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7<TITLE>A Hacker's Guide to Ncurses Internals</TITLE>
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17
18<H1>A Hacker's Guide to NCURSES</H1>
19
20<H1>Contents</H1>
21<UL>
22<LI><A HREF="#abstract">Abstract</A>
23<LI><A HREF="#objective">Objective of the Package</A>
24<UL>
25<LI><A HREF="#whysvr4">Why System V Curses?</A>
26<LI><A HREF="#extensions">How to Design Extensions</A>
27</UL>
28<LI><A HREF="#portability">Portability and Configuration</A>
29<LI><A HREF="#documentation">Documentation Conventions</A>
30<LI><A HREF="#bugtrack">How to Report Bugs</A>
31<LI><A HREF="#ncurslib">A Tour of the Ncurses Library</A>
32<UL>
33<LI><A HREF="#loverview">Library Overview</A>
34<LI><A HREF="#engine">The Engine Room</A>
35<LI><A HREF="#input">Keyboard Input</A>
36<LI><A HREF="#mouse">Mouse Events</A>
37<LI><A HREF="#output">Output and Screen Updating</A>
38</UL>
39<LI><A HREF="#fmnote">The Forms and Menu Libraries</A>
40<LI><A HREF="#tic">A Tour of the Terminfo Compiler</A>
41<UL>
42<LI><A HREF="#nonuse">Translation of Non-<STRONG>use</STRONG> Capabilities</A>
43<LI><A HREF="#uses">Use Capability Resolution</A>
44<LI><A HREF="#translation">Source-Form Translation</A>
45</UL>
46<LI><A HREF="#utils">Other Utilities</A>
47<LI><A HREF="#style">Style Tips for Developers</A>
48<LI><A HREF="#port">Porting Hints</A>
49</UL>
50
51<H1><A NAME="abstract">Abstract</A></H1>
52
53This document is a hacker's tour of the <STRONG>ncurses</STRONG> library and utilities.
54It discusses design philosophy, implementation methods, and the
55conventions used for coding and documentation. It is recommended
56reading for anyone who is interested in porting, extending or improving the
57package.
58
59<H1><A NAME="objective">Objective of the Package</A></H1>
60
61The objective of the <STRONG>ncurses</STRONG> package is to provide a free software API for
62character-cell terminals and terminal emulators with the following
63characteristics:
64
65<UL>
66<LI>Source-compatible with historical curses implementations (including
67 the original BSD curses and System V curses.
68<LI>Conformant with the XSI Curses standard issued as part of XPG4 by
69 X/Open.
70<LI>High-quality -- stable and reliable code, wide portability, good
71 packaging, superior documentation.
72<LI>Featureful -- should eliminate as much of the drudgery of C interface
73 programming as possible, freeing programmers to think at a higher
74 level of design.
75</UL>
76
77These objectives are in priority order. So, for example, source
78compatibility with older version must trump featurefulness -- we cannot
79add features if it means breaking the portion of the API corresponding
80to historical curses versions.
81
82<H2><A NAME="whysvr4">Why System V Curses?</A></H2>
83
84We used System V curses as a model, reverse-engineering their API, in
85order to fulfill the first two objectives. <P>
86
87System V curses implementations can support BSD curses programs with
88just a recompilation, so by capturing the System V API we also
89capture BSD's. <P>
90
91More importantly for the future, the XSI Curses standard issued by X/Open
92is explicitly and closely modeled on System V. So conformance with
93System V took us most of the way to base-level XSI conformance.
94
95<H2><A NAME="extensions">How to Design Extensions</A></H2>
96
97The third objective (standards conformance) requires that it be easy to
98condition source code using <STRONG>ncurses</STRONG> so that the absence of nonstandard
99extensions does not break the code. <P>
100
101Accordingly, we have a policy of associating with each nonstandard extension
102a feature macro, so that ncurses client code can use this macro to condition
103in or out the code that requires the <STRONG>ncurses</STRONG> extension. <P>
104
105For example, there is a macro <CODE>NCURSES_MOUSE_VERSION</CODE> which XSI Curses
106does not define, but which is defined in the <STRONG>ncurses</STRONG> library header.
107You can use this to condition the calls to the mouse API calls.
108
109<H1><A NAME="portability">Portability and Configuration</A></H1>
110
111Code written for <STRONG>ncurses</STRONG> may assume an ANSI-standard C compiler and
112POSIX-compatible OS interface. It may also assume the presence of a
113System-V-compatible <EM>select(2)</EM> call. <P>
114
115We encourage (but do not require) developers to make the code friendly
116to less-capable UNIX environments wherever possible. <P>
117
118We encourage developers to support OS-specific optimizations and methods
119not available under POSIX/ANSI, provided only that:
120
121<UL>
122<LI>All such code is properly conditioned so the build process does not
123 attempt to compile it under a plain ANSI/POSIX environment.
124<LI>Adding such implementation methods does not introduce incompatibilities
125 in the <STRONG>ncurses</STRONG> API between platforms.
126</UL>
127
128We use GNU <CODE>autoconf(1)</CODE> as a tool to deal with portability issues.
129The right way to leverage an OS-specific feature is to modify the autoconf
130specification files (configure.in and aclocal.m4) to set up a new feature
131macro, which you then use to condition your code.
132
133<H1><A NAME="documentation">Documentation Conventions</A></H1>
134
135There are three kinds of documentation associated with this package. Each
136has a different preferred format:
137
138<UL>
139<LI>Package-internal files (README, INSTALL, TO-DO etc.)
140<LI>Manual pages.
141<LI>Everything else (i.e., narrative documentation).
142</UL>
143
144Our conventions are simple:
145<OL>
146<LI><STRONG>Maintain package-internal files in plain text.</STRONG>
147 The expected viewer for them <EM>more(1)</EM> or an editor window; there's
148 no point in elaborate mark-up.
149
150<LI><STRONG>Mark up manual pages in the man macros.</STRONG> These have to be viewable
151 through traditional <EM>man(1)</EM> programs.
152
153<LI><STRONG>Write everything else in HTML.</STRONG>
154</OL>
155
156When in doubt, HTMLize a master and use <EM>lynx(1)</EM> to generate
157plain ASCII (as we do for the announcement document). <P>
158
159The reason for choosing HTML is that it's (a) well-adapted for on-line
160browsing through viewers that are everywhere; (b) more easily readable
161as plain text than most other mark-ups, if you don't have a viewer; and (c)
162carries enough information that you can generate a nice-looking printed
163version from it. Also, of course, it make exporting things like the
164announcement document to WWW pretty trivial.
165
166<H1><A NAME="bugtrack">How to Report Bugs</A></H1>
167
168The <A NAME="bugreport">reporting address for bugs</A> is
169<A HREF="mailto:bug-ncurses@gnu.org">bug-ncurses@gnu.org</A>.
170This is a majordomo list; to join, write
171to <CODE>bug-ncurses-request@gnu.org</CODE> with a message containing the line:
172<PRE>
173 subscribe &lt;name&gt;@&lt;host.domain&gt;
174</PRE>
175
176The <CODE>ncurses</CODE> code is maintained by a small group of
177volunteers. While we try our best to fix bugs promptly, we simply
178don't have a lot of hours to spend on elementary hand-holding. We rely
179on intelligent cooperation from our users. If you think you have
180found a bug in <CODE>ncurses</CODE>, there are some steps you can take
181before contacting us that will help get the bug fixed quickly. <P>
182
183In order to use our bug-fixing time efficiently, we put people who
184show us they've taken these steps at the head of our queue. This
185means that if you don't, you'll probably end up at the tail end and
186have to wait a while.
187
188<OL>
189<LI>Develop a recipe to reproduce the bug.
190<p>
191Bugs we can reproduce are likely to be fixed very quickly, often
192within days. The most effective single thing you can do to get a
193quick fix is develop a way we can duplicate the bad behavior --
194ideally, by giving us source for a small, portable test program that
195breaks the library. (Even better is a keystroke recipe using one of
196the test programs provided with the distribution.)
197
198<LI>Try to reproduce the bug on a different terminal type. <P>
199
200In our experience, most of the behaviors people report as library bugs
201are actually due to subtle problems in terminal descriptions. This is
202especially likely to be true if you're using a traditional
203asynchronous terminal or PC-based terminal emulator, rather than xterm
204or a UNIX console entry. <P>
205
206It's therefore extremely helpful if you can tell us whether or not your
207problem reproduces on other terminal types. Usually you'll have both
208a console type and xterm available; please tell us whether or not your
209bug reproduces on both. <P>
210
211If you have xterm available, it is also good to collect xterm reports for
212different window sizes. This is especially true if you normally use an
213unusual xterm window size -- a surprising number of the bugs we've seen
214are either triggered or masked by these.
215
216<LI>Generate and examine a trace file for the broken behavior. <P>
217
218Recompile your program with the debugging versions of the libraries.
219Insert a <CODE>trace()</CODE> call with the argument set to <CODE>TRACE_UPDATE</CODE>.
220(See <A HREF="ncurses-intro.html#debugging">"Writing Programs with
221NCURSES"</A> for details on trace levels.)
222Reproduce your bug, then look at the trace file to see what the library
223was actually doing. <P>
224
225Another frequent cause of apparent bugs is application coding errors
226that cause the wrong things to be put on the virtual screen. Looking
227at the virtual-screen dumps in the trace file will tell you immediately if
228this is happening, and save you from the possible embarrassment of being
229told that the bug is in your code and is your problem rather than ours. <P>
230
231If the virtual-screen dumps look correct but the bug persists, it's
232possible to crank up the trace level to give more and more information
233about the library's update actions and the control sequences it issues
234to perform them. The test directory of the distribution contains a
235tool for digesting these logs to make them less tedious to wade
236through. <P>
237
238Often you'll find terminfo problems at this stage by noticing that the
239escape sequences put out for various capabilities are wrong. If not,
240you're likely to learn enough to be able to characterize any bug in
241the screen-update logic quite exactly.
242
243<LI>Report details and symptoms, not just interpretations. <P>
244
245If you do the preceding two steps, it is very likely that you'll discover
246the nature of the problem yourself and be able to send us a fix. This
247will create happy feelings all around and earn you good karma for the first
248time you run into a bug you really can't characterize and fix yourself. <P>
249
250If you're still stuck, at least you'll know what to tell us. Remember, we
251need details. If you guess about what is safe to leave out, you are too
252likely to be wrong. <P>
253
254If your bug produces a bad update, include a trace file. Try to make
255the trace at the <EM>least</EM> voluminous level that pins down the
256bug. Logs that have been through tracemunch are OK, it doesn't throw
257away any information (actually they're better than un-munched ones because
258they're easier to read). <P>
259
260If your bug produces a core-dump, please include a symbolic stack trace
261generated by gdb(1) or your local equivalent. <P>
262
263Tell us about every terminal on which you've reproduced the bug -- and
264every terminal on which you can't. Ideally, sent us terminfo sources
265for all of these (yours might differ from ours). <P>
266
267Include your ncurses version and your OS/machine type, of course! You can
268find your ncurses version in the <CODE>curses.h</CODE> file.
269</OL>
270
271If your problem smells like a logic error or in cursor movement or
272scrolling or a bad capability, there are a couple of tiny test frames
273for the library algorithms in the progs directory that may help you
274isolate it. These are not part of the normal build, but do have their
275own make productions. <P>
276
277The most important of these is <CODE>mvcur</CODE>, a test frame for the
278cursor-movement optimization code. With this program, you can see
279directly what control sequences will be emitted for any given cursor
280movement or scroll/insert/delete operations. If you think you've got
281a bad capability identified, you can disable it and test again. The
282program is command-driven and has on-line help. <P>
283
284If you think the vertical-scroll optimization is broken, or just want to
285understand how it works better, build <CODE>hashmap</CODE> and read the
286header comments of <CODE>hardscroll.c</CODE> and <CODE>hashmap.c</CODE>; then try
287it out. You can also test the hardware-scrolling optimization separately
288with <CODE>hardscroll</CODE>. <P>
289
290There's one other interactive tester, <CODE>tctest</CODE>, that exercises
291translation between termcap and terminfo formats. If you have a serious
292need to run this, you probably belong on our development team!
293
294<H1><A NAME="ncurslib">A Tour of the Ncurses Library</A></H1>
295
296<H2><A NAME="loverview">Library Overview</A></H2>
297
298Most of the library is superstructure -- fairly trivial convenience
299interfaces to a small set of basic functions and data structures used
300to manipulate the virtual screen (in particular, none of this code
301does any I/O except through calls to more fundamental modules
302described below). The files
303<blockquote>
304<CODE>
305lib_addch.c
306lib_bkgd.c
307lib_box.c
308lib_chgat.c
309lib_clear.c
310lib_clearok.c
311lib_clrbot.c
312lib_clreol.c
313lib_colorset.c
314lib_data.c
315lib_delch.c
316lib_delwin.c
317lib_echo.c
318lib_erase.c
319lib_gen.c
320lib_getstr.c
321lib_hline.c
322lib_immedok.c
323lib_inchstr.c
324lib_insch.c
325lib_insdel.c
326lib_insstr.c
327lib_instr.c
328lib_isendwin.c
329lib_keyname.c
330lib_leaveok.c
331lib_move.c
332lib_mvwin.c
333lib_overlay.c
334lib_pad.c
335lib_printw.c
336lib_redrawln.c
337lib_scanw.c
338lib_screen.c
339lib_scroll.c
340lib_scrollok.c
341lib_scrreg.c
342lib_set_term.c
343lib_slk.c
344lib_slkatr_set.c
345lib_slkatrof.c
346lib_slkatron.c
347lib_slkatrset.c
348lib_slkattr.c
349lib_slkclear.c
350lib_slkcolor.c
351lib_slkinit.c
352lib_slklab.c
353lib_slkrefr.c
354lib_slkset.c
355lib_slktouch.c
356lib_touch.c
357lib_unctrl.c
358lib_vline.c
359lib_wattroff.c
360lib_wattron.c
361lib_window.c
362</CODE>
363</blockquote>
364are all in this category. They are very
365unlikely to need change, barring bugs or some fundamental
366reorganization in the underlying data structures. <P>
367
368These files are used only for debugging support:
369<blockquote>
370<code>
371lib_trace.c
372lib_traceatr.c
373lib_tracebits.c
374lib_tracechr.c
375lib_tracedmp.c
376lib_tracemse.c
377trace_buf.c
378</code>
379</blockquote>
380It is rather unlikely you will ever need to change these, unless
381you want to introduce a new debug trace level for some reasoon.<P>
382
383There is another group of files that do direct I/O via <EM>tputs()</EM>,
384computations on the terminal capabilities, or queries to the OS
385environment, but nevertheless have only fairly low complexity. These
386include:
387<blockquote>
388<code>
389lib_acs.c
390lib_beep.c
391lib_color.c
392lib_endwin.c
393lib_initscr.c
394lib_longname.c
395lib_newterm.c
396lib_options.c
397lib_termcap.c
398lib_ti.c
399lib_tparm.c
400lib_tputs.c
401lib_vidattr.c
402read_entry.c.
403</code>
404</blockquote>
405They are likely to need revision only if
406ncurses is being ported to an environment without an underlying
407terminfo capability representation. <P>
408
409These files
410have serious hooks into
411the tty driver and signal facilities:
412<blockquote>
413<code>
414lib_kernel.c
415lib_baudrate.c
416lib_raw.c
417lib_tstp.c
418lib_twait.c
419</code>
420</blockquote>
421If you run into porting snafus
422moving the package to another UNIX, the problem is likely to be in one
423of these files.
424The file <CODE>lib_print.c</CODE> uses sleep(2) and also
425falls in this category.<P>
426
427Almost all of the real work is done in the files
428<blockquote>
429<code>
430hardscroll.c
431hashmap.c
432lib_addch.c
433lib_doupdate.c
434lib_getch.c
435lib_mouse.c
436lib_mvcur.c
437lib_refresh.c
438lib_setup.c
439lib_vidattr.c
440</code>
441</blockquote>
442Most of the algorithmic complexity in the
443library lives in these files.
444If there is a real bug in <STRONG>ncurses</STRONG> itself, it's probably here.
445We'll tour some of these files in detail
446below (see <A HREF="#engine">The Engine Room</A>). <P>
447
448Finally, there is a group of files that is actually most of the
449terminfo compiler. The reason this code lives in the <STRONG>ncurses</STRONG>
450library is to support fallback to /etc/termcap. These files include
451<blockquote>
452<code>
453alloc_entry.c
454captoinfo.c
455comp_captab.c
456comp_error.c
457comp_hash.c
458comp_parse.c
459comp_scan.c
460parse_entry.c
461read_termcap.c
462write_entry.c
463</code>
464</blockquote>
465We'll discuss these in the compiler tour.
466
467<H2><A NAME="engine">The Engine Room</A></H2>
468
469<H3><A NAME="input">Keyboard Input</A></H3>
470
471All <CODE>ncurses</CODE> input funnels through the function
472<CODE>wgetch()</CODE>, defined in <CODE>lib_getch.c</CODE>. This function is
473tricky; it has to poll for keyboard and mouse events and do a running
474match of incoming input against the set of defined special keys. <P>
475
476The central data structure in this module is a FIFO queue, used to
477match multiple-character input sequences against special-key
478capabilities; also to implement pushback via <CODE>ungetch()</CODE>. <P>
479
480The <CODE>wgetch()</CODE> code distinguishes between function key
481sequences and the same sequences typed manually by doing a timed wait
482after each input character that could lead a function key sequence.
483If the entire sequence takes less than 1 second, it is assumed to have
484been generated by a function key press. <P>
485
486Hackers bruised by previous encounters with variant <CODE>select(2)</CODE>
487calls may find the code in <CODE>lib_twait.c</CODE> interesting. It deals
488with the problem that some BSD selects don't return a reliable
489time-left value. The function <CODE>timed_wait()</CODE> effectively
490simulates a System V select.
491
492<H3><A NAME="mouse">Mouse Events</A></H3>
493
494If the mouse interface is active, <CODE>wgetch()</CODE> polls for mouse
495events each call, before it goes to the keyboard for input. It is
496up to <CODE>lib_mouse.c</CODE> how the polling is accomplished; it may vary
497for different devices. <P>
498
499Under xterm, however, mouse event notifications come in via the keyboard
500input stream. They are recognized by having the <STRONG>kmous</STRONG> capability
501as a prefix. This is kind of klugey, but trying to wire in recognition of
502a mouse key prefix without going through the function-key machinery would
503be just too painful, and this turns out to imply having the prefix somewhere
504in the function-key capabilities at terminal-type initialization. <P>
505
506This kluge only works because <STRONG>kmous</STRONG> isn't actually used by any
507historic terminal type or curses implementation we know of. Best
508guess is it's a relic of some forgotten experiment in-house at Bell
509Labs that didn't leave any traces in the publicly-distributed System V
510terminfo files. If System V or XPG4 ever gets serious about using it
511again, this kluge may have to change. <P>
512
513Here are some more details about mouse event handling: <P>
514
515The <CODE>lib_mouse()</CODE>code is logically split into a lower level that
516accepts event reports in a device-dependent format and an upper level that
517parses mouse gestures and filters events. The mediating data structure is a
518circular queue of event structures. <P>
519
520Functionally, the lower level's job is to pick up primitive events and
521put them on the circular queue. This can happen in one of two ways:
522either (a) <CODE>_nc_mouse_event()</CODE> detects a series of incoming
523mouse reports and queues them, or (b) code in <CODE>lib_getch.c</CODE> detects the
524<STRONG>kmous</STRONG> prefix in the keyboard input stream and calls _nc_mouse_inline
525to queue up a series of adjacent mouse reports. <P>
526
527In either case, <CODE>_nc_mouse_parse()</CODE> should be called after the
528series is accepted to parse the digested mouse reports (low-level
529events) into a gesture (a high-level or composite event).
530
531<H3><A NAME="output">Output and Screen Updating</A></H3>
532
533With the single exception of character echoes during a <CODE>wgetnstr()</CODE>
534call (which simulates cooked-mode line editing in an ncurses window),
535the library normally does all its output at refresh time. <P>
536
537The main job is to go from the current state of the screen (as represented
538in the <CODE>curscr</CODE> window structure) to the desired new state (as
539represented in the <CODE>newscr</CODE> window structure), while doing as
540little I/O as possible. <P>
541
542The brains of this operation are the modules <CODE>hashmap.c</CODE>,
543<CODE>hardscroll.c</CODE> and <CODE>lib_doupdate.c</CODE>; the latter two use
544<CODE>lib_mvcur.c</CODE>. Essentially, what happens looks like this: <P>
545
546The <CODE>hashmap.c</CODE> module tries to detect vertical motion
547changes between the real and virtual screens. This information
548is represented by the oldindex members in the newscr structure.
549These are modified by vertical-motion and clear operations, and both are
550re-initialized after each update. To this change-journalling
551information, the hashmap code adds deductions made using a modified Heckel
552algorithm on hash values generated from the line contents. <P>
553
554The <CODE>hardscroll.c</CODE> module computes an optimum set of scroll,
555insertion, and deletion operations to make the indices match. It calls
556<CODE>_nc_mvcur_scrolln()</CODE> in <CODE>lib_mvcur.c</CODE> to do those motions. <P>
557
558Then <CODE>lib_doupdate.c</CODE> goes to work. Its job is to do line-by-line
559transformations of <CODE>curscr</CODE> lines to <CODE>newscr</CODE> lines. Its main
560tool is the routine <CODE>mvcur()</CODE> in <CODE>lib_mvcur.c</CODE>. This routine
561does cursor-movement optimization, attempting to get from given screen
562location A to given location B in the fewest output characters posible. <P>
563
564If you want to work on screen optimizations, you should use the fact
565that (in the trace-enabled version of the library) enabling the
566<CODE>TRACE_TIMES</CODE> trace level causes a report to be emitted after
567each screen update giving the elapsed time and a count of characters
568emitted during the update. You can use this to tell when an update
569optimization improves efficiency. <P>
570
571In the trace-enabled version of the library, it is also possible to disable
572and re-enable various optimizations at runtime by tweaking the variable
573<CODE>_nc_optimize_enable</CODE>. See the file <CODE>include/curses.h.in</CODE>
574for mask values, near the end.
575
576<H1><A NAME="fmnote">The Forms and Menu Libraries</A></H1>
577
578The forms and menu libraries should work reliably in any environment you
579can port ncurses to. The only portability issue anywhere in them is what
580flavor of regular expressions the built-in form field type TYPE_REGEXP
581will recognize. <P>
582
583The configuration code prefers the POSIX regex facility, modeled on
584System V's, but will settle for BSD regexps if the former isn't available. <P>
585
586Historical note: the panels code was written primarily to assist in
587porting u386mon 2.0 (comp.sources.misc v14i001-4) to systems lacking
588panels support; u386mon 2.10 and beyond use it. This version has been
589slightly cleaned up for <CODE>ncurses</CODE>.
590
591<H1><A NAME="tic">A Tour of the Terminfo Compiler</A></H1>
592
593The <STRONG>ncurses</STRONG> implementation of <STRONG>tic</STRONG> is rather complex
594internally; it has to do a trying combination of missions. This starts
595with the fact that, in addition to its normal duty of compiling
596terminfo sources into loadable terminfo binaries, it has to be able to
597handle termcap syntax and compile that too into terminfo entries. <P>
598
599The implementation therefore starts with a table-driven, dual-mode
600lexical analyzer (in <CODE>comp_scan.c</CODE>). The lexer chooses its
601mode (termcap or terminfo) based on the first `,' or `:' it finds in
602each entry. The lexer does all the work of recognizing capability
603names and values; the grammar above it is trivial, just "parse entries
604till you run out of file".
605
606<H2><A NAME="nonuse">Translation of Non-<STRONG>use</STRONG> Capabilities</A></H2>
607
608Translation of most things besides <STRONG>use</STRONG> capabilities is pretty
609straightforward. The lexical analyzer's tokenizer hands each capability
610name to a hash function, which drives a table lookup. The table entry
611yields an index which is used to look up the token type in another table,
612and controls interpretation of the value. <P>
613
614One possibly interesting aspect of the implementation is the way the
615compiler tables are initialized. All the tables are generated by various
616awk/sed/sh scripts from a master table <CODE>include/Caps</CODE>; these
617scripts actually write C initializers which are linked to the compiler.
618Furthermore, the hash table is generated in the same way, so it doesn't
619have to be generated at compiler startup time (another benefit of this
620organization is that the hash table can be in shareable text space). <P>
621
622Thus, adding a new capability is usually pretty trivial, just a matter
623of adding one line to the <CODE>include/Caps</CODE> file. We'll have more
624to say about this in the section on <A HREF="#translation">Source-Form
625Translation</A>.
626
627<H2><A NAME="uses">Use Capability Resolution</A></H2>
628
629The background problem that makes <STRONG>tic</STRONG> tricky isn't the capability
630translation itself, it's the resolution of <STRONG>use</STRONG> capabilities. Older
631versions would not handle forward <STRONG>use</STRONG> references for this reason
632(that is, a using terminal always had to follow its use target in the
633source file). By doing this, they got away with a simple implementation
634tactic; compile everything as it blows by, then resolve uses from compiled
635entries. <P>
636
637This won't do for <STRONG>ncurses</STRONG>. The problem is that that the whole
638compilation process has to be embeddable in the <STRONG>ncurses</STRONG> library
639so that it can be called by the startup code to translate termcap
640entries on the fly. The embedded version can't go promiscuously writing
641everything it translates out to disk -- for one thing, it will typically
642be running with non-root permissions. <P>
643
644So our <STRONG>tic</STRONG> is designed to parse an entire terminfo file into a
645doubly-linked circular list of entry structures in-core, and then do
646<STRONG>use</STRONG> resolution in-memory before writing everything out. This
647design has other advantages: it makes forward and back use-references
648equally easy (so we get the latter for free), and it makes checking for
649name collisions before they're written out easy to do. <P>
650
651And this is exactly how the embedded version works. But the stand-alone
652user-accessible version of <STRONG>tic</STRONG> partly reverts to the historical
653strategy; it writes to disk (not keeping in core) any entry with no
654<STRONG>use</STRONG> references. <P>
655
656This is strictly a core-economy kluge, implemented because the
657terminfo master file is large enough that some core-poor systems swap
658like crazy when you compile it all in memory...there have been reports of
659this process taking <STRONG>three hours</STRONG>, rather than the twenty seconds
660or less typical on the author's development box. <P>
661
662So. The executable <STRONG>tic</STRONG> passes the entry-parser a hook that
663<EM>immediately</EM> writes out the referenced entry if it has no use
664capabilities. The compiler main loop refrains from adding the entry
665to the in-core list when this hook fires. If some other entry later
666needs to reference an entry that got written immediately, that's OK;
667the resolution code will fetch it off disk when it can't find it in
668core. <P>
669
670Name collisions will still be detected, just not as cleanly. The
671<CODE>write_entry()</CODE> code complains before overwriting an entry that
672postdates the time of <STRONG>tic</STRONG>'s first call to
673<CODE>write_entry()</CODE>, Thus it will complain about overwriting
674entries newly made during the <STRONG>tic</STRONG> run, but not about
675overwriting ones that predate it.
676
677<H2><A NAME="translation">Source-Form Translation</A></H2>
678
679Another use of <STRONG>tic</STRONG> is to do source translation between various termcap
680and terminfo formats. There are more variants out there than you might
681think; the ones we know about are described in the <STRONG>captoinfo(1)</STRONG>
682manual page. <P>
683
684The translation output code (<CODE>dump_entry()</CODE> in
685<CODE>ncurses/dump_entry.c</CODE>) is shared with the <STRONG>infocmp(1)</STRONG>
686utility. It takes the same internal representation used to generate
687the binary form and dumps it to standard output in a specified
688format. <P>
689
690The <CODE>include/Caps</CODE> file has a header comment describing ways you
691can specify source translations for nonstandard capabilities just by
692altering the master table. It's possible to set up capability aliasing
693or tell the compiler to plain ignore a given capability without writing
694any C code at all. <P>
695
696For circumstances where you need to do algorithmic translation, there
697are functions in <CODE>parse_entry.c</CODE> called after the parse of each
698entry that are specifically intended to encapsulate such
699translations. This, for example, is where the AIX <STRONG>box1</STRONG> capability
700get translated to an <STRONG>acsc</STRONG> string.
701
702<H1><A NAME="utils">Other Utilities</A></H1>
703
704The <STRONG>infocmp</STRONG> utility is just a wrapper around the same
705entry-dumping code used by <STRONG>tic</STRONG> for source translation. Perhaps
706the one interesting aspect of the code is the use of a predicate
707function passed in to <CODE>dump_entry()</CODE> to control which
708capabilities are dumped. This is necessary in order to handle both
709the ordinary De-compilation case and entry difference reporting. <P>
710
711The <STRONG>tput</STRONG> and <STRONG>clear</STRONG> utilities just do an entry load
712followed by a <CODE>tputs()</CODE> of a selected capability.
713
714<H1><A NAME="style">Style Tips for Developers</A></H1>
715
716See the TO-DO file in the top-level directory of the source distribution
717for additions that would be particularly useful. <P>
718
719The prefix <CODE>_nc_</CODE> should be used on library public functions that are
720not part of the curses API in order to prevent pollution of the
721application namespace.
722
723If you have to add to or modify the function prototypes in curses.h.in,
724read ncurses/MKlib_gen.sh first so you can avoid breaking XSI conformance.
725
726Please join the ncurses mailing list. See the INSTALL file in the
727top level of the distribution for details on the list. <P>
728
729Look for the string <CODE>FIXME</CODE> in source files to tag minor bugs
730and potential problems that could use fixing. <P>
731
732Don't try to auto-detect OS features in the main body of the C code.
733That's the job of the configuration system. <P>
734
735To hold down complexity, do make your code data-driven. Especially,
736if you can drive logic from a table filtered out of
737<CODE>include/Caps</CODE>, do it. If you find you need to augment the
738data in that file in order to generate the proper table, that's still
739preferable to ad-hoc code -- that's why the fifth field (flags) is
740there. <P>
741
742Have fun!
743
744<H1><A NAME="port">Porting Hints</A></H1>
745
746The following notes are intended to be a first step towards DOS and Macintosh
747ports of the ncurses libraries. <P>
748
749The following library modules are `pure curses'; they operate only on
750the curses internal structures, do all output through other curses
751calls (not including <CODE>tputs()</CODE> and <CODE>putp()</CODE>) and do not
752call any other UNIX routines such as signal(2) or the stdio library.
753Thus, they should not need to be modified for single-terminal
754ports.
755
756<blockquote>
757<code>
758lib_addch.c
759lib_addstr.c
760lib_bkgd.c
761lib_box.c
762lib_clear.c
763lib_clrbot.c
764lib_clreol.c
765lib_delch.c
766lib_delwin.c
767lib_erase.c
768lib_inchstr.c
769lib_insch.c
770lib_insdel.c
771lib_insstr.c
772lib_keyname.c
773lib_move.c
774lib_mvwin.c
775lib_newwin.c
776lib_overlay.c
777lib_pad.c
778lib_printw.c
779lib_refresh.c
780lib_scanw.c
781lib_scroll.c
782lib_scrreg.c
783lib_set_term.c
784lib_touch.c
785lib_tparm.c
786lib_tputs.c
787lib_unctrl.c
788lib_window.c
789panel.c
790</code>
791</blockquote>
792<P>
793
794This module is pure curses, but calls outstr():
795
796<blockquote>
797<code>
798lib_getstr.c
799</code>
800</blockquote>
801<P>
802
803These modules are pure curses, except that they use <CODE>tputs()</CODE>
804and <CODE>putp()</CODE>:
805
806<blockquote>
807<code>
808lib_beep.c
809lib_color.c
810lib_endwin.c
811lib_options.c
812lib_slk.c
813lib_vidattr.c
814</code>
815</blockquote>
816<P>
817
818This modules assist in POSIX emulation on non-POSIX systems:
819<DL>
820<DT> sigaction.c
821<DD> signal calls
822</DL>
823
824The following source files will not be needed for a
825single-terminal-type port.
826
827<blockquote>
828<code>
829alloc_entry.c
830captoinfo.c
831clear.c
832comp_captab.c
833comp_error.c
834comp_hash.c
835comp_main.c
836comp_parse.c
837comp_scan.c
838dump_entry.c
839infocmp.c
840parse_entry.c
841read_entry.c
842tput.c
843write_entry.c
844</code>
845</blockquote>
846<P>
847
848The following modules will use open()/read()/write()/close()/lseek() on files,
849but no other OS calls.
850
851<DL>
852<DT>lib_screen.c
853<DD>used to read/write screen dumps
854<DT>lib_trace.c
855<DD>used to write trace data to the logfile
856</DL>
857
858Modules that would have to be modified for a port start here: <P>
859
860The following modules are `pure curses' but contain assumptions inappropriate
861for a memory-mapped port.
862
863<dl>
864<dt>lib_longname.c<dd>assumes there may be multiple terminals
865<dt>lib_acs.c<dd>assumes acs_map as a double indirection
866<dt>lib_mvcur.c<dd>assumes cursor moves have variable cost
867<dt>lib_termcap.c<dd>assumes there may be multiple terminals
868<dt>lib_ti.c<dd>assumes there may be multiple terminals
869</dl>
870
871The following modules use UNIX-specific calls:
872
873<dl>
874<dt>lib_doupdate.c<dd>input checking
875<dt>lib_getch.c<dd>read()
876<dt>lib_initscr.c<dd>getenv()
877<dt>lib_newterm.c
878<dt>lib_baudrate.c
879<dt>lib_kernel.c<dd>various tty-manipulation and system calls
880<dt>lib_raw.c<dd>various tty-manipulation calls
881<dt>lib_setup.c<dd>various tty-manipulation calls
882<dt>lib_restart.c<dd>various tty-manipulation calls
883<dt>lib_tstp.c<dd>signal-manipulation calls
884<dt>lib_twait.c<dd>gettimeofday(), select().
885</dl>
886
887<HR>
888<ADDRESS>Eric S. Raymond &lt;esr@snark.thyrsus.com&gt;</ADDRESS>
889(Note: This is <EM>not</EM> the <A HREF="#bugtrack">bug address</A>!)
890</BODY>
891</HTML>
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