The wnoutrefresh and doupdate routines allow multiple updates with
more efficiency than wrefresh alone.
In addition to all the window
structures, curses keeps two data structures representing the terminal
.IP • 4 a physical screen, describing what is actually on the screen, and
.IP • 4 a virtual screen, describing what the programmer wants to have on the screen.
The routine wrefresh works by
.IP • 4 first calling wnoutrefresh, which copies the named window to the virtual screen, and
.IP • 4 then calling doupdate, which compares the virtual screen to the physical screen and does the actual update.
If the programmer wishes to output several windows at once, a series of calls to wrefresh results in alternating calls to wnoutrefresh and doupdate, causing several bursts of output to the screen. By first calling wnoutrefresh for each window, it is then possible to call doupdate once, resulting in only one burst of output, with fewer total characters transmitted and less CPU time used.
If the win argument to wrefresh is the physical screen (i.e., the global variable curscr), the screen is immediately cleared and repainted from scratch.
The phrase ``copies the named window to the virtual screen'' above is ambiguous. What actually happens is that all touched (changed) lines in the window are copied to the virtual screen. This affects programs that use overlapping windows; it means that if two windows overlap, you can refresh them in either order and the overlap region will be modified only when it is explicitly changed. (But see the section on PORTABILITY below for a warning about exploiting this behavior.)
The wredrawln routine indicates to curses that some screen lines are corrupted and should be thrown away before anything is written over them. It touches the indicated lines (marking them changed). The routine redrawwin touches the entire window.
X/Open does not define any error conditions. In this implementation
Whether wnoutrefresh copies to the virtual screen the entire contents of a window or just its changed portions has never been well-documented in historic curses versions (including SVr4). It might be unwise to rely on either behavior in programs that might have to be linked with other curses implementations. Instead, you can do an explicit touchwin before the wnoutrefresh call to guarantee an entire-contents copy anywhere.