DECSCNM Screen Mode

CSI ? 5 h sets reverse screen and CSI ? 5 l puts it back to normal. Reverse screen swaps the foreground and background colors of the whole display, so that a terminal showing light text on a dark background shows dark text on a light one. DEC STD 070 says the actual colors are the implementation’s to choose, and that every character rendition must still work in both modes. Normal is the default in the VT510 manual.

It is a way of showing the screen, not a change to it. The VT510 manual says DECSCNM “does not change the data in page memory”: the characters and their attributes, such as those set with SGR, stay as they were.

libghostty-vt records the mode and leaves drawing it to its host, and the terminals drawn on this site do not show it, so the cases check the mode with DECRQM, and that the cells are unchanged.

Validation

DECSCNM-1: Set, and the cells are unchanged

AB
\e[?5h
\e[?5$p   # DECRQM: is mode 5 set?

|AB___|
attr 1,1 plain
reply \e[?5;1$y

DECSCNM-2: Reset

\e[?5h
\e[?5l
\e[?5$p

|_____|
reply \e[?5;2$y

DECSCNM-3: Normal to begin with

\e[?5$p

|_____|
reply \e[?5;2$y