User:LABoyd2/Conditional and Iterator Functions to manual 151002

For Loop

Iterate over the values in a range or vector.

 for(variable = [start : increment : end]
 for(variable = [start : end]
 for(variable = [vector]

parameters: for range

Note: For range, values are separated by colons rather than commas used in vectors.

start

value for variable on first pass

increment or step

amount to increase variable for each pass

optional, default = 1

end

stop when next value would be past end

vector : alternate

variable is assigned each vector member in turn, one for each pass.

examples:

 for (a =[3:5])echo(a);     // 3 4 5
 for (a =[3:0]){echo(a);}   // 0 1 2 3         start < end deprecated by 2015.3
 for (a =[3:0.5:5])echo(a); // 3 3.5 4 4.5 5
 for (a =[0:2:5])echo(a);   // 0 2 4           a never equals end 
 for (a =[3:-2:-1])echo(a); // 3 1 -1          negative increment requires 2015.3
                                               be sure end < start
 for (a =[3,4,1,5])echo(a); // 3 4 1 5
 for (a =[0.3,PI,1,99]){echo(a);}    // 0.3 3.14159 1 99
 x1=2; x2=8; x3=5.5;
 for (a =[x1,x2,x3]){echo(a);} // 2 8 5 
 for (a =[[1,2],6,"s",[[3,4],[5,6]]])echo(a);  // [1,2] 6 "s" [[3,4],[5,6]]

for() is an operator. Operators require braces {} if more than one action is within it scope. Action end in semicolons ,operators do not.

For() loops are not an exception to the rule about variables having only one value within a scope. A copy of loop contents is created for each pass. Each pass is given its own scope, allowing any variables to have unique values for that pass. No, you still can't do a=a+1;

Nested loops

When loops are nested, all ranges may be include in the same for().

for ( variable1 = <range or vector> , variable2 = <range or vector> ) <do something using both variables>

 example for() nested 3 deep
 
 color_vec = ["black","red","blue","green","pink","purple"];
 for (x = [-20:10:20] )
 for (y = [0:4] )color(color_vec[y])
 for (z = [0,4,10] )
     {translate([x,y*5-10,z])cube();}
 
 shorthand nesting for same result
 
 color_vec = ["black","red","blue","green","pink","purple"];
 for (x = [-20:10:20],
 y = [0:4],
 z = [0,4,10] )
     translate([x,y*5-10,z]){color(color_vec[y])cube();}

Examples using vector of vectors

example 1 - iteration over a vector of vectors (rotation)
  
 for(i = [ [  0,  0,   0],
           [ 10, 20, 300],
           [200, 40,  57],
           [ 20, 88,  57] ])
{
   rotate(i)
   cube([100, 20, 20], center = true);
}

example 2 - iteration over a vector of vectors (translation)
  
for(i = [ [ 0,  0,  0],
          [10, 12, 10],
          [20, 24, 20],
          [30, 36, 30],
          [20, 48, 40],
          [10, 60, 50] ])
{
   translate(i)
   cube([50, 15, 10], center = true);
}

example 3 - iteration over a vector of vectors
for(i = [ [[ 0,  0,  0], 20],
          [[10, 12, 10], 50],
          [[20, 24, 20], 70],
          [[30, 36, 30], 10],
          [[20, 48, 40], 30],
          [[10, 60, 50], 40] ])
{
  translate([i[0][0], 2*i[0][1], 0])
  cube([10, 15, i[1]]);
}

Intersection For Loop

Iterate over the values in a range or vector and create the intersection of objects created by each pass.

Besides creating separate instances for each pass, the standard for() also groups all these instances creating an implicit union. intersection_for() is a work around because the implicit union prevents getting the expected results using a combination of the standard for() and intersection() statements.

intersection_for() uses the same parameters, and works the same as a For Loop, other than eliminating the implicit union.

example 1 - loop over a range:
intersection_for(n = [1 : 6]) { rotate([0, 0, n * 60]) { translate([5,0,0]) sphere(r=12); } }	intersection_for()	either intersection() for() or for() intersection()

example 2 - rotation :
intersection_for(i = [ [ 0, 0, 0], [ 10, 20, 300], [200, 40, 57], [ 20, 88, 57] ]) { rotate(i) cube([100, 20, 20], center = true); }	intersection_for()	intersection() for()

In

If Statement

Performs a test to determine if the actions in a sub scope should be performed of not.

If (test) scope1
If (test){scope1}
If (test) scope1  else  scope2
If (test){scope1} else {scope2}

Parameters

test: Usually a boolean expression, but can be any value or variable.

See here for true or false state of values.

See here for boolean and logical operators

Do not confuse the assignment operator '=' with the equal operator '=='

scope1: one or more actions to take when test is true.

scope2: one or more actions to take when test is false.

if (b==a)  cube(4);
if (b<a)  {cube(4); cylinder(6);}
if (b&&a) {cube(4); cylinder(6);}
if (b!=a)  cube(4); else cylinder(3);
if (b)    {cube(4); cylinder(6);} else {cylinder(10,5,5);} 
if (!true){cube(4); cylinder(6);} else  cylinder(10,5,5); 
if (x>y)   cube(1, center=false); else {cube(size = 2, center = true);}

Since version 2015.03, variables can now be assigned in any scope. Note that assignments are only valid within the scope in which they are defined - you are still not allowed to leak values to an outer scope. See Scope of variables for more details.

Conditional Operator

A function which uses a test to determine which of 2 values to return.

 a =   test ? TrueValue : FalseValue ;
 echo( test ? TrueValue : FalseValue );

Parameters

test: Usually a boolean expression, but can be any value or variable.

See here for true or false state of values.

See here for boolean and logical operators

Do not confuse the assignment operator '=' with the equal operator '=='

TrueValue: the value to return when test is true.

FalseValue: the value to return when test is false.

A value in OpenSCAD is either a Number (like 42), a Boolean (like true), a String (like "foo"), a Vector (like [1,2,3]), or the Undefined value (undef). Values can be stored in variables, passed as function arguments, and returned as function results.

This works like the ?: operator from the family of C-like programming languages.

Examples

 a=1; b=2; c= a==b ? 4 : 5 ;                  //  5
 a=1; b=2; c= a==b ? "a==b" : "a!=b" ;        //  "a!=b"
  
 TrueValue = true; FalseValue = false;
 a=5; test = a==1;
 echo( test ? TrueValue : FalseValue );       // false
  
 L = 75; R = 2; test = (L/R)>25;
 TrueValue =  [test,L,R,L/R,cos(30)];
 FalseValue = [test,L,R,sin(15)];
 a1 = test ? TrueValue : FalseValue ;         // [true, 75, 2, 37.5, 0.866025]

Recursive function calls

Recursive function calls are supported. Using the Conditional Operator "... ? ... : ... " it's possible to ensure the recursion is terminated. Note: There is a built-in recursion limit to prevent the application to crash. If the limit is hit, the result of the function call is undef.

example

 // recursion - find the sum of the values in a vector (array) by calling itself
 // from the start (or s'th element) to the i'th element - remember elements are zero based
 
 function sumv(v,i,s=0) = (i==s ? v[i] : v[i] + sumv(v,i-1,s));
 
 vec=[ 10, 20, 30, 40 ];
 echo("sum vec=", sumv(vec,2,1)); // calculates 20+30=50

Assign Statement

Set variables to a new value for a sub-tree.

Since 2015.03 assign() is unneeded, as variables can now be assigned anywhere.

Parameters

The variables that should be (re-)assigned

example:

for (i = [10:50])
{
    assign (angle = i*360/20, distance = i*10, r = i*2)
    {
        rotate(angle, [1, 0, 0])
        translate([0, distance, 0])
        sphere(r = r);
    }
}