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