1. 11 Reaction Timer Game Session 8.1

2. Session Overview  Find out how an XNA program can measure the passage of time and trigger events at certain points in time  Show how an algorithm can be expressed in terms of a simple flow diagram  Create a reaction timer game  Discover how game play flaws can be discovered, and an algorithm modified to remove them  Find out how an XNA program can measure the passage of time and trigger events at certain points in time  Show how an algorithm can be expressed in terms of a simple flow diagram  Create a reaction timer game  Discover how game play flaws can be discovered, and an algorithm modified to remove them Chapter 8.1: Reaction Timer Game2

3. Game Idea: “Reaction Timer”  The game implements a reaction timer  It measures the time interval between playing a sound sample and the players pressing a button  The fastest player on the button wins  The game implements a reaction timer  It measures the time interval between playing a sound sample and the players pressing a button  The fastest player on the button wins Chapter 8.1: Reaction Timer Game3

4. Using Update to Implement a Timer  We know that the Update method is called 60 times a second by XNA  This means that a game can measure time passing  Each time Update is called we can increase the value in the timer, and use certain timer values to trigger game events  We can also use the value in the timer as a way of working out the time when a particular event occurs  We know that the Update method is called 60 times a second by XNA  This means that a game can measure time passing  Each time Update is called we can increase the value in the timer, and use certain timer values to trigger game events  We can also use the value in the timer as a way of working out the time when a particular event occurs Chapter 8.1: Reaction Timer Game4

5. Game World Variables for Reaction Timer  These variables are used to implement the Reaction Timer game  They are all integers, since there is no need for a fractional part for any of the values  These variables are used to implement the Reaction Timer game  They are all integers, since there is no need for a fractional part for any of the values Chapter 8.1: Reaction Timer Game5 // Game World int timer; // Gamepad 1 scores int ascore1; int bscore1; int xscore1; int yscore1;

6. Reaction Timer Flowchart  One way to describe the behavior required from a program is to draw a “flowchart”  This sets out the flow of the program behavior  It shows the decisions that are made, and the actions that are performed as a result  One way to describe the behavior required from a program is to draw a “flowchart”  This sets out the flow of the program behavior  It shows the decisions that are made, and the actions that are performed as a result Chapter 8.1: Reaction Timer Game6

7. Reaction Timer Code  This is the start behavior  The timer and scores are reset when Start is pressed  This is the start behavior  The timer and scores are reset when Start is pressed Chapter 8.1: Reaction Timer Game7 if (pad1.Buttons.Start == ButtonState.Pressed) { timer = -120; ascore1 = 0; bscore1 = 0; xscore1 = 0; yscore1 = 0; }

8. Reaction Timer Code  The timer variable maintains the state of the game  When it is less than 0 the game is waiting to start  When the timer reaches 0 the sound is played  When the timer is greater than 0 it is timing players  The timer variable maintains the state of the game  When it is less than 0 the game is waiting to start  When the timer reaches 0 the sound is played  When the timer is greater than 0 it is timing players Chapter 8.1: Reaction Timer Game8 timer++;

9. Reaction Timer Code  When the timer reaches 0 it is time for the start sound to play  The dingSound variable is a sound effect that is played in “Fire and Forget” mode  When the timer reaches 0 it is time for the start sound to play  The dingSound variable is a sound effect that is played in “Fire and Forget” mode Chapter 8.1: Reaction Timer Game9 if (timer == 0) { dingSound.Play(); } if (timer == 0) { dingSound.Play(); }

10. Reaction Timer Code  This code is for button A  It uses the button edge detection code  Copying the value of timer is how the game records the score for a player  This code is for button A  It uses the button edge detection code  Copying the value of timer is how the game records the score for a player Chapter 8.1: Reaction Timer Game10 // if A is pressed copy the timer if (oldpad1.Buttons.A == ButtonState.Released && pad1.Buttons.A == ButtonState.Pressed) { ascore1 = timer; } // if A is pressed copy the timer if (oldpad1.Buttons.A == ButtonState.Released && pad1.Buttons.A == ButtonState.Pressed) { ascore1 = timer; }

11. Displaying the Scores  This code should look slightly familiar. Chapter 8.1: Reaction Timer Game11 protected override void Draw(GameTime gameTime) { GraphicsDevice.Clear(Color.CornflowerBlue); spriteBatch.Begin(); if (pad1.IsConnected) { spriteBatch.DrawString(font, ascore1.ToString(), apos1, Color.Green); // repeat for other buttons } spriteBatch.End(); base.Draw(gameTime); } protected override void Draw(GameTime gameTime) { GraphicsDevice.Clear(Color.CornflowerBlue); spriteBatch.Begin(); if (pad1.IsConnected) { spriteBatch.DrawString(font, ascore1.ToString(), apos1, Color.Green); // repeat for other buttons } spriteBatch.End(); base.Draw(gameTime); }

12. 1. Reaction Timer Chapter 8.1: Reaction Timer Game12  This version of the Reaction Timer game uses the algorithm described above  The player with the lowest score is the winner  This version of the Reaction Timer game uses the algorithm described above  The player with the lowest score is the winner

13. Game Play Bugs  We have uncovered a fault in the algorithm that implements the game  If a player presses their button early they can sneak a peek at the time value  They can also repeatedly press their buttons with no penalty  This is not a problem if everyone plays by the rules  But there is no guarantee that they will.  We have uncovered a fault in the algorithm that implements the game  If a player presses their button early they can sneak a peek at the time value  They can also repeatedly press their buttons with no penalty  This is not a problem if everyone plays by the rules  But there is no guarantee that they will. Chapter 8.1: Reaction Timer Game13

14. Finding the Problem  One of these is the fault that allows cheating: 1. The fault occurs because the game does not detect when the player releases the button as well as when it’s pressed. 2. The fault occurs because the game should use level detection on the buttons, not edge detection. 3. The fault occurs because the game should register only the first press of the button. 4. The fault occurs because the game must reset the gamepad after it’s been read.  One of these is the fault that allows cheating: 1. The fault occurs because the game does not detect when the player releases the button as well as when it’s pressed. 2. The fault occurs because the game should use level detection on the buttons, not edge detection. 3. The fault occurs because the game should register only the first press of the button. 4. The fault occurs because the game must reset the gamepad after it’s been read. Chapter 8.1: Reaction Timer Game14

15. Finding the Problem  One of these is the fault that allows cheating: 1. The fault occurs because the game does not detect when the player releases the button as well as when it’s pressed. 2. The fault occurs because the game should use level detection on the buttons, not edge detection. 3. The fault occurs because the game should register only the first press of the button. 4. The fault occurs because the game must reset the gamepad after it’s been read.  One of these is the fault that allows cheating: 1. The fault occurs because the game does not detect when the player releases the button as well as when it’s pressed. 2. The fault occurs because the game should use level detection on the buttons, not edge detection. 3. The fault occurs because the game should register only the first press of the button. 4. The fault occurs because the game must reset the gamepad after it’s been read. Chapter 8.1: Reaction Timer Game15

16. Detecting the First Button Press  When the game resets the scores are all set to 0  When a button is pressed the game copies the timer value into the score for that button  The second time the button is pressed the score value for that button will not be 0  We can use this to detect when a button has already been pressed, and reject subsequent presses  When the game resets the scores are all set to 0  When a button is pressed the game copies the timer value into the score for that button  The second time the button is pressed the score value for that button will not be 0  We can use this to detect when a button has already been pressed, and reject subsequent presses Chapter 8.1: Reaction Timer Game16

17. Improved Flowchart  This flowchart shows the improved version of the algorithm  The extra test is performed when a button is detected  The score value is only updated if the score is zero  This flowchart shows the improved version of the algorithm  The extra test is performed when a button is detected  The score value is only updated if the score is zero Chapter 8.1: Reaction Timer Game17

18. Rejecting Extra Button Presses  This version of the program adds an extra test to the button detection  You can combine many conditions using the && operator  In this case the score is only changed if it is zero  This version of the program adds an extra test to the button detection  You can combine many conditions using the && operator  In this case the score is only changed if it is zero Chapter 8.1: Reaction Timer Game18 if (oldpad1.Buttons.A == ButtonState.Released && pad1.Buttons.A == ButtonState.Pressed && ascore1 == 0) { ascore1 = timer; } if (oldpad1.Buttons.A == ButtonState.Released && pad1.Buttons.A == ButtonState.Pressed && ascore1 == 0) { ascore1 = timer; }

19. 2. Improved Reaction Timer Chapter 8.1: Reaction Timer Game19  This version adds the extra condition so that only the first button press is registered  This could be the basis of a workable game  This version adds the extra condition so that only the first button press is registered  This could be the basis of a workable game

20. Summary  You can use the regular calls of Update as the basis of a timer by creating a variable that counts the number of times that Update has been called  You can trigger actions at a particular time by testing for particular values in the timer variable  Many games do this during their attract behavior  A flow diagram is a quick way of describing an algorithm  The initial version of an algorithm may not be the best one (we have seen this before)  You can use the regular calls of Update as the basis of a timer by creating a variable that counts the number of times that Update has been called  You can trigger actions at a particular time by testing for particular values in the timer variable  Many games do this during their attract behavior  A flow diagram is a quick way of describing an algorithm  The initial version of an algorithm may not be the best one (we have seen this before) Chapter 8.1: Reaction Timer Game20

21. True/False Revision Quiz  A flowchart is used to describe the variables used in a program.  Game players never cheat.  The regular calls made by XNA of the Update method can be used as the basis of timed behaviors.  The && logical operator can be used to combine a number of conditions.  A flowchart is used to describe the variables used in a program.  Game players never cheat.  The regular calls made by XNA of the Update method can be used as the basis of timed behaviors.  The && logical operator can be used to combine a number of conditions. Chapter 8.1: Reaction Timer Game21

22. True/False Revision Quiz  A flowchart is used to describe the variables used in a program.  Game players never cheat.  The regular calls made by XNA of the Update method can be used as the basis of timed behaviors.  The && logical operator can be used to combine a number of conditions.  A flowchart is used to describe the variables used in a program.  Game players never cheat.  The regular calls made by XNA of the Update method can be used as the basis of timed behaviors.  The && logical operator can be used to combine a number of conditions. Chapter 8.1: Reaction Timer Game22

23. True/False Revision Quiz  A flowchart is used to describe the variables used in a program.  Game players never cheat.  The regular calls made by XNA of the Update method can be used as the basis of timed behaviors.  The && logical operator can be used to combine a number of conditions.  A flowchart is used to describe the variables used in a program.  Game players never cheat.  The regular calls made by XNA of the Update method can be used as the basis of timed behaviors.  The && logical operator can be used to combine a number of conditions. Chapter 8.1: Reaction Timer Game23

24. True/False Revision Quiz  A flowchart is used to describe the variables used in a program.  Game players never cheat.  The regular calls made by XNA of the Update method can be used as the basis of timed behaviors.  The && logical operator can be used to combine a number of conditions.  A flowchart is used to describe the variables used in a program.  Game players never cheat.  The regular calls made by XNA of the Update method can be used as the basis of timed behaviors.  The && logical operator can be used to combine a number of conditions. Chapter 8.1: Reaction Timer Game24

25. True/False Revision Quiz  A flowchart is used to describe the variables used in a program.  Game players never cheat.  The regular calls made by XNA of the Update method can be used as the basis of timed behaviors.  The && logical operator can be used to combine a number of conditions.  A flowchart is used to describe the variables used in a program.  Game players never cheat.  The regular calls made by XNA of the Update method can be used as the basis of timed behaviors.  The && logical operator can be used to combine a number of conditions. Chapter 8.1: Reaction Timer Game25