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Chapter 9 Value-Returning Functions and Mouse Input

Chapter 9 Value-Returning Functions and Mouse Input. Starting Out with Games & Graphics in C++ Tony Gaddis. 9.1 Writing a Value-Returning Function. Concept:

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Chapter 9 Value-Returning Functions and Mouse Input

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  1. Chapter 9Value-Returning Functions and Mouse Input Starting Out with Games & Graphics in C++ Tony Gaddis

  2. 9.1 Writing a Value-Returning Function Concept: A value-returning function is a function that returns a value to the part of the program that called it. The Dark GDK provides various value-returning functions that you have already used. You can also write your own value-returning functions.

  3. 9.1 Writing a Value-Returning Function Figure 9-2 The random function returns a value Figure 9-1 A statement that calls the dbRND function • A value-returning function returns a value to the statement that called it • Can be used like any other value • Assigned to a variable • Displayed on the screen • Used in a mathematical expression • And so on

  4. 9.1 Writing a Value-Returning Function Writing Your Own Value-Returning Functions Making the Most of the Return Statement Simplified version returns an expression • You write a value-returning function in the same way you write a void function, with two exceptions: • You must specify a data type • You must have a return statement

  5. 9.1 Writing a Value-Returning Function Returning Boolean Values Boolean functions return the bool values true or false Used to test a condition Return either true or false to indicate whether or not the condition exists

  6. 9.2 Working with the Mouse Concept: The Dark GDK provides functions that your program can use to interact with the mouse.

  7. 9.2 Working with the Mouse Getting the Mouse Coordinates Figure 9-12 Example output of Program 9-6 You can call the dbMouseX and dbMouseY functions to get the current position of the mouse pointer

  8. 9.2 Working with the Mouse Showing, Hiding, and Positioning the Mouse • Mouse pointer is visible by default • You can hide the mouse pointer with the dbHideMouse function • Still active within the program’s window • Can still get position with dbMouseX and dbMouseY functions • You can show the mouse pointer with the dbShowMouse function • You can position the mouse anywhere in the program’s window, at any time, by calling the dbPositionMouse function, passing the X and Y coordinates as arguments

  9. 9.2 Working with the Mouse Detecting Button Clicks • You can use the dbMouseClick function to determine whether the user is pressing a mouse button • The dbMouseClick function can detect up to four buttons • Returns an integer value that indicates which, if any, of the mouse buttons is being pressed • 0 if none of the mouse buttons are being pressed • 1 if the left mouse button is being pressed • 2 if the right mouse button is being pressed • 4 if the third mouse button is being pressed • 8 if the fourth mouse button is being pressed

  10. 9.2 Working with the Mouse Processing Full Mouse Clicks • In some situations you only want to perform an action once per mouse click • This functionality is not provided by the Dark GDK, so we’ll have to write our own function • Determine whether or not the mouse button is being pressed • If so, get the mouse coordinates • Perform a loop that makes the program wait until the mouse button is released before continuing

  11. 9.2 Working with the Mouse Clicking Sprites Figure 9-15 A sprite’s upper-left and lower-right corner coordinates Clicking images with the mouse is a common technique used in games and graphics programs If we know the XY coordinates of the sprite’s upper-left and lower-right corners we can determine if the mouse is inside the sprite’s bounding rectangle

  12. 9.2 Working with the Mouse Creating a Custom Mouse Pointer • Create a sprite with the image you want to use for the mouse pointer • Hide the regular mouse pointer • In the game loop • Get mouse pointer’s location • Move sprite using mouse pointer’s coordinates

  13. 9.3 The Bug Zapper Game The Bug Zapper game displays an animated sprite of a bug The player zaps the bug by clicking it with the mouse After a bug is clicked, a new one appears at a random location on the screen The game will run for 10 seconds, then end Zap as many bugs as possible before time runs out When the game is over, a screen displays how many bugs were zapped

  14. 9.3 The Bug Zapper Game Figure 9-18 Screens from the Bug Zapper game

  15. Chapter 9Value-Returning Functions and Mouse Input QUESTIONS ?

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