1 files changed, 423 insertions, 0 deletions
diff --git a/forwback.c b/forwback.c
new file mode 100755
index 0000000..21b500c
--- /dev/null
+++ b/forwback.c
@@ -0,0 +1,423 @@
+/*
+ * Copyright (C) 1984-2012  Mark Nudelman
+ *
+ * You may distribute under the terms of either the GNU General Public
+ * License or the Less License, as specified in the README file.
+ *
+ * For more information, see the README file.
+ */
+
+
+/*
+ * Primitives for displaying the file on the screen,
+ * scrolling either forward or backward.
+ */
+
+#include "less.h"
+#include "position.h"
+
+public int screen_trashed;
+public int squished;
+public int no_back_scroll = 0;
+public int forw_prompt;
+
+extern int sigs;
+extern int top_scroll;
+extern int quiet;
+extern int sc_width, sc_height;
+extern int plusoption;
+extern int forw_scroll;
+extern int back_scroll;
+extern int ignore_eoi;
+extern int clear_bg;
+extern int final_attr;
+extern int oldbot;
+#if TAGS
+extern char *tagoption;
+#endif
+
+/*
+ * Sound the bell to indicate user is trying to move past end of file.
+ */
+	static void
+eof_bell()
+{
+	if (quiet == NOT_QUIET)
+		bell();
+	else
+		vbell();
+}
+
+/*
+ * Check to see if the end of file is currently displayed.
+ */
+	public int
+eof_displayed()
+{
+	POSITION pos;
+
+	if (ignore_eoi)
+		return (0);
+
+	if (ch_length() == NULL_POSITION)
+		/*
+		 * If the file length is not known,
+		 * we can't possibly be displaying EOF.
+		 */
+		return (0);
+
+	/*
+	 * If the bottom line is empty, we are at EOF.
+	 * If the bottom line ends at the file length,
+	 * we must be just at EOF.
+	 */
+	pos = position(BOTTOM_PLUS_ONE);
+	return (pos == NULL_POSITION || pos == ch_length());
+}
+
+/*
+ * Check to see if the entire file is currently displayed.
+ */
+	public int
+entire_file_displayed()
+{
+	POSITION pos;
+
+	/* Make sure last line of file is displayed. */
+	if (!eof_displayed())
+		return (0);
+
+	/* Make sure first line of file is displayed. */
+	pos = position(0);
+	return (pos == NULL_POSITION || pos == 0);
+}
+
+/*
+ * If the screen is "squished", repaint it.
+ * "Squished" means the first displayed line is not at the top
+ * of the screen; this can happen when we display a short file
+ * for the first time.
+ */
+	public void
+squish_check()
+{
+	if (!squished)
+		return;
+	squished = 0;
+	repaint();
+}
+
+/*
+ * Display n lines, scrolling forward, 
+ * starting at position pos in the input file.
+ * "force" means display the n lines even if we hit end of file.
+ * "only_last" means display only the last screenful if n > screen size.
+ * "nblank" is the number of blank lines to draw before the first
+ *   real line.  If nblank > 0, the pos must be NULL_POSITION.
+ *   The first real line after the blanks will start at ch_zero().
+ */
+	public void
+forw(n, pos, force, only_last, nblank)
+	register int n;
+	POSITION pos;
+	int force;
+	int only_last;
+	int nblank;
+{
+	int eof = 0;
+	int nlines = 0;
+	int do_repaint;
+	static int first_time = 1;
+
+	squish_check();
+
+	/*
+	 * do_repaint tells us not to display anything till the end, 
+	 * then just repaint the entire screen.
+	 * We repaint if we are supposed to display only the last 
+	 * screenful and the request is for more than a screenful.
+	 * Also if the request exceeds the forward scroll limit
+	 * (but not if the request is for exactly a screenful, since
+	 * repainting itself involves scrolling forward a screenful).
+	 */
+	do_repaint = (only_last && n > sc_height-1) || 
+		(forw_scroll >= 0 && n > forw_scroll && n != sc_height-1);
+
+	if (!do_repaint)
+	{
+		if (top_scroll && n >= sc_height - 1 && pos != ch_length())
+		{
+			/*
+			 * Start a new screen.
+			 * {{ This is not really desirable if we happen
+			 *    to hit eof in the middle of this screen,
+			 *    but we don't yet know if that will happen. }}
+			 */
+			pos_clear();
+			add_forw_pos(pos);
+			force = 1;
+			clear();
+			home();
+		}
+
+		if (pos != position(BOTTOM_PLUS_ONE) || empty_screen())
+		{
+			/*
+			 * This is not contiguous with what is
+			 * currently displayed.  Clear the screen image 
+			 * (position table) and start a new screen.
+			 */
+			pos_clear();
+			add_forw_pos(pos);
+			force = 1;
+			if (top_scroll)
+			{
+				clear();
+				home();
+			} else if (!first_time)
+			{
+				putstr("...skipping...\n");
+			}
+		}
+	}
+
+	while (--n >= 0)
+	{
+		/*
+		 * Read the next line of input.
+		 */
+		if (nblank > 0)
+		{
+			/*
+			 * Still drawing blanks; don't get a line 
+			 * from the file yet.
+			 * If this is the last blank line, get ready to
+			 * read a line starting at ch_zero() next time.
+			 */
+			if (--nblank == 0)
+				pos = ch_zero();
+		} else
+		{
+			/* 
+			 * Get the next line from the file.
+			 */
+			pos = forw_line(pos);
+			if (pos == NULL_POSITION)
+			{
+				/*
+				 * End of file: stop here unless the top line 
+				 * is still empty, or "force" is true.
+				 * Even if force is true, stop when the last
+				 * line in the file reaches the top of screen.
+				 */
+				eof = 1;
+				if (!force && position(TOP) != NULL_POSITION)
+					break;
+				if (!empty_lines(0, 0) && 
+				    !empty_lines(1, 1) &&
+				     empty_lines(2, sc_height-1))
+					break;
+			}
+		}
+		/*
+		 * Add the position of the next line to the position table.
+		 * Display the current line on the screen.
+		 */
+		add_forw_pos(pos);
+		nlines++;
+		if (do_repaint)
+			continue;
+		/*
+		 * If this is the first screen displayed and
+		 * we hit an early EOF (i.e. before the requested
+		 * number of lines), we "squish" the display down
+		 * at the bottom of the screen.
+		 * But don't do this if a + option or a -t option
+		 * was given.  These options can cause us to
+		 * start the display after the beginning of the file,
+		 * and it is not appropriate to squish in that case.
+		 */
+		if (first_time && pos == NULL_POSITION && !top_scroll && 
+#if TAGS
+		    tagoption == NULL &&
+#endif
+		    !plusoption)
+		{
+			squished = 1;
+			continue;
+		}
+		put_line();
+#if 0
+		/* {{ 
+		 * Can't call clear_eol here.  The cursor might be at end of line
+		 * on an ignaw terminal, so clear_eol would clear the last char
+		 * of the current line instead of all of the next line.
+		 * If we really need to do this on clear_bg terminals, we need
+		 * to find a better way.
+		 * }}
+		 */
+		if (clear_bg && apply_at_specials(final_attr) != AT_NORMAL)
+		{
+			/*
+			 * Writing the last character on the last line
+			 * of the display may have scrolled the screen.
+			 * If we were in standout mode, clear_bg terminals 
+			 * will fill the new line with the standout color.
+			 * Now we're in normal mode again, so clear the line.
+			 */
+			clear_eol();
+		}
+#endif
+		forw_prompt = 1;
+	}
+
+	if (nlines == 0)
+		eof_bell();
+	else if (do_repaint)
+		repaint();
+	first_time = 0;
+	(void) currline(BOTTOM);
+}
+
+/*
+ * Display n lines, scrolling backward.
+ */
+	public void
+back(n, pos, force, only_last)
+	register int n;
+	POSITION pos;
+	int force;
+	int only_last;
+{
+	int nlines = 0;
+	int do_repaint;
+
+	squish_check();
+	do_repaint = (n > get_back_scroll() || (only_last && n > sc_height-1));
+	while (--n >= 0)
+	{
+		/*
+		 * Get the previous line of input.
+		 */
+		pos = back_line(pos);
+		if (pos == NULL_POSITION)
+		{
+			/*
+			 * Beginning of file: stop here unless "force" is true.
+			 */
+			if (!force)
+				break;
+		}
+		/*
+		 * Add the position of the previous line to the position table.
+		 * Display the line on the screen.
+		 */
+		add_back_pos(pos);
+		nlines++;
+		if (!do_repaint)
+		{
+			home();
+			add_line();
+			put_line();
+		}
+	}
+
+	if (nlines == 0)
+		eof_bell();
+	else if (do_repaint)
+		repaint();
+	else if (!oldbot)
+		lower_left();
+	(void) currline(BOTTOM);
+}
+
+/*
+ * Display n more lines, forward.
+ * Start just after the line currently displayed at the bottom of the screen.
+ */
+	public void
+forward(n, force, only_last)
+	int n;
+	int force;
+	int only_last;
+{
+	POSITION pos;
+
+	if (get_quit_at_eof() && eof_displayed() && !(ch_getflags() & CH_HELPFILE))
+	{
+		/*
+		 * If the -e flag is set and we're trying to go
+		 * forward from end-of-file, go on to the next file.
+		 */
+		if (edit_next(1))
+			quit(QUIT_OK);
+		return;
+	}
+
+	pos = position(BOTTOM_PLUS_ONE);
+	if (pos == NULL_POSITION && (!force || empty_lines(2, sc_height-1)))
+	{
+		if (ignore_eoi)
+		{
+			/*
+			 * ignore_eoi is to support A_F_FOREVER.
+			 * Back up until there is a line at the bottom
+			 * of the screen.
+			 */
+			if (empty_screen())
+				pos = ch_zero();
+			else
+			{
+				do
+				{
+					back(1, position(TOP), 1, 0);
+					pos = position(BOTTOM_PLUS_ONE);
+				} while (pos == NULL_POSITION);
+			}
+		} else
+		{
+			eof_bell();
+			return;
+		}
+	}
+	forw(n, pos, force, only_last, 0);
+}
+
+/*
+ * Display n more lines, backward.
+ * Start just before the line currently displayed at the top of the screen.
+ */
+	public void
+backward(n, force, only_last)
+	int n;
+	int force;
+	int only_last;
+{
+	POSITION pos;
+
+	pos = position(TOP);
+	if (pos == NULL_POSITION && (!force || position(BOTTOM) == 0))
+	{
+		eof_bell();
+		return;   
+	}
+	back(n, pos, force, only_last);
+}
+
+/*
+ * Get the backwards scroll limit.
+ * Must call this function instead of just using the value of
+ * back_scroll, because the default case depends on sc_height and
+ * top_scroll, as well as back_scroll.
+ */
+	public int
+get_back_scroll()
+{
+	if (no_back_scroll)
+		return (0);
+	if (back_scroll >= 0)
+		return (back_scroll);
+	if (top_scroll)
+		return (sc_height - 2);
+	return (10000); /* infinity */
+}