st could easily tear/flicker with animation or other unattended
output. This commit eliminates most of the tear/flicker.
Before this commit, the display timing had two "modes":
- Interactively, st was waiting fixed `1000/xfps` ms after forwarding
the kb/mouse event to the application and before drawing.
- Unattended, and specifically with animations, the draw frequency was
throttled to `actionfps`. Animation at a higher rate would throttle
and likely tear, and at lower rates it was tearing big frames
(specifically, when one `read` didn't get a full "frame").
The interactive behavior was decent, but it was impossible to get good
unattended-draw behavior even with carefully chosen configuration.
This commit changes the behavior such that it draws on idle instead of
using fixed latency/frequency. This means that it tries to draw only
when it's very likely that the application has completed its output
(or after some duration without idle), so it mostly succeeds to avoid
tear, flicker, and partial drawing.
The config values minlatency/maxlatency replace xfps/actionfps and
define the range which the algorithm is allowed to wait from the
initial draw-trigger until the actual draw. The range enables the
flexibility to choose when to draw - when least likely to flicker.
It also unifies the interactive and unattended behavior and config
values, which makes the code simpler as well - without sacrificing
latency during interactive use, because typically interactively idle
arrives very quickly, so the wait is typically minlatency.
While it only slighly improves interactive behavior, for animations
and other unattended-drawing it improves greatly, as it effectively
adapts to any [animation] output rate without tearing, throttling,
redundant drawing, or unnecessary delays (sounds impossible, but it
works).
This patch must be applied on the externalpipe patch. It adds the
function externalpipein to redirect the standard output of the external
command to the slave size of the pty, that is, as if the external
program had been manually executed on the terminal. It can be used to
send desired escape sequences to the terminal with a shortcut.
I created the patch to make use of the dynamic-colors program
(https://github.com/sos4nt/dynamic-colors) that uses the OSC escape
sequences to change the colors of the terminal. The program keeps the
last colorscheme selected in a file, so you can use it to select the
colorscheme for all newly opened terminals from that moment on. If you
want to change the color of the background and foreground independently
from the palette, you have to merge in the patch for the OSC escape
sequences 10, 11, and 12.
This patch includes the changes of the externalpipe sigaction patch to
prevent reseting the signal handler for SIGCHLD when the proces of the
external command exits.
This patch should be applied on top of the externalpipe patch. It
prevents the reset of the signal handler set on SIGCHILD, when the
forked process that executes the external process exits. I opted for
switching from signal to sigaction instead of rearming the signal in the
sigchld function, just because it is the recommended function (although I
tried both ways and both worked).
Support for OSC escape sequences 10, 11 and 12 to modify the bg, fg and
cursor colors. I selected entries in the colorname table after the 255
position for defaultfg, defaultbg and defaultcs
When an OCS sequence was used to change the bg color, the borders where
dirty. This simple patch just clears the window before the redraw of the
terminal when the bg color has been changed. This is apparently enough
and seams to be very smooth. There was a TODO comment for it on the st.c
file, which I removed.
When a read operation returns 0 then it means that we arrived to the end of the
file, and new reads will return 0 unless you do some other operation such as
lseek(). This case happens with USB-232 adapters when they are unplugged.
Scroll is a program that stores all the lines of its child and be used in st as
a way of implementing scrollback.
This solution is much better than implementing the scrollback in st itself
because having a different program allows to use it in any other program
without doing modifications to those programs.
