145 lines
3.1 KiB
Forth
145 lines
3.1 KiB
Forth
Copyright 2019 jmf
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License: WTFPL
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This code prints a Mandelbrot set in ASCII art to terminal.
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First of all, some variables are declared.
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The initial maximum number of iterations is set to 128.
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~~~
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'x var
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'y var
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'iter var
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#128 'max-iter var-n
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#1 'zoom var-n
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#0 'posx var-n
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#0 'posy var-n
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~~~
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We are using fixed-point numbers with a scaling factor of 10'000.
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That means that the float value 1.0 is represented by the number 10'000.
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For that, we need a special multiplication definition.
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~~~
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:f* * #10000 / ;
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~~~
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Now the calculation of the Mandelbrot set value at a specified point is
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defined.
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~~~
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:mb:value (x_y--v)
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#0 !x
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#0 !y
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#-1 !iter
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[
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@iter #1 + !iter
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dup-pair
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#2 @x * @y f* + swap (new_y)
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@x @x f* @y @y f* - + (new_x)
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!x !y
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@x @x f* @y @y f* + #40000 lteq?
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@iter @max-iter lt? and
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] while
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drop drop @iter
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;
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~~~
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In order to display the mandelbrot set nicely, 10 different iteration
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levels are filled with their equivalent ASCII signs.
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~~~
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:ascii-equiv (n--c)
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#9 * @max-iter /
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#0 [ #32 ] case
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#1 [ $. ] case
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#2 [ $: ] case
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#3 [ $- ] case
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#4 [ $= ] case
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#5 [ $+ ] case
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#6 [ $* ] case
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#7 [ $# ] case
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#8 [ $% ] case
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#9 [ $@ ] case
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;
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~~~
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The user can change some parameters by entering key press sequences.
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The following code checks for those key presses...
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~~~
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:zoom+? dup $+ eq? [ @zoom #2 * !zoom ] if ;
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:zoom-? dup $- eq? [ @zoom #2 / #1 n:max !zoom ] if ;
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:up? dup $w eq? [ @posy #10000 @zoom / - !posy ] if ;
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:down? dup $s eq? [ @posy #10000 @zoom / + !posy ] if ;
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:left? dup $a eq? [ @posx #10000 @zoom / - !posx ] if ;
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:right? dup $d eq? [ @posx #10000 @zoom / + !posx ] if ;
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:resinc? dup $e eq? [ @max-iter #2 * !max-iter ] if ;
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:resdec? dup $q eq? [ @max-iter #2 / #1 n:max !max-iter ] if ;
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~~~
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...and this word bundles all those together.
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~~~
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:input:handle
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c:get
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zoom+? zoom-?
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up? down?
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left? right?
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resinc? resdec?
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drop
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nl
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;
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~~~
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A quick function draws some information about key bindings and the
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current zoom level, as well as the current maximum number of iterations.
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~~~
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:info:draw
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'+/-_to_zoom;_w/a/s/d_to_move s:put nl
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'q/e_to_increase_decrease_resolution s:put nl
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'zoom_level_ s:put @zoom n:put nl
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'iterations_ s:put @max-iter n:put nl
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;
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~~~
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Finally the actual drawing code is written. It renders to 25x80
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characters. The width of 80 characters is distributed over a set width
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of 3.5 (35000) units, the height of 25 characters is distributed over a
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set height of 2 units.
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This results in a scaling factor of 438 for the width and 800 for the
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height.
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~~~
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:mb:draw
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#25 [
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#80 [
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I #438 * #25000 - @zoom / @posx +
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J #800 * #10000 - @zoom / @posy +
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mb:value
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ascii-equiv c:put
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] indexed-times
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nl
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] indexed-times ;
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~~~
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Before we start, the terminal is set to character-buffered. This makes
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it possible to react to key presses directly, instead of only after
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the enter key is pressed.
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The last function is a loop that draws the set, some info and gets key-
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presses.
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~~~
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'stty_cbreak unix:system
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[
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mb:draw
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info:draw
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input:handle
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TRUE ] while
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~~~
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