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Dickey * - * Copyright 2000-2013,2017 Free Software Foundation, Inc. * - * * - * Permission is hereby granted, free of charge, to any person obtaining a * - * copy of this software and associated documentation files (the * - * "Software"), to deal in the Software without restriction, including * - * without limitation the rights to use, copy, modify, merge, publish, * - * distribute, distribute with modifications, sublicense, and/or sell * - * copies of the Software, and to permit persons to whom the Software is * - * furnished to do so, subject to the following conditions: * - * * - * The above copyright notice and this permission notice shall be included * - * in all copies or substantial portions of the Software. * - * * - * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS * - * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF * - * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. * - * IN NO EVENT SHALL THE ABOVE COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, * - * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR * - * OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR * - * THE USE OR OTHER DEALINGS IN THE SOFTWARE. * - * * - * Except as contained in this notice, the name(s) of the above copyright * - * holders shall not be used in advertising or otherwise to promote the * - * sale, use or other dealings in this Software without prior written * - * authorization. * - **************************************************************************** ---> -<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN"> -<html> -<head> - <meta name="generator" content= - "HTML Tidy for HTML5 for Linux version 5.6.0"> - <title>A Hacker's Guide to Ncurses Internals</title> - <link rel="author" href="mailto:bugs-ncurses@gnu.org"> - <meta http-equiv="Content-Type" content= - "text/html; charset=us-ascii"><!-- -This document is self-contained, *except* that there is one relative link to -the ncurses-intro.html document, expected to be in the same directory with -this one. ---> -</head> -<body> - <h1 class="no-header">A Hacker's Guide to NCURSES</h1> - - <h2>A Hacker's Guide to NCURSES</h2> - - <div class="nav"> - <h2>Contents</h2> - - <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> - </div> - - <h2><a name="abstract" id="abstract">Abstract</a></h2> - - <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> - - <h2><a name="objective" id="objective">Objective of the - Package</a></h2> - - <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> - - <h3><a name="whysvr4" id="whysvr4">Why System V Curses?</a></h3> - - <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> - - <h3><a name="extensions" id="extensions">How to Design - Extensions</a></h3> - - <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> - - <h2><a name="portability" id="portability">Portability and - Configuration</a></h2> - - <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> - - <h2><a name="documentation" id="documentation">Documentation - Conventions</a></h2> - - <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> - - <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 is <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> - - <h2><a name="bugtrack" id="bugtrack">How to Report Bugs</a></h2> - - <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 class="code-block"> - subscribe <name>@<host.domain> -</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><p>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><p>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><p>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><p>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, send 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> - - <h2><a name="ncurslib" id="ncurslib">A Tour of the Ncurses - Library</a></h2> - - <h3><a name="loverview" id="loverview">Library Overview</a></h3> - - <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> - - <h3><a name="engine" id="engine">The Engine Room</a></h3> - - <h4><a name="input" id="input">Keyboard Input</a></h4> - - <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> - - <h4><a name="mouse" id="mouse">Mouse Events</a></h4> - - <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> - - <h4><a name="output" id="output">Output and Screen Updating</a></h4> - - <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> - - <ul> - <li> - <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> - </li> - - <li> - <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> - </li> - - <li> - <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> - </li> - </ul> - - <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> - - <h2><a name="fmnote" id="fmnote">The Forms and Menu Libraries</a></h2> - - <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> - - <h2><a name="tic" id="tic">A Tour of the Terminfo Compiler</a></h2> - - <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> - - <h3><a name="nonuse" id="nonuse">Translation of - Non-<strong>use</strong> Capabilities</a></h3> - - <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> - - <h3><a name="uses" id="uses">Use Capability Resolution</a></h3> - - <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> - - <h3><a name="translation" id="translation">Source-Form - Translation</a></h3> - - <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> - - <h2><a name="utils" id="utils">Other Utilities</a></h2> - - <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> - - <h2><a name="style" id="style">Style Tips for Developers</a></h2> - - <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> - - <h2><a name="port" id="port">Porting Hints</a></h2> - - <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> |