# Category Archives: javascript

Awhile back I thought it would be interesting to add some quick fake lighting to a personal project of mine - that for lack of a better description is a windows management system.

Here is a screenshot of the windows management system with lighting turned on:

Here is a video of me using the system:

I whipped up this prototype (don’t mind the jQuery)

There are really two keys that make this work. Getting the shadow in place and adjusting the gradient. All we really need is the angle and distance from a given `div` in relation to the “light”:

```1 2 3 4 5 6 7 8 9 10 11 12 13 let calcAng = function(x, y) { let lightPos = light.position() let dx = lightPos.left - x; let dy = lightPos.top - y; return -Math.atan2(dy, dx) / Math.PI * 180; };   let calcDist = function(x, y) { let lightPos = light.position() let dx = lightPos.left - x; let dy = lightPos.top - y; return Math.sqrt(dx * dx, dy * dy); };```

Standard `atan2` and the pythagorean theorem get us this. Once we have those - we can use them to set our gradient and shadow values:

```1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 // warning (apparently this function is slightly speed coded) let calcShade = function(x, y) { let angle = calcAng(x, y); let dist = calcDist(x, y); let sx = dist * Math.cos(-angle * Math.PI / 180) * -1; let sy = dist * Math.sin(-angle * Math.PI / 180) * -1;   sx = Math.min(20, Math.max(sx, -20)); sy = Math.min(20, Math.max(sy, -20)); let blur = Math.min(100, dist); let hBlur = Math.min(50, blur) * 0.5; // consider distance in the eq? return { bg: `-webkit-linear-gradient(\${angle}deg, rgba(0, 0, 0, 0.2), rgba(255, 255, 255, 0.4) \${blur}%)`, shadow: `\${sx}px \${sy}px \${hBlur}px rgba(0, 0, 0, 0.15)` }; };```

There are more videos of the windows management system on my youtube channel. Here’s another from a much earlier version of the system.

Maybe I’ll post more about that in the future…

## SVG to Canvas (good trick)

Awhile back, I wrote some collision detection code that blitted existing interactive SVG to Canvas and then used the pixel data to figure out various aspects of the relationships between arbitrary SVG nodeTypes. A really simple trick I used can be seen in this pen:

The trick is to load the svg data into an image as a datauri. There are other tricks like this - one of which is using an svg `foreignObject` to blit html to canvas:

https://developer.mozilla.org/en-US/docs/Web/API/Canvas_API/Drawing_DOM_objects_into_a_canvas

There were some browser issues at the time with this. The main one being IE 10/11 didn’t really work (tainted canvas if I recall correctly). The `foreignObject` trick didn’t work with image xlink:hrefs in safari at the time… (weirdly if you opened the dev tools it would start to work) anyway…

I ended up forking canvg for various cases. canvg is really cool… just a note, a coworker of mine went in at some point and optimized it like crazy and improved the perf a good deal by “drying things up”. Maybe I’ll suggest that he submit his optimizations at some point.

## Input Field with LocalStorage Predictions

This is a quick example showing how to give an input field “memory”. After you type something once and hit return it will be stored in `localStorage`. String values are ranked based on how often they are selected/entered. I know people don’t like jQuery these days, seems this pen is from a time when I still used it.

There’s definitely room for improvement here - but the key features are covered.

## Quick line in HTML and JavaScript

Usually if you want to draw lines in HTML you use canvas or SVG. Awhile back I wondered how I might do it without those. This is really just a proof of concept speed coded answer to that question:

This works by using a div with a border, rotating it and scaling it as needed so it fits between two arbitrary points.

This could be abstracted a bit more, but it works pretty well. I usually choose `setInterval` over `requestAnimationFrame` when prototyping - because I like to easily be able to change the speed of
framebased things like this. If I were to try and make this code more dynamic, I would probably switch out to `requestAnimationFrame`.

If you try and connect two lines together - you’ll notice some inaccuracy - a good argument for using SVG or canvas over something like this. That said, if you are connecting two elements using a single line, this inaccuracy would become irrelevant.

## Color Breeder (aka Features)

Choose two colors to breed them and create 5 new colors:

This is a speed coded pen from awhile back - the features object is interesting - it allows two objects to be bred together. In this case two colors. I could see this is as part of some advanced/abstract colorpicker that allows the user to home in on a color.

## 3d Point to 2d Point (Easy Mini 3d Engine)

Many years ago when I had just started programming I found this absolute gem by Andries Odendaal.

modern es6 version

```1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 let rotX = 0, rotY = 0, perspective = 500, depth, currX, currY; // learned something like this at Andries Odendaal's www.wireframe.co.za function point3d(x, y, z) { let cosX = Math.cos(rotX), cosY = Math.cos(rotY), sinX = Math.sin(rotX), sinY = Math.sin(rotY), posX, posY, posZ;   posZ = z * cosX - x * sinX, posX = z * sinX + x * cosX, posY = y * cosY - posZ * sinY, posZ = y * sinY + posZ * cosY;   depth = 1 / (posZ / perspective + 1); currX = posX * depth; currY = posY * depth;   return [ currX, currY, depth ]; }```

Here’s is an example of it in action:

I’ve used this code many many times, it’s just easy to throw into any language and instantly get 3d points rendered in 2d. Here is a short video of a Java applet from 2003 called “Catch Env” that made use of it:

Here is the source code for that ^^
http://www.zevanrosser.com/shape2/j/Catchenv.java

You’ll notice in that source, that I nested the equation to allow for local and global transformations. It was around that time that I learned the ins and outs of real 2D and 3D matrix transformation math… Ken Perlin’s classfiles from NYU were a real help when I was learning that stuff. I don’t think this was the exact file I was working with, but it was definitely on his site somewhere.

Before all that, during my junior year in college I created a 3d engine based off Odendaal’s code in Director (Lingo). Here is a video of some of the demos for it:

…and here is a strange screenshot from my personal website at the time:

Just an example of a powerful snippet and a gateway to learning matrix transformation math. When I first really dug in to html5 canvas - before WebGL was supported so widely - having this trick up my sleeve was great. As you can see in the below link, I used it more than a few times back then:

Daily canvas experiments:

http://zreference.com/projects/all-graphics.php

Also posted in 3D, Graphics, graphics algorithms, html5 | Tagged , , , | Leave a comment

## Hermit Crab Curve as PRNG # (a deterministic pseudo-random number generator with contrast and smoothness - inspired by stochastic and organic randomness)

Around 2015 I had the idea for a PRNG that would clamp itself and have moments of “smoothness”. When I got around to trying to create such a thing, the result was something I jokingly called the “Hermit Crab Curve”. I also called it the “Shard Curve”.

The equation for the curve defines a radius in polar coordinates:

Where a and d are paramters that control the detail of the curve. o is a rotation and offset value for the angle and s is a scalar. Note the use of rem. The resulting curve is much less interesting if a standard modulo is used in place of a remainder:

The above variable values were found using this interactive version of the equation:

To illustrate how you might use this as a PRNG I created this fork of the above pen:

That, in combination with the information from my other article from yesterday… Should be enough to see what I mean.

You can read the original description of the Hermit Crab Curve that I created using ArcType here:

If you end up using this for something interesting let me know. I’d love to see it

Also posted in Graphics, Math, functions, graphics algorithms, misc, motion | Tagged , , | Leave a comment

## 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:

```1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 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…

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)…

## Emmet as a Template (aka zen-coding)

This is not the most useful thing in the world - was just an idea I had awhile back… First off, I love Emmet (formerly zen-coding) created by Sergey Chikuyonok. I especially like it for quickly writing html or jsx.

While I don’t use them that often, I really enjoy Jade and Pug. Anyway, I realized you could do similar things with Emmet with just a few little tweaks… So created this codepen:

As you can see - with a few regular expressions you can use Emmet _sort of_ like Jade. Definitely just an experiment, but interesting nevertheless.

## Dynamic Getter

Getters in ES6 are usually defined within a class like this:

```1 2 3 4 5 6 7 8 class RandomPoint { get x() { return Math.random(); } get y() { return Math.random(); } }```

In this case we use getters to make a random point:

``` let pnt = new RandomPoint(); console.log(pnt.x, pnt.y); // outputs something like 0.09403673512366306 0.2717692041118973```

I found myself wanting to be able to dynamically define a getter. This can be done like this:

```let rand = function() { return Math.random(); }; Object.defineProperties(someObj, { ['x']: { get: rand });```

This is really all just sugar, but still fun stuff…