sl0ppty: three ways back from a painted pane

    printf '\033]5577;1;shader;\033\\'                  # from the program
    sl0ppty cmd '{"cmd":"clear-shaders","id":0}'   # from outside it
    bind "z" "clear-shaders"                       # from the keyboard

`app_clear_pane_shaders` empties both of a pane's chains and says whether
there was anything there, which is what lets a key answer "shaders cleared"
or "no shaders on this pane" instead of maybe having done something.

In-band it is not a new verb: naming no rect means all of them. `shader;`
sits under `shader;chrome;` and `shader;content;` as the degenerate case of
"which rect", so a program puts a pane back in one exchange and cannot leave
it half done. `contrib/shader-repl`'s `:both` now uses that rather than two.

**None of the three is gated on `in_band_shaders`.** A chain outlives the
setting that allowed it -- paint a pane, then turn the setting off, and the
paint is still there, because a chain belongs to the pane and not to the file
(there is a test that reloads with it off and clears anyway). A way out that
the setting can take away is not a way out. The operator path matters for the
same reason: the program that made a pane unreadable is not always in a state
to put it back.

They clear what the *pane* set. The config's chains and the session's own
dimming are not this pane's doing and are derived every frame anyway.

The action is bound to nothing, like `scroll-up`: it is in the palette, which
is what the palette is for, and the docs say to bind it if you leave the
setting on. Which is where a second bug turned up -- the palette truncates a
label at 26 characters, so "undo this pane's own shaders" read as "undo this
pane's own shade" on screen. Renamed to fit, and `tests/test_palette.py` now
checks every label against the column, since nothing failed for that: it just
looked like a typo in front of someone.

1 files changed, 8 insertions, 0 deletions

diff --git a/src/cmd.c b/src/cmd.c
index 5c3792a..556b32b 100644
--- a/src/cmd.c
+++ b/src/cmd.c
@@ -168,6 +168,14 @@ static char *cmd_json(app_t *a, screen_t *s, input_parser_t *in,
       return jerr("no such pane");
     return jok_int(NULL, 0);
   }
+  /* The way in from outside the pane, for when the program that painted it will
+   * not or cannot put it back. `ok` either way, with `cleared` saying whether
+   * there was anything there: a script asking for a clean pane got one, and that
+   * is not an error. */
+  if (strcmp(cmd, "clear-shaders") == 0) {
+    bool had = app_clear_pane_shaders(a, (uint32_t)jv_geti(req, "id", 0));
+    return jok_int("cleared", had ? 1 : 0);
+  }
   if (strcmp(cmd, "new-tab") == 0) {
     uint32_t id = app_new_tab(a, jv_gets(req, "name", ""));
     if (!id) return jerr("cannot create tab");