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Index › Programming Questions & Help › Syntax Questions › Drawing within a loop

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Drawing within a loop (Read 1171 times)

gravix

Drawing within a loop
May 11^th, 2010, 12:04pm

I'm attempting to draw each step of a for loop with rectangles that resize based on a changing value. I don't know how to go about this.

Here is an example of what I'm trying to do:

void drawTest()
{
for(int i = 0; i < 20; i++)
{
rect(20*i,20,20,20*i);
}
}

void setup()
{
size(500,500);
noStroke();
colorMode(RGB, 255, 255, 255, 100);
frameRate(1);
}

void draw()
{
drawTest();
}

What happens is only a single rectangle shows up, not a rectangle for each step each frame.

Help would be much appreciated and highly valued.

EDIT: It seems as though something stores all of the rectangles being printed, and then prints them all in a "lump" at the end of the for loop. Is there any way to make it print step by step without storing the values of "i" in a class or something similar?

PhiLho YaBB Moderator Offline Posts: 4190 Near Paris (France)	Re: Drawing within a loop Reply #1 - May 11^th, 2010, 1:29pm Super classical question... Nothing is drawn before the end of draw(). Classical solution: use draw() for what it is: a loop, in place for you for loop. Make i (with a better name) global and increment it on each draw() call. Don't forget to call background() at the start of draw().

gravix

Re: Drawing within a loop
Reply #2 - May 11^th, 2010, 2:09pm

So if my understanding is correct, draw() should not be called explicitly. So a recursive step-printing, like my proposed "for" printing, would be impossible unless each step was "saved" within a class, correct?

For example, if I wanted to do a tree traversal and print step-by-step to the screen, I would have to somehow save my location and locate it again after I print to the screen. Is this correct? How would I go about doing something like that?

Smitty

Re: Drawing within a loop
Reply #3 - May 11^th, 2010, 2:30pm

gravix wrote on May 11^th, 2010, 2:09pm:

So a recursive step-printing, like my proposed "for" printing, would be impossible unless each step was "saved" within a class, correct

Technically true, but the sketch itself is a class, and you can just define a variable to store your current position, like so:

Code:


void setup()
{
 size(500,500);
 noStroke();
 colorMode(RGB, 255, 255, 255, 100);
 frameRate(1);
}

int i = 0;

void draw()
{
  i++;
  if (i >=20) i = 0;

  rect(20*i,20,20,20*i);

}

Quote:

For example, if I wanted to do a tree traversal and print step-by-step to the screen, I would have to somehow save my location and locate it again after I print to the screen. Is this correct? How would I go about doing something like that?

If by "print to the screen" you mean "display it nicely in the sketch window" then yes. You'd need to have a way to advance your tree-traversal one step at a time and store the current state in some way after each step.

(If you're simply trying to get the data to your eyes in some kind of usable format for debugging purposes, then I'd recommend using println().)

gravix YaBB Newbies Offline Posts: 3	Re: Drawing within a loop Reply #4 - May 11^th, 2010, 2:39pm Yes, I wanted it to display in the sketch window. I will try to figure out a way to progress my recursion step by step. Thank you PhiLho and Smitty for your prompt and informed answers. It is greatly appreciated.

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