May 13, 1998 CS102-02 Lecture 7-2

The End of Graphics in Java

CS 102-02

Lecture 7-2

A picture's worth a thousand words

May 13, 1998 CS102-02 Lecture 7-2

Agenda

• Arcs Revisited

• Polygons

• Messing with the Screen

• Paint modes

• Java2D

May 13, 1998 CS102-02 Lecture 7-2

Arc de Triomphe• drawArc takes six arguments:

– The rectangle: int x, int y, int width, int height

• Center of the arc is the center of the rectangle whose origin is (x, y) and whose size is specified by the width and height arguments

– The angle at which to begin drawing the arc: int startAngle

– The size of the arc to draw in degrees: int arcAngle

May 13, 1998 CS102-02 Lecture 7-2

The Arc and The Rectangle

(x, y)heightwidth

- 60°

120° arcAngle

startAngle

May 13, 1998 CS102-02 Lecture 7-2

"Polly want a cracker?""No, polygon!"

• Polygon is just a set of vertices– Array of points {(x1, y1), (x2, y2) ... (xn,

yn)}

• Polygonal methods draw lines and closed figures– Specify either a polygon object, or– A set of points

May 13, 1998 CS102-02 Lecture 7-2

Draw Your Own Polygon

• Two versions of drawPolygondrawPolygon(int xPoints[], int yPoints[], int points)

drawPolygon(Polygon p)

• Polygons are always closed (the book is wrong)

• points <= array length– A logic error?

May 13, 1998 CS102-02 Lecture 7-2

Inside a Polygon

• Java draws and connects points in the order they're listed

• Sometimes you get interior points

May 13, 1998 CS102-02 Lecture 7-2

Building Polygon Objects

• Polygon classpublic Polygon(int xpoints[], int ypoints[], int npoints)

– Constructs and initializes a polygon from the specified parameters

May 13, 1998 CS102-02 Lecture 7-2

Fill a Polygon

• Filled polygons are just like regular polygons, but painted in the foreground colorfillPolygon(int xPoints[], int yPoints[], int points)

fillPolygon(Polygon p)

May 13, 1998 CS102-02 Lecture 7-2

Feeling Disconnected? Draw a Polyline

• Polylines are just like polygons, except– If first and last point are different, they

aren't automatically connecteddrawPolyline(int xPoints[], int yPoints[], int nPoints)

May 13, 1998 CS102-02 Lecture 7-2

Messin' with the Screen

• Copy one portion of a screen to another with copyArea()

• copyArea() needs to know two things– Area you want to copy (a rectangle)– How far to move the copy (dX and dY)

relative to the origin of the rectangular area

May 13, 1998 CS102-02 Lecture 7-2

Start With This...

30, 10

150

150

May 13, 1998 CS102-02 Lecture 7-2

Use copyArea()

copyArea(30, 10, 150, 150,

200, 60)

Rectangle to copy from

Move over dX, dY

May 13, 1998 CS102-02 Lecture 7-2

And Copy To This

30, 10

150

150

30+200, 10+60

May 13, 1998 CS102-02 Lecture 7-2

Painting a la Mode

• Pick a paint mode: overwrite or XOR

• Default as though setPaintMode() were called– When drawing, replace any color with

current foreground color

• Can also

setXORMode(Color xorColor)

May 13, 1998 CS102-02 Lecture 7-2

Paint and XOR Mode

May 13, 1998 CS102-02 Lecture 7-2

How XOR Mode Works• Drawing in XORMode with XORColor

– Pixels in the current color are changed to the specified color

– And vice versa.

• Colors other than those two colors are changed in an unpredictable but reversible manner– If the same figure is drawn twice, then all

pixels are restored to their original values

May 13, 1998 CS102-02 Lecture 7-2

The Code for the Picturepublic void paint(Graphics g) { // Draw in PaintMode g.setColor(Color.blue); g.fillPolygon(xPoints, yPoints, 4);

g.setColor(Color.red); g.fillOval(20, 80, 200, 100);

// Switch to XORMode with yellow g.setXORMode(Color.yellow); g.setColor(Color.blue); g.fillPolygon(xRightPoints, yPoints, 4);

g.setColor(Color.red); g.fillOval(220, 80, 200, 100);}

May 13, 1998 CS102-02 Lecture 7-2

Overlapping Over and Over

g.setColor(Color.red);// Now you see itg.fillOval(220, 80, 200, 100);// ... now you don'tg.fillOval(220, 80, 200, 100);// ... now you see it againg.fillOval(220, 80, 200, 100);

Book's explanation is a little simplistic

May 13, 1998 CS102-02 Lecture 7-2

Java2D

• Set of classes for advanced 2D graphics and imaging– Good for CAD/CAM

– Games

• Included in JDK 1.2 (currently in beta 3)

• Built in to java.awt.*– Inheritance in action

May 13, 1998 CS102-02 Lecture 7-2

What's in Java2D?

• Line art, text, and images in a single comprehensive model

• Support for image compositing and alpha channel images

• Classes to provide accurate color space definition and conversion

• Rich set of display-oriented imaging operators