tui: Reset the scroll region when resizing.

DECSLPP is explicitly documented as not affecting the scroll region. The
dtterm extension is not as well documented, but it is safer than not to
assume that it operates similarly.

This also eliminates a pointlessly repeated test from tui_scroll(). It
additionally uses a non-parameterized DECSTBM sequence when attempting
to reset back to whole-screen scrolling.

1 files changed, 42 insertions, 27 deletions

diff --git a/src/nvim/tui/tui.c b/src/nvim/tui/tui.c
index 4c22495d8e..5614a1738f 100644
--- a/src/nvim/tui/tui.c
+++ b/src/nvim/tui/tui.c
@@ -82,7 +82,7 @@ typedef struct {
   UGrid grid;
   kvec_t(Rect) invalid_regions;
   int out_fd;
-  bool can_use_terminal_scroll;
+  bool scroll_region_is_full_screen;
   bool mouse_enabled;
   bool busy;
   cursorentry_T cursor_shapes[SHAPE_IDX_COUNT];
@@ -96,6 +96,7 @@ typedef struct {
     int set_cursor_color;
     int enable_focus_reporting, disable_focus_reporting;
     int resize_screen;
+    int reset_scroll_region;
   } unibi_ext;
 } TUIData;
 
@@ -147,7 +148,7 @@ UI *tui_start(void)
 static void terminfo_start(UI *ui)
 {
   TUIData *data = ui->data;
-  data->can_use_terminal_scroll = true;
+  data->scroll_region_is_full_screen = true;
   data->bufpos = 0;
   data->bufsize = sizeof(data->buf) - CNORM_COMMAND_MAX_SIZE;
   data->showing_mode = SHAPE_IDX_N;
@@ -159,6 +160,7 @@ static void terminfo_start(UI *ui)
   data->unibi_ext.enable_focus_reporting = -1;
   data->unibi_ext.disable_focus_reporting = -1;
   data->unibi_ext.resize_screen = -1;
+  data->unibi_ext.reset_scroll_region = -1;
   data->out_fd = 1;
   data->out_isatty = os_isatty(data->out_fd);
   // setup unibilium
@@ -424,6 +426,19 @@ static void clear_region(UI *ui, int top, int bot, int left, int right)
   unibi_goto(ui, grid->row, grid->col);
 }
 
+static void reset_scroll_region(UI *ui)
+{
+  TUIData *data = ui->data;
+
+  if (0 <= data->unibi_ext.reset_scroll_region) {
+    unibi_out(ui, data->unibi_ext.reset_scroll_region);
+  } else {
+    data->params[0].i = 0;
+    data->params[1].i = ui->height - 1;
+    unibi_out(ui, unibi_change_scroll_region);
+  }
+}
+
 static void tui_resize(UI *ui, Integer width, Integer height)
 {
   TUIData *data = ui->data;
@@ -433,6 +448,10 @@ static void tui_resize(UI *ui, Integer width, Integer height)
     data->params[0].i = (int)height;
     data->params[1].i = (int)width;
     unibi_out(ui, data->unibi_ext.resize_screen);
+    // DECSLPP does not reset the scroll region.
+    if (data->scroll_region_is_full_screen) {
+      reset_scroll_region(ui);
+    }
   } else {  // Already handled the SIGWINCH signal; avoid double-resize.
     got_winch = false;
   }
@@ -619,10 +638,9 @@ static void tui_set_scroll_region(UI *ui, Integer top, Integer bot,
   TUIData *data = ui->data;
   ugrid_set_scroll_region(&data->grid, (int)top, (int)bot,
                           (int)left, (int)right);
-  data->can_use_terminal_scroll =
+  data->scroll_region_is_full_screen =
     left == 0 && right == ui->width - 1
-    && ((top == 0 && bot == ui->height - 1)
-        || unibi_get_str(data->ut, unibi_change_scroll_region));
+    && top == 0 && bot == ui->height - 1;
 }
 
 static void tui_scroll(UI *ui, Integer count)
@@ -632,31 +650,28 @@ static void tui_scroll(UI *ui, Integer count)
   int clear_top, clear_bot;
   ugrid_scroll(grid, (int)count, &clear_top, &clear_bot);
 
-  if (data->can_use_terminal_scroll) {
+  if (data->scroll_region_is_full_screen || 0 <= unibi_change_scroll_region) {
     // Change terminal scroll region and move cursor to the top
-    data->params[0].i = grid->top;
-    data->params[1].i = grid->bot;
-    unibi_out(ui, unibi_change_scroll_region);
+    if (!data->scroll_region_is_full_screen) {
+      data->params[0].i = grid->top;
+      data->params[1].i = grid->bot;
+      unibi_out(ui, unibi_change_scroll_region);
+    }
     unibi_goto(ui, grid->top, grid->left);
     // also set default color attributes or some terminals can become funny
     HlAttrs clear_attrs = EMPTY_ATTRS;
     clear_attrs.foreground = grid->fg;
     clear_attrs.background = grid->bg;
     update_attrs(ui, clear_attrs);
-  }
 
-  if (count > 0) {
-    if (data->can_use_terminal_scroll) {
+    if (count > 0) {
       if (count == 1) {
         unibi_out(ui, unibi_delete_line);
       } else {
         data->params[0].i = (int)count;
         unibi_out(ui, unibi_parm_delete_line);
       }
-    }
-
-  } else {
-    if (data->can_use_terminal_scroll) {
+    } else {
       if (count == -1) {
         unibi_out(ui, unibi_insert_line);
       } else {
@@ -664,13 +679,11 @@ static void tui_scroll(UI *ui, Integer count)
         unibi_out(ui, unibi_parm_insert_line);
       }
     }
-  }
 
-  if (data->can_use_terminal_scroll) {
     // Restore terminal scroll region and cursor
-    data->params[0].i = 0;
-    data->params[1].i = ui->height - 1;
-    unibi_out(ui, unibi_change_scroll_region);
+    if (!data->scroll_region_is_full_screen) {
+      reset_scroll_region(ui);
+    }
     unibi_goto(ui, grid->row, grid->col);
 
     if (grid->bg != -1) {
@@ -1015,6 +1028,8 @@ static void fix_terminfo(TUIData *data)
     unibi_set_if_empty(ut, unibi_change_scroll_region, "\x1b[%i%p1%d;%p2%dr");
     unibi_set_if_empty(ut, unibi_clear_screen, "\x1b[H\x1b[2J");
     unibi_set_if_empty(ut, unibi_from_status_line, "\x07");
+    data->unibi_ext.reset_scroll_region = (int)unibi_add_ext_str(ut, NULL,
+      "\x1b[r");
   }
 
   data->unibi_ext.enable_bracketed_paste = (int)unibi_add_ext_str(ut, NULL,
@@ -1044,13 +1059,13 @@ static void fix_terminfo(TUIData *data)
   }
 
   // Only define this capability for terminal types that we know understand it.
-  if (data->term == kTermDTTerm      // originated this extension
-      || data->term == kTermXTerm    // per xterm ctlseqs doco
-      || data->term == kTermKonsole  // per commentary in VT102Emulation.cpp
-      || data->term == kTermTeraTerm // per TeraTerm "Supported Control Functions" doco
-      || data->term == kTermRxvt) {  // per command.C
+  if (data->term == kTermDTTerm       // originated this extension
+      || data->term == kTermXTerm     // per xterm ctlseqs doc
+      || data->term == kTermKonsole   // per commentary in VT102Emulation.cpp
+      || data->term == kTermTeraTerm  // per "Supported Control Functions" doc
+      || data->term == kTermRxvt) {   // per command.C
     data->unibi_ext.resize_screen = (int)unibi_add_ext_str(ut, NULL,
-	"\x1b[8;%p1%d;%p2%dt");
+      "\x1b[8;%p1%d;%p2%dt");
   }
 
 end: