OpenSCAD programming question, recursion, functions, and modules

1) A module "returns" an object... whatever object  is generated by a module is its return "value". So you could return a polygon created from a list of points, for example, by having a polygon ([list]) statement at the end of the module. 

You can use the ternary operator to do if-then-else evaluations in a let() call in a function. And a function can call other functions. 

2) The concat () function flattens multiple lists into a single list.

On Friday, February 9, 2018, Dan Shriver <[hidden email]> wrote:

I'm going to attach some code (only look at it if you need it to get an idea of what I am trying to do, I am sure there are bugs plus I didn't copy any of the helper functions...).

I am having trouble figuring out how to deal with recursion on something I am drawing.  My problems are:

1) a Module can't return anything, correct?  At the same time I don't see how to (in a Function) do a lot of code setup, call helper functions, etc.  I guess I could setup a variable in a Function with "let" but how do I do a block of code with conditionals etc.  I would either like to return a list of points from a Module, or figure out how to do "real work" (helper calls, conditionals, etc) from a Function

2) If I have something that generates a list of points, assuming I recursively call that how do I elegantly keep the list one dimensional (not nested lists).  Do I just a call to some flatten function at the end?  Ideally I'd like not to generate nested lists to begin with, but I'm having a little trouble seeing how to do that?

Basically, what I am doing below is what I call a "bat curve" because I imagine it will look slightly like the stylized bats in traditional Chinese art (somewhat, not exactly, I can go into differences later, I don't need it to look exactly like that and am just using that as a convenient description).  The shape is going to be a fractal of arcs of increasingly smaller circles (generations determines how many levels deep the fractal goes).  Basically one large arc subdivides on both sides into a spiral of increasingly smaller radii arcs.  You could think of a letter D where the straight line is removed and at both ends of the D there is a spiral.

------------------------

module bCurve2(radius, number, generations, quadrant, pointsPerGeneration, direction, angle) {

    if (direction > 0) {

        newQuadrant = (quadrant + 1) % 4;

        startAngle = angle;

        endAngle = computeAngle(number, newQuadrant);

    }

    else {

        newQuadrant = (quadrant + 3) % 4;

        startAngle = computeAngle(number, newQuadrant);

        endAngle = angle;

    }

}

//quadrant is the graph quadrant for the next circle except it is C indexed so it is 0 - 3 rather than 1 - 4

module bCurve(radius, number, generations, quadrant, pointsPerGeneration) {

   

    if (generations > -1) {

      angle1 = computeAngle(number, quadrant);

      angle2 = computeAngle(number, nextQuadrant(quadrant));

      

      span = angle1 - angle2;

      stepSize = span/pointsPerGeneration;

      newRadius = radius * sin(atan(2/(number-1))); 

       

      quadrantA = (quadrant + 3)%4;

      quadrantB = (quadrant + 2) %4; 

       

      points = [ for (i = [0:pointsPerGeneration]) [ bCurve2(newRadius, number, (generations -1), quadrantA, pointsPerGeneration, -1, angle1), xArc(radius, angle1, stepSize, i), yArc(radius, angle1, stepSize, i)], bCurve2(newRadius, number, (generations -1), quadrantB, pointsPerGeneration, 1, angle2) ];

        

    difference() {

      offset(0.01) polygon(points);

      polygon(points);

      }

      } 

}

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If your lists contain either 2D points or simple lists of 2D points, a simpler non-recursive solution (by Parkinbot) is:

l = [[1,2],[[3,4]],[[5,6],[7,8]],[[9,10],[11,12],[13,14] ]];

  

function get_2D_points(L) = [for(a=L, v = (a[0][0]!=undef ? a: [a]) ) v ];

  

echo( get_2D_points(l));

// ECHO: [[1, 2], [3, 4], [5, 6], [7, 8], [9, 10], [11, 12], [13, 14]]

2018-02-08 23:40 GMT-02:00 Ronaldo Persiano <[hidden email]>:

If you want to collect all 2D points in a list, whatever depth it has in it, this may help you:

function get_2D_points(L,n=0,res=[]) =

  n>=len(L) ?

    res

  : L[n]*0==[0,0] ? 

      get_2D_points(L,n+1, concat(res,[L[n]]))

    : get_2D_points(L,n+1, get_2D_points(L[n],0,res));

  

l = [[1,2],[[3,4],[[5,6]]],[[[[7,8]],[9,10]]],[11,12]];

  

echo( get_2D_points(l));

// ECHO: [[1, 2], [3, 4], [5, 6], [7, 8], [9, 10], [11, 12]]

​However, this function crashes if the list is not a nested list of 2D points like  [[1,2], 3] or [1,2,3].or ["a"], etc.

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