- Most of the window attribute routines are extensions of older routines
- which assume that color pairs are OR'd into the attribute parameter.
- These older routines use the same name, omitting an underscore (_).
-
- The attrset routine is a legacy feature predating SVr4 curses but kept
+ The X/Open window attribute routines which set or get, turn on or off
+ are extensions of older routines which assume that color pairs are OR'd
+ into the attribute parameter. These newer routines use similar names,
+ because X/Open simply added an underscore (_) for the newer names.
+
+ The int datatype used in the legacy routines is treated as if it is the
+ same size as chtype (used by addch(3x)). It holds the common video at-
+ tributes (such as bold, reverse), as well as a few bits for color.
+ Those bits correspond to the A_COLOR symbol. The COLOR_PAIR macro pro-
+ vides a value which can be OR'd into the attribute parameter. For ex-
+ ample, as long as that value fits into the A_COLOR mask, then these
+ calls produce similar results:
+
+ attrset(A_BOLD | COLOR_PAIR(pair));
+ attr_set(A_BOLD, pair, NULL);
+
+ However, if the value does not fit, then the COLOR_PAIR macro uses only
+ the bits that fit. For example, because in ncurses A_COLOR has eight
+ (8) bits, then COLOR_PAIR(259) is 4 (259-255).
+
+ The PAIR_NUMBER macro extracts a pair number from an int (or chtype).
+ For example, the input and output values in these statements would be
+ the same:
+
+ int value = A_BOLD | COLOR_PAIR(input);
+ int output = PAIR_NUMBER(value);
+
+ The attrset routine is a legacy feature predating SVr4 curses but kept
in X/Open Curses for the same reason that SVr4 curses kept it: compati-
bility.
- The remaining attr* functions operate exactly like the corresponding
- attr_* functions, except that they take arguments of type int rather
+ The remaining attr* functions operate exactly like the corresponding
+ attr_* functions, except that they take arguments of type int rather
than attr_t.
- There is no corresponding attrget function as such in X/Open Curses,
+ There is no corresponding attrget function as such in X/Open Curses,
although ncurses provides getattrs (see curs_legacy(3x)).
- The routine chgat changes the attributes of a given number of charac-
- ters starting at the current cursor location of stdscr. It does not
- update the cursor and does not perform wrapping. A character count of
- -1 or greater than the remaining window width means to change at-
- tributes all the way to the end of the current line. The wchgat func-
- tion generalizes this to any window; the mvwchgat function does a cur-
+ The routine chgat changes the attributes of a given number of charac-
+ ters starting at the current cursor location of stdscr. It does not
+ update the cursor and does not perform wrapping. A character count of
+ -1 or greater than the remaining window width means to change at-
+ tributes all the way to the end of the current line. The wchgat func-
+ tion generalizes this to any window; the mvwchgat function does a cur-
sor move before acting.
- In these functions, the color pair argument is a color-pair index (as
+ In these functions, the color pair argument is a color-pair index (as
in the first argument of init_pair, see curs_color(3x)).
The routine color_set sets the current color of the given window to the
- foreground/background combination described by the color pair parame-
+ foreground/background combination described by the color pair parame-
ter.
- The routine standout is the same as attron(A_STANDOUT). The routine
- standend is the same as attrset(A_NORMAL) or attrset(0), that is, it
+ The routine standout is the same as attron(A_STANDOUT). The routine
+ standend is the same as attrset(A_NORMAL) or attrset(0), that is, it
turns off all attributes.
X/Open does not mark these "restricted", because
o they have well established legacy use, and
- o there is no ambiguity about the way the attributes might be com-
+ o there is no ambiguity about the way the attributes might be com-
bined with a color pair.
The following video attributes, defined in <curses.h>, can be passed to
- the routines attron, attroff, and attrset, or OR'd with the characters
+ the routines attron, attroff, and attrset, or OR'd with the characters
passed to addch (see curs_addch(3x)).
NameDescription
- -----------------------------------------------------------
+ -----------------------------------------------------------------
A_NORMAL Normal display (no highlight)
A_STANDOUT Best highlighting mode of the terminal.
A_UNDERLINE Underlining
@@ -208,8 +240,9 @@
A_ALTCHARSET Alternate character set
A_ITALIC Italics (non-X/Open extension)
A_CHARTEXT Bit-mask to extract a character
+ A_COLOR Bit-mask to extract a color (legacy routines)
- These video attributes are supported by attr_on and related functions
+ These video attributes are supported by attr_on and related functions
(which also support the attributes recognized by attron, etc.):
NameDescription
@@ -221,68 +254,189 @@
WA_TOP Top highlight
WA_VERTICAL Vertical highlight
- The return values of many of these routines are not meaningful (they
- are implemented as macro-expanded assignments and simply return their
- argument). The SVr4 manual page claims (falsely) that these routines
+ The return values of many of these routines are not meaningful (they
+ are implemented as macro-expanded assignments and simply return their
+ argument). The SVr4 manual page claims (falsely) that these routines
always return 1.
These functions may be macros:
- attroff, wattroff, attron, wattron, attrset, wattrset, standend
+ attroff, wattroff, attron, wattron, attrset, wattrset, standend
and standout.
- Color pair values can only be OR'd with attributes if the pair number
+ Color pair values can only be OR'd with attributes if the pair number
is less than 256. The alternate functions such as color_set can pass a
color pair value directly. However, ncurses ABI 4 and 5 simply OR this
- value within the alternate functions. You must use ncurses ABI 6 to
+ value within the alternate functions. You must use ncurses ABI 6 to
support more than 256 color pairs.
+
+ X/Open Curses is largely based on SVr4 curses, adding support for
+ "wide-characters" (not specific to Unicode). Some of the X/Open dif-
+ ferences from SVr4 curses address the way video attributes can be ap-
+ plied to wide-characters. But aside from that, attrset and attr_set
+ are similar. SVr4 curses provided the basic features for manipulating
+ video attributes. However, earlier versions of curses provided a part
+ of these features.
+
+ As seen in 2.8BSD, curses assumed 7-bit characters, using the eighth
+ bit of a byte to represent the standout feature (often implemented as
+ bold and/or reverse video). The BSD curses library provided functions
+ standout and standend which were carried along into X/Open Curses due
+ to their pervasive use in legacy applications.
+
+ Some terminals in the 1980s could support a variety of video at-
+ tributes, although the BSD curses library could do nothing with those.
+ System V (1983) provided an improved curses library. It defined the A_
+ symbols for use by applications to manipulate the other attributes.
+ There are few useful references for the chronology.
+
+ Goodheart's book UNIXCursesExplained (1991) describes SVr3 (1987),
+ commenting on several functions:
+
+ o the attron, attroff, attrset functions (and most of the functions
+ found in SVr4 but not in BSD curses) were introduced by System V,
+
+ o the alternate character set feature with A_ALTCHARSET was added in
+ SVr2 and improved in SVr3 (by adding acs_map[]),
+
+ ostart_color and related color-functions were introduced by System
+ V.3.2,
+
+ o pads, soft-keys were added in SVr3, and
+
+ Goodheart did not mention the background character or the cchar_t type.
+ Those are respectively SVr4 and X/Open features. He did mention the A_
+ constants, but did not indicate their values. Those were not the same
+ in different systems, even for those marked as System V.
+
+ Different Unix systems used different sizes for the bit-fields in
+ chtype for characters and colors, and took into account the different
+ integer sizes (32-bit versus 64-bit).
+
+ This table showing the number of bits for A_COLOR and A_CHARTEXT was
+ gleaned from the curses header files for various operating systems and
+ architectures. The inferred architecture and notes reflect the format
+ and size of the defined constants as well as clues such as the alter-
+ nate character set implementation. A 32-bit library can be used on a
+ 64-bit system, but not necessarily the reverse.
+
+ YearSystemArchColorCharNotes
+ ----------------------------------------------------------------
+ 1992 Solaris 5.2 32 6 17 SVr4 curses
+ 1992 HPUX 9 32 no 8 SVr2 curses
+ 1992 AIX 3.2 32 no 23 SVr2 curses
+ 1994 OSF/1 r3 32 no 23 SVr2 curses
+ 1995 HP-UX 10.00 32 6 16 SVr3 "curses_colr"
+ 1995 HP-UX 10.00 32 6 8 SVr4, X/Open curses
+ 1995 Solaris 5.4 32/64 7 16 X/Open curses
+ 1996 AIX 4.2 32 7 16 X/Open curses
+ 1996 OSF/1 r4 32 6 16 X/Open curses
+ 1997 HP-UX 11.00 32 6 8 X/Open curses
+
+ 2000 U/Win 32/64 7/31 16 uses chtype
+
+ Notes:
+
+ Regarding HP-UX,
+
+ o HP-UX 10.20 (1996) added support for 64-bit PA-RISC processors
+ in 1996.
+
+ o HP-UX 10.30 (1997) marked "curses_colr" obsolete. That version
+ of curses was dropped with HP-UX 11.30 in 2006.
+
+ Regarding OSF/1 (and Tru64),
+
+ o These used 64-bit hardware. Like ncurses, the OSF/1 curses in-
+ terface is not customized for 32-bit and 64-bit versions.
+
+ o Unlike other systems which evolved from AT&T code, OSF/1 provid-
+ ed a new implementation for X/Open curses.
+
+ Regarding Solaris,
+
+ o The initial release of Solaris was in 1992.
+
+ o The xpg4 (X/Open) curses was developed by MKS from 1990 to 1995.
+ Sun's copyright began in 1996.
+
+ o Sun updated the X/Open curses interface after 64-bit support was
+ introduced in 1997, but did not modify the SVr4 curses inter-
+ face.
+
+ Regarding U/Win,
+
+ o Development of the curses library began in 1991, stopped in
+ 2000.
+
+ o Color support was added in 1998.
+
+ o The library uses only chtype (no cchar_t).
+
+ Once X/Open curses was adopted in the mid-1990s, the constraint of a
+ 32-bit interface with many colors and wide-characters for chtype became
+ a moot point. The cchar_t structure (whose size and members are not
+ specified in X/Open Curses) could be extended as needed.
+
+ Other interfaces are rarely used now:
+
+ o BSD curses was improved slightly in 1993/1994 using Keith Bostic's
+ modification to make the library 8-bit clean for nvi. He moved
+ standout attribute to a structure member.
+
+ The resulting 4.4BSD curses was replaced by ncurses over the next
+ ten years.
+
+ o U/Win is rarely used now.
+
+
This implementation provides the A_ITALIC attribute for terminals which
- have the enter_italics_mode (sitm) and exit_italics_mode (ritm) capa-
+ have the enter_italics_mode (sitm) and exit_italics_mode (ritm) capa-
bilities. Italics are not mentioned in X/Open Curses. Unlike the oth-
- er video attributes, A_ITALIC is unrelated to the set_attributes capa-
- bilities. This implementation makes the assumption that exit_at-
+ er video attributes, A_ITALIC is unrelated to the set_attributes capa-
+ bilities. This implementation makes the assumption that exit_at-tribute_mode may also reset italics.
- Each of the functions added by XSI Curses has a parameter opts, which
- X/Open Curses still (after more than twenty years) documents as re-
+ Each of the functions added by XSI Curses has a parameter opts, which
+ X/Open Curses still (after more than twenty years) documents as re-
served for future use, saying that it should be NULL. This implementa-
tion uses that parameter in ABI 6 for the functions which have a color-
pair parameter to support extendedcolorpairs:
- o For functions which modify the color, e.g., wattr_set, if opts is
- set it is treated as a pointer to int, and used to set the color
+ o For functions which modify the color, e.g., wattr_set, if opts is
+ set it is treated as a pointer to int, and used to set the color
pair instead of the shortpair parameter.
o For functions which retrieve the color, e.g., wattr_get, if opts is
- set it is treated as a pointer to int, and used to retrieve the
+ set it is treated as a pointer to int, and used to retrieve the
color pair as an int value, in addition retrieving it via the stan-
dard pointer to short parameter.
- The remaining functions which have opts, but do not manipulate color,
+ The remaining functions which have opts, but do not manipulate color,
e.g., wattr_on and wattr_off are not used by this implementation except
to check that they are NULL.
These functions are supported in the XSI Curses standard, Issue 4. The
- standard defined the dedicated type for highlights, attr_t, which was
+ standard defined the dedicated type for highlights, attr_t, which was
not defined in SVr4 curses. The functions taking attr_t arguments were
not supported under SVr4.
Very old versions of this library did not force an update of the screen
- when changing the attributes. Use touchwin to force the screen to
+ when changing the attributes. Use touchwin to force the screen to
match the updated attributes.
- The XSI Curses standard states that whether the traditional functions
- attron/attroff/attrset can manipulate attributes other than A_BLINK,
- A_BOLD, A_DIM, A_REVERSE, A_STANDOUT, or A_UNDERLINE is "unspecified".
- Under this implementation as well as SVr4 curses, these functions cor-
- rectly manipulate all other highlights (specifically, A_ALTCHARSET,
+ The XSI Curses standard states that whether the traditional functions
+ attron/attroff/attrset can manipulate attributes other than A_BLINK,
+ A_BOLD, A_DIM, A_REVERSE, A_STANDOUT, or A_UNDERLINE is "unspecified".
+ Under this implementation as well as SVr4 curses, these functions cor-
+ rectly manipulate all other highlights (specifically, A_ALTCHARSET,
A_PROTECT, and A_INVIS).
XSI Curses added these entry points:
@@ -290,7 +444,7 @@
attr_get, attr_on, attr_off, attr_set, wattr_on, wattr_off, wat-tr_get, wattr_set
- The new functions are intended to work with a new series of highlight
+ The new functions are intended to work with a new series of highlight
macros prefixed with WA_. The older macros have direct counterparts in
the newer set of names:
@@ -305,13 +459,29 @@
WA_BOLD Extra bright or bold
WA_ALTCHARSET Alternate character set
- The XSI curses standard specifies that each pair of corresponding A_
- and WA_-using functions operates on the same current-highlight informa-
- tion.
+ XSI curses does not assign values to these symbols, nor does it state
+ whether or not they are related to the similarly-named A_NORMAL, etc.:
+
+ o The XSI curses standard specifies that each pair of corresponding
+ A_ and WA_-using functions operates on the same current-highlight
+ information.
+
+ o However, in some implementations, those symbols have unrelated val-
+ ues.
+
+ For example, the Solaris xpg4 (X/Open) curses declares attr_t to be
+ an unsigned short integer (16-bits), while chtype is a unsigned in-
+ teger (32-bits). The WA_ symbols in this case are different from
+ the A_ symbols because they are used for a smaller datatype which
+ does not represent A_CHARTEXT or A_COLOR.
+
+ In this implementation (as in many others), the values happen to be
+ the same because it simplifies copying information between chtype
+ and cchar_t variables.
The XSI standard extended conformance level adds new highlights A_HORI-
- ZONTAL, A_LEFT, A_LOW, A_RIGHT, A_TOP, A_VERTICAL (and corresponding
- WA_ macros for each). As of August 2013, no known terminal provides
+ ZONTAL, A_LEFT, A_LOW, A_RIGHT, A_TOP, A_VERTICAL (and corresponding
+ WA_ macros for each). As of August 2013, no known terminal provides
these highlights (i.e., via the sgr1 capability).
@@ -327,10 +497,10 @@
o returns an error if the color pair parameter for wcolor_set is out-
side the range 0..COLOR_PAIRS-1.
- o does not return an error if either of the parameters of wattr_get
+ o does not return an error if either of the parameters of wattr_get
used for retrieving attribute or color-pair values is NULL.
- Functions with a "mv" prefix first perform a cursor movement using
+ Functions with a "mv" prefix first perform a cursor movement using
wmove, and return an error if the position is outside the window, or if
the window pointer is null.
@@ -358,6 +528,7 @@