This example is for Processing 3+. If you have a previous version, use the examples included with your software. If you see any errors or have suggestions, please let us know.

Follow 3 based on code from Keith Peters.

A segmented line follows the mouse. The relative angle from each segment to the next is calculated with atan2() and the position of the next is calculated with sin() and cos().

float[] x = new float[20];
float[] y = new float[20];
float segLength = 18;

void setup() {
  size(640, 360);
  stroke(255, 100);

void draw() {
  dragSegment(0, mouseX, mouseY);
  for(int i=0; i<x.length-1; i++) {
    dragSegment(i+1, x[i], y[i]);

void dragSegment(int i, float xin, float yin) {
  float dx = xin - x[i];
  float dy = yin - y[i];
  float angle = atan2(dy, dx);  
  x[i] = xin - cos(angle) * segLength;
  y[i] = yin - sin(angle) * segLength;
  segment(x[i], y[i], angle);

void segment(float x, float y, float a) {
  translate(x, y);
  line(0, 0, segLength, 0);