float theta; void setup() { size(640, 360); smooth(); } void draw() { background(0); frameRate(30); stroke(255); // Let's pick an angle 0 to 90 degrees based on the mouse position float a = (mouseX / (float) width) * 90f; // Convert it to radians theta = radians(a); // Start the tree from the bottom of the screen translate(width/2,height); // Draw a line 120 pixels line(0,0,0,-120); // Move to the end of that line translate(0,-120); // Start the recursive branching! branch(120); } void branch(float h) { // Each branch will be 2/3rds the size of the previous one h *= 0.66; // All recursive functions must have an exit condition!!!! // Here, ours is when the length of the branch is 2 pixels or less if (h > 2) { pushMatrix(); // Save the current state of transformation (i.e. where are we now) rotate(theta); // Rotate by theta line(0, 0, 0, -h); // Draw the branch translate(0, -h); // Move to the end of the branch branch(h); // Ok, now call myself to draw two new branches!! popMatrix(); // Whenever we get back here, we "pop" in order to restore the previous matrix state // Repeat the same thing, only branch off to the "left" this time! pushMatrix(); rotate(-theta); line(0, 0, 0, -h); translate(0, -h); branch(h); popMatrix(); } }