From b76852a07f9f2a6ef4b98fd90807e357a9ebb81c Mon Sep 17 00:00:00 2001
From: Sebastien Chapuis <address@hidden>
Date: Thu, 7 Nov 2019 06:36:04 +0800
Subject: [PATCH] Add function window-line-width

* src/window.c: Define the function.
* etc/NEWS: Mention `window-line-width'.
---
 etc/NEWS     |   4 ++
 src/window.c | 112 +++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 116 insertions(+)

diff --git a/etc/NEWS b/etc/NEWS
index bfcb7cf325..2f15185efe 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -221,6 +221,10 @@ To get the old, less-secure behavior, you can set the
 *** When run by root, emacsclient no longer connects to non-root sockets.
 (Instead you can use Tramp methods to run root commands in a non-root Emacs.)
 
+---
+** New function 'window-line-width'.
+Return width in pixels of a text line.
+
 ** New function 'network-lookup-address-info'.
 This does IPv4 and/or IPv6 address lookups on hostnames.
 
diff --git a/src/window.c b/src/window.c
index 0fa0bdf7b9..4bfdfc05de 100644
--- a/src/window.c
+++ b/src/window.c
@@ -1929,6 +1929,115 @@ DEFUN ("pos-visible-in-window-p", Fpos_visible_in_window_p,
   return in_window;
 }
 
+DEFUN ("window-line-width", Fwindow_line_width,
+       Swindow_line_width, 0, 3, 0,
+       doc: /* Return width in pixels of a text line LINE in WINDOW, in AREA.
+
+Return width of current line if LINE is omitted or nil.
+LINE can also be `tab-line', `header-line' and `mode-line'.
+Otherwise, LINE is a row number (zero-based).
+
+WINDOW must be a live window and defaults to the selected one.
+
+AREA can take one of those values:
+- `left-margin': Width of the left margin area
+- `right-margin': Width of the right margin area
+- `text-area': Width of the text area, until the new line (excluded)
+- `text-area-full': Similar to `text-area' but include glyphs after the
+   new line, if any.
+If omitted, AREA defaults to `text-area'.
+
+Return nil if the window display is not up-to-date.  */)
+  (Lisp_Object line, Lisp_Object window, Lisp_Object area)
+{
+  struct window *w = decode_live_window (window);
+  struct buffer *buffer UNINIT;
+  int vpos UNINIT;
+
+  if (noninteractive || w->pseudo_window_p)
+    return Qnil;
+
+  CHECK_BUFFER (w->contents);
+  buffer = XBUFFER (w->contents);
+
+  /* Fail if current matrix is not up-to-date.  */
+  if (!w->window_end_valid
+      || windows_or_buffers_changed
+      || buffer->clip_changed
+      || buffer->prevent_redisplay_optimizations_p
+      || window_outdated (w))
+    return Qnil;
+
+  struct glyph_matrix *matrix = w->current_matrix;
+
+  if (NILP (line))
+    vpos = w->cursor.vpos;
+  else if (EQ (line, Qtab_line))
+    {
+      if (!window_wants_tab_line (w) || !matrix->tab_line_p)
+	return Qnil;
+      vpos = 0;
+    }
+  else if (EQ (line, Qheader_line))
+    {
+      if (!window_wants_header_line (w) || !matrix->header_line_p)
+	return Qnil;
+      vpos = matrix->tab_line_p ? 1 : 0;
+    }
+  else if (EQ (line, Qmode_line))
+    {
+      if (!window_wants_mode_line (w))
+	return Qnil;
+      vpos = matrix->nrows - 1;
+    }
+  else
+    {
+      CHECK_FIXNUM (line);
+      vpos = XFIXNUM (line)
+        + window_wants_tab_line (w)
+        + window_wants_header_line (w);
+    }
+
+  if (vpos < 0 || vpos >= matrix->nrows)
+    error ("Invalid line");
+
+  enum glyph_row_area actual_area UNINIT;
+  bool full_text = false;
+
+  if (EQ (area, Qleft_margin))
+    actual_area = LEFT_MARGIN_AREA;
+  else if (EQ (area, Qright_margin))
+    actual_area = RIGHT_MARGIN_AREA;
+  else
+    {
+      if (EQ (area, Qtext_area_full))
+        full_text = true;
+      actual_area = TEXT_AREA;
+    }
+
+  struct glyph_row *row = MATRIX_ROW (matrix, vpos);
+
+  struct glyph *glyph = row->glyphs[actual_area];
+  int used = row->used[actual_area];
+  int width = 0;
+
+  for (int i = 0; i < used; ++i)
+    {
+      if (actual_area == TEXT_AREA && full_text == false
+          && NILP (glyph[i].object) && glyph[i].charpos >= 0)
+        /*
+          We reached the end of the line in TEXT_AREA.
+          display-line-numbers-mode inserts glyphs with NILP(glyph.object)
+          and glyph.charpos == -1, so we can't check only for
+          NILP (glyph.object)
+        */
+        break;
+      width += glyph[i].pixel_width;
+    }
+
+  return make_fixnum (width);
+}
+
 DEFUN ("window-line-height", Fwindow_line_height,
        Swindow_line_height, 0, 2, 0,
        doc: /* Return height in pixels of text line LINE in window WINDOW.
@@ -8179,6 +8288,8 @@ syms_of_window (void)
   DEFSYM (Qmode_line_format, "mode-line-format");
   DEFSYM (Qheader_line_format, "header-line-format");
   DEFSYM (Qtab_line_format, "tab-line-format");
+  DEFSYM (Qtext_area, "text-area");
+  DEFSYM (Qtext_area_full, "text-area-full");
 
   DEFVAR_LISP ("temp-buffer-show-function", Vtemp_buffer_show_function,
 	       doc: /* Non-nil means call as function to display a help buffer.
@@ -8443,6 +8554,7 @@ syms_of_window (void)
   defsubr (&Sset_frame_selected_window);
   defsubr (&Spos_visible_in_window_p);
   defsubr (&Swindow_line_height);
+  defsubr (&Swindow_line_width);
   defsubr (&Swindow_buffer);
   defsubr (&Swindow_old_buffer);
   defsubr (&Swindow_parent);
-- 
2.21.0