The problem is that there's overlap from two lines filling in the places where the lines end/begin. I'd say the best way to get rid of the dots is to record the mouse position every time you want to draw a new line. Then, in draw(), call vertex() on all of the recorded positions in between a beginShape() and endShape(). This connects all of the lines as one shape, meaning there won't be overlap.

Hey thanks for the response!

By "record" I mean to save the x/y positions, possibly in an Array or List.

Hey,