1 00:00:00,006 --> 00:00:02,000 - [Narrator] Hi. 2 00:00:02,000 --> 00:00:04,004 This video is about building the game engine. 3 00:00:04,004 --> 00:00:06,007 In the last video, we learned structuring 4 00:00:06,007 --> 00:00:08,006 the Thomas Was Late code. 5 00:00:08,006 --> 00:00:10,003 In this video, we're going to take a look 6 00:00:10,003 --> 00:00:14,008 at reusing the texture holder class coding engine.h 7 00:00:14,008 --> 00:00:17,004 and coding engine.cpp. 8 00:00:17,004 --> 00:00:20,000 As suggested in the previous discussion, 9 00:00:20,000 --> 00:00:22,002 we will code a class called engine 10 00:00:22,002 --> 00:00:23,008 that will control and bind together 11 00:00:23,008 --> 00:00:26,009 the different parts of the Thomas Was Late game. 12 00:00:26,009 --> 00:00:30,000 The first thing we will do is make the texture holder class 13 00:00:30,000 --> 00:00:33,004 from the previous project available in this one. 14 00:00:33,004 --> 00:00:35,004 The texture holder class that we discussed 15 00:00:35,004 --> 00:00:37,002 and coded for the zombie arena game 16 00:00:37,002 --> 00:00:39,008 will also be useful in this project. 17 00:00:39,008 --> 00:00:41,008 While it is possible to add the files, 18 00:00:41,008 --> 00:00:45,004 texture holder.h and texture holder.cpp 19 00:00:45,004 --> 00:00:47,001 directly from a previous project 20 00:00:47,001 --> 00:00:50,004 without recoding them or re-creating the files. 21 00:00:50,004 --> 00:00:51,006 I don't want to make the assumption 22 00:00:51,006 --> 00:00:54,005 that you haven't jumped straight to this project. 23 00:00:54,005 --> 00:00:55,009 I'll guide you through few steps 24 00:00:55,009 --> 00:00:57,009 along with the complete code listing 25 00:00:57,009 --> 00:01:01,005 to create the texture holder class. 26 00:01:01,005 --> 00:01:04,001 To create the texture holder class from scratch, 27 00:01:04,001 --> 00:01:07,006 right-click header files in the solution Explorer 28 00:01:07,006 --> 00:01:10,001 and select add new item. 29 00:01:10,001 --> 00:01:14,000 In the add new item window, click header file.h 30 00:01:14,000 --> 00:01:17,005 and then in the name field, type texture holder. 31 00:01:17,005 --> 00:01:20,008 So the name is texture holder.h. 32 00:01:20,008 --> 00:01:24,004 Finally, click the add button. 33 00:01:24,004 --> 00:01:28,002 Now add this code to texture holder.h. 34 00:01:28,002 --> 00:01:30,005 Notice that we have an include directive 35 00:01:30,005 --> 00:01:33,000 for map from the STL. 36 00:01:33,000 --> 00:01:36,004 Then we declare a map that holds string and SFML 37 00:01:36,004 --> 00:01:38,006 texture keyvalue pairs. 38 00:01:38,006 --> 00:01:41,007 This map is called m_textures. 39 00:01:41,007 --> 00:01:44,003 Now, this line of code is quite interesting. 40 00:01:44,003 --> 00:01:47,000 Here we are declaring a static pointer 41 00:01:47,000 --> 00:01:53,001 to an object of type texture holder called m_s_instance. 42 00:01:53,001 --> 00:01:55,008 This means that the texture holder class 43 00:01:55,008 --> 00:01:59,002 has an object that is the same type as itself. 44 00:01:59,002 --> 00:02:01,004 Not only that, but because it is static 45 00:02:01,004 --> 00:02:03,005 it can be used with the class itself 46 00:02:03,005 --> 00:02:06,002 without an instance of the class. 47 00:02:06,002 --> 00:02:08,005 When we code the related.cpp file 48 00:02:08,005 --> 00:02:10,008 we will see how we use this. 49 00:02:10,008 --> 00:02:13,000 Now, in the public part of the class 50 00:02:13,000 --> 00:02:16,001 we have the prototype for the constructor function, 51 00:02:16,001 --> 00:02:17,005 texture holder. 52 00:02:17,005 --> 00:02:20,009 The constructor takes no arguments and as usual, 53 00:02:20,009 --> 00:02:22,007 has no return type. 54 00:02:22,007 --> 00:02:26,002 This is the same as the default constructor. 55 00:02:26,002 --> 00:02:28,004 We're going to override the default constructor 56 00:02:28,004 --> 00:02:30,009 with a definition that makes our singleton work 57 00:02:30,009 --> 00:02:32,004 how we want it to. 58 00:02:32,004 --> 00:02:35,003 We have another function called get texture. 59 00:02:35,003 --> 00:02:37,003 Let's look at the signature again, 60 00:02:37,003 --> 00:02:39,008 and analyze exactly what is happening. 61 00:02:39,008 --> 00:02:42,003 First, notice that the function returns 62 00:02:42,003 --> 00:02:43,008 are referenced to a texture. 63 00:02:43,008 --> 00:02:47,000 This means that get texture will return a reference 64 00:02:47,000 --> 00:02:49,003 which is efficient because it avoids making a copy 65 00:02:49,003 --> 00:02:51,009 of what could be a fairly large graphic. 66 00:02:51,009 --> 00:02:55,000 Also, notice the function is declared as static. 67 00:02:55,000 --> 00:02:57,000 This means the function can be used 68 00:02:57,000 --> 00:02:59,004 without an instance of the class. 69 00:02:59,004 --> 00:03:00,006 The function takes a string 70 00:03:00,006 --> 00:03:03,003 as a constant reference as a parameter. 71 00:03:03,003 --> 00:03:05,000 The effect of this is twofold. 72 00:03:05,000 --> 00:03:07,000 Firstly, the operation is efficient 73 00:03:07,000 --> 00:03:09,007 and secondly, because the reference is constant 74 00:03:09,007 --> 00:03:11,005 it can't be changed. 75 00:03:11,005 --> 00:03:15,006 Now, let's create texture holder.cpp file. 76 00:03:15,006 --> 00:03:18,001 Right-click source files in the solution Explorer 77 00:03:18,001 --> 00:03:20,006 and select add new item. 78 00:03:20,006 --> 00:03:25,006 In the add new item window, click C++ file.cpp 79 00:03:25,006 --> 00:03:29,001 and then in the name field, type texture holder. 80 00:03:29,001 --> 00:03:31,006 Lastly, click the add button. 81 00:03:31,006 --> 00:03:34,007 Add this highlighted code to the file. 82 00:03:34,007 --> 00:03:37,000 See, this is the whole code. 83 00:03:37,000 --> 00:03:40,003 In the code, first we initialize our pointer 84 00:03:40,003 --> 00:03:43,004 to type texture holder to null PTR. 85 00:03:43,004 --> 00:03:45,009 This is a constructor function. 86 00:03:45,009 --> 00:03:48,000 Inside the constructor function, 87 00:03:48,000 --> 00:03:52,004 this line of code ensures that M_S_instance 88 00:03:52,004 --> 00:03:54,008 equals null PTR. 89 00:03:54,008 --> 00:03:57,003 If it doesn't, the game will exit execution. 90 00:03:57,003 --> 00:04:01,008 Then M_S_instance equals to this 91 00:04:01,008 --> 00:04:04,006 assigns the pointer to this instance. 92 00:04:04,006 --> 00:04:07,004 Now, consider where this code is taking place. 93 00:04:07,004 --> 00:04:09,004 The code is in constructor. 94 00:04:09,004 --> 00:04:12,002 The constructor is the way we create instance 95 00:04:12,002 --> 00:04:13,007 of an object from classes. 96 00:04:13,007 --> 00:04:17,007 So effectively, we now have pointer to a texture holder 97 00:04:17,007 --> 00:04:21,005 that points the one and only instance of itself. 98 00:04:21,005 --> 00:04:26,001 In this line of code, we get a reference to M_textures. 99 00:04:26,001 --> 00:04:30,001 Then we attempt to get an iterator to keyvalue pair 100 00:04:30,001 --> 00:04:32,004 using the past in filename. 101 00:04:32,004 --> 00:04:35,003 If we find a matching key, we return the texture 102 00:04:35,003 --> 00:04:37,002 using this line of code. 103 00:04:37,002 --> 00:04:40,006 Otherwise, first we create a new keyvalue pair 104 00:04:40,006 --> 00:04:43,008 using the filename and then we had texture to map 105 00:04:43,008 --> 00:04:46,003 and at last we return it to the calling code 106 00:04:46,003 --> 00:04:48,008 with the help of return texture. 107 00:04:48,008 --> 00:04:52,002 Texture holder class introduced lots of new concepts. 108 00:04:52,002 --> 00:04:55,005 Singleton, static functions, constant references, 109 00:04:55,005 --> 00:04:57,007 auto keyword and syntax. 110 00:04:57,007 --> 00:05:01,003 We can now get on with our new engine class. 111 00:05:01,003 --> 00:05:03,008 As usual we will start with the header file 112 00:05:03,008 --> 00:05:07,003 which holds the function declarations and member variables. 113 00:05:07,003 --> 00:05:10,003 Note that we will revisit this file throughout the project 114 00:05:10,003 --> 00:05:13,002 to add more functions and member variables. 115 00:05:13,002 --> 00:05:15,000 For now, we will just add the code 116 00:05:15,000 --> 00:05:17,008 that is necessary at this stage. 117 00:05:17,008 --> 00:05:20,006 Right-click header files in the solution Explorer 118 00:05:20,006 --> 00:05:22,009 and select add new item. 119 00:05:22,009 --> 00:05:27,001 In the add new item window click header file.h 120 00:05:27,001 --> 00:05:30,001 and then in the name field, type engine. 121 00:05:30,001 --> 00:05:31,008 Then click the add button. 122 00:05:31,008 --> 00:05:34,007 Add this highlighted code to the file. 123 00:05:34,007 --> 00:05:37,005 This code consists of various member variables 124 00:05:37,005 --> 00:05:40,000 as well as the function declarations. 125 00:05:40,000 --> 00:05:42,007 Take note of the function and variable names 126 00:05:42,007 --> 00:05:45,004 as well as whether they are private or public. 127 00:05:45,004 --> 00:05:49,002 Let's go through all of the private variables and functions. 128 00:05:49,002 --> 00:05:52,002 Texture holder TH, the one and only instance 129 00:05:52,002 --> 00:05:54,003 of the texture holder class. 130 00:05:54,003 --> 00:05:58,001 Tile size, a useful constant to remind us 131 00:05:58,001 --> 00:06:01,008 that each tile in the spreadsheet is 50 pixels wide 132 00:06:01,008 --> 00:06:03,007 and 50 pixels high. 133 00:06:03,007 --> 00:06:06,007 Verts in quad, a useful constant 134 00:06:06,007 --> 00:06:10,007 to make our manipulation of a vertex array less error-prone. 135 00:06:10,007 --> 00:06:13,007 There are in fact for vertices in a quad. 136 00:06:13,007 --> 00:06:15,004 Now we can't forget it. 137 00:06:15,004 --> 00:06:18,005 Gravity, an instant INT value 138 00:06:18,005 --> 00:06:20,004 representing the number of pixels 139 00:06:20,004 --> 00:06:23,000 by which the game characters will be pushed outward 140 00:06:23,000 --> 00:06:24,001 each second. 141 00:06:24,001 --> 00:06:25,007 This is quite a fun value to play with 142 00:06:25,007 --> 00:06:27,003 once the game is done. 143 00:06:27,003 --> 00:06:30,004 We initialize it to 300 as this works well 144 00:06:30,004 --> 00:06:32,009 for our initial level designs. 145 00:06:32,009 --> 00:06:37,006 M_window, the usual render window object 146 00:06:37,006 --> 00:06:40,003 like we've had in all of our projects. 147 00:06:40,003 --> 00:06:42,009 Look at these SF ML view objects. 148 00:06:42,009 --> 00:06:48,003 M_main view, M_left view, M_right view, 149 00:06:48,003 --> 00:06:53,001 M_BG main view, M_BG left view, 150 00:06:53,001 --> 00:06:57,002 M_BG right view and M_HUD view. 151 00:06:57,002 --> 00:07:01,006 The first three view objects that is M_main view 152 00:07:01,006 --> 00:07:03,004 is for the full-screen view. 153 00:07:03,004 --> 00:07:07,006 M_left view is for left split screen. 154 00:07:07,006 --> 00:07:12,008 And M_right view right split screen views of the game. 155 00:07:12,008 --> 00:07:16,005 Now these three SF ML view objects 156 00:07:16,005 --> 00:07:18,001 will draw the background behind. 157 00:07:18,001 --> 00:07:21,005 The last view object M_HudView 158 00:07:21,005 --> 00:07:24,003 will be drawn on top of the appropriate combination 159 00:07:24,003 --> 00:07:27,002 of the other six views to display the score, 160 00:07:27,002 --> 00:07:29,009 the remaining time, and any messages to the players. 161 00:07:29,009 --> 00:07:33,004 Having seven different view objects might imply complexity 162 00:07:33,004 --> 00:07:35,005 but when you see how we deal with them 163 00:07:35,005 --> 00:07:36,008 as the section progresses, 164 00:07:36,008 --> 00:07:39,003 you will see they are quite straightforward. 165 00:07:39,003 --> 00:07:41,001 We will have the whole split screen 166 00:07:41,001 --> 00:07:45,000 full-screen conundrum sorted out by the end of the section. 167 00:07:45,000 --> 00:07:50,009 Sprite M_background Sprite and texture M_background texture 168 00:07:50,009 --> 00:07:54,001 this combination of SF ML Sprite and texture 169 00:07:54,001 --> 00:07:56,008 will be for showing and holding the background graphic 170 00:07:56,008 --> 00:07:58,007 from the graphics assets folder. 171 00:07:58,007 --> 00:08:03,004 M_playing, this boolean will keep the game engine informed 172 00:08:03,004 --> 00:08:05,005 about whether the level has started yet 173 00:08:05,005 --> 00:08:07,001 by pressing the enter key. 174 00:08:07,001 --> 00:08:09,008 The player does not have the option to pause the game 175 00:08:09,008 --> 00:08:11,004 once they've started it. 176 00:08:11,004 --> 00:08:14,006 Now, we have set M_playing to false. 177 00:08:14,006 --> 00:08:19,004 M_character one, when the screen is full-screen 178 00:08:19,004 --> 00:08:20,008 should it center on Thomas, 179 00:08:20,008 --> 00:08:23,003 M_character one equal to true 180 00:08:23,003 --> 00:08:27,003 or Bob M_character one equal to false. 181 00:08:27,003 --> 00:08:32,002 Initially, it is initialized to true to center on Thomas. 182 00:08:32,002 --> 00:08:35,008 M_split screen is the game currently being played 183 00:08:35,008 --> 00:08:37,007 in split screen mode are not. 184 00:08:37,007 --> 00:08:40,001 We will use this variable to decide how exactly to use 185 00:08:40,001 --> 00:08:43,006 all the view objects we declared a few steps ago. 186 00:08:43,006 --> 00:08:46,001 M_time remaining variable. 187 00:08:46,001 --> 00:08:49,005 This float variable holds how much time is remaining 188 00:08:49,005 --> 00:08:51,009 to get to the goal of the current level. 189 00:08:51,009 --> 00:08:54,004 We have set it to 10 for the purposes of testing 190 00:08:54,004 --> 00:08:58,001 until we actually get to set a specific time for each level. 191 00:08:58,001 --> 00:09:01,006 M_gametime total variable. 192 00:09:01,006 --> 00:09:04,008 This variable is an SF ML time object. 193 00:09:04,008 --> 00:09:07,009 It keeps track of how long the game has been played for. 194 00:09:07,009 --> 00:09:12,000 M_new level required boolean variable. 195 00:09:12,000 --> 00:09:14,009 This variable keeps a check on whether the player 196 00:09:14,009 --> 00:09:16,009 has just completed or failed the level. 197 00:09:16,009 --> 00:09:19,006 We can then use it to trigger the loading of the next level 198 00:09:19,006 --> 00:09:21,009 or the restarting of the current level. 199 00:09:21,009 --> 00:09:23,006 We have set it to true. 200 00:09:23,006 --> 00:09:24,009 The input function. 201 00:09:24,009 --> 00:09:28,000 This function will handle all the players input 202 00:09:28,000 --> 00:09:30,005 which in this game is entirely from the keyboard. 203 00:09:30,005 --> 00:09:32,002 At first glance, it would appear 204 00:09:32,002 --> 00:09:34,008 that it handles all the keyboard input directly. 205 00:09:34,008 --> 00:09:38,002 In this game however, we will be handling keyboard input 206 00:09:38,002 --> 00:09:40,004 that directly affects Thomas or Bob 207 00:09:40,004 --> 00:09:43,005 within the Thomas and Bob classes directly. 208 00:09:43,005 --> 00:09:45,003 We will call the input function 209 00:09:45,003 --> 00:09:48,002 and this function will directly handle keyboard inputs 210 00:09:48,002 --> 00:09:51,000 such as quitting, switching to split screen 211 00:09:51,000 --> 00:09:53,006 and any other keyboard input. 212 00:09:53,006 --> 00:09:55,003 The update function. 213 00:09:55,003 --> 00:09:58,003 This function will do all the work that we previously did 214 00:09:58,003 --> 00:10:00,002 in the update section of the main function. 215 00:10:00,002 --> 00:10:02,004 We will also call some other functions 216 00:10:02,004 --> 00:10:03,009 from the update function 217 00:10:03,009 --> 00:10:05,008 in order to keep the code organized. 218 00:10:05,008 --> 00:10:07,008 If you look back at the code, 219 00:10:07,008 --> 00:10:10,000 you will see that it receives a float parameter 220 00:10:10,000 --> 00:10:11,008 which will hold the fraction of a second 221 00:10:11,008 --> 00:10:14,000 that has passed since the previous time. 222 00:10:14,000 --> 00:10:16,000 This of course is just what we need 223 00:10:16,000 --> 00:10:18,004 to update all our game objects. 224 00:10:18,004 --> 00:10:22,005 The draw function, this function will hold all the code 225 00:10:22,005 --> 00:10:25,004 that used to go in the drawing section of the main function 226 00:10:25,004 --> 00:10:26,007 in previous projects. 227 00:10:26,007 --> 00:10:28,009 We will however have some drawing code 228 00:10:28,009 --> 00:10:30,009 that is not kept in this function 229 00:10:30,009 --> 00:10:34,000 when we look at other ways to draw with SF ML. 230 00:10:34,000 --> 00:10:37,000 Let's run through all public constructor functions. 231 00:10:37,000 --> 00:10:39,000 The engine constructor function. 232 00:10:39,000 --> 00:10:42,000 As we've come to expect, this function will be called 233 00:10:42,000 --> 00:10:44,004 when refers declare an instance of engine. 234 00:10:44,004 --> 00:10:47,004 It will do all the setup and initialization of the class. 235 00:10:47,004 --> 00:10:52,000 We will see exactly what when we code the engine.cpp file. 236 00:10:52,000 --> 00:10:53,005 The run function. 237 00:10:53,005 --> 00:10:56,001 This is the only public function that we need to call. 238 00:10:56,001 --> 00:10:59,008 It will trigger the execution of input, update and draw 239 00:10:59,008 --> 00:11:01,004 which will do all the work. 240 00:11:01,004 --> 00:11:04,001 Next we'll see the definition of all these functions 241 00:11:04,001 --> 00:11:08,001 and some of the variables in action. 242 00:11:08,001 --> 00:11:10,002 Let's get started by coding engine 243 00:11:10,002 --> 00:11:12,007 and run it in engine.cpp. 244 00:11:12,007 --> 00:11:15,007 Right-click source files in the solution Explorer 245 00:11:15,007 --> 00:11:17,007 and select add new item. 246 00:11:17,007 --> 00:11:23,001 In the add new item window, click C++ file.cpp 247 00:11:23,001 --> 00:11:25,006 and then in the name field, type engine. 248 00:11:25,006 --> 00:11:27,006 Finally click the add button. 249 00:11:27,006 --> 00:11:30,002 In this file, add this entire code. 250 00:11:30,002 --> 00:11:33,009 We will add constructor engine and public run function. 251 00:11:33,009 --> 00:11:37,004 All other functions will go in their own .cpp file 252 00:11:37,004 --> 00:11:40,006 with a name that makes it clear which function goes where. 253 00:11:40,006 --> 00:11:42,004 This will not be a problem for compiling 254 00:11:42,004 --> 00:11:45,004 as long as we had appropriate include directive 255 00:11:45,004 --> 00:11:49,002 hash include engine.h at the top of all files 256 00:11:49,002 --> 00:11:52,006 that contain function definition from engine class. 257 00:11:52,006 --> 00:11:57,001 We are now ready to code the .cpp file for the engine class. 258 00:11:57,001 --> 00:12:00,005 The code for this function will be in the engine.cpp file 259 00:12:00,005 --> 00:12:01,009 we just created. 260 00:12:01,009 --> 00:12:06,002 Here we are adding necessary include directives. 261 00:12:06,002 --> 00:12:08,001 Much of the code we have seen before. 262 00:12:08,001 --> 00:12:10,008 For example, there are the usual lines of code 263 00:12:10,008 --> 00:12:12,002 to get the screen resolution 264 00:12:12,002 --> 00:12:14,005 as well as to create a render window. 265 00:12:14,005 --> 00:12:17,000 At the end of this code, we use the now familiar code 266 00:12:17,000 --> 00:12:20,001 to load a texture and assign it to a Sprite. 267 00:12:20,001 --> 00:12:21,005 In this case, first 268 00:12:21,005 --> 00:12:23,009 we are loading the background.PNG texture 269 00:12:23,009 --> 00:12:27,003 and assigning it to M_background Sprite. 270 00:12:27,003 --> 00:12:29,003 In this code in between, 271 00:12:29,003 --> 00:12:31,009 the four calls to the set viewport function 272 00:12:31,009 --> 00:12:33,009 that needs some explanation. 273 00:12:33,009 --> 00:12:36,009 The set viewport function assigns a portion of the screen 274 00:12:36,009 --> 00:12:39,001 to an SF ML view object. 275 00:12:39,001 --> 00:12:42,003 It doesn't work using pixel coordinates however. 276 00:12:42,003 --> 00:12:44,002 It works using a ratio 277 00:12:44,002 --> 00:12:47,004 where one is the entire screen, width or height. 278 00:12:47,004 --> 00:12:50,005 The first two values in each call to set viewport 279 00:12:50,005 --> 00:12:53,007 are the starting position horizontally and vertically. 280 00:12:53,007 --> 00:12:56,002 And the last two are the ending position. 281 00:12:56,002 --> 00:13:01,006 Notice that the M_left view and M_BG left view 282 00:13:01,006 --> 00:13:03,007 are placed in exactly the same place 283 00:13:03,007 --> 00:13:08,002 starting at virtually the far left, 0.001 of the screen 284 00:13:08,002 --> 00:13:12,006 and ending two 1000s from the center, 0.498. 285 00:13:12,006 --> 00:13:17,000 The M_right view and M_BG right view 286 00:13:17,000 --> 00:13:19,003 are also in exactly the same position, 287 00:13:19,003 --> 00:13:23,003 starting just left of the previous two view objects 0.5 288 00:13:23,003 --> 00:13:26,003 and extending to almost the far right-hand side, 289 00:13:26,003 --> 00:13:28,003 0.998 of the screen. 290 00:13:28,003 --> 00:13:32,005 Furthermore, all the views leave a tiny sliver of a gap 291 00:13:32,005 --> 00:13:34,008 at the top and bottom of the screen. 292 00:13:34,008 --> 00:13:37,005 When we draw these view objects on the screen 293 00:13:37,005 --> 00:13:39,000 on top of a white background, 294 00:13:39,000 --> 00:13:41,005 it will have the effect of splitting the screen 295 00:13:41,005 --> 00:13:44,008 with a thin white line between the two sides of the screen 296 00:13:44,008 --> 00:13:47,004 as well as a thin white border around the edges. 297 00:13:47,004 --> 00:13:50,007 I've tried to represent this effect in this diagram. 298 00:13:50,007 --> 00:13:54,001 The best way to understand it is to finish this section, 299 00:13:54,001 --> 00:13:56,008 run the code and see it in action. 300 00:13:56,008 --> 00:14:00,000 Let's take a look at coding the run function definition. 301 00:14:00,000 --> 00:14:04,001 Add this highlighted code in engine.cpp 302 00:14:04,001 --> 00:14:06,001 just after the constructor code. 303 00:14:06,001 --> 00:14:09,001 The run function is the center of our engine. 304 00:14:09,001 --> 00:14:10,008 It initiates all the other parts. 305 00:14:10,008 --> 00:14:13,007 First, we declare a clock object. 306 00:14:13,007 --> 00:14:17,003 Next, we have the familiar while window is open loop 307 00:14:17,003 --> 00:14:18,009 which creates the game loop. 308 00:14:18,009 --> 00:14:23,002 Inside this while loop, we restart clock and save the time 309 00:14:23,002 --> 00:14:26,000 that the previous loop took in DT. 310 00:14:26,000 --> 00:14:28,006 Then, we keep track of the total time elapsed 311 00:14:28,006 --> 00:14:31,004 in M_gametime total. 312 00:14:31,004 --> 00:14:34,003 Here declare and initialize a float 313 00:14:34,003 --> 00:14:36,005 to represent the fraction of a second that elapsed 314 00:14:36,005 --> 00:14:38,001 during the previous frame. 315 00:14:38,001 --> 00:14:40,007 Next, we call input function. 316 00:14:40,007 --> 00:14:43,009 Then we call update passing in the elapsed time, 317 00:14:43,009 --> 00:14:46,001 DT as seconds. 318 00:14:46,001 --> 00:14:49,005 And at last, we call draw function. 319 00:14:49,005 --> 00:14:51,002 All of this should look very familiar. 320 00:14:51,002 --> 00:14:54,005 What is new is that is wrapped in the run function. 321 00:14:54,005 --> 00:14:59,004 Now let's move on to coding the input function definition. 322 00:14:59,004 --> 00:15:02,004 Right-click source files in the solution Explorer 323 00:15:02,004 --> 00:15:03,009 and select add. 324 00:15:03,009 --> 00:15:06,003 In that, click on new item. 325 00:15:06,003 --> 00:15:10,008 Now we have to select C++ file.cpp 326 00:15:10,008 --> 00:15:12,009 and then in the name field type input. 327 00:15:12,009 --> 00:15:16,001 So the name is now input.cpp. 328 00:15:16,001 --> 00:15:18,000 Finally, click the add button. 329 00:15:18,000 --> 00:15:20,008 We're now ready to code the input function. 330 00:15:20,008 --> 00:15:23,005 Now we have to add this highlighted code. 331 00:15:23,005 --> 00:15:26,003 The code for this function will go in its own file. 332 00:15:26,003 --> 00:15:28,005 This is the entire highlighted code 333 00:15:28,005 --> 00:15:31,009 that we have to add in the input.cpp file. 334 00:15:31,009 --> 00:15:34,006 In this highlighted code, first we will use 335 00:15:34,006 --> 00:15:37,004 hash include engine.h 336 00:15:37,004 --> 00:15:40,000 and prefix the function signature with engine 337 00:15:40,000 --> 00:15:43,000 to make sure the compiler is aware of our intentions. 338 00:15:43,000 --> 00:15:45,009 As usual, when the escape key is pressed 339 00:15:45,009 --> 00:15:48,007 it closes the window and the game will quit. 340 00:15:48,007 --> 00:15:50,008 That is whenever we press escape key, 341 00:15:50,008 --> 00:15:52,004 the game will be closed. 342 00:15:52,004 --> 00:15:57,009 When enter key is pressed, it sets M_playing to true 343 00:15:57,009 --> 00:15:59,003 and eventually this will have the effect 344 00:15:59,003 --> 00:16:00,008 of starting a level. 345 00:16:00,008 --> 00:16:05,005 The cube keypress alternates the value of M_character one 346 00:16:05,005 --> 00:16:06,009 between true and false. 347 00:16:06,009 --> 00:16:09,009 This key only has an effect in full-screen mode. 348 00:16:09,009 --> 00:16:12,000 It will switch between Thomas and Bob 349 00:16:12,000 --> 00:16:13,008 being the center of the main view. 350 00:16:13,008 --> 00:16:17,007 When E key is pressed, it switches M_split screen 351 00:16:17,007 --> 00:16:19,000 between true and false. 352 00:16:19,000 --> 00:16:21,008 This will have the effect of switching between fullscreen 353 00:16:21,008 --> 00:16:23,006 and split screen views. 354 00:16:23,006 --> 00:16:25,008 The majority of this keyboard functionality 355 00:16:25,008 --> 00:16:28,006 will be fully working by the end of the section. 356 00:16:28,006 --> 00:16:31,003 We're getting close to being able to run our game engine. 357 00:16:31,003 --> 00:16:34,001 Next, let's code update function. 358 00:16:34,001 --> 00:16:37,009 As usual, right-click source files in the solution Explorer 359 00:16:37,009 --> 00:16:40,000 and select add new item. 360 00:16:40,000 --> 00:16:44,006 In the add new item window, click C++ file.cpp 361 00:16:44,006 --> 00:16:47,001 and then in the name field type update. 362 00:16:47,001 --> 00:16:49,001 Lastly, click the add button. 363 00:16:49,001 --> 00:16:52,003 We're now ready to write some code for the update function. 364 00:16:52,003 --> 00:16:54,005 Now add this highlighted code. 365 00:16:54,005 --> 00:16:58,003 The code for update function goes in update.cpp. 366 00:16:58,003 --> 00:17:03,000 Just as we did earlier, we will use hash include engine.h 367 00:17:03,000 --> 00:17:05,003 and prefix the function signature with engine 368 00:17:05,003 --> 00:17:08,006 to make sure the compiler is aware of our intentions. 369 00:17:08,006 --> 00:17:11,002 Notice that the update function receives the time 370 00:17:11,002 --> 00:17:13,003 the previous frame took as a parameter. 371 00:17:13,003 --> 00:17:16,002 This of course will be essential for the update function 372 00:17:16,002 --> 00:17:17,007 to fulfill its role. 373 00:17:17,007 --> 00:17:21,001 Then it checks the if condition M is playing. 374 00:17:21,001 --> 00:17:24,009 If yes, then it subtracts the time the previous frame took 375 00:17:24,009 --> 00:17:27,001 from M_time remaining. 376 00:17:27,001 --> 00:17:29,003 It checks whether time has run out, 377 00:17:29,003 --> 00:17:33,006 and if it has, it sets M_new level required to true. 378 00:17:33,006 --> 00:17:36,007 All this code is wrapped in an if statement 379 00:17:36,007 --> 00:17:39,009 that only executes when M_playing is true. 380 00:17:39,009 --> 00:17:42,007 The reason for this is because as with the previous projects 381 00:17:42,007 --> 00:17:46,002 we don't want time advancing and objects updating 382 00:17:46,002 --> 00:17:47,009 when the game is not started. 383 00:17:47,009 --> 00:17:51,003 We will build on this code as the project continues. 384 00:17:51,003 --> 00:17:55,002 Lastly, let's code the draw function definition 385 00:17:55,002 --> 00:17:58,002 right-click source files in the solution Explorer 386 00:17:58,002 --> 00:18:00,006 and select add new item. 387 00:18:00,006 --> 00:18:03,007 Then select C++ file.cpp 388 00:18:03,007 --> 00:18:05,008 and then in the name field, type draw. 389 00:18:05,008 --> 00:18:09,000 Now the name is draw.cpp. 390 00:18:09,000 --> 00:18:10,008 Then click the add button. 391 00:18:10,008 --> 00:18:14,002 We are now ready to add some code to the draw function. 392 00:18:14,002 --> 00:18:16,005 Now we'll add this code to the file 393 00:18:16,005 --> 00:18:18,003 to implement the draw function. 394 00:18:18,003 --> 00:18:21,001 The code for draw function will go in its own file. 395 00:18:21,001 --> 00:18:26,004 You can see we will use hash include engine.h here also 396 00:18:26,004 --> 00:18:29,000 and prefix the function signature with engine. 397 00:18:29,000 --> 00:18:32,005 In this highlighted line of code we clear the screen. 398 00:18:32,005 --> 00:18:35,007 In this project, we clear the screen with white. 399 00:18:35,007 --> 00:18:38,007 What is new is the way the different drawing options 400 00:18:38,007 --> 00:18:40,004 are separated by a condition 401 00:18:40,004 --> 00:18:44,000 which checks whether the screen is currently split or full. 402 00:18:44,000 --> 00:18:45,008 If the screen is not split, 403 00:18:45,008 --> 00:18:48,002 we draw the background sprite in the background view 404 00:18:48,002 --> 00:18:50,009 that is M_BG main view, 405 00:18:50,009 --> 00:18:54,008 and then switch to the main full-screen, view M_main view. 406 00:18:54,008 --> 00:18:56,007 Note that at the moment, 407 00:18:56,007 --> 00:18:59,008 we don't actually do any drawing in M_main view. 408 00:18:59,008 --> 00:19:02,002 On the other hand, if the screen is split 409 00:19:02,002 --> 00:19:04,008 the code in the else block is executed 410 00:19:04,008 --> 00:19:07,005 and we draw M_BG left view 411 00:19:07,005 --> 00:19:10,004 with the background sprite on the left of the screen 412 00:19:10,004 --> 00:19:13,008 followed by switching to M_left view. 413 00:19:13,008 --> 00:19:18,006 Then still in the else block, we draw M_BG right view 414 00:19:18,006 --> 00:19:20,009 with the background sprite on the right of the screen 415 00:19:20,009 --> 00:19:24,001 followed by switching to M_right view. 416 00:19:24,001 --> 00:19:27,004 Outside the if else structure, 417 00:19:27,004 --> 00:19:30,000 we run to M_HUD view. 418 00:19:30,000 --> 00:19:32,007 At this stage, we're not actually drawing anything 419 00:19:32,007 --> 00:19:34,008 in M_HUD view. 420 00:19:34,008 --> 00:19:37,005 At last, we call the display function 421 00:19:37,005 --> 00:19:39,005 to show everything we have just drawn. 422 00:19:39,005 --> 00:19:41,005 As with the other two input update 423 00:19:41,005 --> 00:19:44,000 of the three most significant functions 424 00:19:44,000 --> 00:19:46,005 we will be back here at the draw function often. 425 00:19:46,005 --> 00:19:49,005 We will add new elements of our game that need to be drawn. 426 00:19:49,005 --> 00:19:51,005 You'll notice that each time we do, 427 00:19:51,005 --> 00:19:53,007 we'll add code into each of the main, 428 00:19:53,007 --> 00:19:55,003 left and right sections. 429 00:19:55,003 --> 00:19:57,006 Let's quickly recap the engine class 430 00:19:57,006 --> 00:19:58,009 and then we can fire it up. 431 00:19:58,009 --> 00:20:02,005 What we have achieved is the abstraction of all the code 432 00:20:02,005 --> 00:20:04,004 that used to be in the main function 433 00:20:04,004 --> 00:20:07,001 into the input, update and draw functions. 434 00:20:07,001 --> 00:20:09,001 The continuous looping of these functions 435 00:20:09,001 --> 00:20:12,001 as well as the timing is handled by the run function. 436 00:20:12,001 --> 00:20:18,009 As you can see here, input.cpp, update.cpp and draw.cpp tabs 437 00:20:18,009 --> 00:20:20,006 open in Visual Studio. 438 00:20:20,006 --> 00:20:22,006 I've organized them in order. 439 00:20:22,006 --> 00:20:24,006 We will revisit each of these functions 440 00:20:24,006 --> 00:20:27,005 throughout the course of the project to add more code. 441 00:20:27,005 --> 00:20:29,006 Now that we have the basic structure 442 00:20:29,006 --> 00:20:31,003 and functionality the engine class, 443 00:20:31,003 --> 00:20:34,002 we can create an instance of it in the main function 444 00:20:34,002 --> 00:20:35,007 and see it in action. 445 00:20:35,007 --> 00:20:38,009 In this video, we've looked at building the game engine. 446 00:20:38,009 --> 00:20:41,005 Great, in the next video, 447 00:20:41,005 --> 00:20:44,001 we'll learn coding the main function.