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Annotation of 43BSDReno/share/doc/ps1/18.curses/intro.4, revision 1.1

1.1     ! root        1: .\" Copyright (c) 1980 The Regents of the University of California.
        !             2: .\" All rights reserved.
        !             3: .\"
        !             4: .\" Redistribution and use in source and binary forms are permitted
        !             5: .\" provided that the above copyright notice and this paragraph are
        !             6: .\" duplicated in all such forms and that any documentation,
        !             7: .\" advertising materials, and other materials related to such
        !             8: .\" distribution and use acknowledge that the software was developed
        !             9: .\" by the University of California, Berkeley.  The name of the
        !            10: .\" University may not be used to endorse or promote products derived
        !            11: .\" from this software without specific prior written permission.
        !            12: .\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
        !            13: .\" IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
        !            14: .\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
        !            15: .\"
        !            16: .\"    @(#)intro.4     6.2 (Berkeley) 3/17/89
        !            17: .\"
        !            18: .sh 1 "Cursor Motion Optimization: Standing Alone"
        !            19: .pp
        !            20: It is possible to use the cursor optimization functions of this screen package
        !            21: without the overhead and additional size of the screen updating functions.
        !            22: The screen updating functions are designed for uses
        !            23: where parts of the screen are changed,
        !            24: but the overall image remains the same.
        !            25: This includes such programs as
        !            26: .b rogue
        !            27: and
        !            28: .b vi \**.
        !            29: .(f
        !            30: \**
        !            31: .b rogue
        !            32: actually uses these functions,
        !            33: .b vi
        !            34: does not.
        !            35: .)f
        !            36: Certain other programs
        !            37: will find it difficult to use these functions in this manner
        !            38: without considerable unnecessary program overhead.
        !            39: For such applications,
        !            40: such as some
        !            41: .q "\fIcrt hacks\fR\|" \**
        !            42: .(f
        !            43: \**
        !            44: Graphics programs designed to run on character-oriented terminals.
        !            45: I could name many,
        !            46: but they come and go,
        !            47: so the list would be quickly out of date.
        !            48: Recently, there have been programs such as
        !            49: .b rain ,
        !            50: .b rocket ,
        !            51: and
        !            52: .b gun .
        !            53: .)f
        !            54: and optimizing
        !            55: .b more (1)-type
        !            56: programs,
        !            57: all that is needed is the motion optimizations.
        !            58: This, therefore, is a description
        !            59: of what some of what goes on at the lower levels of this screen package.
        !            60: The descriptions assume a certain amount of familiarity
        !            61: with programming problems and some finer points of C.
        !            62: None of it is terribly difficult,
        !            63: but you should be forewarned.
        !            64: .sh 2 "Terminal Information"
        !            65: .pp
        !            66: In order to use a terminal's
        !            67: features to the best of a program's abilities,
        !            68: it must first know what they are\**.
        !            69: .(f
        !            70: \**
        !            71: If this comes as any surprise to you,
        !            72: there's this tower in Paris they're thinking of junking
        !            73: that I can let you have for a song.
        !            74: .)f
        !            75: The \*(tc \*(db describes these,
        !            76: but a certain amount of decoding is necessary,
        !            77: and there are, of course,
        !            78: both efficient and inefficient ways of reading them in.
        !            79: The algorithm that the uses is taken from
        !            80: .b vi
        !            81: and is hideously efficient.
        !            82: It reads them
        !            83: in a tight loop
        !            84: into a set of variables
        !            85: whose names are two uppercase letters with some mnemonic value.
        !            86: For example,
        !            87: .Vn HO
        !            88: is a string which moves the cursor to the "home" position\**.
        !            89: .(f
        !            90: \**
        !            91: These names are identical to those variables
        !            92: used in the
        !            93: .b termcap (5)
        !            94: \*(db to describe each capability.
        !            95: See Appendix A for a complete list of those read,
        !            96: and the
        !            97: .b termcap (5)
        !            98: manual page
        !            99: for a full description.
        !           100: .)f
        !           101: As there are two types of variables involving ttys,
        !           102: there are two routines.
        !           103: The first,
        !           104: .Fn gettmode ,
        !           105: sets some variables based upon the tty modes accessed by
        !           106: .b gtty (2)
        !           107: and
        !           108: .b stty (2) .
        !           109: The second,
        !           110: .Fn setterm ,
        !           111: a larger task by reading in the descriptions from the \*(tc \*(db.
        !           112: This is the way these routines are used by
        !           113: .Fn initscr :
        !           114: .(b
        !           115: .(l I
        !           116: \*fif\fP (isatty(0)) {
        !           117:        gettmode();
        !           118:        \*fif\fP ((sp=getenv("TERM")) != NULL)
        !           119:                setterm(sp);
        !           120:        \*felse\fP
        !           121:               setterm(Def\*_term);
        !           122: }
        !           123: \*felse\fP
        !           124:        setterm(Def\*_term);
        !           125: \*_puts(TI);
        !           126: \*_puts(VS);
        !           127: .)l
        !           128: .)b
        !           129: .pp
        !           130: .Fn isatty
        !           131: checks to see if file descriptor 0 is a terminal\**.
        !           132: .(f
        !           133: \**
        !           134: .Fn isatty
        !           135: is defined in the default C library function routines.
        !           136: It does a
        !           137: .b gtty (2)
        !           138: on the descriptor and checks the return value.
        !           139: .)f
        !           140: If it is,
        !           141: .Fn gettmode
        !           142: sets the terminal description modes from a
        !           143: .b gtty (2) .
        !           144: .Fn getenv
        !           145: is then called to get the name of the terminal,
        !           146: and that value (if there is one) is passed to
        !           147: .Fn setterm ,
        !           148: which reads in the variables from \*(tc
        !           149: associated with that terminal.
        !           150: .Fn getenv "" (
        !           151: returns a pointer to a string containing the name of the terminal,
        !           152: which we save in the character pointer
        !           153: .Vn sp .)
        !           154: If
        !           155: .Fn isatty
        !           156: returns false,
        !           157: the default terminal
        !           158: .Vn Def\*_term
        !           159: is used.
        !           160: The
        !           161: .Vn TI
        !           162: and
        !           163: .Vn VS
        !           164: sequences initialize the terminal
        !           165: .Fn \*_puts "" (
        !           166: is a macro which uses
        !           167: .Fn tputs
        !           168: (see
        !           169: .b termcap (3))
        !           170: and 
        !           171: .Fn \*_putchar ""
        !           172: to put out a string).
        !           173: .Fn endwin
        !           174: undoes these things.
        !           175: .sh 2 "Movement Optimizations, or, Getting Over Yonder"
        !           176: .pp
        !           177: Now that we have all this useful information,
        !           178: it would be nice to do something with it\**.
        !           179: .(f
        !           180: \**
        !           181: Actually,
        !           182: it
        !           183: .i can
        !           184: be emotionally fulfilling just to get the information.
        !           185: This is usually only true, however,
        !           186: if you have the social life of a kumquat.
        !           187: .)f
        !           188: The most difficult thing to do properly is motion optimization.
        !           189: When you consider how many different features various terminals have
        !           190: (tabs, backtabs, non-destructive space, home sequences, absolute tabs, .....)
        !           191: you can see that deciding how to get from here to there
        !           192: can be a decidedly non-trivial task.
        !           193: The editor
        !           194: .b vi
        !           195: uses many of these features,
        !           196: and the routines it uses to do this take up many pages of code.
        !           197: Fortunately, I was able to liberate them with the author's permission,
        !           198: and use them here.
        !           199: .pp
        !           200: After using
        !           201: .Fn gettmode
        !           202: and
        !           203: .Fn setterm
        !           204: to get the terminal descriptions,
        !           205: the function
        !           206: .Fn mvcur
        !           207: deals with this task.
        !           208: It usage is simple:
        !           209: you simply tell it where you are now and where you want to go.
        !           210: For example
        !           211: .(l
        !           212: mvcur(0\*,0\*,LINES/2\*,COLS/2)
        !           213: .)l
        !           214: .lp
        !           215: would move the cursor from the home position (0\*,0)
        !           216: to the middle of the screen.
        !           217: If you wish to force absolute addressing,
        !           218: you can use the function
        !           219: .Fn tgoto
        !           220: from the
        !           221: .b termlib (7)
        !           222: routines,
        !           223: or you can tell
        !           224: .Fn mvcur
        !           225: that you are impossibly far away,
        !           226: like Cleveland.
        !           227: For example,
        !           228: to absolutely address the lower left hand corner of the screen
        !           229: from anywhere
        !           230: just claim that you are in the upper right hand corner:
        !           231: .(l
        !           232: mvcur(0\*,COLS\-1\*,LINES\-1\*,0)
        !           233: .)l

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