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Implement the Matrix Digital Rain visual effect from the movie "The Matrix" as described in Wikipedia.

Provided is a reference implementation in Common Lisp to be run in a terminal.

Batch File

Works with: Windows 10

This code uses Windows 10 VT100 escape sequences. <lang dos>:: Matrix Digital Rain Task from RosettaCode

Batch File Implementation

@echo off setlocal enabledelayedexpansion

rem escape character (for Windows 10 VT100 escape sequences) rem info: https://docs.microsoft.com/en-us/windows/console/console-virtual-terminal-sequences for /f %%e in ('echo prompt $e^| cmd') do @set "esc=%%e"

rem set window size set "col=120" %== please don't make this too large ==% set "row=30" %== please don't make this too large ==% mode con cols=%col% lines=%row%

rem set up the variables for display set "rain_length=12" for /l %%y in (1,1,%col%) do set "disp_col[%%y]= " %== what to display ==% for /l %%y in (1,1,%col%) do set "ctr_col[%%y]=0" %== counter for rain length ==%

rem hide the cursor, and clear the screen <nul set /p "=%esc%[?25l" cls

matrix_loop

for /l %%y in (1,1,%col%) do (

   if !ctr_col[%%y]! equ 0 (
       set "disp_col[%%y]= "
   ) else (
       set /a "rnd_digit=!random! %% 10"
       if !ctr_col[%%y]! equ 1 (
           set "disp_col[%%y]=%esc%[97m!rnd_digit!%esc%[32m"
       ) else if !ctr_col[%%y]! equ 2 (
           set "disp_col[%%y]=%esc%[92m!rnd_digit!%esc%[32m"
       ) else (
           set "disp_col[%%y]=!rnd_digit!"
       )
       set /a "ctr_col[%%y]=(!ctr_col[%%y]! + 1) %% (%rain_length% + 1)"
   )
   rem drop rain randomly
   set /a "rnd_drop=!random! %% 20"
   if !rnd_drop! equ 0 set "ctr_col[%%y]=1"

) set "disp_line=%esc%[32m" for /l %%y in (1,1,%col%) do set "disp_line=!disp_line!!disp_col[%%y]!" <nul set /p "=%esc%[1T%esc%[1;1H" %== scroll down and set cursor position to home ==% echo(%disp_line% goto matrix_loop</lang>

C

NCURSES version

Adaptation of Dan Ruscoe's C code. Header files added and code rearranged to suppress implicit declaration warnings.

Requires ncurses, install on Ubuntu as follows :

$ sudo apt install libncurses5-dev

Compile with ncurses flag :

$ cc digiRain.c -lncurses

And here's the code : <lang C> /**

* Loosely emulates the "digital rain" effect from The Matrix.
*
* @author Dan Ruscoe <dan@ruscoe.org>
*/

include <unistd.h>
include <time.h>
include <stdio.h>
include <stdlib.h>
include <ncurses.h>

/* Time between row updates in microseconds.

  Controls the speed of the digital rain effect.

/

define ROW_DELAY 40000

/**

* Gets a random integer within a given range.
*
* @param int min The low-end of the range.
* @param int max The high-end of the range.
*
* @return int The random integer.
*/

int get_rand_in_range(int min, int max) {

 return (rand() % ((max + 1) - min) + min);

}

int main(void) {

 /* Basic seed for random numbers. */
 srand(time(NULL));

 /* Characters to randomly appear in the rain sequence. */
 char chars[] = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9'};

 int total_chars = sizeof(chars);

 /* Set up ncurses screen and colors. */
 initscr();
 noecho();
 curs_set(FALSE);

 start_color();
 init_pair(1, COLOR_GREEN, COLOR_BLACK);
 attron(COLOR_PAIR(1));

 int max_x = 0, max_y = 0;

 getmaxyx(stdscr, max_y, max_x);

 /* Create arrays of columns based on screen width. */

 /* Array containing the current row of each column. */
 int columns_row[max_x];

 /* Array containing the active status of each column.
    A column draws characters on a row when active.
 */
 int columns_active[max_x];

 int i;

 /* Set top row as current row for all columns. */
 for (i = 0; i < max_x; i++)
 {
   columns_row[i] = -1;
   columns_active[i] = 0;
 }

 while (1)
 {
   for (i = 0; i < max_x; i++)
   {
     if (columns_row[i] == -1)
     {
       /* If a column is at the top row, pick a
          random starting row and active status.
       */
       columns_row[i] = get_rand_in_range(0, max_y);
       columns_active[i] = get_rand_in_range(0, 1);
     }
   }

   /* Loop through columns and draw characters on rows. */
   for (i = 0; i < max_x; i++)
   {
     if (columns_active[i] == 1)
     {
       /* Draw a random character at this column's current row. */
       int char_index = get_rand_in_range(0, total_chars);
       mvprintw(columns_row[i], i, "%c", chars[char_index]);
     }
     else
     {
       /* Draw an empty character if the column is inactive. */
       mvprintw(columns_row[i], i, " ");
     }

     columns_row[i]++;

     /* When a column reaches the bottom row, reset to top. */
     if (columns_row[i] >= max_y)
     {
       columns_row[i] = -1;
     }

     /* Randomly alternate the column's active status. */
     if (get_rand_in_range(0, 1000) == 0)
     {
       columns_active[i] = (columns_active[i] == 0) ? 1 : 0;
     }
   }

   usleep(ROW_DELAY);
   refresh();
 }

 endwin();
 return 0;

} </lang>

Microsoft Windows console version

Single threaded

Works with: Microsoft Visual Studio C

<lang C>/*******************************************************************************

Digital ASCII rain - the single thread variant.
2012 (C) by Author, 2020 GPL licensed for RossetaCode
- - - - /

include <assert.h> /* assertions */
include <conio.h> /* console operations */
include <locale.h> /* l10n and i18n */
include <string.h> /* operations on strings and memory blocks */
include <process.h> /* Microsoft Windows API for threads etc. */
include <stdio.h> /* standard i/o library */
include <stdlib.h> /* standard library with rand() function */
include <time.h> /* time(NULL) used as srand(time(NULL)) */
include <windows.h> /* just the Microsoft Windows main header for C */

/*

* Global variables - you could use local variables instead... 
* but then e.g. the memory for the buffer variable would be unnecessarily
* allocated and released manifold, which would lead to a worse performance.
*/

HANDLE hStdOut; /* the handle to console "out" */ CONSOLE_SCREEN_BUFFER_INFO csbi; /* numbers of rows, columns etc. */

PCHAR_INFO buffer = NULL; /* an enough big buffer */ COORD bufferSize, bufferCoord; /* the size of buffer etc. */

/*

* A structure that holds data that is distinct for each column.
*/

struct Data {

 DWORD      armed;  /* time in ms to synchronize */
 int        delay;  /* armed = current_time + delay */
 BOOL       show;   /* TRUE - draw, FALSE - erase */
 COORD      ncp;    /* position for drawing new characters */
 SMALL_RECT s, d;   /* source/destination regions for copy */

};

/*

* A function to generate random numbers from the range (a, b).  
* NOTE: POSIX rand () is not thread safe, 
* but we use secure rand() from MS runtime libraries.
*/

int rnd(int a, int b) {

 return a + rand() % (b + 1 - a);

}

BOOL randomShow(void) {

 return rnd(0, 99) < 65;

}

int randomDelay(void) {

 return rnd(0, 150) + rnd(0, 150) + rnd(0, 150);

}

BOOL randomRegenerate(void) {

 return rnd(0, 99) < 2;

}

void column_init(struct Data* data, int k) {

 data->armed = 0;
 data->show  = randomShow();
 data->delay = randomDelay();

 data->s.Left   = k;
 data->s.Top    = 0;
 data->s.Bottom = bufferSize.Y - 2;
 data->s.Right  = k;

 data->d.Left   = data->s.Left;
 data->d.Top    = data->s.Top + 1;
 data->d.Right  = data->s.Right;
 data->d.Bottom = data->s.Bottom + 1;

 data->ncp.X = k;
 data->ncp.Y = 0;

}

void column_run(struct Data* data) {

 char c;
 WORD a;
 DWORD result;

 /*
  * Shift down a column.
  */
 ReadConsoleOutput (hStdOut, buffer, bufferSize, bufferCoord, &data->s);
 WriteConsoleOutput(hStdOut, buffer, bufferSize, bufferCoord, &data->d);

 /*
  * If show == TRUE then generate a new character. 
  * If show == FALSE write the space to erase.
  */
 if(data->show)
 {
   c = (rnd(1,100) <= 15) ? ' ' : rnd( 'a', 'z' );
   a = FOREGROUND_GREEN | ((rnd(1,100) >  10) ? 0 : FOREGROUND_INTENSITY);
 }
 else
 {
   c = ' ';
   a = FOREGROUND_GREEN;
 }

 WriteConsoleOutputCharacter(hStdOut, &c, 1, data->ncp, &result);
 WriteConsoleOutputAttribute(hStdOut, &a, 1, data->ncp, &result);

 /*
  * Randomly regenerate the delay and the visibility state of the column.
  */
 if(randomRegenerate()) data->show  = randomShow();
 if(randomRegenerate()) data->delay = randomDelay();

 data->armed = GetTickCount() + data->delay;

}

int main(int argc, char* argv[]) {

 int j;
 struct Data* table;

 srand((unsigned int)time(NULL));

 hStdOut = GetStdHandle( STD_OUTPUT_HANDLE );
 SetConsoleTitle("Digital ASCII rain");

 /*
  * An attempt to run in the full-screen mode.
  */
 if(argc == 1)
 {
   COORD coord;
   CONSOLE_CURSOR_INFO cci;
   cci.bVisible = FALSE;
   cci.dwSize   = 0;
   SetConsoleDisplayMode(hStdOut, CONSOLE_FULLSCREEN_MODE, &coord);
   SetConsoleCursorInfo(hStdOut, &cci);
 }

 GetConsoleScreenBufferInfo(hStdOut, &csbi );
 //SetConsoleTextAttribute(hStdOut, FOREGROUND_GREEN);

 bufferSize.X  = 1;
 bufferSize.Y  = csbi.dwSize.Y - 1;
 bufferCoord.X = 0;
 bufferCoord.Y = 0;
 buffer = (PCHAR_INFO)calloc(bufferSize.Y, sizeof(CHAR_INFO));
 assert(buffer != NULL);

 table = (struct Data*)calloc(csbi.dwSize.X, sizeof(struct Data));
 assert(table != NULL);

 for(j = 0; j < csbi.dwSize.X; j++) column_init(&table[j], j);

 /*
  * Main loop. Sleep(1) significally decreases the CPU load.
  */

 while(!_kbhit())
 {
   DWORD t = GetTickCount();
   for(j = 0; j < csbi.dwSize.X; j++)
     if(table[j].armed < t) column_run(&table[j]);
   Sleep(1);
 }

 free(table);
 free(buffer);

 return 0;

}</lang>

Multiple threads

Works with: Microsoft Visual Studio C

<lang C>/*******************************************************************************

Digital ASCII rain - multithreaded.
2012 (C) by Author, 2020 GPL licensed for RossetaCode
- - - - /

include <assert.h> /* assertions */
include <conio.h> /* console operations */
include <locale.h> /* l10n and i18n */
include <string.h> /* operations on strings and memory blocks */
include <process.h> /* Microsoft Windows API for threads etc. */
include <stdio.h> /* standard i/o library */
include <stdlib.h> /* standard library with rand() function */
include <time.h> /* time(NULL) used as srand(time(NULL)) */
include <windows.h> /* just the Microsoft Windows main header for C */

//#define SYNCHRONIZED_INIT

/*

* Global variables, common for all threads. 
* The handle eventThreadInitialized is to synchronize threads initializations.
*/

ifdef SYNCHRONIZED_INIT

HANDLE eventThreadInitialized;

endif

BOOL loop = TRUE; /* FALSE - przerwać działanie */ HANDLE hStdOut; /* uchwyt do konsoli "out" */ CONSOLE_SCREEN_BUFFER_INFO csbi; /* liczby wierszy i kolumn itd.*/

struct InitThreadData {

 int      column;
 unsigned seed;

};

/*

* A function to generate random numbers from the range (a, b).  
* NOTE: POSIX rand () is not thread safe, 
* but we use secure rand() from MS runtime libraries.
*/

int rnd(int a, int b) {

 return a + rand() % (b + 1 - a);

}

BOOL randomShow(void) {

 return rnd(0, 99) < 65;

}

int randomDelay(void) {

 return rnd(0,150) + rnd(0,150) + rnd(0,150);

}

BOOL randomRegenerate(void) {

 return rnd(0,99) < 2;

}

/*

* Update a single column.
*/

void one_column(void *arg) {

 BOOL show; 
 int  k;
 char c;
 WORD a;
 int  delay;
 PCHAR_INFO buffer;
 COORD bufferSize, bufferCoord, newCharPosition;
 SMALL_RECT s, d;
 DWORD result;

 /* 
  * Retrieve the column number, initialize the (pseudo)random numbers
  * generator with a "private" seed, check assertions.
  */
 k = ((struct InitThreadData*)arg)->column;
 srand(((struct InitThreadData*)arg)->seed);
 assert(csbi.dwSize.X != 0 && csbi.dwSize.Y != 0);
 assert(0 <= k && k <= csbi.dwSize.X);

 show   = randomShow();
 delay  = randomDelay();

 bufferSize.X = 1;
 bufferSize.Y = csbi.dwSize.Y - 1;
 bufferCoord.X = 0;
 bufferCoord.Y = 0;

 buffer = (PCHAR_INFO)malloc(bufferSize.Y * sizeof(CHAR_INFO));
 assert( buffer != NULL );

 s.Left   = k;
 s.Top    = 0;
 s.Bottom = bufferSize.Y - 2;
 s.Right  = k;

 d.Left   = s.Left;
 d.Top    = s.Top + 1;
 d.Right  = s.Right;
 d.Bottom = s.Bottom + 1;

 newCharPosition.X = k;
 newCharPosition.Y = 0;

ifdef SYNCHRONIZED_INIT

 SetEvent(eventThreadInitialized);

endif

 /*
  * Main loop inside this one thread.
  */
 while(loop)
 {
   ReadConsoleOutput ( hStdOut, buffer, bufferSize, bufferCoord, &s);
   WriteConsoleOutput( hStdOut, buffer, bufferSize, bufferCoord, &d);

   if(show)
   {
     c = (rnd(1,100) <= 15) ? ' ' : rnd( 'a', 'z' );
     a = FOREGROUND_GREEN | ((rnd(1,100) >  1) ? 0 : FOREGROUND_INTENSITY);
   }
   else
   {
     c = ' ';
     a = FOREGROUND_GREEN;
   }

   WriteConsoleOutputCharacter( hStdOut, &c, 1, newCharPosition, &result );
   WriteConsoleOutputAttribute( hStdOut, &a, 1, newCharPosition, &result );

   if(randomRegenerate())  show  = randomShow();
   if(randomRegenerate())  delay = randomDelay();

   Sleep( delay );
 }

 free(buffer);

}

int main(int argc, char* argv[]) {

 int j;
 struct InitThreadData *init = NULL;

 srand((time_t)time(NULL));

 hStdOut = GetStdHandle( STD_OUTPUT_HANDLE );
 SetConsoleTitle("MATRIX");

 if(argc == 1)
 {
   COORD coord;
   CONSOLE_CURSOR_INFO cci;

   cci.bVisible = FALSE;
   cci.dwSize   = 0;
   SetConsoleDisplayMode(hStdOut,CONSOLE_FULLSCREEN_MODE,&coord);
   SetConsoleCursorInfo(hStdOut,&cci);
 }

 GetConsoleScreenBufferInfo( hStdOut, &csbi );
 //SetConsoleTextAttribute(hStdOut,FOREGROUND_GREEN);

ifdef SYNCHRONIZED_INIT

 eventThreadInitialized = CreateEvent(NULL,FALSE,FALSE,NULL);
 assert( eventThreadInitialized != NULL );

endif

 init = (struct InitThreadData*)
         malloc(csbi.dwSize.X * sizeof(struct InitThreadData));
 assert( init != NULL );

 for(j = 0; j < csbi.dwSize.X; j++)
 {
   init[j].column = j;
   init[j].seed = rand();
   _beginthread(one_column, 0, (void*)&init[j]);

ifdef SYNCHRONIZED_INIT

   WaitForSingleObject(eventThreadInitialized,INFINITE);

endif

 getchar();
 free(init);

ifdef SYNCHRONIZED_INIT

 CloseHandle(eventThreadInitialized);

endif SYNCHRONIZED_INIT

 return 0;

}</lang>

Fibers

Works with: Microsoft Visual Studio C

<lang C>/*******************************************************************************

Digital ASCII rain - multithreaded.
2012 (C) by Author, 2020 GPL licensed for RossetaCode
- - - - /

include <assert.h> /* assertions */
include <conio.h> /* console operations */
include <locale.h> /* l10n and i18n */
include <string.h> /* operations on strings and memory blocks */
include <process.h> /* Microsoft Windows API for threads etc. */
include <stdio.h> /* standard i/o library */
include <stdlib.h> /* standard library with rand() function */
include <time.h> /* time(NULL) used as srand(time(NULL)) */
include <windows.h> /* just the Microsoft Windows main header for C */

/*

* Global variables, shared by fibers.
*/

BOOL loop = TRUE; HANDLE hStdOut; CONSOLE_SCREEN_BUFFER_INFO csbi;

LPVOID mainFiber = NULL;

struct WorkingFiber {

 int      column;
 DWORD    callAfter;
 unsigned seed;
 LPVOID   fiber;

} *workingFibersTable = NULL;

/*

* A function to generate random numbers from the range (a, b).  
* NOTE: POSIX rand () is not thread safe, 
* but we use secure rand() from MS runtime libraries.
*/

int rnd(int a, int b) {

 return a + rand() % (b + 1 - a);

}

BOOL randomShow(void) {

 return rnd(0, 99) < 65;

}

int randomDelay(void) {

 return rnd(0,150) + rnd(0,150) + rnd(0,150);

}

BOOL randomRegenerate(void) {

 return rnd(0,99) < 2;

}

VOID CALLBACK one_column(void *arg) {

 struct WorkingFiber *ptr;
 BOOL show; 
 int  k;
 char c;
 WORD a;
 int  delay;
 PCHAR_INFO buffer;
 COORD bufferSize, bufferCoord, newCharPosition;
 SMALL_RECT s, d;
 DWORD result;

 ptr = (struct WorkingFiber*)arg;
 k = ptr->column;
 ptr->callAfter = 0;
 srand(ptr->seed);
 assert(csbi.dwSize.X != 0 && csbi.dwSize.Y != 0);
 assert(0 <= k && k <= csbi.dwSize.X);

 show  = randomShow();
 delay = randomDelay();

 bufferSize.X = 1;
 bufferSize.Y = csbi.dwSize.Y - 1;
 bufferCoord.X = 0;
 bufferCoord.Y = 0;

 buffer = (PCHAR_INFO)malloc(bufferSize.Y * sizeof(CHAR_INFO));
 assert( buffer != NULL );

 s.Left        = k;
 s.Top         = 0;
 s.Bottom      = bufferSize.Y - 2;
 s.Right       = k;

 d.Left   = s.Left;
 d.Top    = s.Top + 1;
 d.Right  = s.Right;
 d.Bottom = s.Bottom + 1;

 newCharPosition.X = k;
 newCharPosition.Y = 0;
 
 while(loop)
 {
   ReadConsoleOutput ( hStdOut, buffer, bufferSize, bufferCoord, &s);
   WriteConsoleOutput( hStdOut, buffer, bufferSize, bufferCoord, &d);

   if(show)
   {
     c = (rnd(1,100) <= 15) ? ' ' : rnd( 'a', 'z' );
     a = FOREGROUND_GREEN | ((rnd(1,100) >  1) ? 0 : FOREGROUND_INTENSITY);
   }
   else
   {
     c = ' ';
     a = FOREGROUND_GREEN;
   }

   WriteConsoleOutputCharacter( hStdOut, &c, 1, newCharPosition, &result );
   WriteConsoleOutputAttribute( hStdOut, &a, 1, newCharPosition, &result );

   if(randomRegenerate())  show  = randomShow();
   if(randomRegenerate())  delay = randomDelay();

   ptr->callAfter = GetTickCount() + delay;
   SwitchToFiber(mainFiber);
 }

 free(buffer);

}

int main(int argc, char* argv[]) {

 int j;

 srand((unsigned int)time(NULL));

 hStdOut = GetStdHandle( STD_OUTPUT_HANDLE );
 SetConsoleTitle("MATRIX - FIBERS");

 if(argc == 1)
 {
   COORD coord;
   CONSOLE_CURSOR_INFO cci;

   cci.bVisible = FALSE;
   cci.dwSize   = 0;
   SetConsoleDisplayMode(hStdOut,CONSOLE_FULLSCREEN_MODE,&coord);
   SetConsoleCursorInfo(hStdOut,&cci);
 }

 GetConsoleScreenBufferInfo( hStdOut, &csbi );
 //SetConsoleTextAttribute(hStdOut,FOREGROUND_GREEN);

 mainFiber = ConvertThreadToFiber(NULL);
 assert( mainFiber != NULL );

 workingFibersTable = (struct WorkingFiber*)
                      calloc(csbi.dwSize.X, sizeof(struct WorkingFiber));
 assert( workingFibersTable != NULL );

 for(j = 0; j < csbi.dwSize.X; j++)
 {
   workingFibersTable[j].column = j;
   workingFibersTable[j].callAfter = 0;
   workingFibersTable[j].seed = rand();
   workingFibersTable[j].fiber = CreateFiber( 0, one_column, &workingFibersTable[j] );
 }

 loop = TRUE;
 while(!_kbhit())
 {
   DWORD t = GetTickCount();
   for(j = 0; j < csbi.dwSize.X; j++)
     if(workingFibersTable[j].callAfter < t)
       SwitchToFiber( workingFibersTable[j].fiber );
   Sleep(1);
 }

 loop = FALSE;
 for(j = 0; j < csbi.dwSize.X; j++)
 {
   SwitchToFiber( workingFibersTable[j].fiber );
   DeleteFiber(workingFibersTable[j].fiber);
 }

 free(workingFibersTable);

 return 0;

}</lang>

Common Lisp

Works with: SBCL

Runs in the terminal (using the Ncurses C library and the croatoan Lisp wrapper).

<lang lisp> (defun matrix-digital-rain ()

 (with-screen (scr :input-echoing nil :input-blocking nil :cursor-visible nil)
   (let* ((width (width scr))
          (height (height scr))
          ;; start at a random height in each column.
          (positions (loop repeat width collect (random height)))
          ;; run each column at a random speed.
          (speeds (loop repeat width collect (random 4))))
     ;; generate a random ascii char
     (flet ((randch () (+ 64 (random 58))))
       ;; hit the q key to exit the main loop.
       (bind scr #\q 'exit-event-loop)
       (bind scr nil
         (lambda (win event)
           (loop for col from 0 to (1- width) do
             (loop repeat (nth col speeds) do
               ;; position of the first point in the current column
               (let ((pos (nth col positions)))
                 (setf (attributes win) '(:bold))
                 (setf (fgcolor win) :green)
                 (add win (randch) :y (mod pos height) :x col :fgcolor :white)
                 (add win (randch) :y (mod (- pos 1) height) :x col)
                 (add win (randch) :y (mod (- pos 2) height) :x col)
                 (setf (attributes win) '())
                 (add win (randch) :y (mod (- pos 3) height) :x col)
                 ;; overwrite the last char half the height from the first char.
                 (add win #\space  :y (mod (- pos (floor height 2)) height) :x col)
                 (refresh win)
                 ;; advance the current column
                 (setf (nth col positions) (mod (+ pos 1) height))))))))
     (setf (frame-rate scr) 20)
     (run-event-loop scr))))

</lang>

Sample output:

https://i.imgur.com/17b36O3.png

Go

Library: goncurses

This is a translation of the C code here which uses the ncurses library.

Rather than pressing Ctrl+C to stop the program, I've added code so that it stops automatically after 1 minute and restores the terminal to its original state. <lang go>package main

import (

   gc "github.com/rthornton128/goncurses"
   "log"
   "math/rand"
   "time"

)

// Time between row updates in microseconds. // Controls the speed of the digital rain effect. const rowDelay = 40000

func main() {

   start := time.Now()
   rand.Seed(time.Now().UnixNano())

   // Characters to randomly appear in the rain sequence.
   chars := []byte("0123456789")
   totalChars := len(chars)

   // Set up ncurses screen and colors.
   stdscr, err := gc.Init()
   if err != nil {
       log.Fatal("init", err)
   }
   defer gc.End()

   gc.Echo(false)
   gc.Cursor(0)

   if !gc.HasColors() {
       log.Fatal("Program requires a colour capable terminal")
   }

   if err := gc.StartColor(); err != nil {
       log.Fatal(err)
   }

   if err := gc.InitPair(1, gc.C_GREEN, gc.C_BLACK); err != nil {
       log.Fatal("InitPair failed: ", err)
   }
   stdscr.ColorOn(1)
   maxY, maxX := stdscr.MaxYX()

   /* Create slices of columns based on screen width. */

   // Slice containing the current row of each column.
   columnsRow := make([]int, maxX)

   // Slice containing the active status of each column.
   // A column draws characters on a row when active.
   columnsActive := make([]int, maxX)

   // Set top row as current row for all columns.
   for i := 0; i < maxX; i++ {
       columnsRow[i] = -1
       columnsActive[i] = 0
   }

   for {
       for i := 0; i < maxX; i++ {
           if columnsRow[i] == -1 {
               // If a column is at the top row, pick a
               // random starting row and active status.
               columnsRow[i] = rand.Intn(maxY + 1)
               columnsActive[i] = rand.Intn(2)
           }
       }

       // Loop through columns and draw characters on rows.
       for i := 0; i < maxX; i++ {
           if columnsActive[i] == 1 {
               // Draw a random character at this column's current row.
               charIndex := rand.Intn(totalChars)
               stdscr.MovePrintf(columnsRow[i], i, "%c", chars[charIndex])
           } else {
               // Draw an empty character if the column is inactive.
               stdscr.MovePrintf(columnsRow[i], i, "%c", ' ')
           }

           columnsRow[i]++

           // When a column reaches the bottom row, reset to top.
           if columnsRow[i] >= maxY {
               columnsRow[i] = -1
           }

           // Randomly alternate the column's active status.
           if rand.Intn(1001) == 0 {
               if columnsActive[i] == 0 {
                   columnsActive[i] = 1
               } else {
                   columnsActive[i] = 0
               }
           }
       }
       time.Sleep(rowDelay * time.Microsecond)
       stdscr.Refresh()
       elapsed := time.Since(start)
       // Stop after 1 minute.
       if elapsed.Minutes() >= 1 {
           break
       }
   }

}</lang>

Julia

The font used is based on Leonardo da Vinci's notebooks. The font is freely obtainable at https://www.wfonts.com/font/leonardos-mirrorwriting. <lang Julia>using Gtk, Colors, Cairo import Base.iterate, Base.IteratorSize, Base.IteratorEltype

const caps = [c for c in "ABCDEFGHIJKLMNOPQRSTUVWXYZ"] startfall() = rand() < 0.2 endfall() = rand() < 0.2 startblank() = rand() < 0.1 endblank() = rand() < 0.05 bechangingchar() = rand() < 0.03

struct RainChars chars::Vector{Char} end Base.IteratorSize(s::RainChars) = Base.IsInfinite() Base.IteratorEltype(s::RainChars) = Char function Base.iterate(rain::RainChars, state = (true, false, 0))

   c = '\0'
   isfalling, isblank, blankcount = state
   if isfalling # falling, so feed the column
       if isblank
           c = ' '
           ((blankcount += 1) > 12) && (isblank = endblank())
       else
           c = bechangingchar() ? '~' : rand(rain.chars)
           isblank, blankcount = startblank(), 0
       end
       endfall() && (isfalling = false)
   else
       isfalling = startfall()
   end   
   return c, (isfalling, isblank, blankcount)

end

function digitalrain()

   mapwidth, mapheight, fontpointsize = 800, 450, 14
   windowmaxx = div(mapwidth, Int(round(fontpointsize * 0.9)))
   windowmaxy = div(mapheight, fontpointsize)
   basebuffer = fill(' ', windowmaxy, windowmaxx)
   bkcolor, rcolor, xcolor = colorant"black", colorant"green", colorant"limegreen"

   columngenerators = [Iterators.Stateful(RainChars(caps)) for _ in 1:windowmaxx]

   win = GtkWindow("Digital Rain Effect", mapwidth, mapheight) |>
       (GtkFrame() |> (can = GtkCanvas()))
   set_gtk_property!(can, :expand, true)

   draw(can) do widget
       ctx = Gtk.getgc(can)
       select_font_face(ctx, "Leonardo\'s mirrorwriting", Cairo.FONT_SLANT_NORMAL,
           Cairo.FONT_WEIGHT_BOLD)
       set_font_size(ctx, fontpointsize)
       set_source(ctx, bkcolor)
       rectangle(ctx, 0, 0, mapwidth, mapheight)
       fill(ctx)
       set_source(ctx, rcolor)
       for i in 1:size(basebuffer)[1], j in 1:size(basebuffer)[2]
           move_to(ctx, j * fontpointsize * 0.9, i * fontpointsize)
           c = basebuffer[i, j]
           if c == '~'

set_source(ctx, xcolor)

               show_text(ctx, String([rand(caps)]))

set_source(ctx, rcolor)

           else
               show_text(ctx, String([c]))
           end
       end
   end

   while true
       for col in 1:windowmaxx
           c = popfirst!(columngenerators[col])
           if c != '\0'
               basebuffer[2:end, col] .= basebuffer[1:end-1, col]
               basebuffer[1, col] = c
           end
       end
       draw(can)
       Gtk.showall(win)
       sleep(0.05)
   end

end

digitalrain() </lang>

Locomotive Basic

<lang locobasic>10 mode 0:defint a-z:randomize time:ink 0,0:ink 1,26:ink 2,19:border 0 20 dim p(20):mm=5:dim act(mm):for i=1 to mm:act(i)=rnd*19+1:next 30 md=mm-2:dim del(md):for i=1 to md:del(i)=rnd*19+1:next 40 for i=1 to mm:x=act(i):locate x,p(x)+1:pen 1:print chr$(rnd*55+145); 50 if p(x)>0 then locate x,p(x):pen 2:print chr$(rnd*55+145); 60 p(x)=p(x)+1:if p(x)=25 then locate x,25:pen 2:print chr$(rnd*55+145);:p(x)=0:act(i)=rnd*19+1 70 next 80 for i=1 to md:x=del(i):locate x,p(x)+1:print " "; 90 p(x)=p(x)+1:if p(x)=25 then p(x)=0:del(i)=rnd*19+1 100 next 110 goto 40</lang> The program above runs at an acceptable speed on a 4 MHz Z80, but can be made much faster by using the CPCBasic JavaScript emulator. CPCBasic also adds an 80x50 display mode ("mode 3") which real CPC hardware lacks. Changing screen size from 20x25 to 80x50 and adding a delay with "frame" in line 100 results in a far more impressive display in CPCBasic: <lang locobasic>10 mode 3:defint a-z:randomize time:ink 0,0:ink 1,26:ink 2,19:border 0 20 dim p(80):mm=12:dim act(mm):for i=1 to mm:act(i)=rnd*79+1:next 30 md=mm-2:dim del(md):for i=1 to md:del(i)=rnd*79+1:next 40 for i=1 to mm:x=act(i):locate x,p(x)+1:pen 1:print chr$(rnd*55+145); 50 if p(x)>0 then locate x,p(x):pen 2:print chr$(rnd*55+145); 60 p(x)=p(x)+1:if p(x)=50 then locate x,50:pen 2:print chr$(rnd*55+145);:p(x)=0:act(i)=rnd*79+1 70 next 80 for i=1 to md:x=del(i):locate x,p(x)+1:print " "; 90 p(x)=p(x)+1:if p(x)=50 then p(x)=0:del(i)=rnd*79+1 100 next:frame 110 goto 40</lang>

Nim

Translation of: C

Library: nim-ncurses

<lang Nim>import os, random, sequtils import ncurses

const RowDelay = 40 # In milliseconds.

proc exit() {.noconv.} =

 endwin()
 quit QuitSuccess

proc run() =

 const
   Chars = "0123456789"    # Characters to randomly appear in the rain sequence.

 let stdscr = initscr()
 noEcho()
 cursSet(0)
 startColor()
 initPair(1, COLOR_GREEN, COLOR_BLACK)
 attron(COLOR_PAIR(1).cint)

 var width, height: cint
 stdscr.getmaxyx(height, width)
 let maxX = width - 1
 let maxY = height - 1

 # Create arrays of columns based on screen width.

 # Array containing the current row of each column.
 # Set top row as current row for all columns.
 var columnsRow = repeat(cint -1, width)

 # Array containing the active status of each column.
 # A column draws characters on a row when active.
 var columnsActive = newSeq[bool](width)

 setControlCHook(exit)
 while true:

   for i in 0..maxX:
     if columnsRow[i] == -1:
       # If a column is at the top row, pick a random starting row and active status.
       columnsRow[i] = cint(rand(maxY))
       columnsActive[i] = bool(rand(1))

   # Loop through columns and draw characters on rows.
   for i in 0..maxX:
     if columnsActive[i]:
       # Draw a random character at this column's current row.
       let charIndex = rand(Chars.high)
       mvprintw(columnsRow[i], i, "%c", Chars[charIndex])
     else:
       # Draw an empty character if the column is inactive.
       mvprintw(columnsRow[i], i, " ")

     inc columnsRow[i]
     # When a column reaches the bottom row, reset to top.
     if columnsRow[i] > maxY: columnsRow[i] = -1

     # Randomly alternate the column's active status.
     if rand(999) == 0: columnsActive[i] = not columnsActive[i]

   sleep(RowDelay)
   refresh()

run()</lang>

Perl

Probably shouldn't, but until someone posts something better... here's something somewhat relevant I wrote back in 2006.

Follow the bouncing Neo!

<lang perl>#!/user/bin/perl

use strict; use warnings; use Tk;

my $delay = 50; # milliseconds my $fade = 8; # number of characters to "fade" my $base_color = '#004000'; # dark green my $fontname = 'Times'; # Whatever my $fontsize = 12; # point size my $font = "{$fontname} $fontsize bold"; my @objects;

my ( $xv, $yv ) = ( 0, 0 );

my $top = MainWindow->new();

$top->geometry('800x600');

my $run = 1;

$top->protocol( 'WM_DELETE_WINDOW' => sub { $run = 0; } );

my @letters = ( 'A' .. 'Z', 'a' .. 'z', '0' .. '9' );

my $canvas = $top->Canvas(

   -background => 'black'

)->pack(

   -fill   => 'both',
   -expand => 'y'

);

my $testch = $canvas->createText(

   100, 100,
   -text => 'o',
   -fill => 'black',
   -font => $font

);

$top->update;

my @coords = $canvas->bbox($testch);

$canvas->delete($testch);

my $lwidth = $coords[2] - $coords[0]; my $lheight = ( $coords[3] - $coords[1] ) * .8; my $cols = int $canvas->width / $lwidth; my $rows = int $canvas->height / $lheight;

for my $y ( 0 .. $rows ) {

   for my $x ( 0 .. $cols ) {
       $objects[$x][$y] = $canvas->createText(
           $x * $lwidth, $y * $lheight,
           -text => $letters[ int rand @letters ],
           -fill => $base_color,
           -font => $font
       );
   }

}

my $neo_image = $top->Photo( -data => neo() );

my $neo = $canvas->createImage(

   $canvas->width / 2,
   $canvas->height / 2,
   -image => $neo_image

);

while ($run) {

   drop('Nothing Like The Matrix');

} exit;

MainLoop;

sub drop {

   my @phrase = split //, reverse shift;
   my $x = int rand $cols;
   my @orig;
   for my $y ( 0 .. $rows ) {
       $orig[$y] = $canvas->itemcget( $objects[$x][$y], '-text' );
   }
   for my $y ( 0 .. $rows + @phrase + $fade ) {
       for my $letter ( 0 .. @phrase ) {
           last if ( $y - $letter < 0 );
           $canvas->itemconfigure(
               $objects[$x][ $y - $letter ],
               -text => $phrase[$letter],
               -fill => "#00FF00"
           );
       }
       if ( $y > @phrase ) {
           $canvas->itemconfigure(
               $objects[$x][ $y - @phrase ],
               -text => $orig[ $y - @phrase ],
               -fill => "#009000"
           );
       }
       if ( $y > @phrase + 2 ) {
           $canvas->itemconfigure( $objects[$x][ $y - @phrase - int ($fade / 2) ],
               -fill => "#006000" );
           $canvas->itemconfigure( $objects[$x][ $y - @phrase - $fade + 1 ],
               -fill => $base_color );
       }
       last unless $run;
       $top->after($delay);
       neo_move();
       $top->update;
   }

}

sub neo_move {

   $xv += ( ( rand 2 ) - 1 > 0 ) ? 1 : -1;
   $yv += ( ( rand 2 ) - 1 > 0 ) ? 1 : -1;
   my ( $x, $y ) = $canvas->coords($neo);
   $xv = -$xv if ( ( $x < 0 ) or ( $x > $canvas->width ) );
   $yv = -$yv if ( ( $y < 0 ) or ( $y > $canvas->height ) );
   $canvas->move( $neo, $xv, $yv );

}

sub neo { return ' R0lGODlhjAC1APcAAAQDBISCZEJDM8nDq6eihGJjSyQjFOzj0oSEhGRlZCktLKKkpEhNTMHFxBES BFBSNDMyJJSSbOru7HFyVGt0aqm1q5OVhMnTy2RELLmzmy0UEUQiDMa1pZSEbCo4MrSVhIh0Z9jO tLSljNPV1IhkSPjy3D9EPCYDBB4VHJGVlCIjHGxKTOrl3GFkVLnCuUU5LQsLCXmDesq9tk9XTBEa FOXVxSEqImRUQvv37HF1dJOahZmkmOzq3Km6tMe8qEJLQJhyVIZ9Z9bFtJeEeLamlG5sVFEzIUAp LKSUfGBeXN/FxBIUFHN7XF9FPiwcDD0kITc9PF5ZTk1LNFlbQ3p9ZYqMdXhqZOna1C4lHREOFOXb xLesl/z6/JeNdj47JJqafLy7pZ+Vhjs+MKurlYl8dBUEBa2chNrQvBUNC9e8qkAsHIqLbGtrTH10 W8O6m1Q+PPXs301EMpyMhMGtpFhURNzbykU+MVBMPS8dHPTq1B4UDD0zI4qTfDo4LU5FPJKclvTm 3G1dTYFjVHhcXIOMhlprZKqrpFxMNJWLbEw+JF1NPqSbfGBQTKyri8XMxEQsFNbb1CYMBB8dHGRa PHR9dD8xLNvNxH1tWbCelOXQvG5lVUgcEIhcTM/KrDAqFPny7bTKvLq+t3RuZC8yLk1STZRqTPz6 5FFeUfz+86B6XNbKt+ve1dTDrG1lTC4jFPTl1Hh1Zru2pNzUxMS0nEAWENW1qaiCaJh2aMzFtFw6 NImFdte9tCEcEzEsIaCchqmmlLa4tZZ7aayGdFQiHMWtnKaNfJ+blo6OiWlsZm9OQbWqjGFeTtvW vFU+MszKtohuaPfu7B4VFH97XIhoZJmUfHRKNGQ6JLyafIeEbKijjBITDFZTPJWSdHJ0XIqUjGJE NEQkFKySjPvy5EJFRB8lJOPm5FtkXFBYVPv59Obs5KR2XNfDvLqmnG5sXC8dFOfczK6djD4tJKSO jHxiXKutrMvMzNnd3CYODCQeJGVcRHx9fEkxNNTOzPz+/OTWvL+elCH5BAEAAP0ALAAAAACMALUA Bwj/APsJHEiwoMGDCBMqXMiwocOHECNKnEixosWLGDNq3Mixo8ePIEOKHEmypMmTKFOqXMmSJReJ LxPGbEkT5EyBM2PerMmT4E6D6NJdAAasgQtHF8qNKFpOwqeeUB+iG4iqH6pyhpCJ8fCDEr0dpGio UKBCGylHUweiwzHwZ1So9kJVoHTKgzYYo855+0PpBwwAKlTYsGHCnDkKlCgQqoD0goR+bt+yRGfP WwJChGgAAGDDw4xxNLRtBqDNg4dxM86pAADDhjYVMbzF+AMpreSeKUbFuKCDHAAa4zzA+Du6+Oi/ MNCQI4eM0igxFW5HNQblD4sdNgAogMJgifHv4AGQ/7PRulAPCY+lW4yM8Ga6GD/+9FC9ZMko7+Hz h18C5RylChdAkp56Gb2UU0ExwKDCDKSIpt+DEALmwSiU2GMbZAqxR2A/TwF1jDY26PbDZsSxFuGJ Jv6lAgM/mPNHPR1qeFtk6NSIHiT9pFNOP+gk+MMpXZVonJAofofGEsmpYNooEyrAgCEXboghTv1I 0MMOLuCAwwihpNOPN4Rc4OUO2lDijVjZgUdkkSSWONwSnf1ggmnjnZNCA5B4yYUEMvYkwR/nnOOB CYWcQg4FFxQCgwl/hGKaNx4sIclwarJZJAza0DAKFB4sp4ACpDRAmYVTShdDWfiZthkNCoimQHY/ /P9Agw1orLkZkpZeCoByo4xCTqYepPBYlJLZYwMNJpggyRKBCkoiAJLcNUMhNHhHnJDKoZHrtkuQ gysAOUzVZ0vHAEAJKBSsRtqE4EkyirbJDYetJNpua1ytQ+JbHHKbESLlMTTEN8qrCghnYnjJoXFk 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AAJ4wHbGhgIQg6WyQm3QlSlPljGgglPwgjozAC1/1imYABb6Anh42lKa0TOog2t8hw8UzA5PQ5aK 0+Ls678ugh+AAF5IvmiAgSzIGz5PFguIhRj4ARvwNSyAgO/cBjZYOF9oqFJ7u5AELMI0kyAXmxl9 DDBoBGpYgzWgginYXJUJi7yRclKvmxhgCM+cUNKkg26oAiP3hccsNTCrKVxwBpdjLixzD3Uagy8Q dhMXA87VBj3PGxogB2XHID4QAF4Y9ELF0CkQ1Qes9sho1YomJb/qdfZrhC/ABiYoACkouIhQEw5S d3bHIGfQBeOzM//pvYMC6G8wllb4E4ExaIRGeD1thQymXaAc1YE1KIJt6AMDMHhdSXflU3gMqgAK gADsrLPqLU2J5+93XhQ+KHJfaGHHdEzF4PlHroIgWHIVoAE9PzQOWnnF2gFzGAUVsOMCNoE7mIIC KIDVLIJ2iJlugIV4nngv/oIid2cqUJ9eoIFD0xsAS/oSGwNzoF4x8AATgOaZBG5p3gYiIzLYZoMi EGYmIGySJngVuEJdATCkT/sS44MBFgBo9mQC7kWx5s4CJuDSvAMToPw+sAEV15WjPzIYKPwSAwMd aIcfSHwC7rU6OsLkA0Z4V4EBX4mIADDBN9bOl7UdAH0CJtTOVBmcSVi+JYDyc3d9BxD86jNWzpd9 WeODHJ7eXiAHLNDHldD95fMLv4DyhzD7wT+y4sc79eFtQmx+lYmGibDCJXgI6yd87PdB22f+XJ2R I2R9vtCDKDf78jf/lCRvGFv9CrRClL/++ffTLM9V/geIfgIHEixo8CDChAoXMmzo8CHEiBInUqxo 8SLGjBo3cuzo8SPIkCJHkixp8iTKiQEBADs= '; } </lang>

Another Perl Solution

<lang perl>#!/usr/bin/perl

use strict; # http://www.rosettacode.org/wiki/Matrix_Digital_Rain use warnings; use Tk; use List::Util qw( shuffle );

my ($rows, $cols) = (20, 40); my @text = shuffle 'a'..'z', 'A'..'Z'; my $n = 0;

my $mw = MainWindow->new; $mw->geometry( '+850+300' ); my $c = $mw->Canvas( -width => $cols * 10, -height => $rows * 20,

 -bg => 'black',
 )->pack;

$c->Tk::bind('<ButtonRelease-1>' => sub { $mw->destroy } );

my @queue = [ 100, 0, 255, 'A' ]; # [ x, y, color, letter ] $mw->after( 5, \&step ); MainLoop;

sub step

 {
 $c->delete('all');
 my @new = [ 10 * int rand $cols, 0, 255, $text[++$n % @text] ];
 for ( @queue )
   {
   my $color = $_->[2] == 255 ? '#ffffff' : sprintf '#00%02x00', $_->[2];
   $c->createText($_->[0], $_->[1],
     -font => '10x20', -text => $_->[3], -fill => $color );
   $_->[2] == 255 and push @new, [ $_->[0], $_->[1] + 20, 255, $_->[3] ];
   $_->[2] -= 13;
   }
 @queue = grep $_->[2] > 0 && $_->[1] < $rows * 20, @queue, @new;
 $mw->after( 63, \&step );
 }</lang>

Phix

Library: Phix/pGUI

<lang Phix>-- demo\rosetta\Matrix_Digital_Rain.exw sequence sushii = {}, -- w x h of unicode char strings

        colours,       --  """  of their fading colours
        droplets       -- w column droplets, or zeroes

include pGUI.e

Ihandle dlg, canvas, timer cdCanvas cddbuffer, cdcanvas

procedure rain(integer w,h)

   for x=1 to w do
       integer y = droplets[x]
       if y or rand(40)=1 then
           if y<h then
               droplets[x] = y+1
               sushii[y+1][x] = utf32_to_utf8({0x30A0 + rand(96)})
               colours[y+1][x] = CD_WHITE
           end if
           if y then
               bool clear_droplet = true
               if colours[y][x]=CD_WHITE then
                   colours[y][x] = #00F800 -- (CD_GREEN to nearest #800)
                   clear_droplet = false
                   y -= 1
               end if
               for y=y to 1 by -1 do
                   integer cy = colours[y][x]
                   if cy=0 then exit end if
                   clear_droplet = false
                   cy -= #000800
                   colours[y][x] = cy
               end for
               if clear_droplet then
                   droplets[x] = 0
               end if
           end if
       end if
   end for

end procedure

function redraw_cb(Ihandle /*ih*/, integer /*posx*/, integer /*posy*/)

   integer {w,h} = IupGetIntInt(canvas, "DRAWSIZE"),
           {dx,dy} = cdCanvasGetTextSize(cddbuffer, "W")
   w = max(1,floor(w/dx))
   h = max(1,floor(h/dy))
   if length(sushii)!=h
   or length(sushii[1])!=w then
       sushii = repeat(repeat(" ",w),h)
       colours = repeat(repeat(CD_BLACK,w),h)
       droplets = repeat(0,w)
   end if
   cdCanvasActivate(cddbuffer)
   cdCanvasClear(cddbuffer)
   rain(w,h)
   for x=1 to w do
       for y=1 to h do
           cdCanvasSetForeground(cddbuffer, colours[y][x])
           cdCanvasText(cddbuffer,x*dx, (h-y)*dy, sushii[y][x]) 
       end for
   end for
   cdCanvasFlush(cddbuffer)
   return IUP_DEFAULT

end function

function timer_cb(Ihandle /*ih*/)

   IupUpdate(canvas)
   return IUP_IGNORE

end function

function map_cb(Ihandle ih)

   cdcanvas = cdCreateCanvas(CD_IUP, ih)
   cddbuffer = cdCreateCanvas(CD_DBUFFER, cdcanvas)
   cdCanvasSetBackground(cddbuffer, CD_BLACK)
   return IUP_DEFAULT

end function

procedure main()

   IupOpen()
   IupSetGlobal("UTF8MODE","YES")

   canvas = IupCanvas(NULL)
   IupSetAttribute(canvas, "RASTERSIZE", "640x480")
   IupSetCallback(canvas, "MAP_CB", Icallback("map_cb"))
   IupSetCallback(canvas, "ACTION", Icallback("redraw_cb"))

   timer = IupTimer(Icallback("timer_cb"), 50)

   dlg = IupDialog(canvas)
   IupSetAttribute(dlg, "TITLE", "Matrix Digital Rain")

   IupShow(dlg)
   IupSetAttribute(canvas, "RASTERSIZE", NULL)
   IupMainLoop()
   IupClose()

end procedure main()</lang>

Python

<lang python> import curses import random import time

"""

Based on C ncurses version

http://rosettacode.org/wiki/Matrix_Digital_Rain#NCURSES_version

"""

""" Time between row updates in seconds Controls the speed of the digital rain effect. """

ROW_DELAY=.0001

def get_rand_in_range(min, max):

   return random.randrange(min,max+1)

try:

   # Characters to randomly appear in the rain sequence.
   chars = ['0', '1', '2', '3', '4', '5', '6', '7', '8', '9']
   
   total_chars = len(chars)
       
   stdscr = curses.initscr()
   curses.noecho()
   curses.curs_set(False)
       
   curses.start_color()
   curses.init_pair(1, curses.COLOR_GREEN, curses.COLOR_BLACK)
   stdscr.attron(curses.color_pair(1))
   
   max_x = curses.COLS - 1
   max_y = curses.LINES - 1
   
        
   # Create arrays of columns based on screen width.
   
   # Array containing the current row of each column.
   
   columns_row = []
   
   # Array containing the active status of each column.
   # A column draws characters on a row when active.
   
   columns_active = []
   
   for i in range(max_x+1):
       columns_row.append(-1)
       columns_active.append(0)
       
   while(True):
       for i in range(max_x):
           if columns_row[i] == -1:
               # If a column is at the top row, pick a
               # random starting row and active status.
               columns_row[i] = get_rand_in_range(0, max_y)
               columns_active[i] = get_rand_in_range(0, 1)
    
       # Loop through columns and draw characters on rows
       
       for i in range(max_x):
           if columns_active[i] == 1:
               # Draw a random character at this column's current row.
               char_index = get_rand_in_range(0, total_chars-1)
               #mvprintw(columns_row[i], i, "%c", chars[char_index])                
               stdscr.addstr(columns_row[i], i, chars[char_index])
           else:
               # Draw an empty character if the column is inactive.
               #mvprintw(columns_row[i], i, " ");
               stdscr.addstr(columns_row[i], i, " ");
               
    
           columns_row[i]+=1
    
           # When a column reaches the bottom row, reset to top.
           if columns_row[i] >= max_y:
               columns_row[i] = -1
   
           # Randomly alternate the column's active status.
           if get_rand_in_range(0, 1000) == 0:
               if columns_active[i] == 0:      
                   columns_active[i] = 1
               else:
                   columns_active[i] = 0
    
           time.sleep(ROW_DELAY)
           stdscr.refresh()

except KeyboardInterrupt as err:

   curses.endwin()

</lang>

Racket

Translation of: Raku

<lang racket>#lang racket

(define codes '((Α Π) (Ѐ ѵ) (Ҋ ԯ) (Ϣ ϯ) (ｦﾝ) (Ⲁ ⳩) (∀ ∗) (℀ ℺) (⨀ ⫿)))

(define (symbol->integer s) (char->integer (string-ref (symbol->string s) 0))) (define (pick xs) (list-ref xs (random (length xs))))

(define glyphs

 (map
  integer->char
  (append*
   (for/list ([c (in-list codes)])
     (range (symbol->integer (first c)) (add1 (symbol->integer (second c))))))))

(define palette (vector-append (vector "\e[38;2;255;255;255m")

                              (for/vector ([n (in-range 245 29 -10)])
                                (format "\e[38;2;0;~a;0m" n))
                              (make-vector 75 "\e[38;2;0;25;0m")))

(match-define (list (app (compose1 sub1 string->number) rows)

                   (app string->number cols))
 (string-split (with-output-to-string (thunk (system "stty size")))))

(define screen (for/vector ([_ (in-range (* rows cols))]) (pick glyphs))) (define offsets (for/vector ([col cols]) (random (vector-length palette))))

(display "\e[?25l\e[48;5;232m") ; hide the cursor, set the background color

(define (main)

 (for ([iter (in-naturals)])
   (sleep 0.1)
   (display "\e[1;1H") ; reset cursor to top left
   (for ([i (in-range 30)]) (vector-set! screen (random (* rows cols)) (pick glyphs)))
   (for ([i (in-range rows)])
     (for ([j (in-range cols)])
       (display (vector-ref palette (modulo (+ (- i) iter (vector-ref offsets j))
                                            (vector-length palette))))
       (display (vector-ref screen (+ (* cols i) j))))
     (display "\n"))))

(with-handlers ([exn:break? (thunk*

                            ; reset ANSI codes, reshow cursor, clear screen
                            (display "\e[0m")
                            (display "\e[H\e[J\e[?25h"))])
 (main))</lang>

Raku

(formerly Perl 6)

Works with: Rakudo version 2018.11

Kind-of cheap and cheesy, but what the heck... Probably will only work in a POSIX compatible terminal. Runs until you hit ^C to exit.

The "lightning" effect is actually a bug, but I liked it so I kept it.

<lang perl6># clean up on exit, reset ANSI codes, scroll, re-show the cursor & clear screen signal(SIGINT).tap: { print "\e[0m", "\n" xx 50, "\e[H\e[J\e[?25h"; exit(0) }

a list of glyphs to use

my @codes = flat 'Α' .. 'Π', 'Ѐ' .. 'ѵ', 'Ҋ' .. 'ԯ', 'Ϣ' .. 'ϯ', 'ｦ'.. 'ﾝ',

                'Ⲁ' .. '⳩', '∀' .. '∗', '℀' .. '℺', '⨀' .. '⫿';

palette of gradient ANSI foreground colors

my @palette = flat "\e[38;2;255;255;255m", (255,245 … 30).map({"\e[38;2;0;$_;0m"}),

             "\e[38;2;0;25;0m" xx 75;

my @screen; # buffer to hold glyphs my @rotate; # palette rotation position buffer

my ($rows, $cols) = qx/stty size/.words; # get the terminal size init($rows, $cols); # set up the screen buffer and palette offsets

my $size-check;

print "\e[?25l\e[48;5;232m"; # hide the cursor, set the background color

loop {

    if ++$size-check %% 20 {                         # periodically check for
        my ($r, $c) = qx/stty size/.words;           # resized terminal and
        init($r, $c) if $r != $rows or $c != $cols;  # re-initialize screen buffer
        $size-check = 0
    }
    print "\e[1;1H";                                 # set cursor to top left
    print join , (^@screen).map: {
        @rotate[$_] = (@rotate[$_] + 1) % +@palette; # rotate the palettes
        flat @palette[@rotate[$_]], @screen[$_]      # and print foreground, glyph
    }
    @screen[(^@screen).pick] = @codes.roll for ^30;  # replace some random glyphs

}

sub init ($r, $c) {

   @screen = @codes.roll($r * $c);
   ($rows, $cols) = $r, $c;
   my @offset = (^@palette).pick xx $cols;
   for ^$rows -> $row {
       @rotate[$row * $cols ..^ $row * $cols + $cols] = @offset;
       # for no "lightning" effect, add   '1 + '  ↓ here: (1 + $_ % 3)
       @offset = (^@offset).map: {(@offset[$_] - ($_ % 3)) % +@palette};
   }

}</lang>

Sample output:

See matrix-digital-rain-perl6.png (offsite png image)

REXX

Digital rain note: This REXX program favors the use of Latin letters (both lower and uppercase) letters over all others characters (glyphs) by a 25% factor. <lang rexx>/*REXX program creates/displays Matrix (the movie) digital rain; favors non-Latin chars.*/ signal on halt /*allow the user to halt/stop this pgm.*/ parse arg pc seed . /*obtain optional arguments from the CL*/ if pc== | pc=="," then pc= 20 /*Not specified? Then use the default.*/ if datatype(seed, 'W') then call random ,,seed /*Numeric? Use seed for repeatability.*/ parse value scrsize() with sd sw . /*obtain the dimensions of the screen. */ if sd==0 then sd= 54; sd= sd - 2 + 1 /*Not defined? Then use default; adjust*/ if sw==0 then sw= 80; sw= sw - 1 /* " " " " " " */ lowC= c2d(' ') + 1 /*don't use any characters ≤ a blank.*/ @.= ' ' /*PC is the % new Matric rain streams.*/ cloud= copies(@., sw) /*the cloud, where matrix rain is born.*/ cls= 'CLS' /*DOS command used to clear the screen.*/

                 do  forever;   call nimbus     /*define bottom of cloud  (the drops). */
                                call rain       /*generate rain, display the raindrops.*/
                 end   /*j*/

halt: exit /*stick a fork in it, we're all done. */ /*──────────────────────────────────────────────────────────────────────────────────────*/ rain: do a=sd by -1 for sd-1; _= a-1; @.a= @._; end; call fogger; return show: cls; @.1= cloud; do r=1 for sd; say strip(@.r, 'T'); end /*r*/; return /*──────────────────────────────────────────────────────────────────────────────────────*/ nimbus: if random(, 100)<pc then call mist /*should this be a new rain stream ? */

                            else call unmist    /*should any of the rain streams cease?*/
       return                                   /*note: this subroutine may pass──►MIST*/
       if random(, 100)<pc         then return  /*should this be a new rain stream ?   */
       ?= random(1, sw)                         /*pick a random rain cloud position.   */
       if substr(cloud,?,1)\==' '  then return  /*Is cloud position not a blank? Return*/

/*───── ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ────────────────────────────────────────────────────*/ mist: ?= random(1, sw) /*obtain a random column in cloud. */

       if substr(cloud,?,1)\==' '  then return  /*if this stream is active, return.    */
       if random(, 100)<pc         then return  /*should this be a new rain stream ?   */
       cloud= overlay(drop(), cloud, ?)         /*seed cloud with new matrix rain drop.*/
       return

/*──────────────────────────────────────────────────────────────────────────────────────*/ unmist: ?= random(1, sw) /*obtain a random column in cloud. */

       if substr(cloud,?,1) ==' '  then return  /*if this stream is dry,  return.      */
       if random(, 100)>pc         then return  /*should this be a new dry stream ?    */
       cloud= overlay(' ', cloud, ?);   return  /*seed cloud with new matrix rain drop.*/

/*──────────────────────────────────────────────────────────────────────────────────────*/ drop: Lat= random(1, 4) /*Now, chose a matrix rain stream char.*/

       tChr= 254;    if Lat==1  then tChr= 127  /*choose the  type of rain stream char.*/
       return d2c( random(lowC, tChr) )         /*Lat = 1?   This favors Latin letters.*/

/*──────────────────────────────────────────────────────────────────────────────────────*/ fogger: do f=1 for sw /*display a screen full of rain streams*/

       if substr(cloud, f, 1) \== ' '   then cloud= overlay( drop(), cloud, f)
       end   /*f*/;        call show;   return  /* [↑]  if raindrop, then change drop. */</lang>

Programming note:

The use of random(, 100) is
the same as random(0, 100) (inclusive).

This REXX program makes use of SCRSIZE REXX program (or BIF) which is used to determine the screen
width and depth of the terminal (console). Some REXXes don't have this BIF.

The SCRSIZE.REX REXX program is included here ───► SCRSIZE.REX.

output when using the default input:

(A screen snapshot shown at half size.)

              ░      O       3              k       ò         cº     Θ     &           F
              ~      Ö       ¡              )       Å         tπ     ÷     ç           ╛
              a      ±       █              q       L         P}     8     ╕           y
              Ü      d       |              Γ       1         P»     ≥     ╙           ù
              ╖      ¥       9              ╠       ▒         SÉ     k     ╟           }
              o      U       '              Æ       í         (N     E     C           0
              e      2       ╜              ─       ₧         bH     ï     Z           ╢
              o      å       -              S       2         ò┘     ║     P           ╖
              s      @       ê              ≈       ╝         ·v     F     4           û
              Æ      k       ┤              .ÿ      s         ╕@     b     U           ^
              9      ╩       «              ┐·      w         ╛-     e     U           =
              ≈      a       ┬              δu      ┬         ît     ╤     ╖           σ
              N      Ä       F              'N      @         ╒R     φ     O
              ô      @       Y              ÷x      X         ∩P     ¡     8
              9      ║       ╔              #■      ▌         d%     v     «
              ô      m       I              xm      :         Um     E     &
              ╚      »       r              >       ~         H@     /     ┤
              ⌂      k       E              1       ╜         Wc     J     s
              8      g       E              m       ƒ         Ωε     q     U
              V      ë       &              |       ï         ■~     ≥     X
              à      Ö       .              î       3         ₧=     ⌂     ±
              π      ì       è              n       ┬         ·▌     Z     W
              ¢      6       n              S       £         [x     £     {
              '      &       ?              ╖       )         jÑ     ╞     α
              î      ╔       x              F       ╨         ☺▌     7     ┘
              á      ë       j              *       -         rⁿ     ú     )
              '      S       ╥              ∙       E         v≡     o     ú
              .      <       V              ²       °         ]G     7     H
              p      8       ╣              o       ╤         FÇ     S      
              ┴      t       ö              ^       ╣         n╟     ╕     >
              *      æ       ò              ╡       4         d_     ├     «
              ╔      â       -              Q       P         un     ≥     M
              6      ²       ╢              ╔       E         ≤A     °     *
              /      :       q              L       R         cë     %     ≡
              3      x       $              ⌡       ¥         .Ω     E     :
              E      ┤       y              i       U         Z      ú     O
              ⌂      Σ                      .       ¥         }      Ä     °
              V      φ                              ≤         ╙      ╫     j
              }      à                      ?       3         '      ≤     .
              í      ▐                      ╞       =         ~      Ä     ç
              B      î                      ö                 (      ¬     ╘
              ┬      [                      6                 ═      ╡     ▌
              r      %                      f                 ╔      [     C
         _    {      è                      %                 ╫      ▒     Z
         1    ≈      ]                      !                 -      ╨     o        ¢
              ?      ÿ                      9                 Å      e     ß        σ
         µ    ■      α                      Z                 h      4     ⌠        4
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Wren

Translation of: Yabasic

Library: DOME

The memory.ttf file is included with the DOME 'fonts' example and can be downloaded from here. <lang ecmascript>import "dome" for Window import "graphics" for Canvas, Color, Font import "random" for Random

var Rand = Random.new()

class MatrixDigitalRain {

   construct new(width, height) {
       Window.resize(width, height)
       Canvas.resize(width, height)
       Window.title = "Matrix digital rain"
       Font.load("Mem12", "memory.ttf", 24)
       Canvas.font = "Mem12"
   }

   letter(x, y, r, g, b) {
       if (y < 0 || y >= _my) return
       var col = Color.rgb(r, g, b)
       var c = String.fromByte(_scr[x][y])
       Canvas.print(c, x * 12.8 , y * 12.8 , col)
   }

   init() {
       _mx = 50
       _my = 42
       _scr = List.filled(_mx, null)
       for (x in 0..._mx) {
           _scr[x] = List.filled(_my, 0)
           for (y in 0..._my) _scr[x][y] = Rand.int(33, 128)
       }
       _ms = 50
       _sx = List.filled(_ms, 0)
       _sy = List.filled(_ms, 0)
   }

   update() {
       for (a in 0..._ms) {
           _sx[a] = Rand.int(_mx)
           _sy[a] = Rand.int(_my)
       }
   }

   draw(alpha) {
       for (s in 0..._ms) {
           var x = _sx[s]
           var y = _sy[s]
           letter(x, y, 0, 255, 0)
           y = y - 1
           letter(x, y, 0, 200, 0)
           y = y - 1
           letter(x, y, 0, 150, 0)
           y = y - 1
           if (y*12.8 + 3 < 0) y = 0
           var c = Color.rgb(0, 0, 0)
           Canvas.rectfill(x*12.8, y*12.8 + 3, 13, 14, c)
           letter(x, y, 0, 70, 0)
           y = y - 24
           if (y*12.8 + 3 < 0) y = 0
           Canvas.rectfill(x*12.8, y*12.8  + 3, 13, 14, c)
       }
       for (s in 0..._ms) {
           if (Rand.int(1, 6) == 1) _sy[s] = _sy[s] + 1
           if (_sy[s] > _my + 25) {
               _sy[s] = 0
               _sx[s] = Rand.int(_mx)
           }
       }               
   }

}

var Game = MatrixDigitalRain.new(640, 550)</lang>

Yabasic

<lang Yabasic>open window 640,512,"swiss12" backcolor 0,0,0 clear window mx=50 my=42 dim scr(mx,my) for y=0 to my

   for x=0 to mx
       scr(x,y)=int(ran(96)+33)
   next x

next y ms=50 dim sx(ms) dim sy(ms) for a=1 to ms

   sx(a)=int(ran(mx))
   sy(a)=int(ran(my))

next a do

   for s=1 to ms
       x=sx(s)
       y=sy(s)
       
       letter(0,255,0)
       y=y-1
       
       letter(0,200,0)
       y=y-1
       
       letter(0,150,0)
       y=y-1
       
       color 0,0,0
       fill rect x*12.8-1,y*12.8+4 to x*12.8+12,y*12.8-10
       letter(0,70,0)
       y=y-24
       
       color 0,0,0
       fill rect x*12.8-1,y*12.8+4 to x*12.8+12,y*12.8-10
   next s
   for s=1 to ms
       if int(ran(5)+1)=1 sy(s)=sy(s)+1
       if sy(s)>my+25 then
           sy(s)=0
           sx(s)=int(ran(mx))
       end if
   next s

loop

sub letter(r,g,b)

   if y<0 or y>my return
   c=scr(x,y)
   color r,g,b
   text x*12.8,y*12.8,chr$(c)

end sub</lang>

zkl

Translation of: Raku

<lang zkl>var [const] codes=Walker.chain( // a bunch of UTF non ascii chars

        [0x0391..0x03a0], [0x03a3..0x0475], [0x0400..0x0475],
        [0x048a..0x052f], [0x03e2..0x03ef], [0x2c80..0x2ce9],
        [0x2200..0x2217], [0x2100..0x213a], [0x2a00..0x2aff])

.apply(fcn(utf){ utf.toString(-8) }), // jeez this is lame

   codeSz=codes.len(),	// 970
   c=L("\e[38;2;255;255;255m",[255..30,-15].apply("\e[38;2;0;%d;0m".fmt),
       (250).pump(List,T(Void,"\e[38;2;0;25;0m"))).flatten(),
   csz=c.len(); // 267, c is ANSI escape code fg colors: 38;2;<r;g;b>m

// query the ANSI terminal rows,cols := System.popen("stty size","r").readln().split().apply("toInt");

o,s,fg := buildScreen(rows,cols); ssz:=s.len();

print("\e[?25l\e[48;5;232m"); // hide the cursor, set background color to dark while(1){ // ignore screen resizes

  print("\e[1;1H");	       // move cursor to 1,1
  foreach n in (ssz){	       // print a screen full
     print( c[fg[n]], s[n] ); // forground color, character
     fg[n]=(fg[n] + 1)%csz;   // fade to black
  }
  do(100){ s[(0).random(ssz)]=codes[(0).random(codeSz)] }  // some new chars
  Atomic.sleep(0.1);	       // frame rate for my system, up to 200x41 terminal

}

fcn buildScreen(rows,cols){ // build a row major array as list

  // s --> screen full of characters
  s:=(rows*cols).pump(List(), fcn{ codes[(0).random(codeSz)]});
  // array fb-->( fg color, fg ..) where fg is an ANSI term 48;5;<n>m color
  fg:=List.createLong(s.len(),0);
  o:=csz.pump(List()).shuffle()[0,cols];  // cols random #s
  foreach row in (rows){		   // set fg indices
     foreach col in (cols){ fg[row*cols + col] = o[col] }
     o=o.apply(fcn(n){ n-=1; if(n<0) n=csz-1; n%csz });  // fade out
  }
  return(o,s,fg);

}</lang> Offsite Image: Matrix rain dance

ZX Spectrum Basic

Appallingly slow (full speed on an emulator strongly recommended), but it works.

Authentic Matrix code includes reversed Latin characters and half-width Japanese. The Spectrum doesn't have anything like the space in the glyphs to support legible Japanese, but this program does use a machine code routine to generate a reversed Spectrum character set - and an upside down one and an upside down and reversed one, for good measure. (This could be duplicated in Basic but the program is slow enough as it is - ZX Spectrum Basic has no bitwise operations.) If you don't want to use the machine code (because this is a Basic demonstration, after all), or the alternate character sets, delete lines 30 and 4000; this will leave you with standard upright characters.

The left-right flip portion of the machine code routine is by John Metcalf, borrowed from his blog. (He has also posted a routine for the Matrix rain in Spectrum Z80 Assembly; his method, filling the screen with characters first and then applying the attributes, was one I had independently considered for this routine, but I didn't feel it resulted in enough character change.)

The PEEKs and POKEs throughout the routine are used for attribute handling. PEEK (22528+32*x+y) is the same thing as ATTR (x,y).

The next step for this routine would be a way to randomise the length of the character trails (currently fixed at 12).

<lang zxbasic>10 CLEAR 61999 20 BORDER 0: POKE 23624,4: POKE 23693,0: CLS: REM easier than "bright 0: flash 0: ink 0: paper 0" 30 PRINT INK 4; FLASH 1;"Initialising": GO SUB 9000: LET m=USR 62000: CLS: REM set up and run machine code; USR is the call function 40 DIM s(32,2): REM current top and bottom of character sequence for each of the 32 spaces across the screen

50 FOR x=1 TO 32: REM main loop 60 IF s(x,1)=0 AND RND>.95 THEN LET s(x,1)=1: LET s(x,2)=2: GO SUB 4000: GO SUB 3000: GO TO 80: REM start a new column; decrease the .95 modifier for a busier - but slower - screen 70 IF s(x,2)>0 THEN GO SUB 1000 80 NEXT x 90 FOR l=1 TO 10: REM matrix code switches existing glyphs occasionally 100 LET x=INT (RND*22): LET y=INT (RND*32) 110 IF PEEK (22528+32*x+y)=0 THEN GO TO 140: REM no point updating a blank space 120 GO SUB 4000 130 PRINT AT x,y; INK 8; BRIGHT 8;CHR$ (33+RND*95): REM ink 8 and bright 8 tells it to keep the cell's existing ink and bright values 140 NEXT l 150 GO TO 50

999 REM continue an existing column 1000 LET s(x,2)=s(x,2)+1 1010 IF s(x,2)<21 THEN GO SUB 3000 1020 IF s(x,2)>12 THEN LET s(x,1)=s(x,1)+1 1030 LET k=2 1040 GO SUB 2000 1050 LET k=6 1060 GO SUB 2000 1070 LET k=12 1080 GO SUB 2000 1090 IF s(x,1)=22 THEN LET s(x,1)=0: LET s(x,2)=0 1100 RETURN

1999 REM update colour 2000 LET a=22527+x+32*(s(x,2)-k) 2010 LET c=PEEK a 2020 IF c=4 THEN POKE a,0 2030 IF c=68 THEN POKE a,4 2040 IF c=71 THEN POKE a,68: REM this poke could be done with 'print at s(x,2)-k-1,x-1; ink 4; bright 1; over 1; " " ' but poking is FAR easier, especially considering the above pokes would be similar 2050 RETURN

2999 REM new character at bottom of column 3000 PRINT AT s(x,2)-1,x-1; INK 7; BRIGHT 1;CHR$ (33+RND*95) 3010 RETURN

3999 REM select character set 4000 POKE 23607,242+3*INT (RND*4): REM the spectrum character set is pointed to by the two-byte system value CHARS at 23606 and 23607, so repoking this selects a new character set - the machine code below has created four copies of the character set at suitable locations 4010 RETURN

8999 REM machine code routine to create multiple character sets 9000 RESTORE 9800 9010 LET h$="0123456789ABCDEF" 9020 LET o=62000 9030 IF PEEK o=33 AND PEEK 62121=201 THEN RETURN: REM saves storing it all again if the machine code is already there 9040 READ a$ 9050 IF a$="eof" THEN RETURN 9060 FOR x=1 TO 8 9070 LET n=0 9080 LET s=(x*2)-1 9090 LET t=s+1 9100 FOR m=1 TO 16 9110 IF h$(m)=a$(s) THEN LET n=n+16*(m-1) 9120 IF h$(m)=a$(t) THEN LET n=n+m-1 9130 NEXT m 9140 POKE o,n 9150 LET o=o+1 9160 NEXT x 9170 GO TO 9040

9800 DATA "21003D1100F30100" 9810 DATA "03EDB02100F31100" 9820 DATA "F6010009EDB01100" 9830 DATA "F901FF051A6F0707" 9840 DATA "ADE6AAAD6F070707" 9850 DATA "CB0DADE666AD1213" 9860 DATA "0B78B120E721FFF5" 9870 DATA "010000E5CD8BF2E1" 9880 DATA "E5CD8BF2E1E5CD8B" 9890 DATA "F2E1CD8BF2232323" 9900 DATA "23AF470C79FEC0C2" 9910 DATA "6BF2C9E5D1043E09" 9920 DATA "90835F8A93577885" 9930 DATA "6F8C95671AE521AA" 9940 DATA "F277E17E123AAAF2" 9950 DATA "77C9000000000000" 9960 DATA "eof"

9999 POKE 23606,0: POKE 23607,60: INK 4: REM reset to default character set and colour if you get lost</lang>

Offsite Image: Spectrum rain at imgur

@@ Line 2,043: / Line 2,043: @@
 {{trans|Yabasic}}
 {{libheader|DOME}}
-The ''memory.ttf'' file is included with the DOM 'fonts' example and can be downloaded from [https://github.com/domeengine/dome/blob/main/examples/fonts/memory.ttf here].
+The ''memory.ttf'' file is included with the DOME 'fonts' example and can be downloaded from [https://github.com/domeengine/dome/blob/main/examples/fonts/memory.ttf here].
 <lang ecmascript>import "dome" for Window
 import "graphics" for Canvas, Color, Font