1 /* 2 * Copyright (C) 1984-2022 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 40 position(sindex) 41 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 */ 61 public void 62 add_forw_pos(pos) 63 POSITION pos; 64 { 65 int i; 66 67 /* 68 * Scroll the position table up. 69 */ 70 for (i = 1; i < sc_height; i++) 71 table[i-1] = table[i]; 72 table[sc_height - 1] = pos; 73 } 74 75 /* 76 * Add a new file position to the top of the position table. 77 */ 78 public void 79 add_back_pos(pos) 80 POSITION pos; 81 { 82 int i; 83 84 /* 85 * Scroll the position table down. 86 */ 87 for (i = sc_height - 1; i > 0; i--) 88 table[i] = table[i-1]; 89 table[0] = pos; 90 } 91 92 /* 93 * Initialize the position table, done whenever we clear the screen. 94 */ 95 public void 96 pos_clear(VOID_PARAM) 97 { 98 int i; 99 100 for (i = 0; i < sc_height; i++) 101 table[i] = NULL_POSITION; 102 } 103 104 /* 105 * Allocate or reallocate the position table. 106 */ 107 public void 108 pos_init(VOID_PARAM) 109 { 110 struct scrpos scrpos; 111 112 if (sc_height <= table_size) 113 return; 114 /* 115 * If we already have a table, remember the first line in it 116 * before we free it, so we can copy that line to the new table. 117 */ 118 if (table != NULL) 119 { 120 get_scrpos(&scrpos, TOP); 121 free((char*)table); 122 } else 123 scrpos.pos = NULL_POSITION; 124 table = (POSITION *) ecalloc(sc_height, sizeof(POSITION)); 125 table_size = sc_height; 126 pos_clear(); 127 if (scrpos.pos != NULL_POSITION) 128 table[scrpos.ln-1] = scrpos.pos; 129 } 130 131 /* 132 * See if the byte at a specified position is currently on the screen. 133 * Check the position table to see if the position falls within its range. 134 * Return the position table entry if found, -1 if not. 135 */ 136 public int 137 onscreen(pos) 138 POSITION pos; 139 { 140 int i; 141 142 if (pos < table[0]) 143 return (-1); 144 for (i = 1; i < sc_height; i++) 145 if (pos < table[i]) 146 return (i-1); 147 return (-1); 148 } 149 150 /* 151 * See if the entire screen is empty. 152 */ 153 public int 154 empty_screen(VOID_PARAM) 155 { 156 return (empty_lines(0, sc_height-1)); 157 } 158 159 public int 160 empty_lines(s, e) 161 int s; 162 int e; 163 { 164 int i; 165 166 for (i = s; i <= e; i++) 167 if (table[i] != NULL_POSITION && table[i] != 0) 168 return (0); 169 return (1); 170 } 171 172 /* 173 * Get the current screen position. 174 * The screen position consists of both a file position and 175 * a screen line number where the file position is placed on the screen. 176 * Normally the screen line number is 0, but if we are positioned 177 * such that the top few lines are empty, we may have to set 178 * the screen line to a number > 0. 179 */ 180 public void 181 get_scrpos(scrpos, where) 182 struct scrpos *scrpos; 183 int where; 184 { 185 int i; 186 int dir; 187 int last; 188 189 switch (where) 190 { 191 case TOP: 192 i = 0; dir = +1; last = sc_height-2; 193 break; 194 case BOTTOM: case BOTTOM_PLUS_ONE: 195 i = sc_height-2; dir = -1; last = 0; 196 break; 197 default: 198 i = where; 199 if (table[i] == NULL_POSITION) { 200 scrpos->pos = NULL_POSITION; 201 return; 202 } 203 /* Values of dir and last don't matter after this. */ 204 break; 205 } 206 207 /* 208 * Find the first line on the screen which has something on it, 209 * and return the screen line number and the file position. 210 */ 211 for (;; i += dir) 212 { 213 if (table[i] != NULL_POSITION) 214 { 215 scrpos->ln = i+1; 216 scrpos->pos = table[i]; 217 return; 218 } 219 if (i == last) break; 220 } 221 /* 222 * The screen is empty. 223 */ 224 scrpos->pos = NULL_POSITION; 225 } 226 227 /* 228 * Adjust a screen line number to be a simple positive integer 229 * in the range { 0 .. sc_height-2 }. 230 * (The bottom line, sc_height-1, is reserved for prompts, etc.) 231 * The given "sline" may be in the range { 1 .. sc_height-1 } 232 * to refer to lines relative to the top of the screen (starting from 1), 233 * or it may be in { -1 .. -(sc_height-1) } to refer to lines 234 * relative to the bottom of the screen. 235 */ 236 public int 237 sindex_from_sline(sline) 238 int sline; 239 { 240 /* 241 * Negative screen line number means 242 * relative to the bottom of the screen. 243 */ 244 if (sline < 0) 245 sline += sc_height; 246 /* 247 * Can't be less than 1 or greater than sc_height. 248 */ 249 if (sline <= 0) 250 sline = 1; 251 if (sline > sc_height) 252 sline = sc_height; 253 /* 254 * Return zero-based line number, not one-based. 255 */ 256 return (sline-1); 257 } 258