1 00:00:01,004 --> 00:00:05,004 - Hi, welcome to Building the Playable Character Class. 2 00:00:05,004 --> 00:00:07,007 Previously, we looked at abstract classes, 3 00:00:07,007 --> 00:00:10,006 virtual and pure virtual functions. 4 00:00:10,006 --> 00:00:13,000 In this video, we're going to look at coding 5 00:00:13,000 --> 00:00:17,008 Playable Character.h and Playable Character.cpp. 6 00:00:17,008 --> 00:00:20,002 Now that we know the basics about inheritance, 7 00:00:20,002 --> 00:00:22,009 polymorphism, and pure virtual functions, 8 00:00:22,009 --> 00:00:24,008 let's put them to use. 9 00:00:24,008 --> 00:00:26,009 We will build a Playable Character Class 10 00:00:26,009 --> 00:00:28,009 that has the vast majority of the functionality 11 00:00:28,009 --> 00:00:32,002 that any character from our game is going to need. 12 00:00:32,002 --> 00:00:35,008 It will have one pure virtual function, handle input. 13 00:00:35,008 --> 00:00:38,000 The handle input function will need to be quite 14 00:00:38,000 --> 00:00:41,003 different in the sub-classes, this makes sense, 15 00:00:41,003 --> 00:00:44,009 as Playable Character will have a pure virtual function. 16 00:00:44,009 --> 00:00:46,008 It will be an abstract class, 17 00:00:46,008 --> 00:00:49,002 and no objects of it, will be possible. 18 00:00:49,002 --> 00:00:52,001 We will then build the both Thomas and Bob Classes, 19 00:00:52,001 --> 00:00:54,001 which will inherit from Playable Character, 20 00:00:54,001 --> 00:00:56,006 implement the definition of the pure virtual function, 21 00:00:56,006 --> 00:00:59,006 and allow us to instantiate Bob and Thomas objects 22 00:00:59,006 --> 00:01:02,001 in our game. 23 00:01:02,001 --> 00:01:05,008 Let's start with coding Playable Character.h 24 00:01:05,008 --> 00:01:08,006 Right click Header Files in the Solution Explorer, 25 00:01:08,006 --> 00:01:11,001 and select, Add New Item. 26 00:01:11,001 --> 00:01:15,002 In the Add New Item window, click Header File.h, 27 00:01:15,002 --> 00:01:18,007 and then, in the name field, type Playable Character. 28 00:01:18,007 --> 00:01:22,003 So, now the name is Playable Character.h. 29 00:01:22,003 --> 00:01:24,004 Lastly, click the Add button. 30 00:01:24,004 --> 00:01:26,002 We are now ready to code the Header File, 31 00:01:26,002 --> 00:01:28,009 for the Playable Character Class. 32 00:01:28,009 --> 00:01:31,005 Add this highlighted code in the file. 33 00:01:31,005 --> 00:01:34,007 As usual, when creating a class, we will start off with 34 00:01:34,007 --> 00:01:37,002 the Header File, that will contain the member variables, 35 00:01:37,002 --> 00:01:39,004 and function declarations. 36 00:01:39,004 --> 00:01:42,002 What is new, is that in this class, we will declare some 37 00:01:42,002 --> 00:01:44,005 protected member variables. 38 00:01:44,005 --> 00:01:47,001 Remember, that protected variables can be used, 39 00:01:47,001 --> 00:01:48,009 as if they are public by classes, 40 00:01:48,009 --> 00:01:52,002 which inherit from the class with the protected variables. 41 00:01:52,002 --> 00:01:54,004 We will add, and discuss, the contents of the 42 00:01:54,004 --> 00:01:57,009 Playable Character.h file in three sections. 43 00:01:57,009 --> 00:02:00,009 First, the protected section, followed by private, 44 00:02:00,009 --> 00:02:02,000 then public. 45 00:02:02,000 --> 00:02:04,003 The first thing to notice in the code we just wrote, 46 00:02:04,003 --> 00:02:06,007 is that all the variables are protected. 47 00:02:06,007 --> 00:02:09,001 This means that when we extend the class, 48 00:02:09,001 --> 00:02:11,008 all the variables we just wrote, will be accessible 49 00:02:11,008 --> 00:02:14,000 to those classes that extended. 50 00:02:14,000 --> 00:02:17,005 We will extend this class with Thomas and Bob Classes. 51 00:02:17,005 --> 00:02:20,004 Apart from the protected access specification, 52 00:02:20,004 --> 00:02:23,004 there's nothing new, or complicated, about this code. 53 00:02:23,004 --> 00:02:26,003 It is worth paying attention to some of the details however. 54 00:02:26,003 --> 00:02:29,004 Then, it will be easy to understand how the class works, 55 00:02:29,004 --> 00:02:30,008 as we progress. 56 00:02:30,008 --> 00:02:33,001 So, let's run through those protected variables, 57 00:02:33,001 --> 00:02:35,000 one at a time. 58 00:02:35,000 --> 00:02:37,004 First of all, we have our, somewhat predictable, 59 00:02:37,004 --> 00:02:40,001 Sprite, m_Sprite. 60 00:02:40,001 --> 00:02:42,003 That is, we are declaring an object of Sprite, 61 00:02:42,003 --> 00:02:44,008 called m_Sprite. 62 00:02:44,008 --> 00:02:48,003 We have a float called m_JumpDuration, 63 00:02:48,003 --> 00:02:50,007 which will hold the value representing the time that the 64 00:02:50,007 --> 00:02:52,007 character is able to jump for. 65 00:02:52,007 --> 00:02:55,001 The greater the value, the higher the character will be 66 00:02:55,001 --> 00:02:56,007 able to jump. 67 00:02:56,007 --> 00:03:00,008 Next, we have boolean, m_ IsJumping, 68 00:03:00,008 --> 00:03:02,008 which is true when the character is jumping, 69 00:03:02,008 --> 00:03:04,005 and falls otherwise. 70 00:03:04,005 --> 00:03:06,008 This will be useful for making sure that the character 71 00:03:06,008 --> 00:03:09,001 can't jump while in mid-air. 72 00:03:09,001 --> 00:03:12,008 The m_ IsFalling variable, has a similar use, 73 00:03:12,008 --> 00:03:15,004 to m_IsJumping. 74 00:03:15,004 --> 00:03:18,003 It will be useful to know when a character is falling. 75 00:03:18,003 --> 00:03:21,000 It's also a bolean variable. 76 00:03:21,000 --> 00:03:23,007 Next we have two boolean's, which would be true, 77 00:03:23,007 --> 00:03:26,000 if the character's left or right keyboard buttons, 78 00:03:26,000 --> 00:03:28,000 are currently being pressed. 79 00:03:28,000 --> 00:03:30,002 These are relative, depending upon the character. 80 00:03:30,002 --> 00:03:35,000 Keys, A and D for Thomas, left and right arrow keys for Bob. 81 00:03:35,000 --> 00:03:37,006 How we respond to these booleans, will be seen in the 82 00:03:37,006 --> 00:03:39,009 Thomas and Bob Classes. 83 00:03:39,009 --> 00:03:43,008 The m_TimeThisJump float variable, is updated, 84 00:03:43,008 --> 00:03:48,000 each and every frame, the m_IsJumping is true. 85 00:03:48,000 --> 00:03:52,002 We can then know when m_Jump duration has been reached. 86 00:03:52,002 --> 00:03:57,003 The final protected variable, is the boolean m_JustJumped, 87 00:03:57,003 --> 00:03:59,006 this will be true if a jump was initiated, 88 00:03:59,006 --> 00:04:01,001 in the current frame. 89 00:04:01,001 --> 00:04:02,004 It will be useful for knowing 90 00:04:02,004 --> 00:04:04,005 when to play a jump sound effect. 91 00:04:04,005 --> 00:04:09,009 As of now, we have set m_JustJumped, to false. 92 00:04:09,009 --> 00:04:12,009 Next, at this highlighted code, where we are adding 93 00:04:12,009 --> 00:04:17,000 private variables to the Playable Character.h file. 94 00:04:17,000 --> 00:04:19,006 We have some interesting private variables here. 95 00:04:19,006 --> 00:04:22,002 Remember that these variables will only be directly 96 00:04:22,002 --> 00:04:25,007 accessible to the code, in the Playable Character Class. 97 00:04:25,007 --> 00:04:28,000 The Thomas and Bob classes, will not be able to 98 00:04:28,000 --> 00:04:29,008 access them directly. 99 00:04:29,008 --> 00:04:33,005 The m_Gravity variable, will hold the number of pixels 100 00:04:33,005 --> 00:04:36,002 per second that the character will fall. 101 00:04:36,002 --> 00:04:39,008 The m_Speed variable, will hold the number of pixels 102 00:04:39,008 --> 00:04:43,006 per second that the character can move left, or right. 103 00:04:43,006 --> 00:04:46,008 The Vector2f m_Position variable, 104 00:04:46,008 --> 00:04:49,006 is the position in the world, not the screen, 105 00:04:49,006 --> 00:04:52,003 where the center of the character is. 106 00:04:52,003 --> 00:04:56,006 The next four float rect objects, are important to discuss. 107 00:04:56,006 --> 00:04:59,005 When we did collision detection in the Zombie Arena game, 108 00:04:59,005 --> 00:05:00,007 we simply checked to see if, 109 00:05:00,007 --> 00:05:03,004 two float rect objects intersected. 110 00:05:03,004 --> 00:05:07,000 Each float rect object, represented an entire character, 111 00:05:07,000 --> 00:05:08,007 a pick up, or a bullet. 112 00:05:08,007 --> 00:05:10,009 For the non-rectangular shaped objects, 113 00:05:10,009 --> 00:05:12,001 zombies and the player, 114 00:05:12,001 --> 00:05:14,005 this was a little bit inaccurate. 115 00:05:14,005 --> 00:05:17,004 In this game, we will need to be more precise. 116 00:05:17,004 --> 00:05:25,003 The m_Feet, m_Head, m_Right and m_Left float rect objects, 117 00:05:25,003 --> 00:05:27,003 will hold the co-ordinates of the different parts 118 00:05:27,003 --> 00:05:28,009 of a character's body. 119 00:05:28,009 --> 00:05:30,006 These co-ordinates will be updated, 120 00:05:30,006 --> 00:05:32,006 in each and every frame. 121 00:05:32,006 --> 00:05:34,009 Through these co-ordinates, we will be able to tell exactly 122 00:05:34,009 --> 00:05:37,007 when a character lands on a platform, bumps his head 123 00:05:37,007 --> 00:05:41,008 during a jump or, rubs shoulders with a tile to his side. 124 00:05:41,008 --> 00:05:44,000 Lastly, we have texture, that is, 125 00:05:44,000 --> 00:05:46,004 we declare an object of type texture, 126 00:05:46,004 --> 00:05:49,001 called m_Texture. 127 00:05:49,001 --> 00:05:52,001 Texture is private, as it is not used directly, 128 00:05:52,001 --> 00:05:54,000 by the Thomas or Bob Classes, 129 00:05:54,000 --> 00:05:56,008 but as we saw, Sprite is protected, 130 00:05:56,008 --> 00:05:59,004 because it is used directly. 131 00:05:59,004 --> 00:06:01,006 Now, add all the public functions to the 132 00:06:01,006 --> 00:06:04,001 Playable Character.h file, 133 00:06:04,001 --> 00:06:08,000 this is the entire highlighted code to be added. 134 00:06:08,000 --> 00:06:10,003 Let's talk about each of the function declarations 135 00:06:10,003 --> 00:06:11,006 that we just added. 136 00:06:11,006 --> 00:06:15,000 This will make coding their definitions, easier to follow. 137 00:06:15,000 --> 00:06:18,005 First, the Spawn function receives a vector2f called, 138 00:06:18,005 --> 00:06:21,006 Start Position, and a float called Gravity. 139 00:06:21,006 --> 00:06:24,002 As the name suggests, Start Position will be the 140 00:06:24,002 --> 00:06:27,001 co-ordinates in the level at which the character will start, 141 00:06:27,001 --> 00:06:29,006 and Gravity will be the number of pixels per second, 142 00:06:29,006 --> 00:06:32,001 at which the character will fall. 143 00:06:32,001 --> 00:06:35,001 The bool virtual handle input = 0, 144 00:06:35,001 --> 00:06:38,006 is, of course, our pure virtual function. 145 00:06:38,006 --> 00:06:41,000 As Playable Character has this function, 146 00:06:41,000 --> 00:06:44,001 any class that extends it, if we want to instantiate it, 147 00:06:44,001 --> 00:06:46,009 must provide a definition for this function. 148 00:06:46,009 --> 00:06:49,007 Therefore, when we write all the function definitions for 149 00:06:49,007 --> 00:06:51,005 Playable Character in the minute, 150 00:06:51,005 --> 00:06:55,000 we will not provide a definition for handle input. 151 00:06:55,000 --> 00:06:56,008 There will, of course, need to be definitions, 152 00:06:56,008 --> 00:06:59,008 in both the Thomas and Bob Classes. 153 00:06:59,008 --> 00:07:02,008 The Get Position function, returns a float rect, 154 00:07:02,008 --> 00:07:05,007 that represents the position of the whole character. 155 00:07:05,007 --> 00:07:08,002 The Get Feet function, as well as Get Head, 156 00:07:08,002 --> 00:07:11,007 Get Right and Get Left, each return a float rect, 157 00:07:11,007 --> 00:07:13,008 that represents the location of a specific part 158 00:07:13,008 --> 00:07:15,004 of the character's body. 159 00:07:15,004 --> 00:07:19,000 This is just what we need, for detailed collision detection. 160 00:07:19,000 --> 00:07:22,002 The Get Sprite function, as usual, returns a copy 161 00:07:22,002 --> 00:07:25,003 of m_Sprite, to the calling code. 162 00:07:25,003 --> 00:07:28,005 The StopFalling, StopRight and StopLeft, 163 00:07:28,005 --> 00:07:30,003 receive a single float value. 164 00:07:30,003 --> 00:07:32,003 Which the function will use, to reposition the 165 00:07:32,003 --> 00:07:34,005 character, and stop it walking or jumping, 166 00:07:34,005 --> 00:07:36,002 through a solid tile. 167 00:07:36,002 --> 00:07:38,007 The StopJump function, will stop the character, 168 00:07:38,007 --> 00:07:41,005 from jumping through a solid tile. 169 00:07:41,005 --> 00:07:44,004 The GetCenter function, returns a vector2f, 170 00:07:44,004 --> 00:07:46,009 to the calling code, to let it know exactly where 171 00:07:46,009 --> 00:07:49,000 the center of the character is. 172 00:07:49,000 --> 00:07:52,006 This value is, of course, held in m_Position. 173 00:07:52,006 --> 00:07:55,006 We will see later, that it is used by the Engine Class, 174 00:07:55,006 --> 00:07:57,003 to center the appropriate view around 175 00:07:57,003 --> 00:07:59,009 the appropriate character. 176 00:07:59,009 --> 00:08:03,001 The update function, we have seen many times before, 177 00:08:03,001 --> 00:08:05,006 and, as usual, it takes float parameter, 178 00:08:05,006 --> 00:08:07,000 which is the fraction of a second, 179 00:08:07,000 --> 00:08:09,002 that the current frame is taken. 180 00:08:09,002 --> 00:08:11,004 This update function, will need to do more work, 181 00:08:11,004 --> 00:08:14,002 than previous update functions, from other projects. 182 00:08:14,002 --> 00:08:16,004 However, it will need to handle jumping, 183 00:08:16,004 --> 00:08:18,005 as well as updating the float rect objects that 184 00:08:18,005 --> 00:08:21,009 represent the head, feet, left and right. 185 00:08:21,009 --> 00:08:24,006 Now, we can write the definitions for all the functions, 186 00:08:24,006 --> 00:08:27,005 except, of course, handle input. 187 00:08:27,005 --> 00:08:31,007 Now, let's move on to coding Playable Character.cpp. 188 00:08:31,007 --> 00:08:34,004 Just like we always do, right click Source Files, 189 00:08:34,004 --> 00:08:37,008 in the Solution Explorer, and select Add New Item. 190 00:08:37,008 --> 00:08:42,000 Click, c++ File.cpp, and then in the name field, 191 00:08:42,000 --> 00:08:46,000 type Playable Character, and click Add. 192 00:08:46,000 --> 00:08:48,006 We are now ready to code the .cpp file, 193 00:08:48,006 --> 00:08:51,007 for the Playable Character Class. 194 00:08:51,007 --> 00:08:53,008 We will break up the code, and discussion, 195 00:08:53,008 --> 00:08:55,007 into a number of chunks. 196 00:08:55,007 --> 00:08:58,006 First, add the Include Directives, and the definition 197 00:08:58,006 --> 00:09:00,007 of the Spawn function. 198 00:09:00,007 --> 00:09:04,001 The Spawn function, initializes m_Position, 199 00:09:04,001 --> 00:09:05,009 with the past in position. 200 00:09:05,009 --> 00:09:10,005 That is, m_Positionx = StartPositionx and, 201 00:09:10,005 --> 00:09:14,005 m_Positiony = StartPositiony. 202 00:09:14,005 --> 00:09:19,001 It also initializes m_Gravity, and this final line of code, 203 00:09:19,001 --> 00:09:23,006 moves m_Sprite, to it's starting position. 204 00:09:23,006 --> 00:09:26,009 Next, add the definition for the Update function. 205 00:09:26,009 --> 00:09:29,004 Add this entire highlighted code immediately after 206 00:09:29,004 --> 00:09:31,006 the preceding code. 207 00:09:31,006 --> 00:09:36,000 Here, first we check whether m_RightPressed is true. 208 00:09:36,000 --> 00:09:40,003 If it is, m_Position is changed, using this formula, 209 00:09:40,003 --> 00:09:43,006 m_Speed into elapse time. 210 00:09:43,006 --> 00:09:47,008 The same is done for m_LeftPressed, in case it's true, 211 00:09:47,008 --> 00:09:52,000 it changes m_Position using this formula. 212 00:09:52,000 --> 00:09:54,001 Then, we see whether or not the character, 213 00:09:54,001 --> 00:09:56,003 is currently executing a jump. 214 00:09:56,003 --> 00:09:58,005 If this if statement is true, 215 00:09:58,005 --> 00:10:03,006 the code first updates m_TimeThisJump, with elapse time. 216 00:10:03,006 --> 00:10:08,004 Then, it checks if m_TimeThisJump is still less than, 217 00:10:08,004 --> 00:10:11,005 m_JumpDuration, if it is, 218 00:10:11,005 --> 00:10:15,000 change the y co-ordinate of m_Position by 219 00:10:15,000 --> 00:10:18,005 twice Gravity multiplied by the elapse time. 220 00:10:18,005 --> 00:10:22,008 In the else clause, it executes when m_TimeThisJump is, 221 00:10:22,008 --> 00:10:25,009 not lower than m_JumpDuration, 222 00:10:25,009 --> 00:10:29,001 then m_Falling is set to true. 223 00:10:29,001 --> 00:10:32,007 Also, m_Jumping is set to false. 224 00:10:32,007 --> 00:10:35,002 This prevents the code we have just been discussing, 225 00:10:35,002 --> 00:10:36,004 from executing. 226 00:10:36,004 --> 00:10:40,007 As if m_IsJumping, is now false. 227 00:10:40,007 --> 00:10:47,001 Next, if m_IsFalling block moves m_Position down each frame, 228 00:10:47,001 --> 00:10:50,009 it is moved, using the current value of m_Gravity 229 00:10:50,009 --> 00:10:52,005 and the elapse time. 230 00:10:52,005 --> 00:10:55,009 That is, using the current value of m_Gravity, 231 00:10:55,009 --> 00:10:57,009 and the elapse time. 232 00:10:57,009 --> 00:11:00,008 This code, which is almost all of the remaining code, 233 00:11:00,008 --> 00:11:03,000 updates the body parts of the character, 234 00:11:03,000 --> 00:11:06,001 relative to the current position of the Sprite, as a whole. 235 00:11:06,001 --> 00:11:08,000 Take a look at this diagram, 236 00:11:08,000 --> 00:11:10,000 to see how the code calculates the position, 237 00:11:10,000 --> 00:11:12,009 of the virtual head, feet, left and right sides, 238 00:11:12,009 --> 00:11:14,005 of the character. 239 00:11:14,005 --> 00:11:17,008 This final line of code, uses the set position of 240 00:11:17,008 --> 00:11:20,000 function, to move the Sprite to it's corrected 241 00:11:20,000 --> 00:11:24,002 location after all the possibilities of the update function. 242 00:11:24,002 --> 00:11:27,009 Now, add this code, right after the previous one. 243 00:11:27,009 --> 00:11:30,009 Here we are adding the definition for the Get Position, 244 00:11:30,009 --> 00:11:35,001 GetCenter, GetFeet, GetHead, GetLeft, GetRight and 245 00:11:35,001 --> 00:11:37,008 GetSprite functions. 246 00:11:37,008 --> 00:11:40,007 The GetPosition function, returns a float rect, 247 00:11:40,007 --> 00:11:43,006 that wraps the entire Sprite and Get Center returns 248 00:11:43,006 --> 00:11:47,005 a vector2f, which contains the center of the Sprite. 249 00:11:47,005 --> 00:11:50,005 Notice, that we divide the height and width of the Sprite, 250 00:11:50,005 --> 00:11:54,005 by two, in order to dynamically arrive at this result. 251 00:11:54,005 --> 00:11:56,005 This is because Thomas and Bob, 252 00:11:56,005 --> 00:11:58,003 will be at different heights. 253 00:11:58,003 --> 00:12:02,000 The GetFeet, GetHead, GetLeft and GetRight functions, 254 00:12:02,000 --> 00:12:04,005 return the float rect objects that represent the 255 00:12:04,005 --> 00:12:07,007 body parts of the character, that we update each frame, 256 00:12:07,007 --> 00:12:09,007 in the update function. 257 00:12:09,007 --> 00:12:11,008 The Get Sprite function, as usual, 258 00:12:11,008 --> 00:12:15,002 returns a copy of m_Sprite. 259 00:12:15,002 --> 00:12:17,008 Finally, for the Playable Character Class, 260 00:12:17,008 --> 00:12:20,007 add the definitions for the, StopFalling, StopRight, 261 00:12:20,007 --> 00:12:23,005 StopLeft and StopJump functions. 262 00:12:23,005 --> 00:12:27,004 Note that to do so, immediately after the previous code. 263 00:12:27,004 --> 00:12:30,003 Each of these function receive a value, as a parameter, 264 00:12:30,003 --> 00:12:32,008 that is used to reposition either the top, 265 00:12:32,008 --> 00:12:35,008 bottom, left or right of the Sprite. 266 00:12:35,008 --> 00:12:39,000 Exactly what these values are, and how they are obtained, 267 00:12:39,000 --> 00:12:40,008 will be seen later. 268 00:12:40,008 --> 00:12:44,008 Each of the previous functions also repositions the Sprite. 269 00:12:44,008 --> 00:12:47,009 The final function is the StopJump function, 270 00:12:47,009 --> 00:12:50,006 that will also be used in collision detection. 271 00:12:50,006 --> 00:12:54,006 It sets the necessary values for m_IsJumping and, 272 00:12:54,006 --> 00:12:57,007 m_IsFalling, to end a jump. 273 00:12:57,007 --> 00:13:01,001 Here we have set m_IsJumping to false, 274 00:13:01,001 --> 00:13:04,000 and m_IsJumping to true. 275 00:13:04,000 --> 00:13:05,005 In this video, we have learned, 276 00:13:05,005 --> 00:13:08,001 Building the Playable Character Class. 277 00:13:08,001 --> 00:13:09,001 Cool. 278 00:13:09,001 --> 00:13:11,001 In the next video, we will see building the 279 00:13:11,001 --> 00:13:13,001 Thomas and Bob Classes.