Category Archives: Uncategorized

Easy i-ching Symbols

I have so many little snippets like this laying around, at first I didn’t remember writing this when I found it the other day… then it slowly came back to me.

Looks like this is another one from the jQuery days:

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<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8" />
    <title></title>
    <script src="http://code.jquery.com/jquery-latest.min.js"></script>
    <script>
      $(function(){
 
        // meaning: http://www.ichingfortune.com/hexagrams.php
        // starting hex: &#x4DC0;
 
        var flash = $('.flash'),
            syms = $('.syms'),
            num = $('.num'),
            start = 0x4DC0,
            total = 64,
            tick = 0;
 
        for (var i = 0; i < total; i++) {
          $('<div>', {
            html: '&#x' + (start + i).toString(16)
          }).appendTo(syms);
        }
 
        flash.html(syms.html());
        flash.find('div').hide().first().show();
 
        setInterval(function() {
          var index = tick % total,
              curr = flash.children().eq(index)
              .show()
              .siblings().hide();
 
          curr = syms.children().eq(index)
            .css('color', 'red')
            .siblings().css('color', 'black');
 
          num.text(index + 1);
          tick++;
        }, 600);
 
      });
    </script>
    <style>
      * {
        font-family: "Helvetica Neue", Helvetica, sans-serif;  
      }
 
      .syms div {
        position: relative;
        float: left;  
        font-size: 3em;
        -webkit-transition: color 300ms ease-out;
        -ms-transition: color 300ms ease-out;
        -o-transition: color 300ms ease-out;
        transition: color 300ms ease-out;
      }
 
      .flash {
        position: relative;
        height: 6em;  
      }
 
      .flash div {
        position: absolute;
        left: 0; top: 0;
        font-size: 6em;
        color: red;
        -webkit-transform: rotate(90deg);
        -ms-transform: rotate(90deg);
        -o-transform: rotate(90deg);
        transform: rotate(90deg);
      }
    </style>
  </head>
  <body>
    <h2>i ching : <span class="num">1</span></h2>
    <div class="flash"></div>
    <div class="syms"></div>
  </body>
</html>

The i-ching is a Chinese divinatory system - the “hexagrams” just look very cool, when I noticed they were available starting at `0×4DC0` I made this snippet… think ancient magic 8 ball.

wikipedia article:
https://en.wikipedia.org/wiki/I_Ching

It’s pretty fun to play with this online version:
https://www.eclecticenergies.com/iching/virtualcoins

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Closest Point on a Line

For some reason I decided to port a snippet from AS3 to JS. Chose this one:

http://actionsnippet.com/?p=2969#comment-5674
…pretty much at random.

Here is the port in a pen:

This is actually a port of a port from this old thread:
http://www.gamedev.net/topic/444154-closest-point-on-a-line/

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Quick SVG with Javascript

If you look into creating SVG dynamically with JavaScript you might stumble upon `document.createElementNS`. In most simple cases, you don’t need to go down that path. Contemporary libraries handle this stuff internally now (they didn’t always) or if you’re going vanilla… you can integrate this kind of thing somewhere:

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PRNG Sine Rendering (Easiest Seeded Random with Index)

Here is a codepen showing seeded random numbers created use `Math.sin`. We’ll get to the code in a bit, first a little backstory…

Over the years I’ve used all manner of famous random number generators. From Tausworthe to Mersenne Twister.

Sometime last year I was trying to find a seeded PRNG, when working in Objective-C `arc4random` seems to be the common choice. I quickly became frustrated however as it didn’t seem possible or at least didn’t seem easy at all to reset the sequence of numbers. Maybe there’s an easy way, but whatever it is, I couldn’t find it. So after probably an hour of frustration trying all the weird different PRNGs, I decided to resort to a super simple old trick.

Why do you care about resetting the sequence?

Having a seed that you save at the beginning of your program can be super powerful. You can use anything for this seed, like the time or just another random number. From that point on your random numbers will be completely deterministic and depending on the complexity of your program you can simply save the seed and use it again later - causing your program to do exactly the same thing it did last time it had that seed. Those of you who dabble with generative artwork are probably familiar with this idea.

This experiment uses that trick:

Those textures will always be the same when the seed is 18. Thats an old experiment from the flash days, I think I used Grant Skinner’s seeded PRNG for that.

On the off chance you still have flash in your browser you can see it here:

Static black and white:
http://zevanrosser.com/sketchbook/things/bw_tex_static.html

Animated black and white:
http://zevanrosser.com/sketchbook/things/bw_tex_animated.html

Ugly colors version:
http://zevanrosser.com/sketchbook/things/col_tex_animated.html

It turns out that if you take sine or cosine and pop very large values for theta into it - you get something that looks very random. Lets look at the code:

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var rc = 0,
  seed = 30,
  MAX_RAND = 0xffffff;
 
function idxRand(nth) {
  if (nth != null) rc = nth;
  rc++;
  return Math.abs(Math.sin(seed * rc) * MAX_RAND);
}
 
var firstFour = [idxRand(), idxRand(), idxRand(), idxRand()],
  second = idxRand(1),
  fourth = idxRand(3);
 
console.log(firstFour);
console.log(second);
console.log(fourth);
 
var canvas = document.createElement("canvas"),
  c = canvas.getContext("2d");
 
canvas.width = 400;
canvas.height = 300;
c.fillStyle = "black";
c.fillRect(0, 0, canvas.width, canvas.height);
document.body.appendChild(canvas);
 
for (var i = 0; i < 300; i++) {
  c.fillStyle = "red";
  c.fillRect(idxRand() % 200, i, 4, 4);
 
  c.fillStyle = "green";
  c.fillRect(200 + Math.random() * 200, i, 4, 4);
}

Will output something like this:

[16576418.984205123, 5113873.3245154265, 14998774.234509233, 9741038.668934602]
5113873.3245154265
9741038.668934602

This code could be improved in a few different ways - but its good enough to illustrate the technique. Lines 1-9 are all you need to have a reproducible random sequence. With a large step value for theta and an even larger coefficient (0xffffff) for sine, you can use modulo to get the range you need (line 30). You can access the old values by passing an index to `idxRand`. This is illustrated in lines 11 through 17 - where we get the first four values and then grab them again using the index argument.

While significantly statistically different - and likely significantly different performance-wise, you’ll notice that visually there is little difference… :D

UPDATE: Had an idea that an alternative post title for this would be Easily Attain the Nth value from a PPRNG(pseudo-pseudo-random-number-generator)…

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