Draw patterns.

From Twitter @aemkei, I'm fascinated by this simple formula to create bit fields that look like alien art.

Usage: install index.html, formula-drawer.js and util.js on a web server.

• f={opName}: displays a preregistered formula by its name. Try with op1 to op15, or anim1 for instance.
• code={expression}: an expression that returns either 0 to draw a white cell, or another number that draws a black cell. See Expression below.
• cs={positive integer}: cell size, defaults to 4.
• v.{variable name}={value}: the value is either a single integer, or an integer range of the form {start}..{end}.
• anim=true: starts the pattern animation, if possible. See Animation below.
• delay={milliseconds}: set the animation delay.
• delta={number}: value added between each animation loop. Defaults to 1.
• drawOver=true : skips clearing the canvas in the drawing loop.
• debug=true: prints debug statements in the console.

Expressions are interpreted with eval and may come from the query string. As such, they are restricted to basic operators, operands (numbers and variables), no function is directly callable.

x and y are reserved variables, they are automatically filled with the current position on the canvas in the drawing loop.

All other variables must be lowercase and have only one letter.

The aliases for special URL characters allow to type expressions in the browser location bar in a more readable way:

• A : &: __A__mpersand for __A__ND operator.
• C : :: __C__olon, separates the result in the ternary operator.
• D : /: __D__ivide operator.
• E : =: __E__qual sign.
• G : >: __G__reater than operator.
• L : <: __L__ess than operator.
• M : %: __M__odulo operator.
• N : !: __N__ot operator.
• P : +: __P__lus operator.
• Q : ?: __Q__uestion mark, ternary operator.

Example: x & y * ((x*y) / y & a) → x A y * ((x*y) D y A a)

Aliases may be combined to represent other operators. For instance: GE → >= : greater than or equal.

For an animation to start, at least one variable with a range greater than 1 must be defined. For instance a=1..3.

• https://localhost/alied/?f=op15: executes the formula named op15.
• https://localhost/alied/?code=((x%20^%20y)%20M%20a%20)%20A%20((x%20^%20y)%20M%20b)&v.a=51..109&v.b=19&anim=true&delay=500: executes the given animated expression. Same as https://localhost/alied/?code=((x ^ y) M a) A ((x ^ y) M b)&v.a=51..109&v.b=19&anim=true&delay=500