Coordinate systems Colors Fonts Drawing shapes Graphics2D … · • Coordinate systems • Colors • Fonts • Drawing shapes ... Graphics in java dr. Amal Khalifa, 2014 7

Programming Seminar

@12:30 – 13:30 pm on Wednesday 9/4/2014

Location : 2.505.01

• Coordinate systems

• Colors

• Fonts

• Drawing shapes

• Graphics2D API

Agenda

By: dr. Amal Khalifa

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Painting components

Every component is responsible for drawing itself.

If you want to use a standard component, you only

have to add it to your applet or frame.

You don’t have to worry about painting it on the screen.

That will happen automatically, since it already knows

how to draw itself.

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dr. Amal Khalifa, 2014

Painting components


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Class JComponent (package javax.swing)

contains a paintComponent(Graphics g)

for drawing graphics.

Not called directly; called only by the system when a

lightweight Swing component needs to be repainted.

Use the component’s repaint() method instead.

repaint() method returns immediately, without doing any

painting itself.

Graphics Objects

A graphics context enables drawing on the screen.

To do any drawing at all in JAVA, you need an

object belonging to the class

java.awt.Graphics

manages a graphics context and draws pixels on the

screen

Instance methods are provided in this class for drawing

shapes, text, and images.

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Graphics Contexts


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To create a drawing surface:

define a subclass of JPanel

provide a custom paintComponent(Graphics g)method.

the paintComponentmethod must be smart enough to

correctly redraw the component at any time A program should store state information in its instance variables decide what to draw.

When the program wants to change the content

of the component change the values of the relevant variables and call repaint().

•a scheme for identifying every point on the screen.

• x-coordinates from left to right.

• y-coordinates from top to bottom.

Java coordinate system 6

Graphics in java


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Colors

JAVA is designed to work with the RGB color system.

An RGB color is specified by three numbers that give the level of red, green, and blue, respectively, in the color.

A color in JAVA is an object of the class, java.awt.Color.

Color class defines several named constants representing common colors

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Color constants 9


Color-related graphics methods 10


JColorChooser Dialog


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Package javax.swing provides the JColorChooser GUI component that enables application users to select colors.

static method showDialog

creates a JColorChooser object,

attaches it to a dialog box

displays the dialog.

Returns the selected Color object, or null if the user presses Cancel or closes the dialog without pressing OK.

Three arguments—a reference to its parent Component, a String to display in the title bar of the dialog and the initial selected Color for the dialog.

Example


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Fonts

A font represents a particular size and style of text.

The available font names are system dependent, but

you can always use the following four strings as font

names: “Serif”, “SansSerif”, “Monospaced”, and

“Dialog”.

Example: Font plainFont = new Font("Serif", Font.PLAIN, 12);

Font bigBoldFont = new Font("Sans Serif", Font.BOLD,

24);

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dr. Amal Khalifa, 2014 14

Drawing Shapes


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Java 2D API

The Java 2D API provides advanced two-dimensional graphics capabilities for programmers who require detailed and complex graphical manipulations.

For an overview, see the Java 2D demo visit download.oracle.com/javase/6/docs/technotes/guides/2d/

Drawing with the Java 2D API is accomplished with a Graphics2D reference (package java.awt).

To access Graphics2D capabilities, we must cast the Graphics reference (g) passed to paintComponent into a Graphics2D reference with a statement such as

Graphics2D g2d = ( Graphics2D ) g;

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http://download.oracle.com/javase/6/docs/technotes/guides/2d/









Example


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Class GradientPaint helps draw a shape in gradually

changing.

Graphics2D method fill draws a filled Shape

object—an object that implements interface Shape

(package java.awt)

method setStroke sets the characteristics of the shape’s border.

Class GeneralPath


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General path—constructed from straight lines and complex curves (package java.awt.geom).

Methods: moveTo moves to the specified point.

lineTo draws a line from the current point to the specified point.

closePath draws a line from the last point to the point specified in the last call to moveTo.

Graphics2D method translate moves the drawing origin to the specified location.

Graphics2D method rotate rotates the next displayed shape.

The argument specifies the rotation angle in radians (with 360° = 2p radians).

Thank you for attending!! 24


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Coordinate systems Colors Fonts Drawing shapes Graphics2D … · • Coordinate systems • Colors • Fonts • Drawing shapes ... Graphics in java dr. Amal Khalifa, 2014 7