/*
* Copyright (C) 1984-2023 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.
*/
/*
* Routines dealing with the "position" table.
* This is a table which tells the position (in the input file) of the
* first char on each currently displayed line.
*
* {{ The position table is scrolled by moving all the entries.
* Would be better to have a circular table
* and just change a couple of pointers. }}
*/
#include "less.h"
#include "position.h"
static POSITION *table = NULL; /* The position table */
static int table_size = 0;
extern int sc_width, sc_height;
extern int header_lines;
/*
* Return the starting file position of a line displayed on the screen.
* The line may be specified as a line number relative to the top
* of the screen, but is usually one of these special cases:
* the top (first) line on the screen
* the second line on the screen
* the bottom line on the screen
* the line after the bottom line on the screen
*/
public POSITION position(int sindex)
{
switch (sindex)
{
case BOTTOM:
sindex = sc_height - 2;
break;
case BOTTOM_PLUS_ONE:
sindex = sc_height - 1;
break;
case MIDDLE:
sindex = (sc_height - 1) / 2;
break;
}
return (table[sindex]);
}
/*
* Add a new file position to the bottom of the position table.
*/
public void add_forw_pos(POSITION pos)
{
int i;
/*
* Scroll the position table up.
*/
for (i = 1; i < sc_height; i++)
table[i-1] = table[i];
table[sc_height - 1] = pos;
}
/*
* Add a new file position to the top of the position table.
*/
public void add_back_pos(POSITION pos)
{
int i;
/*
* Scroll the position table down.
*/
for (i = sc_height - 1; i > 0; i--)
table[i] = table[i-1];
table[0] = pos;
}
/*
* Initialize the position table, done whenever we clear the screen.
*/
public void pos_clear(void)
{
int i;
for (i = 0; i < sc_height; i++)
table[i] = NULL_POSITION;
}
/*
* Allocate or reallocate the position table.
*/
public void pos_init(void)
{
struct scrpos scrpos;
if (sc_height <= table_size)
return;
/*
* If we already have a table, remember the first line in it
* before we free it, so we can copy that line to the new table.
*/
if (table != NULL)
{
get_scrpos(&scrpos, TOP);
free((char*)table);
} else
scrpos.pos = NULL_POSITION;
table = (POSITION *) ecalloc(sc_height, sizeof(POSITION));
table_size = sc_height;
pos_clear();
if (scrpos.pos != NULL_POSITION)
table[scrpos.ln-1] = scrpos.pos;
}
/*
* See if the byte at a specified position is currently on the screen.
* Check the position table to see if the position falls within its range.
* Return the position table entry if found, -1 if not.
*/
public int onscreen(POSITION pos)
{
int i;
if (pos < table[0])
return (-1);
for (i = 1; i < sc_height; i++)
if (pos < table[i])
return (i-1);
return (-1);
}
/*
* See if the entire screen is empty.
*/
public int empty_screen(void)
{
return (empty_lines(0, sc_height-1));
}
public int empty_lines(int s, int e)
{
int i;
for (i = s; i <= e; i++)
if (table[i] != NULL_POSITION && table[i] != 0)
return (0);
return (1);
}
/*
* Get the current screen position.
* The screen position consists of both a file position and
* a screen line number where the file position is placed on the screen.
* Normally the screen line number is 0, but if we are positioned
* such that the top few lines are empty, we may have to set
* the screen line to a number > 0.
*/
public void get_scrpos(struct scrpos *scrpos, int where)
{
int i;
int dir;
int last;
switch (where)
{
case TOP:
i = 0; dir = +1; last = sc_height-2;
break;
case BOTTOM: case BOTTOM_PLUS_ONE:
i = sc_height-2; dir = -1; last = 0;
break;
default:
i = where;
if (table[i] == NULL_POSITION) {
scrpos->pos = NULL_POSITION;
return;
}
/* Values of dir and last don't matter after this. */
break;
}
/*
* Find the first line on the screen which has something on it,
* and return the screen line number and the file position.
*/
for (;; i += dir)
{
if (table[i] != NULL_POSITION)
{
scrpos->ln = i+1;
scrpos->pos = table[i];
return;
}
if (i == last) break;
}
/*
* The screen is empty.
*/
scrpos->pos = NULL_POSITION;
}
/*
* Adjust a screen line number to be a simple positive integer
* in the range { 0 .. sc_height-2 }.
* (The bottom line, sc_height-1, is reserved for prompts, etc.)
* The given "sline" may be in the range { 1 .. sc_height-1 }
* to refer to lines relative to the top of the screen (starting from 1),
* or it may be in { -1 .. -(sc_height-1) } to refer to lines
* relative to the bottom of the screen.
*/
public int sindex_from_sline(int sline)
{
/*
* Negative screen line number means
* relative to the bottom of the screen.
*/
if (sline < 0)
sline += sc_height;
/*
* Can't be less than 1 or greater than sc_height.
*/
if (sline <= 0)
sline = 1;
if (sline > sc_height)
sline = sc_height;
/*
* Return zero-based line number, not one-based.
*/
return (sline-1);
}
