The while loop is an infinite loop because i never reaches 200.

The screen is only updated when the draw method exits !

1. float unkn = 0.09;
2. int cpx1 = width/4;
3. int cpy1 = height/4;
4. int cpx2 = width/4;
5. int cpy2 = height/4;
6. int x = round(cpx1+=unkn);
7. int y = cpy2+=random(10, 390);
8. int k;
9. int m;
10. int x2, y2;
11. int i = 0;
12. 
    
13. void setup( )
14. {
15.   size(400, 600);
16.   background(255);
17.   smooth();
18.   noFill();
19.   stroke(0);
20. }
21. void draw( )
22. {
23.   background(255);
    
24.   // for (int i = 0; i<=200; i++) {
25.   while (i != 200) {
26.     beginShape();
27.     k = int(random(30, 80));
28.     m = int(random(20, 120));
29.     vertex(30, 70); // first point
30.     bezierVertex(cpx1, cpy1, cpx2, cpy2, 50, 100);
31.     x2 = cpx2;
32.     y2 = cpy2;
33.     bezierVertex(x2, y2, cpx2+=k, cpy2+=m, 100, 75);
34.     x2 = cpx2;
35.     y2 = cpy2;  
36.     stroke(random(255), random(255), random(255));
37.     endShape();
38.     i++;
39.   }
40. }

QUARKS!!! It is in there -- and was -- BUT
I'm sorry -- I copied my code piece by piece to leave out large commented sections -- and missed this line.

The behavior is the same. Even with the i++ in there.

And, as I said, the behavior was also the same with the for loop.

I went back and fixed the code in my original post so no one will have to go through what you did.

Remember that canvas is only rendered after the end of each draw() .
It means we only see the final result. We don't see drawings happening at the same time commands are issued.

For example, if we change the background() color many times, we'll only be aware of its last 1:

void draw() {
  for (color i = 0; i != 600000000; background(i += 30000));
  background(0100); // we only see this last gray color here!
  text("Frame: " + frameCount, 20, 55);
}

when you want a blank screen each time you need to put

1.  background(255);

at the start of draw()

(I can't see a black screen here when I press stop and start often in your code)

Chrisir and GoTo --
I don't want a blank canvas -- it's coming up unbidden -- background is ONLY set once in the setup. And it is set to white -- so this doesn't address the problem.

If you drop the code into a sketch you can see it happening -- just keep clicking on and off. Sometimes lines, sometimes, white with nothing, sometimes black with nothing.  And there is nothing in the code that I can see which makes this happen.

I just want to keep on drawing over what is there -- but I'm not going any further with the coding until I get this erratic behavior figured out.

Cheers!

Jeff --
I have almost a full day of work (the money-earning kind) ahead of me, but I've taken a quick look at this and am fascinated and stunned -- I see you've only added two lines of code in my draw section that don't have to do with a camera , and changed one of the 100s in my calls to bezierVertex to 1000-- and it's beautiful -- but I took these out and and am even more stunned by what happens about 3-4 minutes into it (below).

However, I have major questions about the camera and I want so much to learn --

I will come back after I have read about the camera and whatever else is in there that I don't understand at this point.
I hope that is all right to do, after you have already done so much for me.

BUT, I am intensely grateful to you for this. I am a practiced artist, but only a junior programmer!

Clair

Oh hey no problem there. It's some trig to find the x,z,y camera position. Just something everyone gets into after a while.