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Month: October 2008

JavaFX, rectangular collision detection

In a game I wrote some years ago we handled simple rectangular collisions. Given the points:

We did:

// returning 0 means collision
int collision(int ax, int ay, int bx, int by, int cx, int cy, int dx, int dy){
	return ((ax > dx)||(bx < cx)||(ay > dy)||(by < cy));

I'll show here a little demo about how implement simple rectangular collisions on JavaFX.
First I created a movable rectangle using the same idea of draggable nodes I already had posted before.

import javafx.input.MouseEvent;
import javafx.scene.geometry.Rectangle;

public class MovableRectangle extends Rectangle {
    private attribute startX = 0.0;
    private attribute startY = 0.0;

    public attribute onMove = function(e:MouseEvent):Void {}

    override attribute onMousePressed = function(e:MouseEvent):Void {
        startX = e.getDragX()-translateX;
        startY = e.getDragY()-translateY;

    override attribute onMouseDragged = function(e:MouseEvent):Void {
        translateX = e.getDragX()-startX;
        translateY = e.getDragY()-startY;

In the main code I some important things:

  • colide, a color that represents the collision effect. White means no collision and gray means collision.
  • rec1 and rec2, the two rectangles that can collide.
  • checkcollision() the function that checks and handles a possible collision.

Here is the main code:

import javafx.application.Frame;
import javafx.application.Stage;
import javafx.scene.geometry.Rectangle;
import javafx.scene.paint.Color;
import javafx.input.MouseEvent;

var colide = Color.WHITE;

function checkcollision():Void {
    if (
        (rec1.getBoundsX() > rec2.getBoundsX() + rec2.getWidth()) or
        (rec1.getBoundsX() + rec1.getWidth() < rec2.getBoundsX()) or 
        (rec1.getBoundsY() > rec2.getBoundsY() + rec2.getHeight()) or 
        (rec1.getBoundsY() + rec1.getHeight() < rec2.getBoundsY())
    ) {
        colide = Color.WHITE
    } else {
        colide = Color.LIGHTGRAY

var rec1: MovableRectangle = MovableRectangle {
    x: 10, y: 10, width: 50, height: 60, fill: Color.RED
    onMove: function(e:MouseEvent):Void {

var rec2: MovableRectangle = MovableRectangle {
    x: 100, y: 100, width: 70, height: 30, fill: Color.BLUE
    onMove: function(MouseEvent):Void {
Frame {
    title: "Rectangular Collisions", width: 300, height: 300
    closeAction: function() { 
        java.lang.System.exit( 0 ); 
    visible: true

    stage: Stage {
        fill: bind colide
        content: [rec1, rec2]

Try it via Java Web Start:

Java Web Start

Some considerations:

  • You can use rectangular collisions to create bounding boxes to handle collisions in more complex shapes or sprites. Is a common approach in 2d games to avoid more expensive calculations.
  • There are space for optimizations.
  • In this case I'm using only two objects. Some problems raises when I have N objects to handle.

More generally, we can code:

function collission(ax, ay, bx, by, cx, cy, dx, dy): Boolean {
    return not ((ax > dx)or(bx < cx)or(ay > dy)or(by < cy));

function hitnode(a: Node, b:Node): Boolean{
    return (collission(
        a.getBoundsX(), a.getBoundsY(),
        a.getBoundsX() + a.getWidth(), a.getBoundsY() + a.getHeight(),
        b.getX(), b.getY(),
        b.getX() + b.getWidth(), b.getY() + b.getHeight()

This way we can pass just two bounding boxes to hitnode and easily check collision of a node against a list of bounding boxes nodes.
Using the same approach I also wrote this function to test if a Node is inside another Node:

function inside (ax, ay, bx, by, cx, cy, dx, dy):Boolean{
    return ((ax > cx) and (bx < dx) and (ay > cy) and (by < dy));

function insidenode(a:Node,b:Node):Boolean{
    return (inside(
        a.getBoundsX(), a.getBoundsY(),
        a.getBoundsX() + a.getWidth(), a.getBoundsY() + a.getHeight(),
        b.getBoundsX(), b.getBoundsY(),
        b.getBoundsX() + b.getWidth(), b.getBoundsY() + b.getHeight()

Soon I'll post game examples showing how to use this method and others collission detection methods.


Ainda essa semana

Ainda essa semana eu vou fazer três palestras. Olhe aí se você não vai estar por perto. ;)

  • 29/10 – Quarta-feira 20:30 – Palestra sobre NetBeans no na VII Semana de TI e Telecomunicações da FIC.
  • 30/10 – Sexta-feira 09:30 – Palestra sobre OpenSolaris também na VII Semana de TI e Telecomunicações da FIC.
  • 01/11Sábado 15:20 – Palestra Apresentando o CEJUG e o poder do Java em Iguatu no Encontro PHP & Java.

SCSNI Study Guide

This is a draft of study guide based on SCSNI (Sun Certified Specialist Netbeans IDE) exam objectives.

SCSNI Study Guide
Exam Objetive Resources
Section 1: IDE Configuration
1.1 Demonstrate the ability to configure the functionality available in the IDE, including using enabling and disabling functionality and using the Plugin Manager.
1.2 Explain the purpose of the user directory and the netbeans.conf file and how these can be used to configure the IDE.
1.3 Demonstrate the ability to work with servers in the IDE, such as registering new server instances and stopping and starting servers.
1.4 Describe how to integrate external libraries in the IDE and use them in coding and debugging your project.
1.5 Demonstrate knowledge of working with databases in the IDE, including registering new database connections and tables running SQL scripts.
1.6 Describe how to integrate and use different versions of the JDK in the IDE for coding, debugging, and viewing Javadoc documentation.
Section 2: Project Setup
2.1 Describe the characteristics and uses of a free-form project.
2.2 Demonstrate the ability to work with version control systems and the IDE. (Which VCS’s are available, which ones you need an external client for, how to pull sources out of a repository, view changes, and check them back in).
2.3 Describe the ways in which you can change the build process for a standard project, such as configuring project properties and modifying the project’s Ant build script.
2.4 Configure your project to compile against and run on a specific version of the JDK.
Section 3: Java SE Development
3.1 Demonstrate the ability to create NetBeans projects from the source code of an existing Java SE program.
3.2 Describe how to manage the classpath of a Java SE project, including maintaining a separate classpath for compiling and debugging.
3.3 Demonstrate the knowledge of the NetBeans GUI Builder and the ability to lay out and hook up basic forms using it.
3.4 Demonstrate the ability to package and distribute a built Java Desktop project for use by another user.
Section 4: Java EE Web Development
4.1 Describe how to create a NetBeans project from the source code of an existing Web application.
4.2 Distinguish between a visual web application and web application.
4.3 Demonstrate knowledge of which web frameworks are available in NetBeans IDE and how they are added to and used in a web application.
4.4 Describe how to monitor HTTP requests when running a web application.
4.5 Demonstrate a knowledge of basic tasks related to building and deploying web applications to a server, such as changing the target server and undeploying an application.
Section 5: Editing
5.1 Describe the purpose and uses of refactoring and demonstrate the ability to perform basic refactoring on Java source code.
5.2 Describe how to use the Options window to change the default appearance and behavior of the Source Editor.
5.3 Describe the ways that the IDE highlights errors in source code and the tools the IDE offers for correcting those errors.
5.4 Demonstrate the ability to use editor hints, such as implementing all the methods for an implemented interface
5.5 Demonstrate the ability to use live code templates such as automatic generation of constructors, try/catch loops, and getters and setters.
Section 6: Testing, Profiling, and Debugging
6.1 Demonstrate the ability to work with JUnit tests in the IDE, such as creating JUnit tests and interpreting JUnit test output.
6.2 Describe how to debug a local (desktop) application, including setting breakpoints and stepping through code.
6.3 Describe the difference between local and remote debugging and describe how to debug a remote (web) application.
6.4 Describe the purpose of profiling applications and how to profile a local desktop application in the IDE.

More useful resources:

Please, collaborate in the comments with others resource links (with section number). Let’s complete this guide.