Re: chgat() function does not work correctly after refresh()

[Thomas Dickey]

On Fri, May 18, 2007 at 03:03:55PM +0400, Alexey Miheev wrote:
> LSB 3.1 refers to SUSv2 (The Single UNIX Specification, Version 2) for the
> description of the libncurses functions.
> According to the standard chgat() family of functions shall change renditions
> of characters in a window.
> But in the following code chgat() do nothing and renditions stay the
> same. Note that if we will comment out first refresh() call then
> everything is OK and renditions are changed. This behaviour seems to be
> quite unpredictable from the documentation.

When I run this program, I see a blinking cyan-on-black string.
Your comment seems to say that commenting out the first refresh
will make a difference in behavior - I don't see that.

It's likely that you're testing with an older version of ncurses.
I see that in 5.5 it did not handle this case (modifying text before
it was first painted on the screen).

The change is probably this one:

20060715
        + modify wchgat() to mark updated cells as changed so a refresh will
          repaint those cells (comments by Sadrul H Chowdhury and William
          McBrine).

The current version of ncurses is 5.6 (20061217).
 
> #include <ncurses.h>
> 
> int main(int argc, char *argv[])
> {       initscr();                      /* Start curses mode            */
>         start_color();                  /* Start color functionality    */
>         
>         init_pair(1, COLOR_CYAN, COLOR_BLACK);
>         printw("A Big string");
>         refresh(); // IF THIS IS COMMENTED THEN EVERYTHING IS OK
>         /*
>          * First two parameters specify the position at which to start 
>          * Third parameter number of characters to update. -1 means till 
>          * end of line
>          * Forth parameter is the normal attribute you wanted to give 
>          * to the charcter
>          * Fifth is the color index. It is the index given during init_pair()
>          * use 0 if you didn't want color
>          * Sixth one is always NULL 
>          */
>         mvchgat(0, 0, -1, A_BLINK, 1, NULL);
>         refresh();
>         getch();
>         endwin();                       /* End curses mode                */
>         return 0;
> }
> 
> Regards, Alexey Miheev
>  
> Linux Verification Center, ISPRAS
> web:    http://www.linuxtesting.org
> e-mail: address@hidden
> 
> 
> 
> 
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-- 
Thomas E. Dickey <address@hidden>
http://invisible-island.net
ftp://invisible-island.net

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