Creating a graphics program

1
Creating a graphics program

• Color and Shapes

2
Import libraries

• import javax.swing. // for JFrame
• import java.awt. // for Color and Graphics

3
Program Framework

• public class myGrPgm extends JFrame
• // extending JFrame gives us
• // - windows
• // - paint
• // - use of Color
• // end class myGrPgm

4
grab a color

• public Color palette
• new Color ( 25, 120, 200 )
• // palette is a Color object
• // Color (red, green, blue )

note 25, 120, 200 is ocean blue
5
how colors are defined
6
a clarification

• Color boxColor Color.blue
• or
• Color boxColor new Color( )
• boxColor Color.blueobject t to box Color.

7
Color class in Computer Memory Space

• Color boxColor Color.blue

uses library directly!
JFrame library
Color.blue
Color.green
Color.red
Color.pink
8

• Color boxColor new Color( )
• boxColor Color.blue

Color class in Computer Memory Space
Color.blue
a copy!
Color.green
Color.red
Color.pink
ready for Color
Color.blue
9
add the usual main

• public static void main(String args )
• myGrPgm app new myGrPgm( )
• // causes a constructor to be run

10
so far

• import javax.swing. // for JFrame
• import java.awt. // for Color and
  Graphics
• public class myGrPgm extends JFrame
• public Color palette new Color ( 25,
  120, 200 )
• // real work gets done here
• public static void main(String args )
• myGrPgm app new myGrPgm( )
• // end class myGrPgm

11
a constructor

• // sets up a Frame
• public myGrPgm( )
• setSize( 400, 400 )
• setLocation( 20, 40 )
• setDefaultCloseOperation( EXIT_ON_CLOSE )
• setVisible( true )
• // uses JFrame methods, because WE are JFrame
• // i.e. this class were in is a JFrame child

12
graphics on a computer
X direction
( 0, 0 )
( 1024, 0 )
( ?, ? )
y direction
( 0, 768 )
( 1024, 768 )
13
a better constructor

• // sets up a Frame
• public myGrPgm( int width, int height)
• setSize( width, height )
• setLocation( 20, 40 )
• setDefaultCloseOperation( EXIT_ON_CLOSE )
• setVisible( true )
• // uses JFrame methods, because WE are JFrame
• // i.e. this class were in is a JFrame child

14
change main

• public static void main(String args )
• myGrPgm app new myGrPgm( 400, 400 )

supplied to constructor
15
so far

• import javax.swing. // for JFrame
• import java.awt. // for Color and
  Graphics
• public class myGrPgm extends JFrame
• public Color palette new Color ( 25,
  120, 200 )
• public myGrPgm( int width, int height )
• setSize( width, height )
• setLocation( 20, 40 )
• setDefaultCloseOperation( EXIT_ON_CLOSE )
• setVisible( true )
• public static void main(String args )
• myGrPgm app new myGrPgm( 400, 400
  )
• // end class myGrPgm

16
last method

• being a JFrame, means that we can USE JFrame
  methods like setLocation(
• being a JFrame, means that we can re-write
  methods that are IN JFrame for more power, like
  paint(

17
what is paint?

• a method in JFrame
• its a void method (returns nothing to the
  caller )
• called by the computer automatically
• that we re-write (override)
• that someone else wrote
• that uses a Graphics helper class
• that puts colors and shapes in a JFrame

18
Graphics helper class?

• look up the Graphics class on the Sun Java
  website
• It must be used by a paint method in a JFrame
  class
• it contains variables and methods of its own, to
  color and draw shapes

19
structure of a paint method

• public void paint( Graphics g )
• // g is the Graphics copy (object)
• // set a color
• g. setColor( pallette )
• // do something with the color
• // g.fillRect( x, y, width, height )
• g.fillRect( 50, 100, 200, 200 )

20
setting a color

• use our public color pallette
• or use a primary color
• g.setColor( Color.green )

21
helps to set the background

• // make width and height public, and static
• public static int winHeight 400
• public static int winWidth 400
• // use in paint, or wherever you need window
  size
• public void paint( Graphics g ) // set
  background g.setColor( Color.white )
  g.fillRect( 0, 0, winHeight, winWidth )
• g.setColor( palette )
• g.fillRect( 50, 100, 200, 200 )

22
static?

• whenever you decide something is unique, will
  never be anything with the same name anywhere in
  your program
• main is static
• any variable or method used by main must be static

23
use winHeight and winWidth

• public static void main( String args )
• myGrPgm app new myGrPgm( winHeight,
  winWidth )

24
demo

• see the myGrPrm example

25
Using Arrays to draw shapes

• int xValues 245, 245, 260, 260, 230, 230
• int yValues 250, 300, 300, 310, 310, 250
• g.setColor( Color.yellow )
• g.fillPolygon ( xValues, yValues, 6 )
• // connects the dots

26
Arrays are lists of numbers

• int xValues 245, 245, 260, 260, 230, 230
• xValue 0 is 245
• xValue 1 is 245
• xValue 2 is 260
• xValue 3 is 260
• xValue 4 is 230
• xValue 5 is 230

27
A way of organizing variables

• int myArray 41, 16, 55, 26, 30, 0
• myArray is a list of 6 ints
• The ints are indexed 0 thru 5
• myArray 3 is 26
• Example
• int x 4
• myArray x is ?