--- a/src/popupwin.c
+++ b/src/popupwin.c
@@ -1372,4 +1372,310 @@ popup_check_cursor_pos()
 	}
 }
 
+/*
+ * Update "popup_mask" if needed.
+ * Also recomputes the popup size and positions.
+ * Also updates "popup_visible".
+ * Also marks window lines for redrawing.
+ */
+    void
+may_update_popup_mask(int type)
+{
+    win_T	*wp;
+    short	*mask;
+    int		line, col;
+    int		redraw_all = FALSE;
+
+    // Need to recompute when switching tabs.
+    // Also recompute when the type is CLEAR or NOT_VALID, something basic
+    // (such as the screen size) must have changed.
+    if (popup_mask_tab != curtab || type >= NOT_VALID)
+    {
+	popup_mask_refresh = TRUE;
+	redraw_all = TRUE;
+    }
+    if (!popup_mask_refresh)
+    {
+	// Check if any buffer has changed.
+	for (wp = first_popupwin; wp != NULL; wp = wp->w_next)
+	    if (wp->w_popup_last_changedtick != CHANGEDTICK(wp->w_buffer))
+		popup_mask_refresh = TRUE;
+	for (wp = curtab->tp_first_popupwin; wp != NULL; wp = wp->w_next)
+	    if (wp->w_popup_last_changedtick != CHANGEDTICK(wp->w_buffer))
+		popup_mask_refresh = TRUE;
+	if (!popup_mask_refresh)
+	    return;
+    }
+
+    // Need to update the mask, something has changed.
+    popup_mask_refresh = FALSE;
+    popup_mask_tab = curtab;
+    popup_visible = FALSE;
+
+    // If redrawing everything, just update "popup_mask".
+    // If redrawing only what is needed, update "popup_mask_next" and then
+    // compare with "popup_mask" to see what changed.
+    if (type >= SOME_VALID)
+	mask = popup_mask;
+    else
+	mask = popup_mask_next;
+    vim_memset(mask, 0, screen_Rows * screen_Columns * sizeof(short));
+
+    // Find the window with the lowest zindex that hasn't been handled yet,
+    // so that the window with a higher zindex overwrites the value in
+    // popup_mask.
+    popup_reset_handled();
+    while ((wp = find_next_popup(TRUE)) != NULL)
+    {
+	popup_visible = TRUE;
+
+	// Recompute the position if the text changed.
+	if (redraw_all
+		|| wp->w_popup_last_changedtick != CHANGEDTICK(wp->w_buffer))
+	    popup_adjust_position(wp);
+
+	for (line = wp->w_winrow;
+		line < wp->w_winrow + popup_height(wp)
+						 && line < screen_Rows; ++line)
+	    for (col = wp->w_wincol;
+		 col < wp->w_wincol + popup_width(wp)
+						&& col < screen_Columns; ++col)
+		mask[line * screen_Columns + col] = wp->w_zindex;
+    }
+
+    // Only check which lines are to be updated if not already
+    // updating all lines.
+    if (mask == popup_mask_next)
+	for (line = 0; line < screen_Rows; ++line)
+	{
+	    int	    col_done = 0;
+
+	    for (col = 0; col < screen_Columns; ++col)
+	    {
+		int off = line * screen_Columns + col;
+
+		if (popup_mask[off] != popup_mask_next[off])
+		{
+		    popup_mask[off] = popup_mask_next[off];
+
+		    if (line >= cmdline_row)
+		    {
+			// the command line needs to be cleared if text below
+			// the popup is now visible.
+			if (!msg_scrolled && popup_mask_next[off] == 0)
+			    clear_cmdline = TRUE;
+		    }
+		    else if (col >= col_done)
+		    {
+			linenr_T	lnum;
+			int		line_cp = line;
+			int		col_cp = col;
+
+			// The screen position "line" / "col" needs to be
+			// redrawn.  Figure out what window that is and update
+			// w_redraw_top and w_redr_bot.  Only needs to be done
+			// once for each window line.
+			wp = mouse_find_win(&line_cp, &col_cp, IGNORE_POPUP);
+			if (wp != NULL)
+			{
+			    if (line_cp >= wp->w_height)
+				// In (or below) status line
+				wp->w_redr_status = TRUE;
+			    // compute the position in the buffer line from the
+			    // position on the screen
+			    else if (mouse_comp_pos(wp, &line_cp, &col_cp,
+									&lnum))
+				// past bottom
+				wp->w_redr_status = TRUE;
+			    else
+				redrawWinline(wp, lnum);
+
+			    // This line is going to be redrawn, no need to
+			    // check until the right side of the window.
+			    col_done = wp->w_wincol + wp->w_width - 1;
+			}
+		    }
+		}
+	    }
+	}
+}
+
+/*
+ * Return a string of "len" spaces in IObuff.
+ */
+    static char_u *
+get_spaces(int len)
+{
+    vim_memset(IObuff, ' ', (size_t)len);
+    IObuff[len] = NUL;
+    return IObuff;
+}
+
+/*
+ * Update popup windows.  They are drawn on top of normal windows.
+ * "win_update" is called for each popup window, lowest zindex first.
+ */
+    void
+update_popups(void (*win_update)(win_T *wp))
+{
+    win_T   *wp;
+    int	    top_off;
+    int	    left_off;
+    int	    total_width;
+    int	    total_height;
+    int	    popup_attr;
+    int	    border_attr[4];
+    int	    border_char[8];
+    char_u  buf[MB_MAXBYTES];
+    int	    row;
+    int	    i;
+
+    // Find the window with the lowest zindex that hasn't been updated yet,
+    // so that the window with a higher zindex is drawn later, thus goes on
+    // top.
+    popup_reset_handled();
+    while ((wp = find_next_popup(TRUE)) != NULL)
+    {
+	// This drawing uses the zindex of the popup window, so that it's on
+	// top of the text but doesn't draw when another popup with higher
+	// zindex is on top of the character.
+	screen_zindex = wp->w_zindex;
+
+	// adjust w_winrow and w_wincol for border and padding, since
+	// win_update() doesn't handle them.
+	top_off = wp->w_popup_padding[0] + wp->w_popup_border[0];
+	left_off = wp->w_popup_padding[3] + wp->w_popup_border[3];
+	wp->w_winrow += top_off;
+	wp->w_wincol += left_off;
+
+	// Draw the popup text.
+	win_update(wp);
+
+	wp->w_winrow -= top_off;
+	wp->w_wincol -= left_off;
+
+	total_width = wp->w_popup_border[3] + wp->w_popup_padding[3]
+		+ wp->w_width + wp->w_popup_padding[1] + wp->w_popup_border[1];
+	total_height = wp->w_popup_border[0] + wp->w_popup_padding[0]
+		+ wp->w_height + wp->w_popup_padding[2] + wp->w_popup_border[2];
+	popup_attr = get_wcr_attr(wp);
+
+	// We can only use these line drawing characters when 'encoding' is
+	// "utf-8" and 'ambiwidth' is "single".
+	if (enc_utf8 && *p_ambw == 's')
+	{
+	    border_char[0] = border_char[2] = 0x2550;
+	    border_char[1] = border_char[3] = 0x2551;
+	    border_char[4] = 0x2554;
+	    border_char[5] = 0x2557;
+	    border_char[6] = 0x255d;
+	    border_char[7] = 0x255a;
+	}
+	else
+	{
+	    border_char[0] = border_char[2] = '-';
+	    border_char[1] = border_char[3] = '|';
+	    for (i = 4; i < 8; ++i)
+		border_char[i] = '+';
+	}
+	for (i = 0; i < 8; ++i)
+	    if (wp->w_border_char[i] != 0)
+		border_char[i] = wp->w_border_char[i];
+
+	for (i = 0; i < 4; ++i)
+	{
+	    border_attr[i] = popup_attr;
+	    if (wp->w_border_highlight[i] != NULL)
+		border_attr[i] = syn_name2attr(wp->w_border_highlight[i]);
+	}
+
+	if (wp->w_popup_border[0] > 0)
+	{
+	    // top border
+	    screen_fill(wp->w_winrow, wp->w_winrow + 1,
+		    wp->w_wincol,
+		    wp->w_wincol + total_width,
+		    wp->w_popup_border[3] != 0
+					     ? border_char[4] : border_char[0],
+		    border_char[0], border_attr[0]);
+	    if (wp->w_popup_border[1] > 0)
+	    {
+		buf[mb_char2bytes(border_char[5], buf)] = NUL;
+		screen_puts(buf, wp->w_winrow,
+			       wp->w_wincol + total_width - 1, border_attr[1]);
+	    }
+	}
+
+	if (wp->w_popup_padding[0] > 0)
+	{
+	    // top padding
+	    row = wp->w_winrow + wp->w_popup_border[0];
+	    screen_fill(row, row + wp->w_popup_padding[0],
+		    wp->w_wincol + wp->w_popup_border[3],
+		    wp->w_wincol + total_width - wp->w_popup_border[1],
+							 ' ', ' ', popup_attr);
+	}
+
+	for (row = wp->w_winrow + wp->w_popup_border[0];
+		row < wp->w_winrow + total_height - wp->w_popup_border[2];
+		    ++row)
+	{
+	    // left border
+	    if (wp->w_popup_border[3] > 0)
+	    {
+		buf[mb_char2bytes(border_char[3], buf)] = NUL;
+		screen_puts(buf, row, wp->w_wincol, border_attr[3]);
+	    }
+	    // left padding
+	    if (wp->w_popup_padding[3] > 0)
+		screen_puts(get_spaces(wp->w_popup_padding[3]), row,
+			wp->w_wincol + wp->w_popup_border[3], popup_attr);
+	    // right border
+	    if (wp->w_popup_border[1] > 0)
+	    {
+		buf[mb_char2bytes(border_char[1], buf)] = NUL;
+		screen_puts(buf, row,
+			       wp->w_wincol + total_width - 1, border_attr[1]);
+	    }
+	    // right padding
+	    if (wp->w_popup_padding[1] > 0)
+		screen_puts(get_spaces(wp->w_popup_padding[1]), row,
+			wp->w_wincol + wp->w_popup_border[3]
+			   + wp->w_popup_padding[3] + wp->w_width, popup_attr);
+	}
+
+	if (wp->w_popup_padding[2] > 0)
+	{
+	    // bottom padding
+	    row = wp->w_winrow + wp->w_popup_border[0]
+				       + wp->w_popup_padding[0] + wp->w_height;
+	    screen_fill(row, row + wp->w_popup_padding[2],
+		    wp->w_wincol + wp->w_popup_border[3],
+		    wp->w_wincol + total_width - wp->w_popup_border[1],
+							 ' ', ' ', popup_attr);
+	}
+
+	if (wp->w_popup_border[2] > 0)
+	{
+	    // bottom border
+	    row = wp->w_winrow + total_height - 1;
+	    screen_fill(row , row + 1,
+		    wp->w_wincol,
+		    wp->w_wincol + total_width,
+		    wp->w_popup_border[3] != 0
+					     ? border_char[7] : border_char[2],
+		    border_char[2], border_attr[2]);
+	    if (wp->w_popup_border[1] > 0)
+	    {
+		buf[mb_char2bytes(border_char[6], buf)] = NUL;
+		screen_puts(buf, row,
+			       wp->w_wincol + total_width - 1, border_attr[2]);
+	    }
+	}
+
+	// Back to the normal zindex.
+	screen_zindex = 0;
+    }
+}
+
 #endif // FEAT_TEXT_PROP