processing4/java/examples/Topics/GUI/Rollover/applet/Rollover.java

import processing.core.*; 

import java.applet.*; 
import java.awt.*; 
import java.awt.image.*; 
import java.awt.event.*; 
import java.io.*; 
import java.net.*; 
import java.text.*; 
import java.util.*; 
import java.util.zip.*; 
import java.util.regex.*; 

public class Rollover extends PApplet {

/**
 * Rollover. 
 * 
 * Roll over the colored squares in the center of the image
 * to change the color of the outside rectangle. 
 */
 
 
int rectX, rectY;      // Position of square button
int circleX, circleY;  // Position of circle button
int rectSize = 50;     // Diameter of rect
int circleSize = 53;   // Diameter of circle

int rectColor;
int circleColor;
int baseColor;

boolean rectOver = false;
boolean circleOver = false;

public void setup()
{
  size(200, 200);
  smooth();
  rectColor = color(0);
  circleColor = color(255);
  baseColor = color(102);
  circleX = width/2+circleSize/2+10;
  circleY = height/2;
  rectX = width/2-rectSize-10;
  rectY = height/2-rectSize/2;
  ellipseMode(CENTER);
}

public void draw()
{
  update(mouseX, mouseY);

  noStroke();
  if (rectOver) {
    background(rectColor);
  } else if (circleOver) {
    background(circleColor);
  } else {
    background(baseColor);
  }

  stroke(255);
  fill(rectColor);
  rect(rectX, rectY, rectSize, rectSize);
  stroke(0);
  fill(circleColor);
  ellipse(circleX, circleY, circleSize, circleSize);
}

public void update(int x, int y)
{
  if( overCircle(circleX, circleY, circleSize) ) {
    circleOver = true;
    rectOver = false;
  } else if ( overRect(rectX, rectY, rectSize, rectSize) ) {
    rectOver = true;
    circleOver = false;
  } else {
    circleOver = rectOver = false;
  }
}

public boolean overRect(int x, int y, int width, int height) 
{
  if (mouseX >= x && mouseX <= x+width && 
      mouseY >= y && mouseY <= y+height) {
    return true;
  } else {
    return false;
  }
}

public boolean overCircle(int x, int y, int diameter) 
{
  float disX = x - mouseX;
  float disY = y - mouseY;
  if(sqrt(sq(disX) + sq(disY)) < diameter/2 ) {
    return true;
  } else {
    return false;
  }
}

  static public void main(String args[]) {
    PApplet.main(new String[] { "Rollover" });
  }
}