Urxvt patch: VTE like clear screen behavior

Question

I've switched to urxvt last week. I come from the VTE world (gnome-terminal, xfce-terminal and such, the latter in my case). VTE has a nice feature to which I've accustomed myself. This is the way how it handles the clear screen function (ctrl-L).
In VTE when you press ctrl-L, the screen cursor position gets to top row and the lines get scrolled just before the visible portion of the window. This means that the scrollback remains intact so you can scroll back and see it later. If you press ctrl-L again when you are at top you get a bunch of empty lines - you can use this to mark the scrollback with empty portions when you are scrolling back large amounts of texts.  This is handy for example when you want to quickly glance at an output from a command but you want to differentiate from different outputs - I press ctr-L several times before I execute the command and then I can just quickly scroll back - I immediately spot where the command began because it has a large black spot before it.
The way urxvt works in this case that it just positions the cursor to the top row and then just erases everything below that point. This means you lose valuable lines from the scrollback. Example: type "seq 1000", press ctr-L. Now you won't see the last lines of the command's output!
Now it is possible that I have a misconfigured urxvt and I'd be interested in the config option which I have misconfigured.
Here's a patch for urxvt which adds proper clear screen function and also adds the VTE-like functionality:
*** src/command.C 2011-10-29 18:06:07.000000000 +0200
--- src/command.C.patched 2011-10-29 18:05:28.000000000 +0200
*************** rxvt_term::process_csi_seq ()
*** 2932,2937 ****
--- 2932,2948 ----
case CSI_CUP: /* 8.3.21: (1,1) CURSOR POSITION */
case CSI_HVP: /* 8.3.64: (1,1) CHARACTER AND LINE POSITION */
+ if (nargs == 1 && current_screen == 0)
+ {
+ // This is usually followed with clear screen so add some extra
+ // lines to avoid deleting the lines already on screen. If we are
+ // already at the top, add an extra screen height of lines.
+ int extra_lines = nrow-1;
+ if (screen.cur.row == 0)
+ extra_lines += nrow;
+ for (int i = 0; i < extra_lines; ++i)
+ scr_add_lines (L"\r\n", 2);
+ }
scr_gotorc (arg[0] - 1, nargs < 2 ? 0 : (arg[1] - 1), 0);
break;
Last edited by rlblaster (2011-10-29 19:07:32)

Answer 1

Now I see what's happening! Your prompt uses '\e[H' which is used as move to home. I assumed that '\e[H' is usually followed with clear screen. This means if you use it to just move the cursor to home it won't work. I don't really see how could I fix this nicely but here's a workaround for your prompt: use '\e[1;1H'. In other words:
PS1=$'%{\e[s\e[1;1H\e[30;42;1m%}[%~][%M] %{\e[K\e[256C\e[8D\e[30;42;1m%} [%D{%H:%M}]%(?,%{\e[32;32m%}\u2588,%{\e[31;41;1m\u2588)%}%{\e[u\e[1A%}\n%{\e[0;32m%}> %{\e[0m%}'
By the way the feature of adding extra blank lines if your cursor is already at top won't work in your prompt because your cursor is always at least on row 1. You could change the patch from
if (screen.cur.row == 0)
to
if (screen.cur.row <= 1)
to have this feature.