processing4/java/examples/Topics/Motion/MovingOnCurves/applet/MovingOnCurves.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 MovingOnCurves extends PApplet {

/**
 * Moving On Curves. 
 * 
 * In this example, the circles moves along the curve y = x^4.
 * Click the mouse to have it move to a new position.
 */

float beginX = 20.0f;  // Initial x-coordinate
float beginY = 10.0f;  // Initial y-coordinate
float endX = 570.0f;   // Final x-coordinate
float endY = 320.0f;   // Final y-coordinate
float distX;          // X-axis distance to move
float distY;          // Y-axis distance to move
float exponent = 4;   // Determines the curve
float x = 0.0f;        // Current x-coordinate
float y = 0.0f;        // Current y-coordinate
float step = 0.01f;    // Size of each step along the path
float pct = 0.0f;      // Percentage traveled (0.0 to 1.0)

public void setup() 
{
  size(640, 360);
  noStroke();
  smooth();
  distX = endX - beginX;
  distY = endY - beginY;
}

public void draw() 
{
  fill(0, 2);
  rect(0, 0, width, height);
  pct += step;
  if (pct < 1.0f) {
    x = beginX + (pct * distX);
    y = beginY + (pow(pct, exponent) * distY);
  }
  fill(255);
  ellipse(x, y, 20, 20);
}

public void mousePressed() {
  pct = 0.0f;
  beginX = x;
  beginY = y;
  endX = mouseX;
  endY = mouseY;
  distX = endX - beginX;
  distY = endY - beginY;
}

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