here I update the player movement if they are still in the process of moving from one tile to another. http://pastebin.java-gaming.org/9854530468e

private void updatePlayerPosition() {
       
        switch (facing) {
            case "north":
                if (!detectCollision(tileX, tileY - 1)) {
                    northAnimator.update(System.currentTimeMillis());
                    y -= moveSpeed;
                    if (y % 32 == 0) {
                        moving = false;
                        tileY = (int) pixelsToTileY(y);
                    }
                }
                break;
            case "south":
*SNIPSNIP*
        }
    }

This simply changes facing direction, sets moving to true, and lets the above method handle the rest. http://pastebin.java-gaming.org/4506e684f89

private void moveUp() { // move player up
        // if not facing north, make facing north

        if (!facing.equals("north")) {
            facing = "north";
        } else {

            // else, detect collision in the direction            
            if (!detectCollision(tileX, tileY - 1)) {
                moving = true;
            }
        }
    }

Somewhere in here there is a bug going on. I know the detectcollision method is working properly as I debugged it with println’s. It seems that sometimes, while I am actively “Moving”, my direction can change and place me in a wall. Note that this code has double collision checking, I tried with one and it simply let me into impassable walls, with two checks i actually get stuck in the wall and cant move at all.

Can anyone help me out here. Is there a simpler way of getting animated tile movement?

#2

You shouldn’t need multithreading for a simple 2D game.

Multithreading is a nightmare and introduces lots of problems. It’s probably best you don’t use it unless you’re absolutely certain you need it.

#3

You are most likely dealing with rounding issues with the player’s position when checking against the tile coordinates on the map.

#4

I’m doing stuff like this to start up my game, not sure if this is multithreading or just one thread getting started up?

public class TileGame extends Canvas implements Runnable {

public synchronized void start() {
        if (running) {
            return;
        }
        running = true;
        gameThread = new Thread(this);
        gameThread.start();}
@Override
    public void run() {
*snipsnip*

    }

On second thought, I dont think it is multithreaded. I kinda followed a tutorial for the basic game loop stuff, and I think all this just starts up one thread for the game.

#5

Here you go, a full proof tutorial on collision within tiles.

#6

Thank you, I will review this.

#7

Is that theChernoProject? If it is, I have to say he’s an ok programmer, but one thing that has always bugged me is his use of threads. You don’t need to manually create a thread just to start a game. There is absolutely (as far as I know) no advantage to it, and it really isn’t a good design.

#8

You need to create a separate thread for your game when you’re using JFrame. If you don’t, you will have problems with JFrame.

#9

The great tutorial maker arrives! I was just reading your tutorial linked above! Thanks for it, I’m just fiddling with the LWJGL keyboard stuff there.

Also, how would I go about making a seperate thread for my jframe? I have no experience with threads really.
Here is my main, which pretty much just makes a frame and launches it. I assume I would have to modify this?

public static void main(String[] args) {
       TileGame game = new TileGame();
        game.setPreferredSize(new Dimension(TileGame.WIDTH * TileGame.SCALE, TileGame.HEIGHT * TileGame.SCALE));
        game.setMaximumSize(new Dimension(TileGame.WIDTH * TileGame.SCALE, TileGame.HEIGHT * TileGame.SCALE));
        game.setMinimumSize(new Dimension(TileGame.WIDTH * TileGame.SCALE, TileGame.HEIGHT * TileGame.SCALE));

        JFrame frame = new JFrame("Autumn Cornucopia");
        frame.setSize(TileGame.WIDTH * TileGame.SCALE, TileGame.HEIGHT * TileGame.SCALE);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setResizable(false);
        frame.add(game);
        frame.setLocationRelativeTo(null);
        frame.requestFocus();
        frame.toFront();

        frame.setVisible(true);

        //gsm = new GameStateManager();
        //gsm.start();
        game.start();
    }
#10

Ok, regarding the initial problem:

Thanks to the tutorial, I figured it out. In the end I ran into a simple semantics problem.
The code above references a “CanMove” method which checks a tile to see if the player can move there, while my collision layer was using the term “DetectCollision”.

It took me a bit to figure out that (CanMove = true) != (DetectCollision = true). One says “yes you can move there”, the other says “yes there is a collision”.

Now I am trying to alter this new movement method so I can have similar movement as before. IE: Press button,ignore input, move player image a few pixels, repeat for X ticks until centered on a tile, allow input again.

Also! I noticed a slight bug in the tutorial code, which was mentioned. Even if the player wasnt moving, it continued to call the CanMove functions a total of 10+ times every tick.