I am relatively new to Java and have been trying to simulate the motion of an object (say a car) on a straight path.
I want my object to move in steps in the output, instead of appearing just at the last point of the line.
I have used 2 classes :Veh.java - the vehicle object and SimuFrame.java - to create the simulation environment.
I have referred to some online tutorials for ideas: http://www.newthinktank.com/2012/07/java-video-tutorial-52/ (This simulates the asteroids game. Howeer I want my object to move in a straight line instead of in a random direction)
Please help me understand where I am wrong and what to do next..
Thanks a lot.
Here's my code:
import java.awt.*;
import java.awt.event.*;
public class Veh extends Rectangle{
int uLeftX, uLeftY; //upper LH Position for Rectangle
static int height = 20;
static int width = 20;
int[] pathCoords=new int[1000];
int startPosY; // start position of the objet - anywhere on the left bounday of the frame.
int goalPosY; // end position of the objet - anywhere on the right boundary of the frame.
//Constructor to Create a new Veh
public Veh(int startPosY,int goalPosY){
//Create a new rectangle vehicle from super class constructor
super(0, startPosY, height, width);
this.startPosY=startPosY;
this.goalPosY=goalPosY;
this.pathCoords = Pathmove();
}
//Calculating the 1000 points on the line joining (0,startPosY) and (goalPosY,999)
int[] Pathmove(){
//Slope calculation
float s=(float)(this.goalPosY-this.startPosY)/999;
pathCoords[0]=this.startPosY;
System.out.println("First xy pair is: 0," +this.pathCoords[0]);
for(int m=1; m<1000; m++){
pathCoords[m]= (int)(m*s)-(int)((m-1)*s)+ pathCoords[m-1];
}
return pathCoords;
}
//Function to move the Reactangular object along the line using the Y coordinate values from Pathmove()
void move(){
int[] a = (int[])this.pathCoords.clone();
for (int c=0; c<a.length;c++){
this.setLocation(c,a[c]);
}
}
}
This is the code for creating the simulation environment.
import javax.swing.*;
import java.awt.*;
import java.util.*;
import java.util.concurrent.ScheduledThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
public class SimuFrame extends JFrame{
public static int frameWidth=1000;
public static int frameHeight=1000;
public static void main(String[] args){
new SimuFrame();
}
public SimuFrame(){
this.setSize(frameWidth,frameHeight);
this.setTitle("Path Planning Results");
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
SimuObject SO=new SimuObject();
this.add(SO);
// Used to execute code after a given delay
// The attribute is corePoolSize - the number of threads to keep in
// the pool, even if they are idle
ScheduledThreadPoolExecutor executor= new ScheduledThreadPoolExecutor(5);
executor.scheduleAtFixedRate(new RepaintTheFrame(this), 0L, 20L, TimeUnit.MILLISECONDS);
this.setVisible(true);
}
}
// Class implements the runnable interface
// By creating this thread I want to continually redraw the screen
// while other code continues to execute
class RepaintTheFrame implements Runnable{
SimuFrame theFrame;
public RepaintTheFrame(SimuFrame theFrame){
}
#Override
public void run() {
theFrame.repaint();
}
}
class SimuObject extends JComponent{
//Holds every Veh created
public ArrayList<Veh> vehs=new ArrayList<Veh>();
public SimuObject(){
int startPosY = (int)(Math.random()*999);
int goalPosY = (int)(Math.random()*999);
vehs.add(new Veh(startPosY,goalPosY));
}
public void paint(Graphics g){
// Allows me to make many settings changes in regards to graphics
Graphics2D graphicSettings = (Graphics2D)g;
// Draw a background that is as big as the Simu board
graphicSettings.setColor(Color.WHITE);
graphicSettings.fillRect(0, 0, getWidth(), getHeight());
// Set rendering rules
graphicSettings.setRenderingHint( RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
// Set the drawing color to red
graphicSettings.setPaint( Color.RED);
// Cycle through all of the Rock objects
for(Veh veh : vehs){
// Move the vehicle
veh.move();
graphicSettings.draw(veh);
}
}
}
You have a number of problems in your code:
You have a (swallowed) NullPointerException (NPE) in RepaintTheFrame.run(), which causes ScheduledThreadPoolExecutor.scheduleAtFixedRate() to run only once, per scheduleAtFixedRate()'s javadoc.
You are moving your car in JComponent.paint().
In any graphical framework, the repaint will be called automatically by the framework, usually on an OS event, e.g. moving the window, moving the mouse over the window, etc.
Your paint() method should only draw. It should not modify your domain model.
Your move() method always ends up with the vehicle at the end. That's probably not your intent. You probably want your move() method to merely increment the car's position.
Moving from a start value to an end value in steps is called interpolation. You want linear interpolation specifically here. Its one of the easiest to grasp.
This page will be of great assistance to you.
Without getting fancy with interpolation, you could just change your move routine like so:
int index =0;
void move(){
//int[] a = (int[])this.pathCoords.clone();
if(index<this.pathCoords.length)
this.setLocation(c,pathCoords[index]);
index+=1;
}
Not sure why you were cloning the array there. It probably isn't necessary.
Related
I'm trying to create a solar system using processing but I'm stuck at trying to set an image instead of using the java standard elipse image.
I started this at school and it consisted of an ellipse rotating around another ellipse.
package processing;
import processing.core.PApplet;
import processing.core.PImage;
public class SolarSystem extends PApplet{
PImage background;
Pianets earth;
public void settings() {
size(650,500);
}
public void setup() {
background = loadImage("C:\\background\\bg.jpg");
earth = new Pianets(this, width/2,height/2,40, 200, 0);
}
public void draw() {
background(background);
earth.showEarth();
earth.rotateEarth(0.007f);
}
public static void main(String[] args) {
PApplet.main("processing.SolarSystem");
}
}
Planets class
package processing;
import processing.core.PApplet;
public class Pianets {
PApplet vis;
float x0,y0; //centre
float diam;
float r; //distance from the centre
float alpha; //rotation angle
public Pianeti(PApplet applet, float x, float y, float diam,float r, float alpha){
vis = applet;
this.x0=x;
this.y0=y;
this.diam=diam;
this.r=r;
this.alpha=alpha;
}
void rotateEarth(float deltaAlpha){
alpha +=deltaAlpha;
}
void showEarth(){
//drawing the body of object at the centre
vis.ellipse(x0, y0, diam, diam);
float x = x0 + r*vis.cos(alpha);
float y = y0 + r*vis.sin(alpha);
vis.ellipse(x,y,diam,diam);
}
I created two images on paint that are the earth and the sun but I don't know how to set the image up.
Questions like this are best answered by looking at the Processing reference. There's an Image section that lists a loadImage() function for loading an image file, and an image() function for drawing it. Please read those.
You should also get into the habit of breaking your problem down into smaller pieces. For example, instead of posting your whole project (which has nothing to do with loading images right now), try to create a smaller example program that just shows a single image. Get that working perfectly before moving on. Then if you're confused about something, you can post a MCVE along with a specific technical question.
Shameless self-promotion: I wrote a tutorial on images in Processing available here.
I am making an RTS game using Slick 2D. I have a building class and it contains an int called resources. I want the resources variable to become a string and be rendered onto the center of my building (which is just supposed to be a rectangle).
Here's my building class:
package test;
import org.newdawn.slick.Color;
import org.newdawn.slick.Graphics;
import org.newdawn.slick.geom.Rectangle;
public class BaseBuilding extends Rectangle{
private int resources;
private Graphics g;
public BaseBuilding(float x, float y, float width, float height) {
super(x, y, width, height);
resources = 0;
g = new Graphics();
} // end constructor
public void render(){
g.drawString("bro wat", resources, resources);
g.setColor(Color.gray);
g.fill(this);
g.drawString(Integer.toString(resources), this.width/2, this.height/2);
} // end update
public int getResources(){
return resources;
} // end getResources
public void addResources(int mulla){
resources += mulla;
if (resources < 0)
resources = 0;
} // end addResources
public void createBasicUnit(){
// create a BasicUnit object in a randomly, valid position close to this object
// TODO
} // end createBasicUnit
} // end class def
So far all my states are working and i got the rectangle to appear appropriately. My g.drawString(str, float, float) code with correct parameters will work on my GameState class(not shown) in its render function, but it gives me this error in my BaseBuilding class:
java.lang.NullPointerException
at org.newdawn.slick.Graphics.drawString(Graphics.java:1366)
at test.BaseBuilding.render(BaseBuilding.java:19)
at test.GameState.render(GameState.java:34)
at org.newdawn.slick.state.StateBasedGame.render(StateBasedGame.java:199)
at org.newdawn.slick.GameContainer.updateAndRender(GameContainer.java:688)
at org.newdawn.slick.AppGameContainer.gameLoop(AppGameContainer.java:411)
at org.newdawn.slick.AppGameContainer.start(AppGameContainer.java:321)
at test.StateBaseGame.main(StateBaseGame.java:22)
Sat Apr 18 03:18:55 EDT 2015 ERROR:Game.render() failure - check the game code.
org.newdawn.slick.SlickException: Game.render() failure - check the game code.
at org.newdawn.slick.GameContainer.updateAndRender(GameContainer.java:691)
at org.newdawn.slick.AppGameContainer.gameLoop(AppGameContainer.java:411)
at org.newdawn.slick.AppGameContainer.start(AppGameContainer.java:321)
at test.StateBaseGame.main(StateBaseGame.java:22)
So i dug around and found out it's this line that's causing me problems:
g.drawString(Integer.toString(resources), this.width/2, this.height/2);
Couldn't find it on the internet; help if you can please thanks.
After taking a look at the Slick source code, your problem comes from the font variable inside the Graphics class which is null.
You are instantiating Graphics with the default constructor which does not provide a default value for the font variable. And the other one, as the doc says, only the container should be instantiate Graphics.
So, you should never instantiate Graphics, instead just retrieve it from the GameContainer (getGraphics) which is everywhere, or you can also get g from the render method of your game class (Game, BasicGame, BasicGameState, StateBasedGame, depending on what you use...).
To keep it simple, just pass your Graphics object through your render method:
public void render(Graphics g){
g.drawString("bro wat", resources, resources);
g.setColor(Color.gray);
g.fill(this);
g.drawString(Integer.toString(resources), this.width/2, this.height/2);
} // end update
And inside your Game:
render(GameContainer container, Graphics g) {
myBaseBuilding.render(g);
}
Ok, so, what I've been trying to figure out is how I can make a custom MouseListener for all my buttons that would not require listing every single one of them in the Handler, because I'm going to have a lot of them. Here's the code I have in my Listener as of now:
package com.dinobuilding.handler;
import java.awt.Graphics;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import com.BLANK.BLANKScreen;
import com.BLANK.BLANKWindow;
import com.BLANK.menufeature.Button;
public class ButtonHandler implements MouseListener {
public BLANKWindow dbw;
public BLANK Screen dbs;
static Button button = new Button();
public int buttonX = button.x;
public int buttonY = button.y;
public int buttonSizeX = button.xSize;
public int buttonSizeY = button.ySize;
public ButtonHandler(BLANKWindow dbw, BLANKScreen dbs) {
this.dbw = dbw;
this.dbs = dbs;
}
public static void setButton(Button b) {
button = b;
}
public int mouseEventX;
public int mouseEventY;
Graphics g;
public void mouseClicked(MouseEvent e) {
mouseEventX = e.getLocationOnScreen().x;
mouseEventY = e.getLocationOnScreen().y;
if(mouseEventX <= buttonX && mouseEventX >= buttonX + buttonSizeX) {
if(mouseEventY <= buttonY && mouseEventY >= buttonY + buttonSizeY) {
button.onClicked(dbs, dbw, g);
}
}
}
public void mousePressed(MouseEvent e) {
}
public void mouseReleased(MouseEvent e) {
}
public void mouseEntered(MouseEvent e) {
}
public void mouseExited(MouseEvent e) {
}
And here's the code in the first button that I'm trying to implement:
package com.BLANK.menus;
import java.awt.Color;
import java.awt.Graphics;
import com.BLANK.BLANKScreen;
import com.BLANK.BLANKWindow;
import com.BLANK.handler.ButtonHandler;
import com.BLANK.menufeature.Button;
public class MainMenuPlayButton extends Button {
public static int x;
public static int y;
public static int xSize;
public static int ySize;
public static String s;
public static Graphics g;
public MainMenuPlayButton(int x, int y, int xSize, int ySize, String s, Graphics g) {
super(x, y, xSize, ySize, s, g);
this.x = x;
this.y = y;
this.xSize = xSize;
this.ySize = ySize;
this.s = s;
this.g = g;
setColor(new Color(0, 226, 26));
draw();
}
public MainMenuPlayButton() {
}
public static void draw() {
drawButton(x, y, xSize, ySize, g, s);
ButtonHandler.setButton(new MainMenuPlayButton());
}
public void onClicked(BLANKScreen dbs, BLANKWindow dbw, Graphics g) {
setColor(new Color(216, 0, 0));
}
I think my main problem is that the code in the ButtonHandler gets called before the code in the Button class and therefore the ButtonHandler is utilizing the Button class itself, not the MainMenuPlayButton class. If you need the Button class as well, simply tell me, however I can't imagine why. Thank you in advance!
Edit
Ok, after debugging some, I have found that I in fact have the opposite problem. The button is never being clicked. The getSource() method could work, however I don't really know how to use that and I don't think that I could use that without hardcoding every single button, which is really something I do not want to do.
EDIT 1:
Do you think maybe I could do use the MouseEvent's getX or getXOnScreen? By the way, I registered the ButtonHandler using frame.addMouseListener on my JFrame, so...
EDIT 2:
It would seem that the getX method does not work either. If you could help me on that, I would very much appreciate that.
If you want to get the object that was pressed and tripped the MouseListener, use the MouseEvent's getSource() method. For example, this might work:
public void mouseClicked(MouseEvent e) {
(YourButton) button = (YourButton) e.getSource();
button.onClicked(...);
}
Other bits:
Rename your class from Button to something else, since the Button name clashes with the java.awt.Button class, and this can cause difficult to debug errors.
I cringe any time I see a Graphics field declared in a class, as it suggests possible inappropriate painting. Make sure that you really know what you're doing if you ever use one of these as a field since it's easy to get image loss or a NullPointerException if not used correctly, since the Graphics object is frequently changed by Java, and this change is completely out of your (the programmer's) control. Don't say that you haven't been warned.
Edit
Regarding your comments:
Yes, I do know what I'm doing with the Graphics field, however, if it makes you feel better, know that it's only temporary and I will be changing it to something else later.
OK, I've just been burned on this before. As long as you get it from a BufferedImage and don't try to get it by calling getGraphics() on a component or by pulling it out of a paint or paintComponent method, then you might be OK.
Also, I'm pretty sure that I'm getting the object it clicked correctly, but I can't get it to access the correct subclass of Button. It's only getting the Button class itself, not the MainMenuPlayButton.
Sorry, but this doesn't make sense since you don't get "classes" when you obtain a reference, an object pure and simple, and in fact you would get the very same object that the ButtonListener was added to and that tripped the listener, and the class of this reference will be whatever class your button is. I am assuming that you're adding your MouseListener directly to your "Button" object, correct? Again, time to do some debugging.
Edit 2
Regarding the most recent edit to your question:
Ok, after debugging some, I have found that I in fact have the opposite problem. The button is never being clicked. The getSource() method could work, however I don't really know how to use that and I don't think that I could use that without hardcoding every single button, which is really something I do not want to do.
No, there is no need to hard-code each button, trust me. That's the whole reason for using listeners that are added to the buttons.
EDIT 1: Do you think maybe I could do use the MouseEvent's getX or getXOnScreen? By the way, I registered the ButtonHandler using frame.addMouseListener on my JFrame, so... the
There's one of your problems. If you want to listen to your buttons, you're going to want to be able to register listeners on the button itself. If you have an array or collection of them registering listeners is easy. And no, I don't recommend using x and y on screen since it makes your program extremely fragile. If you did this, any changes to the structure of your GUI would require subsequent hard-code changes to your x and y handling. Ugh.
This begs the question of why create your own Button class, and why not instead use JButtons or a subclass of JButtons. You appear to be re-inventing the wheel, but (sorry to be blunt) creating one that is square.
Edit 3
But you cast the variable to a button, meaning that if I have multiple buttons I have to cast each and every one of them to a different thing.
No absolutely not as the magic of polymorphism should work here. But they're objects of the same type, no? Or do you have many different subclasses of your Button class? And regardless, inside of the mouseClicked(...) method, you appear to want to call only one method on your button, onClicked(...), which I imagine has to be an object of the super class, right? So by calling this method on the current button, It should call its own correct code.
The problem I have with JButton is that they already exist. I can't edit them and I can't customize them, ...
This is patently not true. You can change their appearance and behaviors by many means, including by subclassing or by a factory creation method. Plus they already come with the machinery for being able to register listeners and respond to mouse actions.
...Also, would I have to register/make a new handler for each and every one of the buttons?
Again, you appear to be forgetting that polymorphism should take care of all of this. One handler should do, depending on how well-behaved your code is.
I am going to have a LOT of buttons, and I don't think that that would be a viable solution. If not the getX how would I get it to do something when the thing is clicked?
I've given you my recommendation, other than sometimes it is better to re-write sections of code if the design can be improved, meaning again you may want to consider retrofitting your code to use JButtons.
So, for some reason when I try to use a for loop to initialize panels in chess board, it actually loops the loop itself. In other words, it doesn't go on forever, but it starts and completes again and again.
package chessgame;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class ChessGame extends JFrame implements ActionListener{
public static final int WIDTH=800;
public static final int HEIGHT=800;
public static void main(String[] args) {
ChessGame gui = new ChessGame();
gui.setVisible(true);
}
public ChessGame(){
super("Chess Game Demo");
setSize(WIDTH, HEIGHT);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setLayout(new GridLayout(8,8));
JPanel[] chessSquares = new JPanel[64];
for (int a=0;a<64;a++){
System.out.println(a);
}
}
}
I have included all potentially relevant code because I plan to use indices of chessSquares to color squares black and white. When I do this I also get a NullPointerException. I can understand why I'm getting that given the following error, but I cannot at all understand why a would be printed 0, 1....62, 63 over and over again. I am relatively new to Swing and have absolutely no idea why it does this. If anyone could explain that would be tremendously helpful. Thanks.
Don't put meaningful initialization in ChessGame's constructor, but instead override frameInit. When you do, also be sure to call super.frameInit(). See the javadoc or this tutorial.
I would like to move a sphere in a random direction within a simple universe. How could i achieve this with behaviours by changing the location a small amount frame by frame. The reason I am trying to do this is to produce random movement within the universe and eventually build in simple collision detection between the particles.
Any advice/links would be appreciated
Add a new class that extends Behavior, using this skeleton:
public class XXXBehavior extends Behavior
{
private WakeupCondition wc = new WakeupOnElapsedTimer(1000); // 1000 ms
public void initialize()
{
wakeupOn(wc);
}
public void processStimulus(Enumeration criteria)
{
// Move the shape here
// prepare for the next update
wakeupOn(wc);
}
}
You later need to instantiate the class and add it to the scene graph. You also need to defined the bounds, otherwise nothing will happen!
xxxEffect = new XXXBehavior();
xxxEffect.setSchedulingBounds(bounds);
sceneBG.addChild(xxxEffect);