1/* $NetBSD: position.c,v 1.6 2023/10/06 07:33:49 simonb Exp $ */ 2 3/* 4 * Copyright (C) 1984-2023 Mark Nudelman 5 * 6 * You may distribute under the terms of either the GNU General Public 7 * License or the Less License, as specified in the README file. 8 * 9 * For more information, see the README file. 10 */ 11 12 13/* 14 * Routines dealing with the "position" table. 15 * This is a table which tells the position (in the input file) of the 16 * first char on each currently displayed line. 17 * 18 * {{ The position table is scrolled by moving all the entries. 19 * Would be better to have a circular table 20 * and just change a couple of pointers. }} 21 */ 22 23#include "less.h" 24#include "position.h" 25 26static POSITION *table = NULL; /* The position table */ 27static int table_size = 0; 28 29extern int sc_width, sc_height; 30extern int header_lines; 31 32/* 33 * Return the starting file position of a line displayed on the screen. 34 * The line may be specified as a line number relative to the top 35 * of the screen, but is usually one of these special cases: 36 * the top (first) line on the screen 37 * the second line on the screen 38 * the bottom line on the screen 39 * the line after the bottom line on the screen 40 */ 41public POSITION position(int sindex) 42{ 43 switch (sindex) 44 { 45 case BOTTOM: 46 sindex = sc_height - 2; 47 break; 48 case BOTTOM_PLUS_ONE: 49 sindex = sc_height - 1; 50 break; 51 case MIDDLE: 52 sindex = (sc_height - 1) / 2; 53 break; 54 } 55 return (table[sindex]); 56} 57 58/* 59 * Add a new file position to the bottom of the position table. 60 */ 61public void add_forw_pos(POSITION pos) 62{ 63 int i; 64 65 /* 66 * Scroll the position table up. 67 */ 68 for (i = 1; i < sc_height; i++) 69 table[i-1] = table[i]; 70 table[sc_height - 1] = pos; 71} 72 73/* 74 * Add a new file position to the top of the position table. 75 */ 76public void add_back_pos(POSITION pos) 77{ 78 int i; 79 80 /* 81 * Scroll the position table down. 82 */ 83 for (i = sc_height - 1; i > 0; i--) 84 table[i] = table[i-1]; 85 table[0] = pos; 86} 87 88/* 89 * Initialize the position table, done whenever we clear the screen. 90 */ 91public void pos_clear(void) 92{ 93 int i; 94 95 for (i = 0; i < sc_height; i++) 96 table[i] = NULL_POSITION; 97} 98 99/* 100 * Allocate or reallocate the position table. 101 */ 102public void pos_init(void) 103{ 104 struct scrpos scrpos; 105 106 if (sc_height <= table_size) 107 return; 108 /* 109 * If we already have a table, remember the first line in it 110 * before we free it, so we can copy that line to the new table. 111 */ 112 if (table != NULL) 113 { 114 get_scrpos(&scrpos, TOP); 115 free((char*)table); 116 } else 117 scrpos.pos = NULL_POSITION; 118 table = (POSITION *) ecalloc(sc_height, sizeof(POSITION)); 119 table_size = sc_height; 120 pos_clear(); 121 if (scrpos.pos != NULL_POSITION) 122 table[scrpos.ln-1] = scrpos.pos; 123} 124 125/* 126 * See if the byte at a specified position is currently on the screen. 127 * Check the position table to see if the position falls within its range. 128 * Return the position table entry if found, -1 if not. 129 */ 130public int onscreen(POSITION pos) 131{ 132 int i; 133 134 if (pos < table[0]) 135 return (-1); 136 for (i = 1; i < sc_height; i++) 137 if (pos < table[i]) 138 return (i-1); 139 return (-1); 140} 141 142/* 143 * See if the entire screen is empty. 144 */ 145public int empty_screen(void) 146{ 147 return (empty_lines(0, sc_height-1)); 148} 149 150public int empty_lines(int s, int e) 151{ 152 int i; 153 154 for (i = s; i <= e; i++) 155 if (table[i] != NULL_POSITION && table[i] != 0) 156 return (0); 157 return (1); 158} 159 160/* 161 * Get the current screen position. 162 * The screen position consists of both a file position and 163 * a screen line number where the file position is placed on the screen. 164 * Normally the screen line number is 0, but if we are positioned 165 * such that the top few lines are empty, we may have to set 166 * the screen line to a number > 0. 167 */ 168public void get_scrpos(struct scrpos *scrpos, int where) 169{ 170 int i; 171 int dir; 172 int last; 173 174 switch (where) 175 { 176 case TOP: 177 i = 0; dir = +1; last = sc_height-2; 178 break; 179 case BOTTOM: case BOTTOM_PLUS_ONE: 180 i = sc_height-2; dir = -1; last = 0; 181 break; 182 default: 183 i = where; 184 if (table[i] == NULL_POSITION) { 185 scrpos->pos = NULL_POSITION; 186 return; 187 } 188 /* Values of dir and last don't matter after this. */ 189 break; 190 } 191 192 /* 193 * Find the first line on the screen which has something on it, 194 * and return the screen line number and the file position. 195 */ 196 for (;; i += dir) 197 { 198 if (table[i] != NULL_POSITION) 199 { 200 scrpos->ln = i+1; 201 scrpos->pos = table[i]; 202 return; 203 } 204 if (i == last) break; 205 } 206 /* 207 * The screen is empty. 208 */ 209 scrpos->pos = NULL_POSITION; 210} 211 212/* 213 * Adjust a screen line number to be a simple positive integer 214 * in the range { 0 .. sc_height-2 }. 215 * (The bottom line, sc_height-1, is reserved for prompts, etc.) 216 * The given "sline" may be in the range { 1 .. sc_height-1 } 217 * to refer to lines relative to the top of the screen (starting from 1), 218 * or it may be in { -1 .. -(sc_height-1) } to refer to lines 219 * relative to the bottom of the screen. 220 */ 221public int sindex_from_sline(int sline) 222{ 223 /* 224 * Negative screen line number means 225 * relative to the bottom of the screen. 226 */ 227 if (sline < 0) 228 sline += sc_height; 229 /* 230 * Can't be less than 1 or greater than sc_height. 231 */ 232 if (sline <= 0) 233 sline = 1; 234 if (sline > sc_height) 235 sline = sc_height; 236 /* 237 * Return zero-based line number, not one-based. 238 */ 239 return (sline-1); 240} 241