JDK and AWT

6.1 RANDERING
The original JDK 1.0 had a very simple mechanism for drawing shapes. You
select color and paint mode, and call methods of the Graphics class such as
drawRect or fillOval.
The Java 2D API supports many more options.
 You can easily produce a wide variety of shapes.
 You have control over the stroke, the pen that traces shape boundaries.
 You can fill shapes with solid colors, varying hues, and repeating
patterns.
 You can use transformations to move, scale, rotate, or stretch shapes.
 You can clip shapes to restrict them to arbitrary areas.
 You can select composition rules to describe how to combine the pixels of
a new shape with existing pixels.
 You can give rendering hints to make trade-offs between speed and
drawing quality.
To draw a shape, you go through the following steps:
1. Obtain an object of the Graphics2D class. This class is a subclass of the
Graphics class. If you use a version of the JDK that is enabled for Java 2D
technology, methods such as paint and paintComponent automatically
receive an object of the Graphics2D class. Simply use a cast, as follows:
public void paintComponent(Graphics g)
{
Graphics2D g2 = (Graphics2D)g;
. . .
}
2. Use the setRenderingHints method to set rendering hints: trade-offs between
speed and drawing quality.
RenderingHints hints = . . .;
g2.setRenderingHints(hints);
3. Use the setStroke method to set the stroke. The stroke is used to draw the
outline of the shape. You can select the thickness and choose among solid
and dotted lines.
Stroke stroke = . . .;
g2.setStroke(stroke);
4. Use the setPaint method to set the paint. The paint is used to fill areas such
as the stroke path or the interior of a shape. You can create solid color paint,
paint with changing hues, or tiled fill patterns.
Paint paint = . . .;

g2.setPaint(paint);
5. Use the setClip method to set the clipping region.
Shape clip = . . .;
g2.clip(clip);
6. Use the setTransform method to set a transformation from user space to
device space. You use transformations if it is easier for you to define your
shapes in a custom coordinate system than by using pixel coordinates.
AffineTransform transform = . . .;
g2.transform(transform);
7. Use the setComposite method to set a composition rule that describes how to
combine the new pixels with the existing pixels.
Composite composite = . . .;
g2.setComposite(composite);
8. Create a shape. The Java 2D API supplies many shape objects and methods
to combine shapes.
Shape shape = . . .;
9. Draw or fill the shape. If you draw the shape, its outline is stroked. If you fill
the shape, the interior is painted.
g2.draw(shape);
g2.fill(shape);
The various set methods simply set the state of the 2D graphics context. They don't
cause any drawing. Similarly, when you construct Shape objects, no drawing takes
place. A shape is only rendered when you call draw() or fill(). At that time, the
new shape is computed in a rendering pipeline.
java.awt.Graphics2D package contains two methods:
a) void draw(Shape s) – draws the outline of the given shape.
b) void fill(Shape s) – fills the interior of the given shape.
In the rendering pipeline, the following steps take place to render a shape:
1) The path of the shape is stroked.
2) The shape is transformed.

3) The shape is clipped. If there is no intersection b/w the shape & the
clipping area, then the process stops.
4) The remainder of the shape after clipping is filled.
5) The pixels of the filled shape are composed with the existing pixels.
6.2 SHAPES
Here are some of the methods in the Graphics class to draw shapes:
drawLine
drawRectangle
drawRoundRect
draw3DRect
drawPolygon
drawPolyline
drawOval
drawArc
There are also corresponding fill methods. These methods have been in the
Graphics class ever since JDK 1.0. The Java 2D API uses a completely
different, object-oriented approach. Instead of methods, there are classes:
Line2D
Rectangle2D
RoundRectangle2D
Ellipse2D
Arc2D
QuadCurve2D
CubicCurve2D
GeneralPath
These classes all implement the Shape interface.
Finally, there is a Point2D class that describes a point with an x- and a y-
coordinate. Points are useful to define shapes, but they aren't themselves
shapes.
To draw a shape, you first create an object of a class that implements the
Shape interface and then call the draw method of the Graphics2D class.

Each of the classes whose name ends in "2D" has two subclasses for specifying
coordinates as float or double quantities.
Internally all graphics classes use float coordinates because float numbers use
less storage space, but java programming language makes it a bit more tedious
to manipulate float numbers.
For this reason most methods of the graphics classes use double parameters &
return values.
Only when constructing a 2D object you must choose between a constructor
with float or double coordinates.
For ex:
Rectangle2D floatRect=new
Rectangle2D.Float(5F,10F,7.5F,15F);
Rectangle2D doubleRect=new
Rectangle2D.Double(5,10,7.5,15);
6.2.1 2D SHAPES CLASSES
For the RoundRectangle2D shape, you specify the top left corner, width &
height & the x & y dimensions of the corner area that should be rounded.
RoundRectangle2D r = new
RoundRectangle2D.Double(150,200,100,50,20,20);
here w=150, h=200, x=100, y=50, r=20.
The code above, produces a rounded rectangle with circles of radius 20 at each
of the corners.
The Java 2D API supplies two additional classes:
Quadratic & cubic curves.
Quadratic & cubic curves are specified by two end points & one or two control
points. Moving the control points changes the shape of the curves.
To construct quadratic & cubic curves, you give the coordinates of the end
points & the control points.
For Ex:
Quadcurve2d q =new QuadCurve2d.Double(startX, startY, controlX, controlY,
endX, endY );
CubicCurve2D c = new CubicCurve2D.Double(startX, startY,control1X,
control1Y, control2X,control2Y endX, endY);

A quadratic curve A cubic curve
Quadratic curves are not very flexible & they are not commonly used, whereas
cubic curves are common.
You can build arbitrary sequences of line segments, quadratic curves & cubic
curves & store them in a GeneralPath object. You specify the first coordinate of
the path with the moveTo method. GeneralPath class describes paths that are
made up from lines, quadratic & cubic curves.
For Ex:
GeneralPath path =new GeneralPath();
path.moveTo(10, 20);
You then extend the path by calling one of the methods lineTo, quadTo or
curveTo. These methods extend the path by a line, a quadratic curve, or a
cubic curve.
To call lineTo, supply the endpoint.
For Ex:
Path.lineTo(20, 30);
6.3 AREAS
However, occasionally, it is easier to describe a shape by composing it from
areas, such as rectangles, polygons, or ellipses. The Java 2D API supports four
constructive area geometry operations that combine two areas to a new area:
 add— The combined area contains all points that are in the first or the
second area.

 subtract— The combined area contains all points that are in the first but
not the second area.
 intersect— The combined area contains all points that are in the first
and the second area.
 exclusiveOr— The combined area contains all points that are in either
the first or the second area, but not in both.
To construct a complex area, you start out with a default area object.
Area a = new Area();
Then, you combine the area with any shape:
a.add(new Rectangle2D.Double(. . .));
a.subtract(path);
. . .
The Area class implements the Shape interface. You can stroke the boundary of
the area with the draw method or paint the interior with the fill method of the
Graphics2D class.

6.4 STROKE
The draw operation of the Graphics2D class draws the boundary of a shape by
using the currently selected stroke. By default, the stroke is a solid line that is
one pixel wide. You can select a different stroke by calling the setStroke
method. You supply an object of a class that implements the Stroke interface.
The Java 2D API defines only one such class, called BasicStroke.
You can construct strokes of arbitrary thickness. For example, here is how you
draw lines that are 10 pixels wide.
g2.setStroke(new BasicStroke(10.0F));
g2.draw(new Line2D.Double(. . .));
When a stroke is more than a pixel thick, then the end of the stroke can have
different styles. These are called end cap styles. There are three choices:

 A butt cap simply ends the stroke at its end point.
 A round cap adds a half-circle to the end of the stroke.
 A square cap adds a half-square to the end of the stroke.
When two thick strokes meet, there are three choices for the join style:

 A bevel join joins the strokes with a straight line that is perpendicular to
the bisector of the angle between the two strokes.
 A round join extends each stroke to have a round cap.
 A miter join extends both strokes by adding a "spike."
The miter join is not suitable for lines that meet at small angles. If two lines
join with an angle that is less than the miter limit, then a bevel join is used
instead. That usage prevents extremely long spikes. By default, the miter limit
is ten degrees.
These choices can be specified in the BasicStroke constructor, for example:
g2.setStroke(new BasicStroke(10.0F, BasicStroke.CAP_ROUND,
BasicStroke.JOIN_ROUND));
g2.setStroke(new BasicStroke(10.0F, BasicStroke.CAP_BUTT,
BasicStroke.JOIN_MITER, 15.0F /* miter limit */));
Finally, one can specify dashed lines by setting a dash pattern.
The dash pattern is a float[ ] array of numbers that contains the lengths of the
―on‖ & ― off― strokes.
The dash pattern & a dash phase are specified when constructing the
BasicStroke. The dash phase indicates where in the dash pattern each line
should start.
For Ex:
float[ ] dashPattern= {10,10,10,10,10, 10, 30, 10 ,30 …..};
g2.setStroke(new
BasicStroke(10.0F,BasicStroke.CAP_BUTT,basicStroke.JOIN_MITER,
10.0F));
6.5
When you fill a shape, its inside is covered with paint.
Use the setPaint() method to set the paint style to an object with a class that
implements the Paint interface.
The java 2D API provides three such classes:

a) Color class – To fill shapes with a solid color, simply call setPaint
with a color object, such as:
g2.setPaint(Color.red);
b) GradientPaint class – It varies colors by interpolating b/w two
given colors values. u construct a GradientPaint object by specifying
two points & the colors u want at these two points, such as:
g2.setPaint(new GradientPaint(p1,color.red, p2, color.pink));
Colors are interpolated along the line joining the two points. Colors
are constant along lines that are perpendicular to that joining line.
c) TexturePaint class – It fills an area with repetitions of an image. To
construct a TexturePaint object, you specify a BufferedImage & an
anchor rectangle. The anchor rectangle is extended indefinitely in x &
y directions to tile the entire coordinate plane. The image is scaled to
fit into the anchor & then replicated into each tile.

You create a BufferedImage object by giving the image size & image type. The
most common image type is TYPE_INT_ARGB, in which each pixel is specified
by an integer that describes the alpha or red, green & blue values.
For Ex:
BufferedImage bufferedImage = new BufferedImage(width,
height, BufferedImage.TYPE_INT_ARGB);
You then obtain a graphics context to draw into the buffered image:
Graphics 2D g2 = bufferedImage.createGraphics();
Any drawing operations on g2 now fill the buffered image with pixels. Now you
can create your TexturePaint object:
g2.setPaint(new TexturePaint( bufferedImage, anchorRectangle));

JDK and AWT

More Related Content

What's hot (20)

Similar to JDK and AWT (20)

More from Thesis Scientist Private Limited (20)

Recently uploaded (20)

JDK and AWT