DECSTR Soft Terminal Reset

DECSTR is the reset a program sends: it puts back the state a program may have changed, and leaves what is on the screen and where the cursor is. RIS, the full reset, also erases the screen and restores the user’s own settings, and both DEC STD 070 and the VT510 manual recommend DECSTR instead.

DEC STD 070 lists what DECSTR resets, and the VT510 manual’s table agrees:

• the top and bottom margins, to the whole screen, and the left and right margins likewise;
• the current rendition, to normal, and the selective erase attribute (DECSCA), to erasable;
• the character sets and which are in use, to their defaults;
• the saved cursor (DECSC), to its default, the home position;
• insert mode (IRM), to replace;
• origin mode (DECOM), to absolute;
• the cursor (DECTCEM), to shown;
• the keyboard: cursor key mode, keypad mode, keyboard action mode.

It also lists what DECSTR leaves alone: the data on the screen, the cursor position (“DECSTR has no affect on the Active Position”), the tab stops, column mode, screen mode, new line mode and line attributes.

Auto wrap mode is where the sources part. DEC STD 070 sets it to “Auto Wrap Off (NVM if present)”, the user’s stored setting when there is one, and the VT510 manual’s table says “No autowrap”. xterm leaves it on, and esctest2’s test_DECSTR_DECAWM checks that autowrap is still on afterwards. There is no case for it here.

libghostty-vt does not implement DECSTR. Its dispatch for CSI … p in stream.zig handles only DECRQM, and logs any other intermediate byte as unimplemented, so CSI ! p changes nothing. The cases below show what it should reset; each fails for that one reason. The two that pass are about what DECSTR keeps.

Validation

DECSTR-1: The screen and the cursor stay

AB
\e[2;3H
\e[!p

|AB___|
|_____|
cursor 2,3

DECSTR-2: Insert mode is reset

ABC
\e[4h     # insert mode
\e[!p
\e[1;1H
X         # replaces A

|XBC__|

libghostty-vt ignores the DECSTR, so insert mode stays on and the X is inserted before A. DEC STD 070, the VT510 manual and esctest2’s test_DECSTR_IRM all reset IRM to replace.

DECSTR-3: Origin mode is reset

\e[2;3r   # region is lines 2 and 3
\e[?6h    # origin mode
\e[!p
\e[1;1H   # the corner of the screen again
X

|X____|
|_____|
|_____|

Origin mode stays on, so CSI 1 ; 1 H goes to the top of the region, line 2. DEC STD 070, the VT510 manual and esctest2’s test_DECSTR_DECOM reset it to absolute.

DECSTR-4: The rendition is reset

\e[1;31m  # bold red
\e[!p
A

|A____|
attr 1,1 plain

The A is still bold and red. Both manuals reset the rendition to normal.

DECSTR-5: The margins are reset

1\r\n2\r\n3\r\n4
\e[2;3r   # region is lines 2 and 3
\e[!p
\e[3;1H
\n        # would scroll lines 2 and 3 if the region were still set
X

|1____|
|2____|
|3____|
|X____|

The region stays at lines 2 and 3, so the line feed scrolls them and the X lands on line 3. DEC STD 070, the VT510 manual and esctest2’s test_DECSTR_STBM reset the margins to the whole screen.

DECSTR-6: The cursor is shown again

\e[?25l   # hide the cursor
\e[!p

|_____|
cursor-visible yes

The cursor stays hidden. DEC STD 070 turns it on, “ignore NVM”, and the VT510 manual’s table says “Cursor enabled”.

DECSTR-7: The saved cursor goes back to its default

\e[2;3H
\e7       # save the cursor at 2,3
\e[!p
\e8       # restore it
X

|X____|
|_____|

The saved position survives, so the X is written at 2,3. The VT510 manual’s table resets the saved cursor state to the home position, and esctest2’s test_DECSTR_DECSC checks that a restore afterwards goes there.