Update screen from recursive function

Programming Questions

JeffThomp..

Update screen from recursive function

in Programming Questions • 1 year ago

Hi all, I have what is perhaps a strange question: I'm enumerating combinations using a recursive function. I'd like to get one combination, do something with it, then the next, do something, etc. The problem is that draw() updates the window only when done. Is there a way to draw and update the screen outside the draw() function? I'm thinking there might be a Java method that skips the draw()...?

Here is a shorter version of my code to demonstrate:

String input = "0123";
int len = 3;

void setup() {
size(300, 300);
noLoop();
}

void draw() {

background(255);
line(0,0, width,height);

recursiveCombinations(input, len, new String());
}

// the recursive function which generates all combinations in one go
void recursiveCombinations(String input, int depth, String output) {

if (depth == 0) {

    // not sure why -'0' works to cast to an int... but it does!
    int r = (output.charAt(0) - '0') * (255/input.length()); // scale to 0-255 based on input size
    int g = (output.charAt(1) - '0') * (255/input.length());
    int b = (output.charAt(2) - '0') * (255/input.length());
    println(r + "\t" + g + "\t" + b);

    // should write the text to the screen and wait 2 seconds before continuing...
    fill(0);
    text(r + ", " + g + ", " + b, 20, height/2);
    delay(2000);
}
else {
    for (int i=0; i<input.length(); i++) {
      output += input.charAt(i);
      recursiveCombinations(input, depth-1, output);
      output = output.substring(0, output.length() - 1);
    }
}
}

Replies(8)

Chrisir

Re: Update screen from recursive function

1 year ago

I think the answer is no.

What you could do is to call recursiveCombinations() from setup(), put all results in an arrayList and in draw show this arrayList one by one to show how the recursion ran.

Better readable:

String input = "0123";
int len = 3;
//
void setup() {
size(300, 300);
noLoop();
}
//
void draw() {
background(255);
line(0, 0, width, height);
recursiveCombinations(input, len, new String());
} // the recursive function which generates all combinations in one go
//
void recursiveCombinations(String input, int depth, String output) {
if (depth == 0) { // not sure why -'0' works to cast to an int... but it does!
int r = (output.charAt(0) - '0') * (255/input.length()); // scale to 0-255 based on input size
int g = (output.charAt(1) - '0') * (255/input.length());
int b = (output.charAt(2) - '0') * (255/input.length());
println(r + "\t" + g + "\t" + b); // should write the text to the screen and wait 2 seconds before continuing...
fill(0);
text(r + ", " + g + ", " + b, 20, height/2);
delay(2000);
}
else {
for (int i=0; i<input.length(); i++) {
output += input.charAt(i);
recursiveCombinations(input, depth-1, output);
output = output.substring(0, output.length() - 1);
}
}
}
//

JeffThomp..

Re: Update screen from recursive function

1 year ago

Thanks, my first tests did save to an array. The problem is that I want to ultimately work with very large sets, which will not be possible if first enumerating them all. Perhaps the opposite: is there a way to create a recursive function that lives inside the draw()?

< I tried in vain to paste the HTML - regular paste always makes it just one line... >

Chrisir

Re: Update screen from recursive function

1 year ago

In Procesiing Menu Edit | Copy as HTML.

I think to paste HTML in the forum you must open the HTML dialogbox in the forums tools and paste it there

String input = "0123"; 
int len = 3; 
//
void setup() {   
  size(300, 300);   
  noLoop();
} 
//
void draw() {      
  background(255);   
  line(0, 0, width, height);      
  recursiveCombinations(input, len, new String());
} // the recursive function which generates all combinations in one go 
//
void recursiveCombinations(String input, int depth, String output) {   
  if (depth == 0) {     // not sure why -'0' works to cast to an int... but it does!   
    int r = (output.charAt(0) - '0') * (255/input.length()); // scale to 0-255 based on input size   
    int g = (output.charAt(1) - '0') * (255/input.length());     
    int b = (output.charAt(2) - '0') * (255/input.length());     
    println(r + "\t" + g + "\t" + b);     // should write the text to the screen and wait 2 seconds before continuing...  
    fill(0);     
    text(r + ", " + g + ", " + b, 20, height/2);    
    delay(2000);
  } 
  else {     
    for (int i=0; i
              
               length(); i++) {     
      output += input.
               charAt(i);       
      recursiveCombinations(input, depth-1, output);       
      output = output.
               substring(0, output.
               length() - 1);
    }
  }
} 

               //

Chrisir

Re: Update screen from recursive function

1 year ago

I dunno how it is in real JAVA (eclipse/proclipse) but in processing it all gets drawn at the end of draw() once. Bad for you.

But maybe you can write your recursion also iterativ

it has been asked on the forum.

JeffThomp..

Re: Update screen from recursive function

1 year ago

In this case, it seems using a class is the best structure using a getNext() method. By no means a good overall answer, since some things are really easy to write recursively (like factorials) but that I would have no idea how to write as a class.

For my project, I found that Michael Gilleland's combination generation class ( http://www.merriampark.com/comb.htm) is pretty simple and works well. Didn't end up working for my purposes, since it doesn't generate combinations with repetitions, but in any case, here it is formatted for Processing:

class CombinationGenerator {
int[] a;
int n;
int r;
BigInteger numLeft;
BigInteger total;
// constructor
CombinationGenerator(int n, int r) {
if (r > n) {
throw new IllegalArgumentException();
}
if (n < 1) {
throw new IllegalArgumentException();
}
this.n = n;
this.r = r;
a = new int[r];
BigInteger nFact = getFactorial(n);
BigInteger rFact = getFactorial(r);
BigInteger nminusrFact = getFactorial(n - r);
total = nFact.divide(rFact.multiply(nminusrFact));
reset();
}
// reset
void reset() {
for (int i = 0; i < a.length; i++) {
a[i] = i;
}
numLeft = new BigInteger (total.toString());
}
// return number of combinations not yet generated
BigInteger getNumLeft() {
return numLeft;
}
// are there more combinations?
boolean hasMore() {
return numLeft.compareTo(BigInteger.ZERO) == 1;
}
// return total number of combinations
BigInteger getTotal() {
return total;
}
// compute factorial
BigInteger getFactorial(int n) {
BigInteger fact = BigInteger.ONE;
for (int i = n; i > 1; i--) {
fact = fact.multiply(new BigInteger (Integer.toString (i)));
}
return fact;
}
// generate next combination (algorithm from Rosen p. 286)
int[] getNext() {
if (numLeft.equals(total)) {
numLeft = numLeft.subtract(BigInteger.ONE);
return a;
}
int i = r - 1;
while (a[i] == n - r + i) {
i--;
}
a[i] = a[i] + 1;
for (int j = i + 1; j < r; j++) {
a[j] = a[i] + j - i;
}
numLeft = numLeft.subtract(BigInteger.ONE);
return a;
}
}

Chrisir

Re: Update screen from recursive function

1 year ago

hello,

I was thinking of another solution to tackle the problem "Update screen from recursive function".

At 1st glance it is not possible since the recursion works within a function a only after finishing it it gets back to draw() and then shows the results (in an added up form).
I brought in a work-around above.

Another work-around would be to have 2 programs working a the same time:

the recursive program, pushing data in a csv-file
a display program reading the same csv-file continously and displaying it

not tested, but if possible it could work. Slows things down of course.

I also noted that it is possible to use println during recursion since that is shown immediately and not only at the end of draw. When text is enough.

Greetings, Chrisir

rbrauer

Re: Update screen from recursive function

1 year ago

I gave it a try. This version using a Thread seems to work well. Inserting HTML on the forum wasn't working for me so no highlighting. This is the same basic code from the first post with slight name changes and threading.

String input = "0123";

void setup() {
size(300, 300);
noLoop();

class RecTest extends Thread {
    public void run() {
      reco(this, input, input.length(), "");
    }
}
new RecTest().start();
}

void draw() {
line(0, 0, width, height);
}

void reco(Thread thrd, String in, int dpth, String out) {
if (dpth == 0) {
    int r = (out.charAt(0) - '0') * (255/in.length());
    int g = (out.charAt(1) - '0') * (255/in.length());
    int b = (out.charAt(2) - '0') * (255/in.length());
    background(255);
    fill(0);
    text(r + ", " + g + ", " + b, 20, height/2);
    redraw();
    try {
      thrd.sleep(250);
    } catch(Throwable ex) {}
}
else {
    for (int i=0; i<input.length(); i++) {
      out += input.charAt(i);
      reco(thrd, in, dpth-1, out);
      out = out.substring(0, out.length() - 1);
    }
}
}

Chrisir

Re: Update screen from recursive function

1 year ago

Thank you so much!

That's amazing how both threads write in the same window...

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