Question

I cannot get this koch snowflake drawing working recursively.

Recursive method

 public void koch(int n, double size) {
    if (n == 0) {
        t.forward(size);
    } else {

        koch(n - 1, size / 3);   // line 1
        stdTort.rotate(60);            // line 2
        koch(n - 1, size/3);     // line 3
        stdTort.rotate(120);           // line 4
        koch(n - 1, size/3);     // line 5
        stdTort.rotate(60);            // line 6
        koch(n - 1, size/3);     // line 7
    }
}

Any help would be appreciated.

Answer 1

All of your angles are wrong, because they are rotating clockwise where you are expecting them to go anti-clockwise. In order to get the angle shown in figure 2 you actually need to rotate 120, not 60. Then to get your final line you want to rotate -60, not 60.

    koch(n - 1, size / 3);   // line 1
    t.rotate(120);            // line 2
    koch(n - 1, size/3);     // line 3
    t.rotate(120);           // line 4
    koch(n - 1, size/3);     // line 5
    t.rotate(-60);            // line 6
    koch(n - 1, size/3);     // line 7

Thinking about this, I think the reason you are confused is because the rotation doesn’t seem to be intuitive. If your turtle is walking forward to do the first line, then you would expect a rotation to be either clockwise or anti-clockwise from that direction. But it seems your rotation all starts from the opposite direction.

Expected:

        /
-60 = --

+60 = --
        \

Actual:

-60 = --
       /

       \
+60 = --