Setting Up and Tearing Down a Curses Program

Problem

To write a program that uses Curses or Ncurses, you have to write a lot of setup and cleanup code. Youd like to factor that out.

Solution

Heres a wrapper method that sets up the Curses library and passes the main screen object into a code block:

	require curses

	module Curses
	 def self.program
	 main_screen = init_screen
	 noecho
	 cbreak
	 curs_set(0)
	 main_screen.keypad = true
	 yield main_screen
	 end
	end

Heres a simple Ruby program that uses the wrapper method to fill up the screen with random placements of a given string:

	Curses.program do |scr|
	 str = ARGV[0] || Test
	 max_x = scr.maxx-str.size+1
	 max_y = scr.maxy
	 100.times do
	 scr.setpos(rand(max_y), rand(max_x))
	 scr.addstr(str)
	 end
	 scr.getch
	end

Discussion

The initialization, which is hidden in Curses.program, does the following things:

• Stops keystrokes from being echoed to the screen (noecho)
• Hides the cursor (curs_set(0))
• Turns off buffered input so keys can be processed as they e typed (cbreak)
• Makes the keyboards arrow keys generate recognizable key events (keypad=true)

The code is a little different if you e using the third-party ncurses binding instead of the curses library that comes with Ruby. The main difference is that with ncurses, you must write some of the cleanup code that the curses library handles automatically. A wrapper method is also a good place to set up the ncurses color code if you plan to use colored text (see Recipe 21.8 for more on this).

Heres an Ncurses.program method thats equivalent to Curses.program, except that it performs its cleanup manually by registering an at_exit block to run just before the interpreter exits. This wrapper also turns on color and initializes a few default color pairs. If your terminal has no color support, the color code will run but it won do anything.

	require 
curses

	module Ncurses
	 COLORS = [COLOR_BLACK, COLOR_RED, COLOR_GREEN, COLOR_YELLOW, COLOR_BLUE,
	 COLOR_MAGENTA, COLOR_CYAN, COLOR_WHITE]

	 def self.program
	 stdscr = Ncurses.initscr

	 # Run ncurses 
cleanup code when the program exits.
	 at_exit do
	 echo
	 nocbreak
	 curs_set(1)
	 stdscr.keypad(0)
	 endwin
	 end

	 noecho
	 cbreak
	 curs_set(0)
	 stdscr.keypad(1)
	 start_color

	 COLORS[1…COLORS.size].each_with_index do |color, i|
	 init_pair(i+1, color, COLOR_BLACK)
	 end

	 yield stdscr
	 end
	end

Heres the ncurses equivalent of the curses program given earlier:

	Ncurses.program do |scr|
	 str = ARGV[0] || Test
	 max_y, max_x = [], []
	 scr.getmaxyx(max_y, max_x)
	 max_y = max_y[0]
	 max_x = max_x[0] - str.size + 1
	 100.times do
	 scr.mvaddstr(rand(max_y), rand(max_x), str)
	 end
	 scr.getch
	end

See Also

• See this chapters introduction for information on installing Ncurses
• "Writing Programs with NCURSES" is a good general overview of the Ncurses library; its written for C programmers, but its useful for Rubyists because Rubys interfaces to Curses and Ncurses are little more than wrappers (http://dickey.his.com/ncurses/ncurses-intro.html)