Ncurses mouse wheel scroll up

Question

I want to handle scroll with the mouse wheel using ncurses but I am having a problem similar to this issue :

http://lists.gnu.org/archive/html/bug-ncurses/2012-01/msg00011.html

Besides, mouse wheel-up event is only reported as mask 02000000
(BUTTON4_PRESSED) just one time, even if I scroll the wheel continuously.

I tried ncurses 5.7 to 5.9 on debian 5,6,7 and archlinux. Every single ncurses lib had NCURSES_MOUSE_VERSION 1, tried recompiling with --enable-ext-mouse.

Scrolling down works perfectly, ncurses reports multiple REPORT_MOUSE_POSITION 0x8000000 per scroll and a single BUTTON2_PRESSED 0x128.

Scrolling up causes only a single report of BUTTON4_PRESSED 0x80000

MEVENT event;

mousemask(BUTTON1_CLICKED|BUTTON4_PRESSED|BUTTON2_PRESSED, NULL); // Tried with REPORT_MOUSE_POSITION also

while(run)
{
  switch(in = getch())
  {
     case KEY_MOUSE:
         if(getmouse(&event) == OK)
         { 
           else if (event.bstate & BUTTON4_PRESSED)
             line_up();
           else if (event.bstate & BUTTON2_PRESSED || event.bstate == 0x8000000)
             line_down();
         }
         break;
   }
 }

If you try xev, wheel up is button 4 and wheel down is button 4, so wheel down is not working properly. Scrolling does not change the mouse position. On Debian, (mouse version 1) I get multiple button 4 pressed events scrolling up and multiple report mouse position events scrolling down — parkydr
I will watch xev, activating terminal report showed multiple events in both cases, but inside ncurses context I can say that only a single button4 is reported when scrolling up, I am using readline aswell could that be an issue? — Zild

Thormme Thormme · Accepted Answer · 2014-03-25T07:40:26

Add mouseinterval(0); somewhere outside of your main loop. (Perhaps right after keypad(stdscr, TRUE);)

This command causes there to be no delay with mouse events, so you won't be able to detect BUTTON1_CLICKED or BUTTON1_DOUBLE_CLICKED and similar things (though you can implement that yourself by keeping track of BUTTON1_PRESSED, BUTTON1_RELEASED, and the time between mouse events).

A small caveat though, when I tested this with C everything worked, except that getmouse returned ERR on scroll wheel down events. This could potentially still be useful though, as it was the only event which gave this result. When I tested the same code in Rust it worked perfectly though, so your mileage may vary.

Ncurses mouse wheel scroll up

2 Answers