1/* 2 $Id$ 3 4 Copyright (C) 2001 Alexandre Courbot 5 Part of the Adonthell Project http://adonthell.linuxgames.com 6 7 This program is free software; you can redistribute it and/or modify 8 it under the terms of the GNU General Public License. 9 This program is distributed in the hope that it will be useful, 10 but WITHOUT ANY WARRANTY. 11 12 See the COPYING file for more details. 13*/ 14 15/*! 16 17\page page6 Saving/Loading 18 19\section objdatobjst Object data and object state 20 21This is another important part of the %game engine. Quite a few %objects should 22be loadable and saveable, but there is a difference between two things 23that may look like one: an %object's %data itself and an %object's state. 24 25But there is a significant difference. Data is all the information that stays 26the same during an %object's lifetime. As a consequence, %data remains persistent 27over the whole %game. An %object's state is the information that changes while the 28%game progresses. 29 30For example, when loading a map, all the actual graphics are persistant %data. 31OTOH, player and NPC's are certainly no longer at their initial position, so 32this information belongs to the map's state. 33 34Let's see precisely how it works with a simple %animation class: 35 36\verbatim 37class animation 38{ 39public: 40 // Constructor / Destructor. 41 animation (); 42 ~animation (); 43 44 ..... 45 46 // Saving / Loading methods. 47 void get (FILE * in); 48 void put (FILE * out); 49 50 // State saving / loading methods. 51 void get_state (FILE * in); 52 void put_state (FILE * out); 53 54private: 55 vector <image> frames; 56 57 u_int32 currentframe; 58} 59\endverbatim 60 61The difference between the %object %data and the %object state is quite obvious here: the 62\e frames vector is an array containing the raw %images - they won't change during 63gameplay, so they are considered as the %object \e %data, while the \e currentframe 64member will change during the %game, and actually when we load a %game we would like 65it to have the same value than when we saved it. That's why \e get and \e put will 66save the \e frames vector (and maybe put \e currentframe to 0 for \e get, to make sure 67the %object is in a stable state), and \e get_state and \e put_state will save/load the 68currentframe member. That way, when you load a %game, you can simply get the %object state 69from the save file, while the %object itself will be loaded from the %data directory. 70 71\section convsave Conventions for saving/loading methods 72To reduce the amount of space needed for the %game, loading/saving methods use the igzstream 73and ogzstream classes for disk access. See their own documentation for more details. 74 75The saving methods should be constant - that is, they doesn't change the state of the %object 76itself. The loading methods should always bring the %object into a stable state once they 77return (think of what would happen if you load an %animation and the \e currenframe member 78remains with a value superior to the actual number of %images in this %animation). The 79declaration conventions are the following (you can use this template declaration for your 80own classes, as it also shows you the proper way to document your code with sections): 81 82\verbatim 83class myclass 84{ 85public: 86 87..... 88 89 /** 90 * @name Loading/Saving methods 91 * 92 */ 93 //@{ 94 95 /** 96 * Loads a <myobject> from an opened file. 97 * @param file the opened file from which to load. 98 * @return 0 in case of success, error code otherwise. 99 * 100 * @sa load () 101 * 102 */ 103 s_int8 get (igzstream& file); 104 105 /** 106 * Loads a <myobject> from it's filename. 107 * 108 * @param fname the name of the file to load. 109 * @return 0 in case of success, error code otherwise. 110 * 111 * @sa get () 112 */ 113 s_int8 load (string fname); 114 115 /** 116 * Saves a <myobject> into an opened file. 117 * 118 * @param file opened file where to save into. 119 * @return 0 in case of success, error code otherwise. 120 * 121 * @sa save () 122 */ 123 s_int8 put (ogzstream& file) const; 124 125 /** Saves a <myobject> into a file from it's name. 126 * @param fname file name where to save into. 127 * @return 0 in case of success, error code otherwise. 128 * 129 * @sa put () 130 */ 131 s_int8 save (string fname) const; 132 //@} 133 134 135 /** 136 * @name State loading/saving methods 137 * 138 */ 139 //@{ 140 141 /** 142 * Restore the <myobject> state from an opened file. 143 * 144 * @param file the opened file from which to load the state. 145 * @return 0 in case of success, error code otherwise. 146 */ 147 s_int8 get_state (igzstream& file); 148 149 /** 150 * Saves the <myobject> state into an opened file. 151 * 152 * @param file the opened file where to the state. 153 * @return 0 in case of success, error code otherwise. 154 */ 155 s_int8 put_state (ogzstream& file) const; 156 157 //@} 158 159 160 .... 161 162} 163\endverbatim 164 165\section objreuse Making your objects reusable 166Another issue that can decrease the %game performance is %objects lifetime. 167Take our sample %animation class. Say that I've already loaded an %animation that 168I don't need anymore, and I need to load another one. If my %object doesn't have 169a cleaning method, I'll have to delete my %animation %object and reallocate another 170one. And destructor call + deallocation + allocation + constructor call = a lot of 171time wasted. This can easily be avoided if your %object has a cleaning method, that 172restores it to it's post-constructor state and allow you to reuse it as if it was 173a new one. The loading method is a good place where to call this cleaning function, 174as you can't expect to load something if your %object isn't empty. In our %animation 175sample class, the \e clear () method would delete the \e frames vector (cleaning up 176the %datas) and put \e currentframe to 0 (safe, post-constructor state). And I now 177can use the same %object multiple times. Most often too, the destructor will be a 178simple call to clear (), as it also frees all the memory occupied by the %object. 179 180The declaration convention is quite straightforward then: 181\verbatim 182class myclass 183{ 184public: 185 .... 186 187 /** 188 * Puts the <myobject> back to it's post-constructor state. 189 * 190 */ 191 void clear (); 192 193 .... 194} 195\endverbatim 196 197Note that not every %object int the %game needs to be state-saveable. First, they must 198have a changeable state, and second, they have to be saved/loaded during %game 199saving/loading. 200 201*/ 202