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.

**Reach 1** based on code from Keith Peters.

The arm follows the position of the mouse by calculating the angles with atan2().

float segLength = 80; float x, y, x2, y2; void setup() { size(640, 360); strokeWeight(20.0); stroke(255, 100); x = width/2; y = height/2; x2 = x; y2 = y; } void draw() { background(0); float dx = mouseX - x; float dy = mouseY - y; float angle1 = atan2(dy, dx); float tx = mouseX - cos(angle1) * segLength; float ty = mouseY - sin(angle1) * segLength; dx = tx - x2; dy = ty - y2; float angle2 = atan2(dy, dx); x = x2 + cos(angle2) * segLength; y = y2 + sin(angle2) * segLength; segment(x, y, angle1); segment(x2, y2, angle2); } void segment(float x, float y, float a) { pushMatrix(); translate(x, y); rotate(a); line(0, 0, segLength, 0); popMatrix(); }