Border: allow to enable/disable specific border edges

src/nvim/api/private/helpers.c

@@ -1760,10 +1760,12 @@ static void parse_border_style(Object style, FloatConfig *fconfig, Error *err)
   struct {
     const char *name;
     schar_T chars[8];
+    bool shadow_color;
   } defaults[] = {
-    { "double", { "╔", "═", "╗", "║", "╝", "═", "╚", "║" } },
-    { "single", { "┌", "─", "┐", "│", "┘", "─", "└", "│" } },
-    { NULL, { { NUL } } },
+    { "double", { "╔", "═", "╗", "║", "╝", "═", "╚", "║" }, false },
+    { "single", { "┌", "─", "┐", "│", "┘", "─", "└", "│" }, false },
+    { "shadow", { "", "", " ", " ", " ", " ", " ", "" }, true },
+    { NULL, { { NUL } } , false },
   };
 
   schar_T *chars = fconfig->border_chars;
@@ -1807,13 +1809,16 @@ static void parse_border_style(Object style, FloatConfig *fconfig, Error *err)
         api_set_error(err, kErrorTypeValidation, "invalid border char");
         return;
       }
-      if (!string.size
-          || mb_string2cells_len((char_u *)string.data, string.size) != 1) {
+      if (string.size
+          && mb_string2cells_len((char_u *)string.data, string.size) > 1) {
         api_set_error(err, kErrorTypeValidation,
                       "border chars must be one cell");
+        return;
       }
       size_t len = MIN(string.size, sizeof(*chars)-1);
-      memcpy(chars[i], string.data, len);
+      if (len) {
+        memcpy(chars[i], string.data, len);
+      }
       chars[i][len] = NUL;
       hl_ids[i] = hl_id;
     }
@@ -1822,6 +1827,13 @@ static void parse_border_style(Object style, FloatConfig *fconfig, Error *err)
       memcpy(hl_ids+size, hl_ids, sizeof(*hl_ids) * size);
       size <<= 1;
     }
+    if ((chars[7][0] && chars[1][0] && !chars[0][0])
+        || (chars[1][0] && chars[3][0] && !chars[2][0])
+        || (chars[3][0] && chars[5][0] && !chars[4][0])
+        || (chars[5][0] && chars[7][0] && !chars[6][0])) {
+      api_set_error(err, kErrorTypeValidation,
+                    "corner between used edges must be specified");
+    }
   } else if (style.type == kObjectTypeString) {
     String str = style.data.string;
     if (str.size == 0 || strequal(str.data, "none")) {
@@ -1832,6 +1844,15 @@ static void parse_border_style(Object style, FloatConfig *fconfig, Error *err)
       if (strequal(str.data, defaults[i].name)) {
         memcpy(chars, defaults[i].chars, sizeof(defaults[i].chars));
         memset(hl_ids, 0, 8 * sizeof(*hl_ids));
+        if (defaults[i].shadow_color) {
+          int hl_blend = SYN_GROUP_STATIC("FloatShadow");
+          int hl_through = SYN_GROUP_STATIC("FloatShadowThrough");
+          hl_ids[2] = hl_through;
+          hl_ids[3] = hl_blend;
+          hl_ids[4] = hl_blend;
+          hl_ids[5] = hl_blend;
+          hl_ids[6] = hl_through;
+        }
         return;
       }
     }

src/nvim/api/vim.c

@@ -1421,6 +1421,7 @@ void nvim_chan_send(Integer chan, String data, Error *err)
 ///     - "none" No border. This is the default
 ///     - "single" a single line box
 ///     - "double" a double line box
+///     - "shadow" a drop shadow effect by blending with the background.
 ///     If it is an array it should be an array of eight items or any divisor of
 ///     eight. The array will specifify the eight chars building up the border
 ///     in a clockwise fashion starting with the top-left corner. As, an
@@ -1431,6 +1432,9 @@ void nvim_chan_send(Integer chan, String data, Error *err)
 ///       [ "/", "-", "\\", "|" ]
 ///     or all chars the same as:
 ///       [ "x" ]
+///     An empty string can be used to turn off a specific border, for instance:
+///       [ "", "", "", ">", "", "", "", "<" ]
+///     will only make vertical borders but not horizontal ones.
 ///     By default `FloatBorder` highlight is used which links to `VertSplit`
 ///     when not defined.  It could also be specified by character:
 ///       [ {"+", "MyCorner"}, {"x", "MyBorder"} ]

src/nvim/buffer_defs.h

@@ -1085,6 +1085,7 @@ typedef struct {
   bool focusable;
   WinStyle style;
   bool border;
+  bool shadow;
   schar_T border_chars[8];
   int border_hl_ids[8];
   int border_attr[8];
@@ -1266,7 +1267,7 @@ struct window_S {
   int w_height_request;
   int w_width_request;
 
-  int w_border_adj;
+  int w_border_adj[4];  // top, right, bottom, left
   // outer size of window grid, including border
   int w_height_outer;
   int w_width_outer;

src/nvim/highlight.c

@@ -8,6 +8,7 @@
 #include "nvim/highlight_defs.h"
 #include "nvim/map.h"
 #include "nvim/message.h"
+#include "nvim/option.h"
 #include "nvim/popupmnu.h"
 #include "nvim/screen.h"
 #include "nvim/syntax.h"
@@ -342,16 +343,24 @@ void update_window_hl(win_T *wp, bool invalid)
     wp->w_hl_attrs[hlf] = attr;
   }
 
+  wp->w_float_config.shadow = false;
   if (wp->w_floating && wp->w_float_config.border) {
     for (int i = 0; i < 8; i++) {
       int attr = wp->w_hl_attrs[HLF_BORDER];
       if (wp->w_float_config.border_hl_ids[i]) {
         attr = hl_get_ui_attr(HLF_BORDER, wp->w_float_config.border_hl_ids[i],
                               false);
+        HlAttrs a = syn_attr2entry(attr);
+        if (a.hl_blend) {
+          wp->w_float_config.shadow = true;
+        }
       }
       wp->w_float_config.border_attr[i] = attr;
     }
   }
+
+  // shadow might cause blending
+  check_blending(wp);
 }
 
 /// Gets HL_UNDERLINE highlight.

src/nvim/option.c

@@ -3437,6 +3437,12 @@ skip:
   return NULL;    // no error
 }
 
+void check_blending(win_T *wp)
+{
+  wp->w_grid_alloc.blending =
+    wp->w_p_winbl > 0 || (wp->w_floating && wp->w_float_config.shadow);
+}
+
 
 /// Handle setting 'listchars' or 'fillchars'.
 /// Assume monocell characters
@@ -4380,7 +4386,7 @@ static char *set_num_option(int opt_idx, char_u *varp, long value,
     // 'floatblend'
     curwin->w_p_winbl = MAX(MIN(curwin->w_p_winbl, 100), 0);
     curwin->w_hl_needs_update = true;
-    curwin->w_grid_alloc.blending = curwin->w_p_winbl > 0;
+    check_blending(curwin);
   }
 
 
@@ -5895,6 +5901,7 @@ void didset_window_options(win_T *wp)
   set_chars_option(wp, &wp->w_p_fcs, true);
   set_chars_option(wp, &wp->w_p_lcs, true);
   parse_winhl_opt(wp);  // sets w_hl_needs_update also for w_p_winbl
+  check_blending(wp);
   wp->w_grid_alloc.blending = wp->w_p_winbl > 0;
 }
 

src/nvim/screen.c

@@ -5454,32 +5454,50 @@ static void win_redr_border(win_T *wp)
   schar_T *chars = wp->w_float_config.border_chars;
   int *attrs = wp->w_float_config.border_attr;
 
-  int endrow = grid->Rows-1, endcol = grid->Columns-1;
 
-  grid_puts_line_start(grid, 0);
-  grid_put_schar(grid, 0, 0, chars[0], attrs[0]);
-  for (int i = 1; i < endcol; i++) {
-    grid_put_schar(grid, 0, i, chars[1], attrs[1]);
-  }
-  grid_put_schar(grid, 0, endcol, chars[2], attrs[2]);
-  grid_puts_line_flush(false);
+  int *adj = wp->w_border_adj;
+  int irow = wp->w_height_inner, icol = wp->w_width_inner;
 
-  for (int i = 1; i < endrow; i++) {
-    grid_puts_line_start(grid, i);
-    grid_put_schar(grid, i, 0, chars[7], attrs[7]);
-    grid_puts_line_flush(false);
-    grid_puts_line_start(grid, i);
-    grid_put_schar(grid, i, endcol, chars[3], attrs[3]);
+  if (adj[0]) {
+    grid_puts_line_start(grid, 0);
+    if (adj[3]) {
+      grid_put_schar(grid, 0, 0, chars[0], attrs[0]);
+    }
+    for (int i = 0; i < icol; i++) {
+      grid_put_schar(grid, 0, i+adj[3], chars[1], attrs[1]);
+    }
+    if (adj[1]) {
+      grid_put_schar(grid, 0, icol+adj[3], chars[2], attrs[2]);
+    }
     grid_puts_line_flush(false);
   }
 
-  grid_puts_line_start(grid, endrow);
-  grid_put_schar(grid, endrow, 0, chars[6], attrs[6]);
-  for (int i = 1; i < endcol; i++) {
-    grid_put_schar(grid, endrow, i, chars[5], attrs[5]);
+  for (int i = 0; i < irow; i++) {
+    if (adj[3]) {
+      grid_puts_line_start(grid, i+adj[0]);
+      grid_put_schar(grid, i+adj[0], 0, chars[7], attrs[7]);
+      grid_puts_line_flush(false);
+    }
+    if (adj[1]) {
+      int ic = (i == 0 && !adj[0] && chars[2][0]) ? 2 : 3;
+      grid_puts_line_start(grid, i+adj[0]);
+      grid_put_schar(grid, i+adj[0], icol+adj[3], chars[ic], attrs[ic]);
+      grid_puts_line_flush(false);
+    }
+  }
+
+  if (adj[2]) {
+    grid_puts_line_start(grid, irow+adj[0]);
+    if (adj[3]) {
+      grid_put_schar(grid, irow+adj[0], 0, chars[6], attrs[6]);
+    }
+    for (int i = 0; i < icol; i++) {
+      int ic = (i == 0 && !adj[3] && chars[6][0]) ? 6 : 5;
+      grid_put_schar(grid, irow+adj[0], i+adj[3], chars[ic], attrs[ic]);
+    }
+    grid_put_schar(grid, irow+adj[0], icol+adj[3], chars[4], attrs[4]);
+    grid_puts_line_flush(false);
   }
-  grid_put_schar(grid, endrow, endcol, chars[4], attrs[4]);
-  grid_puts_line_flush(false);
 }
 
 // Low-level functions to manipulate invidual character cells on the
@@ -6247,7 +6265,7 @@ void win_grid_alloc(win_T *wp)
     grid_alloc(grid_allocated, total_rows, total_cols,
                wp->w_grid_alloc.valid, false);
     grid_allocated->valid = true;
-    if (wp->w_border_adj) {
+    if (wp->w_floating && wp->w_float_config.border) {
       wp->w_redr_border = true;
     }
     was_resized = true;
@@ -6267,8 +6285,8 @@ void win_grid_alloc(win_T *wp)
 
   if (want_allocation) {
     grid->target = grid_allocated;
-    grid->row_offset = wp->w_border_adj;
-    grid->col_offset = wp->w_border_adj;
+    grid->row_offset = wp->w_border_adj[0];
+    grid->col_offset = wp->w_border_adj[3];
   } else {
     grid->target = &default_grid;
     grid->row_offset = wp->w_winrow;

src/nvim/syntax.c

@@ -6047,6 +6047,8 @@ static const char *highlight_init_both[] = {
   "default link MsgSeparator StatusLine",
   "default link NormalFloat Pmenu",
   "default link FloatBorder VertSplit",
+  "default FloatShadow blend=80 guibg=Black",
+  "default FloatShadowThrough blend=100 guibg=Black",
   "RedrawDebugNormal cterm=reverse gui=reverse",
   "RedrawDebugClear ctermbg=Yellow guibg=Yellow",
   "RedrawDebugComposed ctermbg=Green guibg=Green",

src/nvim/syntax.h

@@ -27,6 +27,8 @@
 #define HL_CONCEAL     0x20000 /* can be concealed */
 #define HL_CONCEALENDS 0x40000 /* can be concealed */
 
+#define SYN_GROUP_STATIC(s) syn_check_group((char_u *)S_LEN(s))
+
 typedef struct {
   char *name;
   RgbValue color;

src/nvim/window.c

@@ -668,7 +668,11 @@ void win_config_float(win_T *wp, FloatConfig fconfig)
   }
 
   bool change_external = fconfig.external != wp->w_float_config.external;
-  bool change_border = fconfig.border != wp->w_float_config.border;
+  bool change_border = (fconfig.border != wp->w_float_config.border
+                        || memcmp(fconfig.border_hl_ids,
+                                  wp->w_float_config.border_hl_ids,
+                                  sizeof fconfig.border_hl_ids));
+
 
   wp->w_float_config = fconfig;
 
@@ -5731,9 +5735,16 @@ void win_set_inner_size(win_T *wp)
     terminal_check_size(wp->w_buffer->terminal);
   }
 
-  wp->w_border_adj = wp->w_floating && wp->w_float_config.border ? 1 : 0;
-  wp->w_height_outer = wp->w_height_inner + 2 * wp->w_border_adj;
-  wp->w_width_outer = wp->w_width_inner + 2 * wp->w_border_adj;
+  bool has_border = wp->w_floating && wp->w_float_config.border;
+  for (int i = 0; i < 4; i++) {
+    wp->w_border_adj[i] =
+      has_border && wp->w_float_config.border_chars[2 * i+1][0];
+  }
+
+  wp->w_height_outer = (wp->w_height_inner
+                        + wp->w_border_adj[0] + wp->w_border_adj[2]);
+  wp->w_width_outer = (wp->w_width_inner
+                       + wp->w_border_adj[1] + wp->w_border_adj[3]);
 }
 
 /// Set the width of a window.