refactor(screen): simplify grid_clear() and win_draw_end()

grid_put_linebuf() used grid_clear() internally to handle clearing the
left part of a rightleft line. By reimplementing that internally, we
can instead use grid_put_linebuf() as the implementation of
grid_clear(), which in the end is a net reduction of code as grid_fill()
is used for nothing else.

win_draw_end: Implement "draw_margin" on a per-row basis which closer reflects how
terminals work. Also use the magic mirror for 'rightleft'

5 files changed, 126 insertions, 204 deletions

diff --git a/src/nvim/drawline.c b/src/nvim/drawline.c
index a4d98f09f4..aae374c8a7 100644
--- a/src/nvim/drawline.c
+++ b/src/nvim/drawline.c
@@ -2611,8 +2611,7 @@ int win_line(win_T *wp, linenr_T lnum, int startrow, int endrow, bool number_onl
 
       // When the window is too narrow draw all "@" lines.
       if (leftcols_width >= wp->w_grid.cols && wp->w_p_wrap) {
-        win_draw_end(wp, schar_from_ascii('@'), schar_from_ascii(' '), true, wlv.row,
-                     wp->w_grid.rows, HLF_AT);
+        win_draw_end(wp, schar_from_ascii('@'), true, wlv.row, wp->w_grid.rows, HLF_AT);
         set_empty_rows(wp, wlv.row);
         wlv.row = endrow;
       }
@@ -2836,8 +2835,7 @@ int win_line(win_T *wp, linenr_T lnum, int startrow, int endrow, bool number_onl
 
       // When the window is too narrow draw all "@" lines.
       if (wlv.col <= leftcols_width) {
-        win_draw_end(wp, schar_from_ascii('@'), schar_from_ascii(' '), true, wlv.row,
-                     wp->w_grid.rows, HLF_AT);
+        win_draw_end(wp, schar_from_ascii('@'), true, wlv.row, wp->w_grid.rows, HLF_AT);
         set_empty_rows(wp, wlv.row);
         wlv.row = endrow;
       }
@@ -2883,8 +2881,7 @@ static void win_put_linebuf(win_T *wp, int row, int coloff, int endcol, int clea
   int start_col = 0;
 
   if (wp->w_p_rl) {
-    linebuf_mirror(&start_col, &clear_width, grid->cols);
-    endcol = grid->cols - 1 - endcol;
+    linebuf_mirror(&start_col, &endcol, &clear_width, grid->cols);
   }
 
   // Take care of putting "<<<" on the first line for 'smoothscroll'.
diff --git a/src/nvim/drawscreen.c b/src/nvim/drawscreen.c
index 12f06e13cc..964fdb141a 100644
--- a/src/nvim/drawscreen.c
+++ b/src/nvim/drawscreen.c
@@ -1296,9 +1296,11 @@ static void draw_vsep_win(win_T *wp)
   }
 
   // draw the vertical separator right of this window
-  int hl = win_hl_attr(wp, HLF_C);
-  schar_T c = wp->w_p_fcs_chars.vert;
-  grid_fill(&default_grid, wp->w_winrow, W_ENDROW(wp), W_ENDCOL(wp), W_ENDCOL(wp) + 1, c, c, hl);
+  for (int row = wp->w_winrow; row < W_ENDROW(wp); row++) {
+    grid_line_start(&default_grid, row);
+    grid_line_put_schar(W_ENDCOL(wp), wp->w_p_fcs_chars.vert, win_hl_attr(wp, HLF_C));
+    grid_line_flush();
+  }
 }
 
 /// Draw the horizontal separator below window "wp"
@@ -1309,9 +1311,9 @@ static void draw_hsep_win(win_T *wp)
   }
 
   // draw the horizontal separator below this window
-  int hl = win_hl_attr(wp, HLF_C);
-  schar_T c = wp->w_p_fcs_chars.horiz;
-  grid_fill(&default_grid, W_ENDROW(wp), W_ENDROW(wp) + 1, wp->w_wincol, W_ENDCOL(wp), c, c, hl);
+  grid_line_start(&default_grid, W_ENDROW(wp));
+  grid_line_fill(wp->w_wincol, W_ENDCOL(wp), wp->w_p_fcs_chars.horiz, win_hl_attr(wp, HLF_C));
+  grid_line_flush();
 }
 
 /// Get the separator connector for specified window corner of window "wp"
@@ -2395,7 +2397,7 @@ static void win_update(win_T *wp)
       set_empty_rows(wp, srow);
       wp->w_botline = lnum;
     } else {
-      win_draw_end(wp, wp->w_p_fcs_chars.lastline, schar_from_ascii(' '), true, srow,
+      win_draw_end(wp, wp->w_p_fcs_chars.lastline, true, srow,
                    wp->w_grid.rows, HLF_AT);
       set_empty_rows(wp, srow);
       wp->w_botline = lnum;
@@ -2429,7 +2431,7 @@ static void win_update(win_T *wp)
       lastline = 0;
     }
 
-    win_draw_end(wp, wp->w_p_fcs_chars.eob, schar_from_ascii(' '), false, MAX(lastline, row),
+    win_draw_end(wp, wp->w_p_fcs_chars.eob, false, MAX(lastline, row),
                  wp->w_grid.rows,
                  HLF_EOB);
     set_empty_rows(wp, row);
@@ -2517,60 +2519,43 @@ void win_scroll_lines(win_T *wp, int row, int line_count)
   }
 }
 
-/// Call grid_clear() with columns adjusted for 'rightleft' if needed.
-/// Return the new offset.
-static int win_clear_end(win_T *wp, int off, int width, int row, int endrow, int attr)
-{
-  int nn = off + width;
-  const int endcol = wp->w_grid.cols;
-
-  if (nn > endcol) {
-    nn = endcol;
-  }
-
-  if (wp->w_p_rl) {
-    grid_clear(&wp->w_grid, row, endrow, endcol - nn, endcol - off, attr);
-  } else {
-    grid_clear(&wp->w_grid, row, endrow, off, nn, attr);
-  }
-
-  return nn;
-}
-
 /// Clear lines near the end of the window and mark the unused lines with "c1".
-/// Use "c2" as filler character.
 /// When "draw_margin" is true, then draw the sign/fold/number columns.
-void win_draw_end(win_T *wp, schar_T c1, schar_T c2, bool draw_margin, int row, int endrow,
-                  hlf_T hl)
+void win_draw_end(win_T *wp, schar_T c1, bool draw_margin, int startrow, int endrow, hlf_T hl)
 {
   assert(hl >= 0 && hl < HLF_COUNT);
-  int n = 0;
-
-  if (draw_margin) {
-    // draw the fold column
-    int fdc = compute_foldcolumn(wp, 0);
-    if (fdc > 0) {
-      n = win_clear_end(wp, n, fdc, row, endrow, win_hl_attr(wp, HLF_FC));
-    }
-    // draw the sign column
-    int count = wp->w_scwidth;
-    if (count > 0) {
-      n = win_clear_end(wp, n, SIGN_WIDTH * count, row, endrow, win_hl_attr(wp, HLF_SC));
+  for (int row = startrow; row < endrow; row++) {
+    grid_line_start(&wp->w_grid, row);
+
+    int n = 0;
+    if (draw_margin) {
+      // draw the fold column
+      int fdc = MAX(0, compute_foldcolumn(wp, 0));
+      n = grid_line_fill(n, n + fdc, schar_from_ascii(' '), win_hl_attr(wp, HLF_FC));
+
+      // draw the sign column
+      n = grid_line_fill(n, n + wp->w_scwidth, schar_from_ascii(' '), win_hl_attr(wp, HLF_FC));
+
+      // draw the number column
+      if ((wp->w_p_nu || wp->w_p_rnu) && vim_strchr(p_cpo, CPO_NUMCOL) == NULL) {
+        int width = number_width(wp) + 1;
+        n = grid_line_fill(n, n + width, schar_from_ascii(' '), win_hl_attr(wp, HLF_N));
+      }
     }
-    // draw the number column
-    if ((wp->w_p_nu || wp->w_p_rnu) && vim_strchr(p_cpo, CPO_NUMCOL) == NULL) {
-      n = win_clear_end(wp, n, number_width(wp) + 1, row, endrow, win_hl_attr(wp, HLF_N));
+
+    int attr = hl_combine_attr(win_bg_attr(wp), win_hl_attr(wp, (int)hl));
+
+    if (n < wp->w_grid.cols) {
+      grid_line_put_schar(n, c1, 0);  // base attr is inherited from clear
+      n++;
     }
-  }
 
-  int attr = hl_combine_attr(win_bg_attr(wp), win_hl_attr(wp, (int)hl));
+    grid_line_clear_end(n, wp->w_grid.cols, attr);
 
-  const int endcol = wp->w_grid.cols;
-  if (wp->w_p_rl) {
-    grid_fill(&wp->w_grid, row, endrow, 0, endcol - 1 - n, c2, c2, attr);
-    grid_fill(&wp->w_grid, row, endrow, endcol - 1 - n, endcol - n, c1, c2, attr);
-  } else {
-    grid_fill(&wp->w_grid, row, endrow, n, endcol, c1, c2, attr);
+    if (wp->w_p_rl) {
+      grid_line_mirror();
+    }
+    grid_line_flush();
   }
 }
 
diff --git a/src/nvim/grid.c b/src/nvim/grid.c
index f529e14b35..0f8a0f8ab8 100644
--- a/src/nvim/grid.c
+++ b/src/nvim/grid.c
@@ -334,6 +334,9 @@ static int grid_line_coloff = 0;
 static int grid_line_maxcol = 0;
 static int grid_line_first = INT_MAX;
 static int grid_line_last = 0;
+static int grid_line_clear_to = 0;
+static int grid_line_clear_attr = 0;
+static bool grid_line_rl = false;
 
 /// Start a group of grid_line_puts calls that builds a single grid line.
 ///
@@ -342,14 +345,18 @@ static int grid_line_last = 0;
 void grid_line_start(ScreenGrid *grid, int row)
 {
   int col = 0;
+  grid_line_maxcol = grid->cols;
   grid_adjust(&grid, &row, &col);
   assert(grid_line_grid == NULL);
   grid_line_row = row;
   grid_line_grid = grid;
   grid_line_coloff = col;
   grid_line_first = (int)linebuf_size;
-  grid_line_maxcol = grid->cols - grid_line_coloff;
+  grid_line_maxcol = MIN(grid_line_maxcol, grid->cols - grid_line_coloff);
   grid_line_last = 0;
+  grid_line_clear_to = 0;
+  grid_line_clear_attr = 0;
+  grid_line_rl = false;
 
   assert((size_t)grid_line_maxcol <= linebuf_size);
 
@@ -465,11 +472,11 @@ int grid_line_puts(int col, const char *text, int textlen, int attr)
   return col - start_col;
 }
 
-void grid_line_fill(int start_col, int end_col, schar_T sc, int attr)
+int grid_line_fill(int start_col, int end_col, schar_T sc, int attr)
 {
   end_col = MIN(end_col, grid_line_maxcol);
   if (start_col >= end_col) {
-    return;
+    return end_col;
   }
 
   for (int col = start_col; col < end_col; col++) {
@@ -480,6 +487,17 @@ void grid_line_fill(int start_col, int end_col, schar_T sc, int attr)
 
   grid_line_first = MIN(grid_line_first, start_col);
   grid_line_last = MAX(grid_line_last, end_col);
+  return end_col;
+}
+
+void grid_line_clear_end(int start_col, int end_col, int attr)
+{
+  if (grid_line_first > start_col) {
+    grid_line_first = start_col;
+    grid_line_last = start_col;
+  }
+  grid_line_clear_to = end_col;
+  grid_line_clear_attr = attr;
 }
 
 /// move the cursor to a position in a currently rendered line.
@@ -490,13 +508,15 @@ void grid_line_cursor_goto(int col)
 
 void grid_line_mirror(void)
 {
-  if (grid_line_first >= grid_line_last) {
+  grid_line_clear_to = MAX(grid_line_last, grid_line_clear_to);
+  if (grid_line_first >= grid_line_clear_to) {
     return;
   }
-  linebuf_mirror(&grid_line_first, &grid_line_last, grid_line_maxcol);
+  linebuf_mirror(&grid_line_first, &grid_line_last, &grid_line_clear_to, grid_line_maxcol);
+  grid_line_rl = true;
 }
 
-void linebuf_mirror(int *firstp, int *lastp, int maxcol)
+void linebuf_mirror(int *firstp, int *lastp, int *clearp, int maxcol)
 {
   int first = *firstp;
   int last = *lastp;
@@ -529,8 +549,9 @@ void linebuf_mirror(int *firstp, int *lastp, int maxcol)
     linebuf_vcol[mirror - col] = scratch_vcol[col];
   }
 
-  *lastp = maxcol - first;
-  *firstp = maxcol - last;
+  *firstp = maxcol - *clearp;
+  *clearp = maxcol - first;
+  *lastp = maxcol - last;
 }
 
 /// End a group of grid_line_puts calls and send the screen buffer to the UI layer.
@@ -538,13 +559,14 @@ void grid_line_flush(void)
 {
   ScreenGrid *grid = grid_line_grid;
   grid_line_grid = NULL;
-  assert(grid_line_last <= grid_line_maxcol);
-  if (grid_line_first >= grid_line_last) {
+  grid_line_clear_to = MAX(grid_line_last, grid_line_clear_to);
+  assert(grid_line_clear_to <= grid_line_maxcol);
+  if (grid_line_first >= grid_line_clear_to) {
     return;
   }
 
   grid_put_linebuf(grid, grid_line_row, grid_line_coloff, grid_line_first, grid_line_last,
-                   grid_line_last, false, 0, false);
+                   grid_line_clear_to, grid_line_rl, grid_line_clear_attr, false);
 }
 
 /// flush grid line but only if on a valid row
@@ -565,94 +587,15 @@ void grid_line_flush_if_valid_row(void)
 
 void grid_clear(ScreenGrid *grid, int start_row, int end_row, int start_col, int end_col, int attr)
 {
-  grid_fill(grid, start_row, end_row, start_col, end_col, schar_from_ascii(' '),
-            schar_from_ascii(' '), attr);
-}
-
-/// Fill the grid from "start_row" to "end_row" (exclusive), from "start_col"
-/// to "end_col" (exclusive) with character "c1" in first column followed by
-/// "c2" in the other columns.  Use attributes "attr".
-void grid_fill(ScreenGrid *grid, int start_row, int end_row, int start_col, int end_col, schar_T c1,
-               schar_T c2, int attr)
-{
-  int row_off = 0;
-  int col_off = 0;
-  grid_adjust(&grid, &row_off, &col_off);
-  start_row += row_off;
-  end_row += row_off;
-  start_col += col_off;
-  end_col += col_off;
-
-  // safety check
-  if (end_row > grid->rows) {
-    end_row = grid->rows;
-  }
-  if (end_col > grid->cols) {
-    end_col = grid->cols;
-  }
-
-  // nothing to do
-  if (start_row >= end_row || start_col >= end_col) {
-    return;
-  }
-
   for (int row = start_row; row < end_row; row++) {
-    int dirty_first = INT_MAX;
-    int dirty_last = 0;
-    size_t lineoff = grid->line_offset[row];
-
-    // When drawing over the right half of a double-wide char clear
-    // out the left half.  When drawing over the left half of a
-    // double wide-char clear out the right half.  Only needed in a
-    // terminal.
-    if (start_col > 0 && grid->chars[lineoff + (size_t)start_col] == NUL) {
-      size_t off = lineoff + (size_t)start_col - 1;
-      grid->chars[off] = schar_from_ascii(' ');
-      grid->attrs[off] = attr;
-      dirty_first = start_col - 1;
-    }
-    if (end_col < grid->cols && grid->chars[lineoff + (size_t)end_col] == NUL) {
-      size_t off = lineoff + (size_t)end_col;
-      grid->chars[off] = schar_from_ascii(' ');
-      grid->attrs[off] = attr;
-      dirty_last = end_col + 1;
-    }
-
-    int col = start_col;
-    schar_T sc = c1;
-    for (col = start_col; col < end_col; col++) {
-      size_t off = lineoff + (size_t)col;
-      if (grid->chars[off] != sc || grid->attrs[off] != attr || rdb_flags & RDB_NODELTA) {
-        grid->chars[off] = sc;
-        grid->attrs[off] = attr;
-        if (dirty_first == INT_MAX) {
-          dirty_first = col;
-        }
-        dirty_last = col + 1;
-      }
-      grid->vcols[off] = -1;
-      if (col == start_col) {
-        sc = c2;
-      }
-    }
-    if (dirty_last > dirty_first) {
-      if (grid->throttled) {
-        // Note: assumes msg_grid is the only throttled grid
-        assert(grid == &msg_grid);
-        int dirty = 0;
-        if (attr != HL_ATTR(HLF_MSG) || c2 != ' ') {
-          dirty = dirty_last;
-        } else if (c1 != ' ') {
-          dirty = dirty_first + 1;
-        }
-        if (grid->dirty_col && dirty > grid->dirty_col[row]) {
-          grid->dirty_col[row] = dirty;
-        }
-      } else {
-        int last = c2 != ' ' ? dirty_last : dirty_first + (c1 != ' ');
-        ui_line(grid, row, dirty_first, last, dirty_last, attr, false);
-      }
+    grid_line_start(grid, row);
+    end_col = MIN(end_col, grid_line_maxcol);
+    if (grid_line_row >= grid_line_grid->rows || start_col >= end_col) {
+      grid_line_grid = NULL;  // TODO(bfredl): make callers behave instead
+      return;
     }
+    grid_line_clear_end(start_col, end_col, attr);
+    grid_line_flush();
   }
 }
 
@@ -712,19 +655,12 @@ void grid_put_linebuf(ScreenGrid *grid, int row, int coloff, int col, int endcol
     col--;
   }
 
+  int clear_start = endcol;
   if (rl) {
-    // Clear rest first, because it's left of the text.
-    if (clear_width > 0) {
-      while (col <= endcol && grid->chars[off_to + (size_t)col] == schar_from_ascii(' ')
-             && grid->attrs[off_to + (size_t)col] == bg_attr) {
-        col++;
-      }
-      if (col <= endcol) {
-        grid_clear(grid, row, row + 1, col + coloff, endcol + coloff + 1, bg_attr);
-      }
-    }
-    col = endcol + 1;
+    clear_start = col;
+    col = endcol;
     endcol = clear_width;
+    clear_width = col;
   }
 
   if (p_arshape && !p_tbidi && endcol > col) {
@@ -797,45 +733,49 @@ void grid_put_linebuf(ScreenGrid *grid, int row, int coloff, int col, int endcol
     end_dirty++;
   }
 
-  int clear_end = -1;
-  if (clear_width > 0 && !rl) {
-    // blank out the rest of the line
-    // TODO(bfredl): we could cache winline widths
-    while (col < clear_width) {
-      size_t off = (size_t)col + off_to;
-      if (grid->chars[off] != schar_from_ascii(' ')
-          || grid->attrs[off] != bg_attr
-          || rdb_flags & RDB_NODELTA) {
-        grid->chars[off] = schar_from_ascii(' ');
-        grid->attrs[off] = bg_attr;
-        if (start_dirty == -1) {
-          start_dirty = col;
-          end_dirty = col;
-        } else if (clear_end == -1) {
-          end_dirty = endcol;
-        }
-        clear_end = col + 1;
+  int clear_dirty_start = -1, clear_end = -1;
+  // blank out the rest of the line
+  // TODO(bfredl): we could cache winline widths
+  col = clear_start;
+  while (col < clear_width) {
+    size_t off = (size_t)col + off_to;
+    if (grid->chars[off] != schar_from_ascii(' ')
+        || grid->attrs[off] != bg_attr
+        || rdb_flags & RDB_NODELTA) {
+      grid->chars[off] = schar_from_ascii(' ');
+      grid->attrs[off] = bg_attr;
+      if (clear_dirty_start == -1) {
+        clear_dirty_start = col;
       }
-      grid->vcols[off] = MAXCOL;
-      col++;
+      clear_end = col + 1;
     }
+    grid->vcols[off] = MAXCOL;
+    col++;
   }
 
-  if (clear_end < end_dirty) {
+  if (rl && start_dirty != -1 && clear_dirty_start != -1) {
+    if (grid->throttled || clear_dirty_start >= start_dirty - 5) {
+      // cannot draw now or too small to be worth a separate "clear" event
+      start_dirty = clear_dirty_start;
+    } else {
+      ui_line(grid, row, invalid_row, coloff + clear_dirty_start, coloff + clear_dirty_start,
+              coloff + clear_end, bg_attr, wrap);
+    }
     clear_end = end_dirty;
+  } else {
+    if (start_dirty == -1) {  // clear only
+      start_dirty = clear_dirty_start;
+      end_dirty = clear_dirty_start;
+    } else if (clear_end < end_dirty) {  // put only
+      clear_end = end_dirty;
+    } else {
+      end_dirty = endcol;
+    }
   }
-  if (start_dirty == -1) {
-    start_dirty = end_dirty;
-  }
+
   if (clear_end > start_dirty) {
     if (!grid->throttled) {
-      int start_pos = coloff + start_dirty;
-      // When drawing over the right half of a double-wide char clear out the
-      // left half.  Only needed in a terminal.
-      if (invalid_row && start_pos == 0) {
-        start_pos = -1;
-      }
-      ui_line(grid, row, start_pos, coloff + end_dirty, coloff + clear_end,
+      ui_line(grid, row, invalid_row, coloff + start_dirty, coloff + end_dirty, coloff + clear_end,
               bg_attr, wrap);
     } else if (grid->dirty_col) {
       // TODO(bfredl): really get rid of the extra pseudo terminal in message.c
diff --git a/src/nvim/message.c b/src/nvim/message.c
index 2b668db7cd..35cf7d71fb 100644
--- a/src/nvim/message.c
+++ b/src/nvim/message.c
@@ -204,6 +204,7 @@ void msg_grid_validate(void)
   } else if (msg_grid.chars && !msg_scrolled && msg_grid_pos != max_rows) {
     msg_grid_set_pos(max_rows, false);
   }
+  msg_grid_adj.cols = Columns;
 
   if (msg_grid.chars && !msg_scrolled && cmdline_row < msg_grid_pos) {
     // TODO(bfredl): this should already be the case, but fails in some
@@ -2349,7 +2350,7 @@ void msg_scroll_flush(void)
     for (int i = MAX(Rows - MAX(delta, 1), 0); i < Rows; i++) {
       int row = i - msg_grid_pos;
       assert(row >= 0);
-      ui_line(&msg_grid, row, 0, msg_grid.dirty_col[row], msg_grid.cols,
+      ui_line(&msg_grid, row, false, 0, msg_grid.dirty_col[row], msg_grid.cols,
               HL_ATTR(HLF_MSG), false);
       msg_grid.dirty_col[row] = 0;
     }
diff --git a/src/nvim/ui.c b/src/nvim/ui.c
index 9116bb22a2..5303a25acc 100644
--- a/src/nvim/ui.c
+++ b/src/nvim/ui.c
@@ -448,13 +448,12 @@ void ui_set_ext_option(UI *ui, UIExtension ext, bool active)
   }
 }
 
-void ui_line(ScreenGrid *grid, int row, int startcol, int endcol, int clearcol, int clearattr,
-             bool wrap)
+void ui_line(ScreenGrid *grid, int row, bool invalid_row, int startcol, int endcol, int clearcol,
+             int clearattr, bool wrap)
 {
   assert(0 <= row && row < grid->rows);
   LineFlags flags = wrap ? kLineFlagWrap : 0;
-  if (startcol == -1) {
-    startcol = 0;
+  if (startcol == 0 && invalid_row) {
     flags |= kLineFlagInvalid;
   }