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-</HEAD>
-<BODY>
-
-<H1>A Hacker's Guide to NCURSES</H1>
-
-<H1>Contents</H1>
-<UL>
-<LI><A HREF="#abstract">Abstract</A>
-<LI><A HREF="#objective">Objective of the Package</A>
-<UL>
-<LI><A HREF="#whysvr4">Why System V Curses?</A>
-<LI><A HREF="#extensions">How to Design Extensions</A>
-</UL>
-<LI><A HREF="#portability">Portability and Configuration</A>
-<LI><A HREF="#documentation">Documentation Conventions</A>
-<LI><A HREF="#bugtrack">How to Report Bugs</A>
-<LI><A HREF="#ncurslib">A Tour of the Ncurses Library</A>
-<UL>
-<LI><A HREF="#loverview">Library Overview</A>
-<LI><A HREF="#engine">The Engine Room</A>
-<LI><A HREF="#input">Keyboard Input</A>
-<LI><A HREF="#mouse">Mouse Events</A>
-<LI><A HREF="#output">Output and Screen Updating</A>
-</UL>
-<LI><A HREF="#fmnote">The Forms and Menu Libraries</A>
-<LI><A HREF="#tic">A Tour of the Terminfo Compiler</A>
-<UL>
-<LI><A HREF="#nonuse">Translation of Non-<STRONG>use</STRONG> Capabilities</A>
-<LI><A HREF="#uses">Use Capability Resolution</A>
-<LI><A HREF="#translation">Source-Form Translation</A>
-</UL>
-<LI><A HREF="#utils">Other Utilities</A>
-<LI><A HREF="#style">Style Tips for Developers</A>
-<LI><A HREF="#port">Porting Hints</A>
-</UL>
-
-<H1><A NAME="abstract">Abstract</A></H1>
-
-This document is a hacker's tour of the <STRONG>ncurses</STRONG> library and utilities.
-It discusses design philosophy, implementation methods, and the
-conventions used for coding and documentation. It is recommended
-reading for anyone who is interested in porting, extending or improving the
-package.
-
-<H1><A NAME="objective">Objective of the Package</A></H1>
-
-The objective of the <STRONG>ncurses</STRONG> package is to provide a free software API for
-character-cell terminals and terminal emulators with the following
-characteristics:
-
-<UL>
-<LI>Source-compatible with historical curses implementations (including
- the original BSD curses and System V curses.
-<LI>Conformant with the XSI Curses standard issued as part of XPG4 by
- X/Open.
-<LI>High-quality -- stable and reliable code, wide portability, good
- packaging, superior documentation.
-<LI>Featureful -- should eliminate as much of the drudgery of C interface
- programming as possible, freeing programmers to think at a higher
- level of design.
-</UL>
-
-These objectives are in priority order. So, for example, source
-compatibility with older version must trump featurefulness -- we cannot
-add features if it means breaking the portion of the API corresponding
-to historical curses versions.
-
-<H2><A NAME="whysvr4">Why System V Curses?</A></H2>
-
-We used System V curses as a model, reverse-engineering their API, in
-order to fulfill the first two objectives. <P>
-
-System V curses implementations can support BSD curses programs with
-just a recompilation, so by capturing the System V API we also
-capture BSD's. <P>
-
-More importantly for the future, the XSI Curses standard issued by X/Open
-is explicitly and closely modeled on System V. So conformance with
-System V took us most of the way to base-level XSI conformance.
-
-<H2><A NAME="extensions">How to Design Extensions</A></H2>
-
-The third objective (standards conformance) requires that it be easy to
-condition source code using <STRONG>ncurses</STRONG> so that the absence of nonstandard
-extensions does not break the code. <P>
-
-Accordingly, we have a policy of associating with each nonstandard extension
-a feature macro, so that ncurses client code can use this macro to condition
-in or out the code that requires the <STRONG>ncurses</STRONG> extension. <P>
-
-For example, there is a macro <CODE>NCURSES_MOUSE_VERSION</CODE> which XSI Curses
-does not define, but which is defined in the <STRONG>ncurses</STRONG> library header.
-You can use this to condition the calls to the mouse API calls.
-
-<H1><A NAME="portability">Portability and Configuration</A></H1>
-
-Code written for <STRONG>ncurses</STRONG> may assume an ANSI-standard C compiler and
-POSIX-compatible OS interface. It may also assume the presence of a
-System-V-compatible <EM>select(2)</EM> call. <P>
-
-We encourage (but do not require) developers to make the code friendly
-to less-capable UNIX environments wherever possible. <P>
-
-We encourage developers to support OS-specific optimizations and methods
-not available under POSIX/ANSI, provided only that:
-
-<UL>
-<LI>All such code is properly conditioned so the build process does not
- attempt to compile it under a plain ANSI/POSIX environment.
-<LI>Adding such implementation methods does not introduce incompatibilities
- in the <STRONG>ncurses</STRONG> API between platforms.
-</UL>
-
-We use GNU <CODE>autoconf(1)</CODE> as a tool to deal with portability issues.
-The right way to leverage an OS-specific feature is to modify the autoconf
-specification files (configure.in and aclocal.m4) to set up a new feature
-macro, which you then use to condition your code.
-
-<H1><A NAME="documentation">Documentation Conventions</A></H1>
-
-There are three kinds of documentation associated with this package. Each
-has a different preferred format:
-
-<UL>
-<LI>Package-internal files (README, INSTALL, TO-DO etc.)
-<LI>Manual pages.
-<LI>Everything else (i.e., narrative documentation).
-</UL>
-
-Our conventions are simple:
-<OL>
-<LI><STRONG>Maintain package-internal files in plain text.</STRONG>
- The expected viewer for them <EM>more(1)</EM> or an editor window; there's
- no point in elaborate mark-up.
-
-<LI><STRONG>Mark up manual pages in the man macros.</STRONG> These have to be viewable
- through traditional <EM>man(1)</EM> programs.
-
-<LI><STRONG>Write everything else in HTML.</STRONG>
-</OL>
-
-When in doubt, HTMLize a master and use <EM>lynx(1)</EM> to generate
-plain ASCII (as we do for the announcement document). <P>
+</head>
+
+<body>
+ <h1>A Hacker's Guide to NCURSES</h1>
+
+ <h1>Contents</h1>
+
+ <ul>
+ <li><a href="#abstract">Abstract</a></li>
+
+ <li>
+ <a href="#objective">Objective of the Package</a>
+
+ <ul>
+ <li><a href="#whysvr4">Why System V Curses?</a></li>
+
+ <li><a href="#extensions">How to Design Extensions</a></li>
+ </ul>
+ </li>
+
+ <li><a href="#portability">Portability and
+ Configuration</a></li>
+
+ <li><a href="#documentation">Documentation Conventions</a></li>
+
+ <li><a href="#bugtrack">How to Report Bugs</a></li>
+
+ <li>
+ <a href="#ncurslib">A Tour of the Ncurses Library</a>
+
+ <ul>
+ <li><a href="#loverview">Library Overview</a></li>
+
+ <li><a href="#engine">The Engine Room</a></li>
+
+ <li><a href="#input">Keyboard Input</a></li>
+
+ <li><a href="#mouse">Mouse Events</a></li>
+
+ <li><a href="#output">Output and Screen Updating</a></li>
+ </ul>
+ </li>
+
+ <li><a href="#fmnote">The Forms and Menu Libraries</a></li>
+
+ <li>
+ <a href="#tic">A Tour of the Terminfo Compiler</a>
+
+ <ul>
+ <li><a href="#nonuse">Translation of
+ Non-<strong>use</strong> Capabilities</a></li>
+
+ <li><a href="#uses">Use Capability Resolution</a></li>
+
+ <li><a href="#translation">Source-Form Translation</a></li>
+ </ul>
+ </li>
+
+ <li><a href="#utils">Other Utilities</a></li>
+
+ <li><a href="#style">Style Tips for Developers</a></li>
+
+ <li><a href="#port">Porting Hints</a></li>
+ </ul>
+
+ <h1><a name="abstract" id="abstract">Abstract</a></h1>
+
+ <p>This document is a hacker's tour of the
+ <strong>ncurses</strong> library and utilities. It discusses
+ design philosophy, implementation methods, and the conventions
+ used for coding and documentation. It is recommended reading for
+ anyone who is interested in porting, extending or improving the
+ package.</p>
+
+ <h1><a name="objective" id="objective">Objective of the
+ Package</a></h1>
+
+ <p>The objective of the <strong>ncurses</strong> package is to
+ provide a free software API for character-cell terminals and
+ terminal emulators with the following characteristics:</p>
+
+ <ul>
+ <li>Source-compatible with historical curses implementations
+ (including the original BSD curses and System V curses.</li>
+
+ <li>Conformant with the XSI Curses standard issued as part of
+ XPG4 by X/Open.</li>
+
+ <li>High-quality — stable and reliable code, wide
+ portability, good packaging, superior documentation.</li>
+
+ <li>Featureful — should eliminate as much of the drudgery
+ of C interface programming as possible, freeing programmers to
+ think at a higher level of design.</li>
+ </ul>
+
+ <p>These objectives are in priority order. So, for example,
+ source compatibility with older version must trump featurefulness
+ — we cannot add features if it means breaking the portion
+ of the API corresponding to historical curses versions.</p>
+
+ <h2><a name="whysvr4" id="whysvr4">Why System V Curses?</a></h2>
+
+ <p>We used System V curses as a model, reverse-engineering their
+ API, in order to fulfill the first two objectives.</p>
+
+ <p>System V curses implementations can support BSD curses
+ programs with just a recompilation, so by capturing the System V
+ API we also capture BSD's.</p>
+
+ <p>More importantly for the future, the XSI Curses standard
+ issued by X/Open is explicitly and closely modeled on System V.
+ So conformance with System V took us most of the way to
+ base-level XSI conformance.</p>
+
+ <h2><a name="extensions" id="extensions">How to Design
+ Extensions</a></h2>
+
+ <p>The third objective (standards conformance) requires that it
+ be easy to condition source code using <strong>ncurses</strong>
+ so that the absence of nonstandard extensions does not break the
+ code.</p>
+
+ <p>Accordingly, we have a policy of associating with each
+ nonstandard extension a feature macro, so that ncurses client
+ code can use this macro to condition in or out the code that
+ requires the <strong>ncurses</strong> extension.</p>
+
+ <p>For example, there is a macro
+ <code>NCURSES_MOUSE_VERSION</code> which XSI Curses does not
+ define, but which is defined in the <strong>ncurses</strong>
+ library header. You can use this to condition the calls to the
+ mouse API calls.</p>
+
+ <h1><a name="portability" id="portability">Portability and
+ Configuration</a></h1>
+
+ <p>Code written for <strong>ncurses</strong> may assume an
+ ANSI-standard C compiler and POSIX-compatible OS interface. It
+ may also assume the presence of a System-V-compatible
+ <em>select(2)</em> call.</p>
+
+ <p>We encourage (but do not require) developers to make the code
+ friendly to less-capable UNIX environments wherever possible.</p>
+
+ <p>We encourage developers to support OS-specific optimizations
+ and methods not available under POSIX/ANSI, provided only
+ that:</p>
+
+ <ul>
+ <li>All such code is properly conditioned so the build process
+ does not attempt to compile it under a plain ANSI/POSIX
+ environment.</li>
+
+ <li>Adding such implementation methods does not introduce
+ incompatibilities in the <strong>ncurses</strong> API between
+ platforms.</li>
+ </ul>
+
+ <p>We use GNU <code>autoconf(1)</code> as a tool to deal with
+ portability issues. The right way to leverage an OS-specific
+ feature is to modify the autoconf specification files
+ (configure.in and aclocal.m4) to set up a new feature macro,
+ which you then use to condition your code.</p>
+
+ <h1><a name="documentation" id="documentation">Documentation
+ Conventions</a></h1>
+
+ <p>There are three kinds of documentation associated with this
+ package. Each has a different preferred format:</p>
+
+ <ul>
+ <li>Package-internal files (README, INSTALL, TO-DO etc.)</li>
+
+ <li>Manual pages.</li>
-The reason for choosing HTML is that it's (a) well-adapted for on-line
-browsing through viewers that are everywhere; (b) more easily readable
-as plain text than most other mark-ups, if you don't have a viewer; and (c)
-carries enough information that you can generate a nice-looking printed
-version from it. Also, of course, it make exporting things like the
-announcement document to WWW pretty trivial.
-
-<H1><A NAME="bugtrack">How to Report Bugs</A></H1>
-
-The <A NAME="bugreport">reporting address for bugs</A> is
-<A HREF="mailto:bug-ncurses@gnu.org">bug-ncurses@gnu.org</A>.
-This is a majordomo list; to join, write
-to <CODE>bug-ncurses-request@gnu.org</CODE> with a message containing the line:
-<PRE>
+ <li>Everything else (i.e., narrative documentation).</li>
+ </ul>
+
+ <p>Our conventions are simple:</p>
+
+ <ol>
+ <li><strong>Maintain package-internal files in plain
+ text.</strong> The expected viewer for them <em>more(1)</em> or
+ an editor window; there is no point in elaborate mark-up.</li>
+
+ <li><strong>Mark up manual pages in the man macros.</strong>
+ These have to be viewable through traditional <em>man(1)</em>
+ programs.</li>
+
+ <li><strong>Write everything else in HTML.</strong></li>
+ </ol>
+
+ <p>When in doubt, HTMLize a master and use <em>lynx(1)</em> to
+ generate plain ASCII (as we do for the announcement
+ document).</p>
+
+ <p>The reason for choosing HTML is that it is (a) well-adapted
+ for on-line browsing through viewers that are everywhere; (b)
+ more easily readable as plain text than most other mark-ups, if
+ you do not have a viewer; and (c) carries enough information that
+ you can generate a nice-looking printed version from it. Also, of
+ course, it make exporting things like the announcement document
+ to WWW pretty trivial.</p>
+
+ <h1><a name="bugtrack" id="bugtrack">How to Report Bugs</a></h1>
+
+ <p>The <a name="bugreport" id="bugreport">reporting address for
+ bugs</a> is <a href=
+ "mailto:bug-ncurses@gnu.org">bug-ncurses@gnu.org</a>. This is a
+ majordomo list; to join, write to
+ <code>bug-ncurses-request@gnu.org</code> with a message
+ containing the line:</p>
+ <pre>
subscribe <name>@<host.domain>
-</PRE>
-
-The <CODE>ncurses</CODE> code is maintained by a small group of
-volunteers. While we try our best to fix bugs promptly, we simply
-don't have a lot of hours to spend on elementary hand-holding. We rely
-on intelligent cooperation from our users. If you think you have
-found a bug in <CODE>ncurses</CODE>, there are some steps you can take
-before contacting us that will help get the bug fixed quickly. <P>
-
-In order to use our bug-fixing time efficiently, we put people who
-show us they've taken these steps at the head of our queue. This
-means that if you don't, you'll probably end up at the tail end and
-have to wait a while.
-
-<OL>
-<LI>Develop a recipe to reproduce the bug.
-<p>
-Bugs we can reproduce are likely to be fixed very quickly, often
-within days. The most effective single thing you can do to get a
-quick fix is develop a way we can duplicate the bad behavior --
-ideally, by giving us source for a small, portable test program that
-breaks the library. (Even better is a keystroke recipe using one of
-the test programs provided with the distribution.)
-
-<LI>Try to reproduce the bug on a different terminal type. <P>
-
-In our experience, most of the behaviors people report as library bugs
-are actually due to subtle problems in terminal descriptions. This is
-especially likely to be true if you're using a traditional
-asynchronous terminal or PC-based terminal emulator, rather than xterm
-or a UNIX console entry. <P>
-
-It's therefore extremely helpful if you can tell us whether or not your
-problem reproduces on other terminal types. Usually you'll have both
-a console type and xterm available; please tell us whether or not your
-bug reproduces on both. <P>
-
-If you have xterm available, it is also good to collect xterm reports for
-different window sizes. This is especially true if you normally use an
-unusual xterm window size -- a surprising number of the bugs we've seen
-are either triggered or masked by these.
-
-<LI>Generate and examine a trace file for the broken behavior. <P>
-
-Recompile your program with the debugging versions of the libraries.
-Insert a <CODE>trace()</CODE> call with the argument set to <CODE>TRACE_UPDATE</CODE>.
-(See <A HREF="ncurses-intro.html#debugging">"Writing Programs with
-NCURSES"</A> for details on trace levels.)
-Reproduce your bug, then look at the trace file to see what the library
-was actually doing. <P>
-
-Another frequent cause of apparent bugs is application coding errors
-that cause the wrong things to be put on the virtual screen. Looking
-at the virtual-screen dumps in the trace file will tell you immediately if
-this is happening, and save you from the possible embarrassment of being
-told that the bug is in your code and is your problem rather than ours. <P>
-
-If the virtual-screen dumps look correct but the bug persists, it's
-possible to crank up the trace level to give more and more information
-about the library's update actions and the control sequences it issues
-to perform them. The test directory of the distribution contains a
-tool for digesting these logs to make them less tedious to wade
-through. <P>
-
-Often you'll find terminfo problems at this stage by noticing that the
-escape sequences put out for various capabilities are wrong. If not,
-you're likely to learn enough to be able to characterize any bug in
-the screen-update logic quite exactly.
-
-<LI>Report details and symptoms, not just interpretations. <P>
-
-If you do the preceding two steps, it is very likely that you'll discover
-the nature of the problem yourself and be able to send us a fix. This
-will create happy feelings all around and earn you good karma for the first
-time you run into a bug you really can't characterize and fix yourself. <P>
-
-If you're still stuck, at least you'll know what to tell us. Remember, we
-need details. If you guess about what is safe to leave out, you are too
-likely to be wrong. <P>
-
-If your bug produces a bad update, include a trace file. Try to make
-the trace at the <EM>least</EM> voluminous level that pins down the
-bug. Logs that have been through tracemunch are OK, it doesn't throw
-away any information (actually they're better than un-munched ones because
-they're easier to read). <P>
-
-If your bug produces a core-dump, please include a symbolic stack trace
-generated by gdb(1) or your local equivalent. <P>
-
-Tell us about every terminal on which you've reproduced the bug -- and
-every terminal on which you can't. Ideally, sent us terminfo sources
-for all of these (yours might differ from ours). <P>
-
-Include your ncurses version and your OS/machine type, of course! You can
-find your ncurses version in the <CODE>curses.h</CODE> file.
-</OL>
-
-If your problem smells like a logic error or in cursor movement or
-scrolling or a bad capability, there are a couple of tiny test frames
-for the library algorithms in the progs directory that may help you
-isolate it. These are not part of the normal build, but do have their
-own make productions. <P>
-
-The most important of these is <CODE>mvcur</CODE>, a test frame for the
-cursor-movement optimization code. With this program, you can see
-directly what control sequences will be emitted for any given cursor
-movement or scroll/insert/delete operations. If you think you've got
-a bad capability identified, you can disable it and test again. The
-program is command-driven and has on-line help. <P>
-
-If you think the vertical-scroll optimization is broken, or just want to
-understand how it works better, build <CODE>hashmap</CODE> and read the
-header comments of <CODE>hardscroll.c</CODE> and <CODE>hashmap.c</CODE>; then try
-it out. You can also test the hardware-scrolling optimization separately
-with <CODE>hardscroll</CODE>. <P>
-
-<H1><A NAME="ncurslib">A Tour of the Ncurses Library</A></H1>
-
-<H2><A NAME="loverview">Library Overview</A></H2>
-
-Most of the library is superstructure -- fairly trivial convenience
-interfaces to a small set of basic functions and data structures used
-to manipulate the virtual screen (in particular, none of this code
-does any I/O except through calls to more fundamental modules
-described below). The files
-<blockquote>
-<CODE>
-lib_addch.c
-lib_bkgd.c
-lib_box.c
-lib_chgat.c
-lib_clear.c
-lib_clearok.c
-lib_clrbot.c
-lib_clreol.c
-lib_colorset.c
-lib_data.c
-lib_delch.c
-lib_delwin.c
-lib_echo.c
-lib_erase.c
-lib_gen.c
-lib_getstr.c
-lib_hline.c
-lib_immedok.c
-lib_inchstr.c
-lib_insch.c
-lib_insdel.c
-lib_insstr.c
-lib_instr.c
-lib_isendwin.c
-lib_keyname.c
-lib_leaveok.c
-lib_move.c
-lib_mvwin.c
-lib_overlay.c
-lib_pad.c
-lib_printw.c
-lib_redrawln.c
-lib_scanw.c
-lib_screen.c
-lib_scroll.c
-lib_scrollok.c
-lib_scrreg.c
-lib_set_term.c
-lib_slk.c
-lib_slkatr_set.c
-lib_slkatrof.c
-lib_slkatron.c
-lib_slkatrset.c
-lib_slkattr.c
-lib_slkclear.c
-lib_slkcolor.c
-lib_slkinit.c
-lib_slklab.c
-lib_slkrefr.c
-lib_slkset.c
-lib_slktouch.c
-lib_touch.c
-lib_unctrl.c
-lib_vline.c
-lib_wattroff.c
-lib_wattron.c
-lib_window.c
-</CODE>
-</blockquote>
-are all in this category. They are very
-unlikely to need change, barring bugs or some fundamental
-reorganization in the underlying data structures. <P>
-
-These files are used only for debugging support:
-<blockquote>
-<code>
-lib_trace.c
-lib_traceatr.c
-lib_tracebits.c
-lib_tracechr.c
-lib_tracedmp.c
-lib_tracemse.c
-trace_buf.c
-</code>
-</blockquote>
-It is rather unlikely you will ever need to change these, unless
-you want to introduce a new debug trace level for some reason.<P>
-
-There is another group of files that do direct I/O via <EM>tputs()</EM>,
-computations on the terminal capabilities, or queries to the OS
-environment, but nevertheless have only fairly low complexity. These
-include:
-<blockquote>
-<code>
-lib_acs.c
-lib_beep.c
-lib_color.c
-lib_endwin.c
-lib_initscr.c
-lib_longname.c
-lib_newterm.c
-lib_options.c
-lib_termcap.c
-lib_ti.c
-lib_tparm.c
-lib_tputs.c
-lib_vidattr.c
-read_entry.c.
-</code>
-</blockquote>
-They are likely to need revision only if
-ncurses is being ported to an environment without an underlying
-terminfo capability representation. <P>
-
-These files
-have serious hooks into
-the tty driver and signal facilities:
-<blockquote>
-<code>
-lib_kernel.c
-lib_baudrate.c
-lib_raw.c
-lib_tstp.c
-lib_twait.c
-</code>
-</blockquote>
-If you run into porting snafus
-moving the package to another UNIX, the problem is likely to be in one
-of these files.
-The file <CODE>lib_print.c</CODE> uses sleep(2) and also
-falls in this category.<P>
-
-Almost all of the real work is done in the files
-<blockquote>
-<code>
-hardscroll.c
-hashmap.c
-lib_addch.c
-lib_doupdate.c
-lib_getch.c
-lib_mouse.c
-lib_mvcur.c
-lib_refresh.c
-lib_setup.c
-lib_vidattr.c
-</code>
-</blockquote>
-Most of the algorithmic complexity in the
-library lives in these files.
-If there is a real bug in <STRONG>ncurses</STRONG> itself, it's probably here.
-We'll tour some of these files in detail
-below (see <A HREF="#engine">The Engine Room</A>). <P>
-
-Finally, there is a group of files that is actually most of the
-terminfo compiler. The reason this code lives in the <STRONG>ncurses</STRONG>
-library is to support fallback to /etc/termcap. These files include
-<blockquote>
-<code>
-alloc_entry.c
-captoinfo.c
-comp_captab.c
-comp_error.c
-comp_hash.c
-comp_parse.c
-comp_scan.c
-parse_entry.c
-read_termcap.c
-write_entry.c
-</code>
-</blockquote>
-We'll discuss these in the compiler tour.
-
-<H2><A NAME="engine">The Engine Room</A></H2>
-
-<H3><A NAME="input">Keyboard Input</A></H3>
-
-All <CODE>ncurses</CODE> input funnels through the function
-<CODE>wgetch()</CODE>, defined in <CODE>lib_getch.c</CODE>. This function is
-tricky; it has to poll for keyboard and mouse events and do a running
-match of incoming input against the set of defined special keys. <P>
-
-The central data structure in this module is a FIFO queue, used to
-match multiple-character input sequences against special-key
-capabilities; also to implement pushback via <CODE>ungetch()</CODE>. <P>
-
-The <CODE>wgetch()</CODE> code distinguishes between function key
-sequences and the same sequences typed manually by doing a timed wait
-after each input character that could lead a function key sequence.
-If the entire sequence takes less than 1 second, it is assumed to have
-been generated by a function key press. <P>
-
-Hackers bruised by previous encounters with variant <CODE>select(2)</CODE>
-calls may find the code in <CODE>lib_twait.c</CODE> interesting. It deals
-with the problem that some BSD selects don't return a reliable
-time-left value. The function <CODE>timed_wait()</CODE> effectively
-simulates a System V select.
-
-<H3><A NAME="mouse">Mouse Events</A></H3>
-
-If the mouse interface is active, <CODE>wgetch()</CODE> polls for mouse
-events each call, before it goes to the keyboard for input. It is
-up to <CODE>lib_mouse.c</CODE> how the polling is accomplished; it may vary
-for different devices. <P>
-
-Under xterm, however, mouse event notifications come in via the keyboard
-input stream. They are recognized by having the <STRONG>kmous</STRONG> capability
-as a prefix. This is kind of klugey, but trying to wire in recognition of
-a mouse key prefix without going through the function-key machinery would
-be just too painful, and this turns out to imply having the prefix somewhere
-in the function-key capabilities at terminal-type initialization. <P>
-
-This kluge only works because <STRONG>kmous</STRONG> isn't actually used by any
-historic terminal type or curses implementation we know of. Best
-guess is it's a relic of some forgotten experiment in-house at Bell
-Labs that didn't leave any traces in the publicly-distributed System V
-terminfo files. If System V or XPG4 ever gets serious about using it
-again, this kluge may have to change. <P>
-
-Here are some more details about mouse event handling: <P>
-
-The <CODE>lib_mouse()</CODE>code is logically split into a lower level that
-accepts event reports in a device-dependent format and an upper level that
-parses mouse gestures and filters events. The mediating data structure is a
-circular queue of event structures. <P>
-
-Functionally, the lower level's job is to pick up primitive events and
-put them on the circular queue. This can happen in one of two ways:
-either (a) <CODE>_nc_mouse_event()</CODE> detects a series of incoming
-mouse reports and queues them, or (b) code in <CODE>lib_getch.c</CODE> detects the
-<STRONG>kmous</STRONG> prefix in the keyboard input stream and calls _nc_mouse_inline
-to queue up a series of adjacent mouse reports. <P>
-
-In either case, <CODE>_nc_mouse_parse()</CODE> should be called after the
-series is accepted to parse the digested mouse reports (low-level
-events) into a gesture (a high-level or composite event).
-
-<H3><A NAME="output">Output and Screen Updating</A></H3>
-
-With the single exception of character echoes during a <CODE>wgetnstr()</CODE>
-call (which simulates cooked-mode line editing in an ncurses window),
-the library normally does all its output at refresh time. <P>
-
-The main job is to go from the current state of the screen (as represented
-in the <CODE>curscr</CODE> window structure) to the desired new state (as
-represented in the <CODE>newscr</CODE> window structure), while doing as
-little I/O as possible. <P>
-
-The brains of this operation are the modules <CODE>hashmap.c</CODE>,
-<CODE>hardscroll.c</CODE> and <CODE>lib_doupdate.c</CODE>; the latter two use
-<CODE>lib_mvcur.c</CODE>. Essentially, what happens looks like this: <P>
-
-The <CODE>hashmap.c</CODE> module tries to detect vertical motion
-changes between the real and virtual screens. This information
-is represented by the oldindex members in the newscr structure.
-These are modified by vertical-motion and clear operations, and both are
-re-initialized after each update. To this change-journalling
-information, the hashmap code adds deductions made using a modified Heckel
-algorithm on hash values generated from the line contents. <P>
-
-The <CODE>hardscroll.c</CODE> module computes an optimum set of scroll,
-insertion, and deletion operations to make the indices match. It calls
-<CODE>_nc_mvcur_scrolln()</CODE> in <CODE>lib_mvcur.c</CODE> to do those motions. <P>
-
-Then <CODE>lib_doupdate.c</CODE> goes to work. Its job is to do line-by-line
-transformations of <CODE>curscr</CODE> lines to <CODE>newscr</CODE> lines. Its main
-tool is the routine <CODE>mvcur()</CODE> in <CODE>lib_mvcur.c</CODE>. This routine
-does cursor-movement optimization, attempting to get from given screen
-location A to given location B in the fewest output characters possible. <P>
-
-If you want to work on screen optimizations, you should use the fact
-that (in the trace-enabled version of the library) enabling the
-<CODE>TRACE_TIMES</CODE> trace level causes a report to be emitted after
-each screen update giving the elapsed time and a count of characters
-emitted during the update. You can use this to tell when an update
-optimization improves efficiency. <P>
-
-In the trace-enabled version of the library, it is also possible to disable
-and re-enable various optimizations at runtime by tweaking the variable
-<CODE>_nc_optimize_enable</CODE>. See the file <CODE>include/curses.h.in</CODE>
-for mask values, near the end.
-
-<H1><A NAME="fmnote">The Forms and Menu Libraries</A></H1>
-
-The forms and menu libraries should work reliably in any environment you
-can port ncurses to. The only portability issue anywhere in them is what
-flavor of regular expressions the built-in form field type TYPE_REGEXP
-will recognize. <P>
-
-The configuration code prefers the POSIX regex facility, modeled on
-System V's, but will settle for BSD regexps if the former isn't available. <P>
-
-Historical note: the panels code was written primarily to assist in
-porting u386mon 2.0 (comp.sources.misc v14i001-4) to systems lacking
-panels support; u386mon 2.10 and beyond use it. This version has been
-slightly cleaned up for <CODE>ncurses</CODE>.
-
-<H1><A NAME="tic">A Tour of the Terminfo Compiler</A></H1>
-
-The <STRONG>ncurses</STRONG> implementation of <STRONG>tic</STRONG> is rather complex
-internally; it has to do a trying combination of missions. This starts
-with the fact that, in addition to its normal duty of compiling
-terminfo sources into loadable terminfo binaries, it has to be able to
-handle termcap syntax and compile that too into terminfo entries. <P>
-
-The implementation therefore starts with a table-driven, dual-mode
-lexical analyzer (in <CODE>comp_scan.c</CODE>). The lexer chooses its
-mode (termcap or terminfo) based on the first `,' or `:' it finds in
-each entry. The lexer does all the work of recognizing capability
-names and values; the grammar above it is trivial, just "parse entries
-till you run out of file".
-
-<H2><A NAME="nonuse">Translation of Non-<STRONG>use</STRONG> Capabilities</A></H2>
-
-Translation of most things besides <STRONG>use</STRONG> capabilities is pretty
-straightforward. The lexical analyzer's tokenizer hands each capability
-name to a hash function, which drives a table lookup. The table entry
-yields an index which is used to look up the token type in another table,
-and controls interpretation of the value. <P>
-
-One possibly interesting aspect of the implementation is the way the
-compiler tables are initialized. All the tables are generated by various
-awk/sed/sh scripts from a master table <CODE>include/Caps</CODE>; these
-scripts actually write C initializers which are linked to the compiler.
-Furthermore, the hash table is generated in the same way, so it doesn't
-have to be generated at compiler startup time (another benefit of this
-organization is that the hash table can be in shareable text space). <P>
-
-Thus, adding a new capability is usually pretty trivial, just a matter
-of adding one line to the <CODE>include/Caps</CODE> file. We'll have more
-to say about this in the section on <A HREF="#translation">Source-Form
-Translation</A>.
-
-<H2><A NAME="uses">Use Capability Resolution</A></H2>
-
-The background problem that makes <STRONG>tic</STRONG> tricky isn't the capability
-translation itself, it's the resolution of <STRONG>use</STRONG> capabilities. Older
-versions would not handle forward <STRONG>use</STRONG> references for this reason
-(that is, a using terminal always had to follow its use target in the
-source file). By doing this, they got away with a simple implementation
-tactic; compile everything as it blows by, then resolve uses from compiled
-entries. <P>
-
-This won't do for <STRONG>ncurses</STRONG>. The problem is that that the whole
-compilation process has to be embeddable in the <STRONG>ncurses</STRONG> library
-so that it can be called by the startup code to translate termcap
-entries on the fly. The embedded version can't go promiscuously writing
-everything it translates out to disk -- for one thing, it will typically
-be running with non-root permissions. <P>
-
-So our <STRONG>tic</STRONG> is designed to parse an entire terminfo file into a
-doubly-linked circular list of entry structures in-core, and then do
-<STRONG>use</STRONG> resolution in-memory before writing everything out. This
-design has other advantages: it makes forward and back use-references
-equally easy (so we get the latter for free), and it makes checking for
-name collisions before they're written out easy to do. <P>
-
-And this is exactly how the embedded version works. But the stand-alone
-user-accessible version of <STRONG>tic</STRONG> partly reverts to the historical
-strategy; it writes to disk (not keeping in core) any entry with no
-<STRONG>use</STRONG> references. <P>
-
-This is strictly a core-economy kluge, implemented because the
-terminfo master file is large enough that some core-poor systems swap
-like crazy when you compile it all in memory...there have been reports of
-this process taking <STRONG>three hours</STRONG>, rather than the twenty seconds
-or less typical on the author's development box. <P>
-
-So. The executable <STRONG>tic</STRONG> passes the entry-parser a hook that
-<EM>immediately</EM> writes out the referenced entry if it has no use
-capabilities. The compiler main loop refrains from adding the entry
-to the in-core list when this hook fires. If some other entry later
-needs to reference an entry that got written immediately, that's OK;
-the resolution code will fetch it off disk when it can't find it in
-core. <P>
-
-Name collisions will still be detected, just not as cleanly. The
-<CODE>write_entry()</CODE> code complains before overwriting an entry that
-postdates the time of <STRONG>tic</STRONG>'s first call to
-<CODE>write_entry()</CODE>, Thus it will complain about overwriting
-entries newly made during the <STRONG>tic</STRONG> run, but not about
-overwriting ones that predate it.
-
-<H2><A NAME="translation">Source-Form Translation</A></H2>
-
-Another use of <STRONG>tic</STRONG> is to do source translation between various termcap
-and terminfo formats. There are more variants out there than you might
-think; the ones we know about are described in the <STRONG>captoinfo(1)</STRONG>
-manual page. <P>
-
-The translation output code (<CODE>dump_entry()</CODE> in
-<CODE>ncurses/dump_entry.c</CODE>) is shared with the <STRONG>infocmp(1)</STRONG>
-utility. It takes the same internal representation used to generate
-the binary form and dumps it to standard output in a specified
-format. <P>
-
-The <CODE>include/Caps</CODE> file has a header comment describing ways you
-can specify source translations for nonstandard capabilities just by
-altering the master table. It's possible to set up capability aliasing
-or tell the compiler to plain ignore a given capability without writing
-any C code at all. <P>
-
-For circumstances where you need to do algorithmic translation, there
-are functions in <CODE>parse_entry.c</CODE> called after the parse of each
-entry that are specifically intended to encapsulate such
-translations. This, for example, is where the AIX <STRONG>box1</STRONG> capability
-get translated to an <STRONG>acsc</STRONG> string.
-
-<H1><A NAME="utils">Other Utilities</A></H1>
-
-The <STRONG>infocmp</STRONG> utility is just a wrapper around the same
-entry-dumping code used by <STRONG>tic</STRONG> for source translation. Perhaps
-the one interesting aspect of the code is the use of a predicate
-function passed in to <CODE>dump_entry()</CODE> to control which
-capabilities are dumped. This is necessary in order to handle both
-the ordinary De-compilation case and entry difference reporting. <P>
-
-The <STRONG>tput</STRONG> and <STRONG>clear</STRONG> utilities just do an entry load
-followed by a <CODE>tputs()</CODE> of a selected capability.
-
-<H1><A NAME="style">Style Tips for Developers</A></H1>
-
-See the TO-DO file in the top-level directory of the source distribution
-for additions that would be particularly useful. <P>
-
-The prefix <CODE>_nc_</CODE> should be used on library public functions that are
-not part of the curses API in order to prevent pollution of the
-application namespace.
-
-If you have to add to or modify the function prototypes in curses.h.in,
-read ncurses/MKlib_gen.sh first so you can avoid breaking XSI conformance.
-
-Please join the ncurses mailing list. See the INSTALL file in the
-top level of the distribution for details on the list. <P>
-
-Look for the string <CODE>FIXME</CODE> in source files to tag minor bugs
-and potential problems that could use fixing. <P>
-
-Don't try to auto-detect OS features in the main body of the C code.
-That's the job of the configuration system. <P>
-
-To hold down complexity, do make your code data-driven. Especially,
-if you can drive logic from a table filtered out of
-<CODE>include/Caps</CODE>, do it. If you find you need to augment the
-data in that file in order to generate the proper table, that's still
-preferable to ad-hoc code -- that's why the fifth field (flags) is
-there. <P>
-
-Have fun!
-
-<H1><A NAME="port">Porting Hints</A></H1>
-
-The following notes are intended to be a first step towards DOS and Macintosh
-ports of the ncurses libraries. <P>
-
-The following library modules are `pure curses'; they operate only on
-the curses internal structures, do all output through other curses
-calls (not including <CODE>tputs()</CODE> and <CODE>putp()</CODE>) and do not
-call any other UNIX routines such as signal(2) or the stdio library.
-Thus, they should not need to be modified for single-terminal
-ports.
-
-<blockquote>
-<code>
-lib_addch.c
-lib_addstr.c
-lib_bkgd.c
-lib_box.c
-lib_clear.c
-lib_clrbot.c
-lib_clreol.c
-lib_delch.c
-lib_delwin.c
-lib_erase.c
-lib_inchstr.c
-lib_insch.c
-lib_insdel.c
-lib_insstr.c
-lib_keyname.c
-lib_move.c
-lib_mvwin.c
-lib_newwin.c
-lib_overlay.c
-lib_pad.c
-lib_printw.c
-lib_refresh.c
-lib_scanw.c
-lib_scroll.c
-lib_scrreg.c
-lib_set_term.c
-lib_touch.c
-lib_tparm.c
-lib_tputs.c
-lib_unctrl.c
-lib_window.c
-panel.c
-</code>
-</blockquote>
-<P>
-
-This module is pure curses, but calls outstr():
-
-<blockquote>
-<code>
-lib_getstr.c
-</code>
-</blockquote>
-<P>
-
-These modules are pure curses, except that they use <CODE>tputs()</CODE>
-and <CODE>putp()</CODE>:
-
-<blockquote>
-<code>
-lib_beep.c
-lib_color.c
-lib_endwin.c
-lib_options.c
-lib_slk.c
-lib_vidattr.c
-</code>
-</blockquote>
-<P>
-
-This modules assist in POSIX emulation on non-POSIX systems:
-<DL>
-<DT> sigaction.c
-<DD> signal calls
-</DL>
-
-The following source files will not be needed for a
-single-terminal-type port.
-
-<blockquote>
-<code>
-alloc_entry.c
-captoinfo.c
-clear.c
-comp_captab.c
-comp_error.c
-comp_hash.c
-comp_main.c
-comp_parse.c
-comp_scan.c
-dump_entry.c
-infocmp.c
-parse_entry.c
-read_entry.c
-tput.c
-write_entry.c
-</code>
-</blockquote>
-<P>
-
-The following modules will use open()/read()/write()/close()/lseek() on files,
-but no other OS calls.
-
-<DL>
-<DT>lib_screen.c
-<DD>used to read/write screen dumps
-<DT>lib_trace.c
-<DD>used to write trace data to the logfile
-</DL>
-
-Modules that would have to be modified for a port start here: <P>
-
-The following modules are `pure curses' but contain assumptions inappropriate
-for a memory-mapped port.
-
-<dl>
-<dt>lib_longname.c<dd>assumes there may be multiple terminals
-<dt>lib_acs.c<dd>assumes acs_map as a double indirection
-<dt>lib_mvcur.c<dd>assumes cursor moves have variable cost
-<dt>lib_termcap.c<dd>assumes there may be multiple terminals
-<dt>lib_ti.c<dd>assumes there may be multiple terminals
-</dl>
-
-The following modules use UNIX-specific calls:
-
-<dl>
-<dt>lib_doupdate.c<dd>input checking
-<dt>lib_getch.c<dd>read()
-<dt>lib_initscr.c<dd>getenv()
-<dt>lib_newterm.c
-<dt>lib_baudrate.c
-<dt>lib_kernel.c<dd>various tty-manipulation and system calls
-<dt>lib_raw.c<dd>various tty-manipulation calls
-<dt>lib_setup.c<dd>various tty-manipulation calls
-<dt>lib_restart.c<dd>various tty-manipulation calls
-<dt>lib_tstp.c<dd>signal-manipulation calls
-<dt>lib_twait.c<dd>gettimeofday(), select().
-</dl>
-
-<HR>
-<ADDRESS>Eric S. Raymond <esr@snark.thyrsus.com></ADDRESS>
-(Note: This is <EM>not</EM> the <A HREF="#bugtrack">bug address</A>!)
-</BODY>
-</HTML>
+</pre>
+
+ <p>The <code>ncurses</code> code is maintained by a small group
+ of volunteers. While we try our best to fix bugs promptly, we
+ simply do not have a lot of hours to spend on elementary
+ hand-holding. We rely on intelligent cooperation from our users.
+ If you think you have found a bug in <code>ncurses</code>, there
+ are some steps you can take before contacting us that will help
+ get the bug fixed quickly.</p>
+
+ <p>In order to use our bug-fixing time efficiently, we put people
+ who show us they have taken these steps at the head of our queue.
+ This means that if you do not, you will probably end up at the
+ tail end and have to wait a while.</p>
+
+ <ol>
+ <li>Develop a recipe to reproduce the bug.
+
+ <p>Bugs we can reproduce are likely to be fixed very quickly,
+ often within days. The most effective single thing you can do
+ to get a quick fix is develop a way we can duplicate the bad
+ behavior — ideally, by giving us source for a small,
+ portable test program that breaks the library. (Even better
+ is a keystroke recipe using one of the test programs provided
+ with the distribution.)</p>
+ </li>
+
+ <li>Try to reproduce the bug on a different terminal type.
+
+ <p>In our experience, most of the behaviors people report as
+ library bugs are actually due to subtle problems in terminal
+ descriptions. This is especially likely to be true if you are
+ using a traditional asynchronous terminal or PC-based
+ terminal emulator, rather than xterm or a UNIX console
+ entry.</p>
+
+ <p>It is therefore extremely helpful if you can tell us
+ whether or not your problem reproduces on other terminal
+ types. Usually you will have both a console type and xterm
+ available; please tell us whether or not your bug reproduces
+ on both.</p>
+
+ <p>If you have xterm available, it is also good to collect
+ xterm reports for different window sizes. This is especially
+ true if you normally use an unusual xterm window size —
+ a surprising number of the bugs we have seen are either
+ triggered or masked by these.</p>
+ </li>
+
+ <li>Generate and examine a trace file for the broken behavior.
+
+ <p>Recompile your program with the debugging versions of the
+ libraries. Insert a <code>trace()</code> call with the
+ argument set to <code>TRACE_UPDATE</code>. (See <a href=
+ "ncurses-intro.html#debugging">"Writing Programs with
+ NCURSES"</a> for details on trace levels.) Reproduce your
+ bug, then look at the trace file to see what the library was
+ actually doing.</p>
+
+ <p>Another frequent cause of apparent bugs is application
+ coding errors that cause the wrong things to be put on the
+ virtual screen. Looking at the virtual-screen dumps in the
+ trace file will tell you immediately if this is happening,
+ and save you from the possible embarrassment of being told
+ that the bug is in your code and is your problem rather than
+ ours.</p>
+
+ <p>If the virtual-screen dumps look correct but the bug
+ persists, it is possible to crank up the trace level to give
+ more and more information about the library's update actions
+ and the control sequences it issues to perform them. The test
+ directory of the distribution contains a tool for digesting
+ these logs to make them less tedious to wade through.</p>
+
+ <p>Often you will find terminfo problems at this stage by
+ noticing that the escape sequences put out for various
+ capabilities are wrong. If not, you are likely to learn
+ enough to be able to characterize any bug in the
+ screen-update logic quite exactly.</p>
+ </li>
+
+ <li>Report details and symptoms, not just interpretations.
+
+ <p>If you do the preceding two steps, it is very likely that
+ you will discover the nature of the problem yourself and be
+ able to send us a fix. This will create happy feelings all
+ around and earn you good karma for the first time you run
+ into a bug you really cannot characterize and fix
+ yourself.</p>
+
+ <p>If you are still stuck, at least you will know what to
+ tell us. Remember, we need details. If you guess about what
+ is safe to leave out, you are too likely to be wrong.</p>
+
+ <p>If your bug produces a bad update, include a trace file.
+ Try to make the trace at the <em>least</em> voluminous level
+ that pins down the bug. Logs that have been through
+ tracemunch are OK, it does not throw away any information
+ (actually they are better than un-munched ones because they
+ are easier to read).</p>
+
+ <p>If your bug produces a core-dump, please include a
+ symbolic stack trace generated by gdb(1) or your local
+ equivalent.</p>
+
+ <p>Tell us about every terminal on which you have reproduced
+ the bug — and every terminal on which you cannot.
+ Ideally, sent us terminfo sources for all of these (yours
+ might differ from ours).</p>
+
+ <p>Include your ncurses version and your OS/machine type, of
+ course! You can find your ncurses version in the
+ <code>curses.h</code> file.</p>
+ </li>
+ </ol>
+
+ <p>If your problem smells like a logic error or in cursor
+ movement or scrolling or a bad capability, there are a couple of
+ tiny test frames for the library algorithms in the progs
+ directory that may help you isolate it. These are not part of the
+ normal build, but do have their own make productions.</p>
+
+ <p>The most important of these is <code>mvcur</code>, a test
+ frame for the cursor-movement optimization code. With this
+ program, you can see directly what control sequences will be
+ emitted for any given cursor movement or scroll/insert/delete
+ operations. If you think you have got a bad capability
+ identified, you can disable it and test again. The program is
+ command-driven and has on-line help.</p>
+
+ <p>If you think the vertical-scroll optimization is broken, or
+ just want to understand how it works better, build
+ <code>hashmap</code> and read the header comments of
+ <code>hardscroll.c</code> and <code>hashmap.c</code>; then try it
+ out. You can also test the hardware-scrolling optimization
+ separately with <code>hardscroll</code>.</p>
+
+ <h1><a name="ncurslib" id="ncurslib">A Tour of the Ncurses
+ Library</a></h1>
+
+ <h2><a name="loverview" id="loverview">Library Overview</a></h2>
+
+ <p>Most of the library is superstructure — fairly trivial
+ convenience interfaces to a small set of basic functions and data
+ structures used to manipulate the virtual screen (in particular,
+ none of this code does any I/O except through calls to more
+ fundamental modules described below). The files</p>
+
+ <blockquote>
+ <code>lib_addch.c lib_bkgd.c lib_box.c lib_chgat.c lib_clear.c
+ lib_clearok.c lib_clrbot.c lib_clreol.c lib_colorset.c
+ lib_data.c lib_delch.c lib_delwin.c lib_echo.c lib_erase.c
+ lib_gen.c lib_getstr.c lib_hline.c lib_immedok.c lib_inchstr.c
+ lib_insch.c lib_insdel.c lib_insstr.c lib_instr.c
+ lib_isendwin.c lib_keyname.c lib_leaveok.c lib_move.c
+ lib_mvwin.c lib_overlay.c lib_pad.c lib_printw.c lib_redrawln.c
+ lib_scanw.c lib_screen.c lib_scroll.c lib_scrollok.c
+ lib_scrreg.c lib_set_term.c lib_slk.c lib_slkatr_set.c
+ lib_slkatrof.c lib_slkatron.c lib_slkatrset.c lib_slkattr.c
+ lib_slkclear.c lib_slkcolor.c lib_slkinit.c lib_slklab.c
+ lib_slkrefr.c lib_slkset.c lib_slktouch.c lib_touch.c
+ lib_unctrl.c lib_vline.c lib_wattroff.c lib_wattron.c
+ lib_window.c</code>
+ </blockquote>
+
+ <p>are all in this category. They are very unlikely to need
+ change, barring bugs or some fundamental reorganization in the
+ underlying data structures.</p>
+
+ <p>These files are used only for debugging support:</p>
+
+ <blockquote>
+ <code>lib_trace.c lib_traceatr.c lib_tracebits.c lib_tracechr.c
+ lib_tracedmp.c lib_tracemse.c trace_buf.c</code>
+ </blockquote>
+
+ <p>It is rather unlikely you will ever need to change these,
+ unless you want to introduce a new debug trace level for some
+ reason.</p>
+
+ <p>There is another group of files that do direct I/O via
+ <em>tputs()</em>, computations on the terminal capabilities, or
+ queries to the OS environment, but nevertheless have only fairly
+ low complexity. These include:</p>
+
+ <blockquote>
+ <code>lib_acs.c lib_beep.c lib_color.c lib_endwin.c
+ lib_initscr.c lib_longname.c lib_newterm.c lib_options.c
+ lib_termcap.c lib_ti.c lib_tparm.c lib_tputs.c lib_vidattr.c
+ read_entry.c.</code>
+ </blockquote>
+
+ <p>They are likely to need revision only if ncurses is being
+ ported to an environment without an underlying terminfo
+ capability representation.</p>
+
+ <p>These files have serious hooks into the tty driver and signal
+ facilities:</p>
+
+ <blockquote>
+ <code>lib_kernel.c lib_baudrate.c lib_raw.c lib_tstp.c
+ lib_twait.c</code>
+ </blockquote>
+
+ <p>If you run into porting snafus moving the package to another
+ UNIX, the problem is likely to be in one of these files. The file
+ <code>lib_print.c</code> uses sleep(2) and also falls in this
+ category.</p>
+
+ <p>Almost all of the real work is done in the files</p>
+
+ <blockquote>
+ <code>hardscroll.c hashmap.c lib_addch.c lib_doupdate.c
+ lib_getch.c lib_mouse.c lib_mvcur.c lib_refresh.c lib_setup.c
+ lib_vidattr.c</code>
+ </blockquote>
+
+ <p>Most of the algorithmic complexity in the library lives in
+ these files. If there is a real bug in <strong>ncurses</strong>
+ itself, it is probably here. We will tour some of these files in
+ detail below (see <a href="#engine">The Engine Room</a>).</p>
+
+ <p>Finally, there is a group of files that is actually most of
+ the terminfo compiler. The reason this code lives in the
+ <strong>ncurses</strong> library is to support fallback to
+ /etc/termcap. These files include</p>
+
+ <blockquote>
+ <code>alloc_entry.c captoinfo.c comp_captab.c comp_error.c
+ comp_hash.c comp_parse.c comp_scan.c parse_entry.c
+ read_termcap.c write_entry.c</code>
+ </blockquote>
+
+ <p>We will discuss these in the compiler tour.</p>
+
+ <h2><a name="engine" id="engine">The Engine Room</a></h2>
+
+ <h3><a name="input" id="input">Keyboard Input</a></h3>
+
+ <p>All <code>ncurses</code> input funnels through the function
+ <code>wgetch()</code>, defined in <code>lib_getch.c</code>. This
+ function is tricky; it has to poll for keyboard and mouse events
+ and do a running match of incoming input against the set of
+ defined special keys.</p>
+
+ <p>The central data structure in this module is a FIFO queue,
+ used to match multiple-character input sequences against
+ special-key capabilities; also to implement pushback via
+ <code>ungetch()</code>.</p>
+
+ <p>The <code>wgetch()</code> code distinguishes between function
+ key sequences and the same sequences typed manually by doing a
+ timed wait after each input character that could lead a function
+ key sequence. If the entire sequence takes less than 1 second, it
+ is assumed to have been generated by a function key press.</p>
+
+ <p>Hackers bruised by previous encounters with variant
+ <code>select(2)</code> calls may find the code in
+ <code>lib_twait.c</code> interesting. It deals with the problem
+ that some BSD selects do not return a reliable time-left value.
+ The function <code>timed_wait()</code> effectively simulates a
+ System V select.</p>
+
+ <h3><a name="mouse" id="mouse">Mouse Events</a></h3>
+
+ <p>If the mouse interface is active, <code>wgetch()</code> polls
+ for mouse events each call, before it goes to the keyboard for
+ input. It is up to <code>lib_mouse.c</code> how the polling is
+ accomplished; it may vary for different devices.</p>
+
+ <p>Under xterm, however, mouse event notifications come in via
+ the keyboard input stream. They are recognized by having the
+ <strong>kmous</strong> capability as a prefix. This is kind of
+ klugey, but trying to wire in recognition of a mouse key prefix
+ without going through the function-key machinery would be just
+ too painful, and this turns out to imply having the prefix
+ somewhere in the function-key capabilities at terminal-type
+ initialization.</p>
+
+ <p>This kluge only works because <strong>kmous</strong> is not
+ actually used by any historic terminal type or curses
+ implementation we know of. Best guess is it is a relic of some
+ forgotten experiment in-house at Bell Labs that did not leave any
+ traces in the publicly-distributed System V terminfo files. If
+ System V or XPG4 ever gets serious about using it again, this
+ kluge may have to change.</p>
+
+ <p>Here are some more details about mouse event handling:</p>
+
+ <p>The <code>lib_mouse()</code>code is logically split into a
+ lower level that accepts event reports in a device-dependent
+ format and an upper level that parses mouse gestures and filters
+ events. The mediating data structure is a circular queue of event
+ structures.</p>
+
+ <p>Functionally, the lower level's job is to pick up primitive
+ events and put them on the circular queue. This can happen in one
+ of two ways: either (a) <code>_nc_mouse_event()</code> detects a
+ series of incoming mouse reports and queues them, or (b) code in
+ <code>lib_getch.c</code> detects the <strong>kmous</strong>
+ prefix in the keyboard input stream and calls _nc_mouse_inline to
+ queue up a series of adjacent mouse reports.</p>
+
+ <p>In either case, <code>_nc_mouse_parse()</code> should be
+ called after the series is accepted to parse the digested mouse
+ reports (low-level events) into a gesture (a high-level or
+ composite event).</p>
+
+ <h3><a name="output" id="output">Output and Screen
+ Updating</a></h3>
+
+ <p>With the single exception of character echoes during a
+ <code>wgetnstr()</code> call (which simulates cooked-mode line
+ editing in an ncurses window), the library normally does all its
+ output at refresh time.</p>
+
+ <p>The main job is to go from the current state of the screen (as
+ represented in the <code>curscr</code> window structure) to the
+ desired new state (as represented in the <code>newscr</code>
+ window structure), while doing as little I/O as possible.</p>
+
+ <p>The brains of this operation are the modules
+ <code>hashmap.c</code>, <code>hardscroll.c</code> and
+ <code>lib_doupdate.c</code>; the latter two use
+ <code>lib_mvcur.c</code>. Essentially, what happens looks like
+ this:</p>
+
+ <p>The <code>hashmap.c</code> module tries to detect vertical
+ motion changes between the real and virtual screens. This
+ information is represented by the oldindex members in the newscr
+ structure. These are modified by vertical-motion and clear
+ operations, and both are re-initialized after each update. To
+ this change-journalling information, the hashmap code adds
+ deductions made using a modified Heckel algorithm on hash values
+ generated from the line contents.</p>
+
+ <p>The <code>hardscroll.c</code> module computes an optimum set
+ of scroll, insertion, and deletion operations to make the indices
+ match. It calls <code>_nc_mvcur_scrolln()</code> in
+ <code>lib_mvcur.c</code> to do those motions.</p>
+
+ <p>Then <code>lib_doupdate.c</code> goes to work. Its job is to
+ do line-by-line transformations of <code>curscr</code> lines to
+ <code>newscr</code> lines. Its main tool is the routine
+ <code>mvcur()</code> in <code>lib_mvcur.c</code>. This routine
+ does cursor-movement optimization, attempting to get from given
+ screen location A to given location B in the fewest output
+ characters possible.</p>
+
+ <p>If you want to work on screen optimizations, you should use
+ the fact that (in the trace-enabled version of the library)
+ enabling the <code>TRACE_TIMES</code> trace level causes a report
+ to be emitted after each screen update giving the elapsed time
+ and a count of characters emitted during the update. You can use
+ this to tell when an update optimization improves efficiency.</p>
+
+ <p>In the trace-enabled version of the library, it is also
+ possible to disable and re-enable various optimizations at
+ runtime by tweaking the variable
+ <code>_nc_optimize_enable</code>. See the file
+ <code>include/curses.h.in</code> for mask values, near the
+ end.</p>
+
+ <h1><a name="fmnote" id="fmnote">The Forms and Menu
+ Libraries</a></h1>
+
+ <p>The forms and menu libraries should work reliably in any
+ environment you can port ncurses to. The only portability issue
+ anywhere in them is what flavor of regular expressions the
+ built-in form field type TYPE_REGEXP will recognize.</p>
+
+ <p>The configuration code prefers the POSIX regex facility,
+ modeled on System V's, but will settle for BSD regexps if the
+ former is not available.</p>
+
+ <p>Historical note: the panels code was written primarily to
+ assist in porting u386mon 2.0 (comp.sources.misc v14i001-4) to
+ systems lacking panels support; u386mon 2.10 and beyond use it.
+ This version has been slightly cleaned up for
+ <code>ncurses</code>.</p>
+
+ <h1><a name="tic" id="tic">A Tour of the Terminfo
+ Compiler</a></h1>
+
+ <p>The <strong>ncurses</strong> implementation of
+ <strong>tic</strong> is rather complex internally; it has to do a
+ trying combination of missions. This starts with the fact that,
+ in addition to its normal duty of compiling terminfo sources into
+ loadable terminfo binaries, it has to be able to handle termcap
+ syntax and compile that too into terminfo entries.</p>
+
+ <p>The implementation therefore starts with a table-driven,
+ dual-mode lexical analyzer (in <code>comp_scan.c</code>). The
+ lexer chooses its mode (termcap or terminfo) based on the first
+ “,” or “:” it finds in each entry. The
+ lexer does all the work of recognizing capability names and
+ values; the grammar above it is trivial, just "parse entries till
+ you run out of file".</p>
+
+ <h2><a name="nonuse" id="nonuse">Translation of
+ Non-<strong>use</strong> Capabilities</a></h2>
+
+ <p>Translation of most things besides <strong>use</strong>
+ capabilities is pretty straightforward. The lexical analyzer's
+ tokenizer hands each capability name to a hash function, which
+ drives a table lookup. The table entry yields an index which is
+ used to look up the token type in another table, and controls
+ interpretation of the value.</p>
+
+ <p>One possibly interesting aspect of the implementation is the
+ way the compiler tables are initialized. All the tables are
+ generated by various awk/sed/sh scripts from a master table
+ <code>include/Caps</code>; these scripts actually write C
+ initializers which are linked to the compiler. Furthermore, the
+ hash table is generated in the same way, so it doesn't have to be
+ generated at compiler startup time (another benefit of this
+ organization is that the hash table can be in shareable text
+ space).</p>
+
+ <p>Thus, adding a new capability is usually pretty trivial, just
+ a matter of adding one line to the <code>include/Caps</code>
+ file. We will have more to say about this in the section on
+ <a href="#translation">Source-Form Translation</a>.</p>
+
+ <h2><a name="uses" id="uses">Use Capability Resolution</a></h2>
+
+ <p>The background problem that makes <strong>tic</strong> tricky
+ is not the capability translation itself, it is the resolution of
+ <strong>use</strong> capabilities. Older versions would not
+ handle forward <strong>use</strong> references for this reason
+ (that is, a using terminal always had to follow its use target in
+ the source file). By doing this, they got away with a simple
+ implementation tactic; compile everything as it blows by, then
+ resolve uses from compiled entries.</p>
+
+ <p>This will not do for <strong>ncurses</strong>. The problem is
+ that that the whole compilation process has to be embeddable in
+ the <strong>ncurses</strong> library so that it can be called by
+ the startup code to translate termcap entries on the fly. The
+ embedded version cannot go promiscuously writing everything it
+ translates out to disk — for one thing, it will typically
+ be running with non-root permissions.</p>
+
+ <p>So our <strong>tic</strong> is designed to parse an entire
+ terminfo file into a doubly-linked circular list of entry
+ structures in-core, and then do <strong>use</strong> resolution
+ in-memory before writing everything out. This design has other
+ advantages: it makes forward and back use-references equally easy
+ (so we get the latter for free), and it makes checking for name
+ collisions before they are written out easy to do.</p>
+
+ <p>And this is exactly how the embedded version works. But the
+ stand-alone user-accessible version of <strong>tic</strong>
+ partly reverts to the historical strategy; it writes to disk (not
+ keeping in core) any entry with no <strong>use</strong>
+ references.</p>
+
+ <p>This is strictly a core-economy kluge, implemented because the
+ terminfo master file is large enough that some core-poor systems
+ swap like crazy when you compile it all in memory...there have
+ been reports of this process taking <strong>three hours</strong>,
+ rather than the twenty seconds or less typical on the author's
+ development box.</p>
+
+ <p>So. The executable <strong>tic</strong> passes the
+ entry-parser a hook that <em>immediately</em> writes out the
+ referenced entry if it has no use capabilities. The compiler main
+ loop refrains from adding the entry to the in-core list when this
+ hook fires. If some other entry later needs to reference an entry
+ that got written immediately, that is OK; the resolution code
+ will fetch it off disk when it cannot find it in core.</p>
+
+ <p>Name collisions will still be detected, just not as cleanly.
+ The <code>write_entry()</code> code complains before overwriting
+ an entry that postdates the time of <strong>tic</strong>'s first
+ call to <code>write_entry()</code>, Thus it will complain about
+ overwriting entries newly made during the <strong>tic</strong>
+ run, but not about overwriting ones that predate it.</p>
+
+ <h2><a name="translation" id="translation">Source-Form
+ Translation</a></h2>
+
+ <p>Another use of <strong>tic</strong> is to do source
+ translation between various termcap and terminfo formats. There
+ are more variants out there than you might think; the ones we
+ know about are described in the <strong>captoinfo(1)</strong>
+ manual page.</p>
+
+ <p>The translation output code (<code>dump_entry()</code> in
+ <code>ncurses/dump_entry.c</code>) is shared with the
+ <strong>infocmp(1)</strong> utility. It takes the same internal
+ representation used to generate the binary form and dumps it to
+ standard output in a specified format.</p>
+
+ <p>The <code>include/Caps</code> file has a header comment
+ describing ways you can specify source translations for
+ nonstandard capabilities just by altering the master table. It is
+ possible to set up capability aliasing or tell the compiler to
+ plain ignore a given capability without writing any C code at
+ all.</p>
+
+ <p>For circumstances where you need to do algorithmic
+ translation, there are functions in <code>parse_entry.c</code>
+ called after the parse of each entry that are specifically
+ intended to encapsulate such translations. This, for example, is
+ where the AIX <strong>box1</strong> capability get translated to
+ an <strong>acsc</strong> string.</p>
+
+ <h1><a name="utils" id="utils">Other Utilities</a></h1>
+
+ <p>The <strong>infocmp</strong> utility is just a wrapper around
+ the same entry-dumping code used by <strong>tic</strong> for
+ source translation. Perhaps the one interesting aspect of the
+ code is the use of a predicate function passed in to
+ <code>dump_entry()</code> to control which capabilities are
+ dumped. This is necessary in order to handle both the ordinary
+ De-compilation case and entry difference reporting.</p>
+
+ <p>The <strong>tput</strong> and <strong>clear</strong> utilities
+ just do an entry load followed by a <code>tputs()</code> of a
+ selected capability.</p>
+
+ <h1><a name="style" id="style">Style Tips for Developers</a></h1>
+
+ <p>See the TO-DO file in the top-level directory of the source
+ distribution for additions that would be particularly useful.</p>
+
+ <p>The prefix <code>_nc_</code> should be used on library public
+ functions that are not part of the curses API in order to prevent
+ pollution of the application namespace. If you have to add to or
+ modify the function prototypes in curses.h.in, read
+ ncurses/MKlib_gen.sh first so you can avoid breaking XSI
+ conformance. Please join the ncurses mailing list. See the
+ INSTALL file in the top level of the distribution for details on
+ the list.</p>
+
+ <p>Look for the string <code>FIXME</code> in source files to tag
+ minor bugs and potential problems that could use fixing.</p>
+
+ <p>Do not try to auto-detect OS features in the main body of the
+ C code. That is the job of the configuration system.</p>
+
+ <p>To hold down complexity, do make your code data-driven.
+ Especially, if you can drive logic from a table filtered out of
+ <code>include/Caps</code>, do it. If you find you need to augment
+ the data in that file in order to generate the proper table, that
+ is still preferable to ad-hoc code — that is why the fifth
+ field (flags) is there.</p>
+
+ <p>Have fun!</p>
+
+ <h1><a name="port" id="port">Porting Hints</a></h1>
+
+ <p>The following notes are intended to be a first step towards
+ DOS and Macintosh ports of the ncurses libraries.</p>
+
+ <p>The following library modules are “pure curses”;
+ they operate only on the curses internal structures, do all
+ output through other curses calls (not including
+ <code>tputs()</code> and <code>putp()</code>) and do not call any
+ other UNIX routines such as signal(2) or the stdio library. Thus,
+ they should not need to be modified for single-terminal
+ ports.</p>
+
+ <blockquote>
+ <code>lib_addch.c lib_addstr.c lib_bkgd.c lib_box.c lib_clear.c
+ lib_clrbot.c lib_clreol.c lib_delch.c lib_delwin.c lib_erase.c
+ lib_inchstr.c lib_insch.c lib_insdel.c lib_insstr.c
+ lib_keyname.c lib_move.c lib_mvwin.c lib_newwin.c lib_overlay.c
+ lib_pad.c lib_printw.c lib_refresh.c lib_scanw.c lib_scroll.c
+ lib_scrreg.c lib_set_term.c lib_touch.c lib_tparm.c lib_tputs.c
+ lib_unctrl.c lib_window.c panel.c</code>
+ </blockquote>
+
+ <p>This module is pure curses, but calls outstr():</p>
+
+ <blockquote>
+ <code>lib_getstr.c</code>
+ </blockquote>
+
+ <p>These modules are pure curses, except that they use
+ <code>tputs()</code> and <code>putp()</code>:</p>
+
+ <blockquote>
+ <code>lib_beep.c lib_color.c lib_endwin.c lib_options.c
+ lib_slk.c lib_vidattr.c</code>
+ </blockquote>
+
+ <p>This modules assist in POSIX emulation on non-POSIX
+ systems:</p>
+
+ <dl>
+ <dt>sigaction.c</dt>
+
+ <dd>signal calls</dd>
+ </dl>
+
+ <p>The following source files will not be needed for a
+ single-terminal-type port.</p>
+
+ <blockquote>
+ <code>alloc_entry.c captoinfo.c clear.c comp_captab.c
+ comp_error.c comp_hash.c comp_main.c comp_parse.c comp_scan.c
+ dump_entry.c infocmp.c parse_entry.c read_entry.c tput.c
+ write_entry.c</code>
+ </blockquote>
+
+ <p>The following modules will use
+ open()/read()/write()/close()/lseek() on files, but no other OS
+ calls.</p>
+
+ <dl>
+ <dt>lib_screen.c</dt>
+
+ <dd>used to read/write screen dumps</dd>
+
+ <dt>lib_trace.c</dt>
+
+ <dd>used to write trace data to the logfile</dd>
+ </dl>
+
+ <p>Modules that would have to be modified for a port start
+ here:</p>
+
+ <p>The following modules are “pure curses” but
+ contain assumptions inappropriate for a memory-mapped port.</p>
+
+ <dl>
+ <dt>lib_longname.c</dt>
+
+ <dd>assumes there may be multiple terminals</dd>
+
+ <dt>lib_acs.c</dt>
+
+ <dd>assumes acs_map as a double indirection</dd>
+
+ <dt>lib_mvcur.c</dt>
+
+ <dd>assumes cursor moves have variable cost</dd>
+
+ <dt>lib_termcap.c</dt>
+
+ <dd>assumes there may be multiple terminals</dd>
+
+ <dt>lib_ti.c</dt>
+
+ <dd>assumes there may be multiple terminals</dd>
+ </dl>
+
+ <p>The following modules use UNIX-specific calls:</p>
+
+ <dl>
+ <dt>lib_doupdate.c</dt>
+
+ <dd>input checking</dd>
+
+ <dt>lib_getch.c</dt>
+
+ <dd>read()</dd>
+
+ <dt>lib_initscr.c</dt>
+
+ <dd>getenv()</dd>
+
+ <dt>lib_newterm.c</dt>
+
+ <dt>lib_baudrate.c</dt>
+
+ <dt>lib_kernel.c</dt>
+
+ <dd>various tty-manipulation and system calls</dd>
+
+ <dt>lib_raw.c</dt>
+
+ <dd>various tty-manipulation calls</dd>
+
+ <dt>lib_setup.c</dt>
+
+ <dd>various tty-manipulation calls</dd>
+
+ <dt>lib_restart.c</dt>
+
+ <dd>various tty-manipulation calls</dd>
+
+ <dt>lib_tstp.c</dt>
+
+ <dd>signal-manipulation calls</dd>
+
+ <dt>lib_twait.c</dt>
+
+ <dd>gettimeofday(), select().</dd>
+ </dl>
+ <hr>
+
+ <address>
+ Eric S. Raymond <esr@snark.thyrsus.com>
+ </address>(Note: This is <em>not</em> the <a href="#bugtrack">bug
+ address</a>!)
+</body>
+</html>
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