Chapter 2 Graphics Programming with C++ and the Dark GDK Library
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Transcript of Chapter 2 Graphics Programming with C++ and the Dark GDK Library
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Chapter 2Graphics Programming with C++ and
the Dark GDK Library
Starting Out with
Games & Graphics in C++
Tony Gaddis
Copyright © 2010 Pearson Addison-Wesley 1-2
2.1 Getting Your Feet Wet with C++ and the Dark GDK Library
Concept:
All C++ programs that use the Dark GDK library start out with the same code. The first step in learning to write a graphics program is to learn how to start a Dark GDK program in C++.
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2.1 Getting Your Feet Wet with C++ and the Dark GDK Library
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Minimum framework of a C++/Dark GDK program
Figure 2-6 Summary of the skeleton
program
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2.1 Getting Your Feet Wet with C++ and the Dark GDK Library
• Include directive – causes the contents of a file to be included in a program– DarkGDK.h contains the setup code
needed for the Dark GDK library to work correctly with our C++ programs
– We must include the DarkGDK.h file in every program that will use the Dark GDK library
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2.1 Getting Your Feet Wet with C++ and the Dark GDK Library
• Function – group of statements that collectively has a name
– Function named DarkGDK is required by any program that uses the Dark GDK library
–DarkGDK function contains the statements that will be executed when program runs
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2.1 Getting Your Feet Wet with C++ and the Dark GDK Library
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• C++ is a case-sensitive language, which means it regards uppercase letters as being entirely different than their lowercase counterparts
• The name of the function DarkGDK must be written with
– uppercase D– lowercase ark– uppercase GDK
• Pay attention to the case!– C++ does not see
• darkgdk the same as DarkGDK• VOID the same as void
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2.1 Getting Your Feet Wet with C++ and the Dark GDK Library
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• Function Call – causes the statements in a function to execute
• dbWaitKey – when this function is called, it causes the program to pause until a key is pressed on the keyboard
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2.1 Getting Your Feet Wet with C++ and the Dark GDK Library
• Comments are:– Short notes explaining how parts of a program
work– Not intended for the compiler– Intended for anyone who is reading the code
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Comments
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2.1 Getting Your Feet Wet with C++ and the Dark GDK Library
• Two types of comments:– Line comments
• begin with two forward slashes– // used to comment a single line
– Block comments• Begin with /* and end with */
– /* used to comment– multiple lines */
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Comments
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2.1 Getting Your Feet Wet with C++ and the Dark GDK Library
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Comments
• An example of a program that contains line comments:
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2.1 Getting Your Feet Wet with C++ and the Dark GDK Library
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Comments• An example of how block comments may
be used:
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2.1 Getting Your Feet Wet with C++ and the Dark GDK Library
• Use blank lines and indentations to create a sense of visual organization
• For example, one convention virtually all programmers follow is:– indenting statements inside a function
• Following conventions, such as indenting statements inside a function, is known as programming style
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Programming Style:
Making Your Code Easier to Read
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2.2 The Screen Coordinate System
Concept:
A system of X and Y coordinates is used to identify the locations of pixels in a window.
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2.2 The Screen Coordinate System
• The images that are displayed on a computer screen are made up of tiny dots called pixels
• The default Dark GDK window is 640 pixels wide and 480 pixels high
• It has a resolution of 640 by 480
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2.2 The Screen Coordinate System
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Figure 2-3 The width and height of the default window
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2.2 The Screen Coordinate System
• A screen coordinate system is used to identify the position of each pixel in the window.
• Each pixel has – X coordinate
• Identifies the horizontal position
And– Y coordinate
• identifies the vertical position
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2.2 The Screen Coordinate System
• Coordinates are written in the form (X, Y)– For example:
• Upper-left corner pixel coordinates are (0, 0)– X is 0– Y is 0
• The X coordinates increase from left to right• The Y coordinates increase from top to bottom
– This is different from the Cartesian coordinate system you learned about in mathematics
• Coordinate numbering begins at 0 in the upper-left corner– Lower-right corner pixel coordinates are (639, 479)
• X is 639• Y is 479
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2.2 The Screen Coordinate System
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Figure 2-4 various pixel locations in a 640 by 480 window
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2.2 The Screen Coordinate System
• The dbDot function draws a dot at a specific pixel location in the Dark GDK window.
• Here is the general format of how you call the dbDot function:
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dbDot(x, y);
Drawing Dots with the dbDot Function
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2.2 The Screen Coordinate System
• In the general format, – the x argument is the X coordinate– the y argument is the Y coordinate
• For example, the following statement draws a dot at the X coordinate 319 and the Y coordinate 239:
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Drawing Dots with the dbDot Function
dbDot(319, 239);
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2.2 The Screen Coordinate System
• The values that you write inside the function’s parentheses are called arguments
• Arguments are pieces of data that you send to a function when you call it
• When an argument is sent to a function, you are passing the argument to the function
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2.2 The Screen Coordinate System
• The dbWait function causes the program to wait for a specified amount of time before continuing
• Here is the general format of how you call the dbWait function:
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dbWait(time);
The dbWait Function
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2.2 The Screen Coordinate System
• The value that you provide for the time argument is the number of milliseconds you want the program to wait.– There are 1000 milliseconds in a second
• The following statement will cause the program to wait for 1 second:
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dbWait(1000);
The dbWait Function
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2.2 The Screen Coordinate System
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• Dark GDK function names start with the letters db• For example:
– dbDot– dbWait– dbWaitKey
• The Game Creators, the software company that created the Dark GDK library, have also created a programming language called Dark BASIC– Most Dark GDK functions are the C++ equivalents of
Dark BASIC commands• For this reason, Dark GDK function names start
with the letters db, meaning Dark BASIC
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2.3 Basic 2D Shapes
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Concept:
The Dark GDK library contains several functions for drawing basic 2D shapes.
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2.3 Basic 2D Shapes
• Objects that appear in 2D have only two dimensions:– Width– Height
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Figure 2-6 A two-
dimensional game
character
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2.3 Basic 2D Shapes
• The Dark GDK library provides several functions for drawing simple 2D shapes– Lines– Circles– Ellipses– Rectangles
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2.3 Basic 2D Shapes
• The dbLine function draws a line between two points in the Dark GDK window.
• Here is the general format of how you call the dbLine function:
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dbLine(x1, y1, x2, y2);
Drawing Lines: The dbLine Function
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2.3 Basic 2D Shapes
• You pass four arguments to the dbLine function– X1 and Y1 are the coordinates for the starting
point of the line– X2 and Y2 are the coordinates for the line’s
ending point
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Drawing Lines: The dbLine Function
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2.3 Basic 2D Shapes
• For example, the following statement draws a line between the points (80, 120) and (400, 520):
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Drawing Lines: The dbLine Function
dbLine(80, 120, 400, 520);
Figure 2-6 A line drawn from (80,
120) to (400, 520)
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2.3 Basic 2D Shapes
• The dbBox function draws a filled rectangle– Filled means it is filled with color
• Here is the general format of how you call the dbBox function:
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Drawing Rectangles: The dbBox Function
dbBox(x1, y1, x2, y2);
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2.3 Basic 2D Shapes
• You pass four arguments to the dbBox function– X1 and Y1 are the X and Y coordinates for the
rectangle’s upper-left corner– X2 and Y2 are the X and Y coordinates for the
rectangle’s lower-right corner
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Drawing Rectangles: The dbBox Function
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2.3 Basic 2D Shapes
• For example, look at the following statement:
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Drawing Rectangles: The dbBox Function
dbBox(100, 80, 540, 380);
Figure 2-12 A rectangle with corners at
(100, 80) and (540, 380)
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2.3 Basic 2D Shapes
• The dbCircle function draws a circle
• Here is the general format of how you call the dbCircle function:
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Drawing Circles: The dbCircle Function
dbCircle(x, y, radius);
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2.3 Basic 2D Shapes
• The x and y arguments are the coordinates of the circle’s center point
• The radius argument specifies the circle’s radius– The radius is the distance, in pixels, from the
center point to the outer edge
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Drawing Circles: The dbCircle Function
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2.3 Basic 2D Shapes
• Here is an example:
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Drawing Circles: The dbCircle Function
dbCircle(320, 240, 100);
Figure 2-16 A circle with its
center at (320, 240) and a
radius of 100
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2.3 Basic 2D Shapes
• The dbEllipse function draws an ellipse– an ellipse is an oval shape
• Here is the general format of how you call the dbEllipse function:
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Drawing Ellipses: The dbEllipse Function
dbEllipse(x, y, xrad, yrad);
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2.3 Basic 2D Shapes
• The x and y arguments are the coordinates of the ellipse’s center point
• The xrad argument specifies the ellipse’s radius along the X axis
• The yrad argument specifies the ellipse’s radius along the Y axis
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Drawing Ellipses: The dbEllipse Function
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2.3 Basic 2D Shapes
• Here is an example:
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Drawing Ellipses: The dbEllipse Function
Figure 2-18 An ellipse’s
center point, x-radius, and y-
radius
dbEllipse(320, 240, 140, 100);
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2.3 Basic 2D Shapes
• Any point that has– X coordinate from 0 through 639– Y coordinate from 0 through 479
• Is visible in the Dark GDK window
• You can use points that have coordinates outside these ranges but…– They are not visible in the window
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Drawing Outside the Dark GDK Window
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2.3 Basic 2D Shapes
• For example, the following statement draws a dot at the coordinates (800, 600)
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Drawing Outside the Dark GDK Window
dbDot(800, 600);
• But because that location is outside the Dark GDK window, it will not be visible
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2.3 Basic 2D Shapes
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Drawing Outside the Dark GDK Window
• Points that are above the top row of pixels in the window have a negative Y coordinate
• Points that are to the left of the leftmost column of pixels have a negative X coordinate
Figure 2-20 Negative coordinates
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2.3 Basic 2D Shapes
• The following statement draws a circle with its center point located at (-50, -20) and with a radius of 200
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Drawing Outside the Dark GDK Window
dbCircle(-50, -20, 200);
Figure 2-21 Circle drawn partially off-screen
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2.4 Displaying Text
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Concept:
You can use the dbPrint, dbText, or dbCenterText functions to display text in the Dark GDK window. You can use the dbSetWindowTitle function to display text in the window’s title bar.
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2.4 Displaying Text
• You can use these functions to display text in the Dark GDK Window– dbPrint– dbText– dbCenterText
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Displaying Text Inside the Dark GDK Window
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2.4 Displaying Text
• The dbPrint function displays a string of characters– String is a term used in programming to mean
“string of characters”
• Here is the general format of how you call the dbPrint function:
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Displaying Text Inside the Dark GDK Window
dbPrint(string);
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2.4 Displaying Text
• The string argument is the string you want to display• The string is printed as a line of output in the Dark GDK
window• If no argument is passed
– a blank line will be displayed• The first call to the dbPrint function
– output is printed at the top of the window, justified along the left side
• Each subsequent call to the dbPrint function– prints a line of output below the previous line of output.
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Displaying Text Inside the Dark GDK Window
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2.4 Displaying Text
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• The dbText function displays a string of characters at a specific location in the window
• Here is the general format of how you call the dbText function:
Displaying Text Inside the Dark GDK Window
dbText(x, y, string);
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2.4 Displaying Text
• The x and y arguments are a set of coordinates
• The string argument is the string that is to be displayed
• When the string is displayed– The upper-left corner of the first character will
be positioned at the X and Y coordinates
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Displaying Text Inside the Dark GDK Window
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2.4 Displaying Text
• For example, the following statement displays the string “Hello World” in the window
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Displaying Text Inside the Dark GDK Window
dbText(10, 10, “Hello World”);
Figure 2-23 Results of the
dbText function
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2.4 Displaying Text
• Text can be centered horizontally with the dbCenterText Function• Here is an example:
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Displaying Text Inside the Dark GDK Window
dbCenterText(319, 239, “Game Over”);
Figure 2-25 A string centered
just below the point at (319,
239)
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2.4 Displaying Text
• The dbSetWindowTitle function displays text in the window’s title bar
• Here is the general format of how you call the dbSetWindowTitle function:
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Displaying Text in the Window’s Title Bar
dbSetWindowTitle(string);
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2.5 The Program Development Cycle
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Concept:
When creating programs, programmers typically follow a process known as the program development cycle.
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2.5 The Program Development Cycle
• Design the Program• Write the Code• Correct Syntax Errors• Test the Program• Correct Logic Errors• Repeat until error free
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Figure 2-37 The program development cycle
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Chapter 2Graphics Programming with C++ and the
Dark GDK Library
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