1 /* 2 * Copyright (C) 1984-2007 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 about less, or for information on how to 8 * contact the author, see the README file. 9 */ 10 11 12 /* 13 * Routines dealing with the "position" table. 14 * This is a table which tells the position (in the input file) of the 15 * first char on each currently displayed line. 16 * 17 * {{ The position table is scrolled by moving all the entries. 18 * Would be better to have a circular table 19 * and just change a couple of pointers. }} 20 */ 21 22 #include "less.h" 23 #include "position.h" 24 25 static POSITION *table = NULL; /* The position table */ 26 static int table_size; 27 28 extern int sc_width, sc_height; 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(where) 41 int where; 42 { 43 switch (where) 44 { 45 case BOTTOM: 46 where = sc_height - 2; 47 break; 48 case BOTTOM_PLUS_ONE: 49 where = sc_height - 1; 50 break; 51 case MIDDLE: 52 where = (sc_height - 1) / 2; 53 } 54 return (table[where]); 55 } 56 57 /* 58 * Add a new file position to the bottom of the position table. 59 */ 60 public void 61 add_forw_pos(pos) 62 POSITION pos; 63 { 64 register int i; 65 66 /* 67 * Scroll the position table up. 68 */ 69 for (i = 1; i < sc_height; i++) 70 table[i-1] = table[i]; 71 table[sc_height - 1] = pos; 72 } 73 74 /* 75 * Add a new file position to the top of the position table. 76 */ 77 public void 78 add_back_pos(pos) 79 POSITION pos; 80 { 81 register int i; 82 83 /* 84 * Scroll the position table down. 85 */ 86 for (i = sc_height - 1; i > 0; i--) 87 table[i] = table[i-1]; 88 table[0] = pos; 89 } 90 91 /* 92 * Initialize the position table, done whenever we clear the screen. 93 */ 94 public void 95 pos_clear() 96 { 97 register int i; 98 99 for (i = 0; i < sc_height; i++) 100 table[i] = NULL_POSITION; 101 } 102 103 /* 104 * Allocate or reallocate the position table. 105 */ 106 public void 107 pos_init() 108 { 109 struct scrpos scrpos; 110 111 if (sc_height <= table_size) 112 return; 113 /* 114 * If we already have a table, remember the first line in it 115 * before we free it, so we can copy that line to the new table. 116 */ 117 if (table != NULL) 118 { 119 get_scrpos(&scrpos); 120 free((char*)table); 121 } else 122 scrpos.pos = NULL_POSITION; 123 table = (POSITION *) ecalloc(sc_height, sizeof(POSITION)); 124 table_size = sc_height; 125 pos_clear(); 126 if (scrpos.pos != NULL_POSITION) 127 table[scrpos.ln-1] = scrpos.pos; 128 } 129 130 /* 131 * See if the byte at a specified position is currently on the screen. 132 * Check the position table to see if the position falls within its range. 133 * Return the position table entry if found, -1 if not. 134 */ 135 public int 136 onscreen(pos) 137 POSITION pos; 138 { 139 register int i; 140 141 if (pos < table[0]) 142 return (-1); 143 for (i = 1; i < sc_height; i++) 144 if (pos < table[i]) 145 return (i-1); 146 return (-1); 147 } 148 149 /* 150 * See if the entire screen is empty. 151 */ 152 public int 153 empty_screen() 154 { 155 return (empty_lines(0, sc_height-1)); 156 } 157 158 public int 159 empty_lines(s, e) 160 int s; 161 int e; 162 { 163 register int i; 164 165 for (i = s; i <= e; i++) 166 if (table[i] != NULL_POSITION) 167 return (0); 168 return (1); 169 } 170 171 /* 172 * Get the current screen position. 173 * The screen position consists of both a file position and 174 * a screen line number where the file position is placed on the screen. 175 * Normally the screen line number is 0, but if we are positioned 176 * such that the top few lines are empty, we may have to set 177 * the screen line to a number > 0. 178 */ 179 public void 180 get_scrpos(scrpos) 181 struct scrpos *scrpos; 182 { 183 register int i; 184 185 /* 186 * Find the first line on the screen which has something on it, 187 * and return the screen line number and the file position. 188 */ 189 for (i = 0; i < sc_height; i++) 190 if (table[i] != NULL_POSITION) 191 { 192 scrpos->ln = i+1; 193 scrpos->pos = table[i]; 194 return; 195 } 196 /* 197 * The screen is empty. 198 */ 199 scrpos->pos = NULL_POSITION; 200 } 201 202 /* 203 * Adjust a screen line number to be a simple positive integer 204 * in the range { 0 .. sc_height-2 }. 205 * (The bottom line, sc_height-1, is reserved for prompts, etc.) 206 * The given "sline" may be in the range { 1 .. sc_height-1 } 207 * to refer to lines relative to the top of the screen (starting from 1), 208 * or it may be in { -1 .. -(sc_height-1) } to refer to lines 209 * relative to the bottom of the screen. 210 */ 211 public int 212 adjsline(sline) 213 int sline; 214 { 215 /* 216 * Negative screen line number means 217 * relative to the bottom of the screen. 218 */ 219 if (sline < 0) 220 sline += sc_height; 221 /* 222 * Can't be less than 1 or greater than sc_height-1. 223 */ 224 if (sline <= 0) 225 sline = 1; 226 if (sline >= sc_height) 227 sline = sc_height - 1; 228 /* 229 * Return zero-based line number, not one-based. 230 */ 231 return (sline-1); 232 } 233