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-<TITLE>A Hacker's Guide to Ncurses Internals</TITLE>
-<link rev="made" href="mailto:bugs-ncurses@gnu.org">
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-</HEAD>
-<BODY>
-
-<H1>A Hacker's Guide to NCURSES</H1>
-
-<H1>Contents</H1>
-<UL>
-<LI><A HREF="#abstract">Abstract</A>
-<P>
-<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><UL>
-</UL>
-<LI><A HREF="#documentation">Documentation Conventions</A>
-<P>
-<LI><A HREF="#bugtrack">How to Report Bugs</A>
-<P>
-<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>
-<P>
-<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>
-<P>
-<LI><A HREF="#style">Style Tips for Developers</A>
-<P>
-<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. <P>
-
-<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: <P>
-
-<UL>
-<LI>Source-compatible with historical curses implementations (including
- the original BSD curses and System V curses.
-<P>
-<LI>Conformant with the XSI Curses standard issued as part of XPG4 by
- X/Open.
-<P>
-<LI>High-quality -- stable and reliable code, wide portability, good
- packaging, superior documentation.
-<P>
-<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. <P>
-
-<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. <P>
-
-<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. <P>
-
-<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: <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.
-<P>
-<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. <P>
-
-<H1><A NAME="documentation">Documentation Conventions</A></H1>
-
-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>Manual pages.
-<LI>Everything else (i.e., narrative documentation).
-</UL>
-
-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's
- no point in elaborate mark-up. <P>
-
-<LI><STRONG>Mark up manual pages in the man macros.</STRONG> These have to be viewable
- through traditional <EM>man(1)</EM> programs. <P>
-
-<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>
-
-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.<P>
-
-<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>
- 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. <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>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. <P>
-
-<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. <P>
-
-<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>
-
-There's one other interactive tester, <CODE>tctest</CODE>, that exercises
-translation between termcap and terminfo formats. If you have a serious
-need to run this, you probably belong on our development team! <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
-</blockquote></code>
-It is rather unlikely you will ever need to change these, unless
-you want to introduce a new debug trace level for some reasoon.<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.
-</blockquote></code>
-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
-</blockquote></code>
-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
-</blockquote></code>
-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
-</blockquote></code>
-We'll discuss these in the compiler tour. <P>
-
-<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. <P>
-
-<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). <P>
-
-<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 posible. <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. <P>
-
-<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>. <P>
-
-<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". <P>
-
-<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>. <P>
-
-<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. <P>
-
-<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.<P>
-
-<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. <P>
-
-<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! <P>
-
-<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. <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
-</blockquote></code>
-<P>
-
-This module is pure curses, but calls outstr(): <P>
-
-<blockquote><code>
-lib_getstr.c
-</blockquote></code>
-<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
-</blockquote></code>
-<P>
-
-This modules assist in POSIX emulation on non-POSIX systems: <P>
-<DL>
-<DT> sigaction.c
-<DD> signal calls
-</DL>
-
-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
-</blockquote></code>
-<P>
-
-The following modules will use open()/read()/write()/close()/lseek() on files,
-but no other OS calls. <P>
-
-<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. <P>
-
-<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>
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