- The bkgdset and wbkgdset routines manipulate the background of the
- named window. The window background is a chtype consisting of any com-
- bination of attributes (i.e., rendition) and a character. The
- attribute part of the background is combined (OR'ed) with all non-blank
- characters that are written into the window with waddch. Both the
- character and attribute parts of the background are combined with the
- blank characters. The background becomes a property of the character
- and moves with the character through any scrolling and insert/delete
- line/character operations.
+ The bkgdset and wbkgdset routines set the background for a window. A
+ window's background is a chtype consisting of any combination of
+ attributes (i.e., rendition) and a character:
+
+ o The attribute part of the background is combined (OR'ed) with all
+ non-blank characters that are written into the window with waddch.
+
+ o Both the character and attribute parts of the background are
+ combined with blank characters that are written into the window.
+
+ The background becomes a property of each character and moves with the
+ character through any scrolling and insert/delete line/character
+ operations.
To the extent possible on a particular terminal, the attribute part of
the background is displayed as the graphic rendition of the character
@@ -97,69 +103,74 @@
This implementation, like SVr4 curses, does not store the background
and window attribute contributions to each cell separately. It updates
- the rendition by comparing the character, non-color attributes and col-
- ors contained in the background. For each cell in the window, whether
- or not it is blank:
+ the rendition by comparing the character, non-color attributes and
+ colors contained in the background. For each cell in the window,
+ whether or not it is blank:
o The library first compares the character, and if it matches the
current character part of the background, it replaces that with the
new background character.
- o The library then checks if the cell uses color, i.e., its color
- pair value is nonzero. If not, it simply replaces the attributes
- and color pair in the cell with those from the new background char-
- acter.
+ When bkgdset is used to set the background character, that does not
+ update each cell in the window. A subsequent call to bkgd will
+ only modify the character in cells which match the current
+ background character.
+
+ o The library then checks if the cell uses color, i.e., its color
+ pair value is nonzero. If not, it simply replaces the attributes
+ and color pair in the cell with those from the new background
+ character.
- o If the cell uses color, and that matches the color in the current
+ o If the cell uses color, and that matches the color in the current
background, the library removes attributes which may have come from
the current background and adds attributes from the new background.
- It finishes by setting the cell to use the color from the new back-
- ground.
+ It finishes by setting the cell to use the color from the new
+ background.
- o If the cell uses color, and that does not match the color in the
- current background, the library updates only the non-color
- attributes, first removing those which may have come from the cur-
- rent background, and then adding attributes from the new back-
- ground.
+ o If the cell uses color, and that does not match the color in the
+ current background, the library updates only the non-color
+ attributes, first removing those which may have come from the
+ current background, and then adding attributes from the new
+ background.
- If the background's character value is zero, a space is assumed.
+ If the background's character value is zero (0), a space is assumed.
- If the terminal does not support color, or if color has not been
- started with start_color, the new background character's color
+ If the terminal does not support color, or if color has not been
+ started with start_color, the new background character's color
attribute will be ignored.
- The getbkgd function returns the given window's current background
+ The getbkgd function returns the given window's current background
character/attribute pair.
- These functions are described in the XSI Curses standard, Issue 4. It
- specifies that bkgd and wbkgd return ERR on failure, but gives no fail-
- ure conditions.
+ These functions are described in the XSI Curses standard, Issue 4. It
+ specifies that bkgd and wbkgd return ERR on failure, but gives no
+ failure conditions.
- The routines bkgd and wbkgd return the integer OK, unless the library
+ The routines bkgd and wbkgd return the integer OK, unless the library
has not been initialized.
- In contrast, the SVr4.0 manual says bkgd and wbkgd may return OK "or a
- non-negative integer if immedok is set", which refers to the return
- value from wrefresh (used to implement the immediate repainting). The
- SVr4 curses wrefresh returns the number of characters written to the
+ In contrast, the SVr4.0 manual says bkgd and wbkgd may return OK "or a
+ non-negative integer if immedok is set", which refers to the return
+ value from wrefresh (used to implement the immediate repainting). The
+ SVr4 curses wrefresh returns the number of characters written to the
screen during the refresh. This implementation does not do that.
Note that bkgdset and bkgd may be macros.
- X/Open Curses mentions that the character part of the background must
- be a single-byte value. This implementation, like SVr4, checks to
- ensure that, and will reuse the old background character if the check
+ X/Open Curses mentions that the character part of the background must
+ be a single-byte value. This implementation, like SVr4, checks to
+ ensure that, and will reuse the old background character if the check
fails.
- These functions are described in the XSI Curses standard, Issue 4
+ These functions are described in the XSI Curses standard, Issue 4
(X/Open Curses).