Please how to get line with constant length following mouse ?
(I was looking on Google but I don't even/already know what words to look for)
I have made this, but there must be smarter way to make it  - without loop just with calculation.
I want to make line to follow mouse (for start), like if I pick solid stick at first point, second point will follow my hand at the same distance. Even better line with fixed length moving on a curve with both points. (Like wagon on a curved railway - and that's what's going on about here - more lines moving on a curve like train). Btw sorry for my weak english.
Thank you very much

1. ConstLenLine lin;
2. void setup() {
3.   size(640, 480, P2D);
4.   background(250);
5.   stroke(0);
6.   smooth();
7.   lin = new ConstLenLine();
8. }
9. void draw() {
10.   background(250);
11.   lin.update();
12.   lin.draw();
13. }
14. class ConstLenLine {
15.   float len = 50; // length of the line
16.   PVector A, B, eq;
17.   ConstLenLine() {
18.     A = new PVector(mouseX, mouseY);
19.     B = new PVector(A.x, A.y+len);
20.     eq = new PVector(0, 0);
21.   }
22.   void update() {
23.     A = new PVector(mouseX, mouseY);
24.     if (round(A.dist(B))>len)
25.       eq.add(PVector.sub(A, B));
26.     if (round(A.dist(B))<len)
27.       eq.sub(PVector.sub(A, B));
28.     eq.normalize();
29.     int count=0;
30.     while (round (A.dist (B)) != len) {
31.       //how to do it without this lame loop, just with computing
32.       B.add(eq);
33.       if (count>1000) 
34.         break; // just for sure, I don't like infinite loops
35.       count++;
36.     }
37.   }
38.   void draw() {
39.     pushStyle();
40.     strokeWeight(len/20);
41.     line(A.x, A.y, B.x, B.y);
42.     popStyle();
43.   }
44. }