Java 2D API

1
Chapter 4

• Java 2D API

2
Drawing Basics (review)

• Upper left corner is (0,0)
• Y-coordinate increases as move down from upper
  left
• X-coordinate increases as move to the right
• A graphics context enables drawing on the
  screen.  The Graphics class manages a graphics
  context, controlling how information is drawn. 
  It includes methods for drawing, font
  manipulation, color manipulation etc.
• Graphics is an abstract class.  This contributes
  to portability.  For each platform, a Graphics
  subclass implements the drawing capabilities.
• Class Component is the superclass for many
  classes in java.awt. 
• Method paint of class Component is called when
  the contents should be painted, such as when
  first displayed, when window is resized, etc. 
• Method paint takes a Graphics reference as an
  argument (which allows a subclass to be passed
  in).  The actual reference is platform-specific. 
  
• paint should not be called directly!  Drawing
  graphics is an event-driven process.  Should
  invoke method repaint of class Component.  This
  requests a call to method update as soon as
  possible, to clear the Component's  background. 
  Method update then calls paint. 

3
Basics continued

• Class JComponent is the superclass for many
  classes in javax.swing.  The Swing mechanism
  calls method paintComponent of class JComponent. 
  As above, the developer should call repaint.
• Packages included in the Java 2D API
• java.awt.image deal with jpg, gif etc.
• java.awt.color Grayscale and RGB
• java.awt.font
• java.awt.geom 2D images like ellipse, line,
  point, etc.
• java.awt.print for printing
• java.awt.image.renderable allows images to be
  manipulated independent from rendering

4
Graphics 2D Classes
Shape
Polygon RectangularShape Rectangle Line2D
CubicCurve2D Area GeneralPath QuadCurve2D
Area methods add, subtract, intersect,
exclusiveOr Rectangle2D methods intersection,
union
Rectangle2D RoundRectangle2D Arc2D Ellipse2D

• Methods of Shape interface
• boolean contains(double x, double y)
• boolean contains(double x, double y, double w,
  double h)
• Rectangle getBounds()
• PathIterator getPathIterator(AffineTranform at)
• boolean intersects(double x, double y, double w,
  double h)

5
Graphics2D

• Class java.awt.Graphics2D enables drawing.  Need
  to cast the Graphics reference passed to paint to
  a Graphics2D.
• Java 2D can render three types of graphics
  primitives images, text and geometrical shapes.
  
• Seven Graphics2D state attributes determine how
  graphics primitives are rendered 
• clipping - defines the area in which rendering
  operations take effect.  Can be any geometrical
  shape.
• compositing - a set of blending rules that
  control how the pixels in a source image mix with
  the pixels in a destination image.
• font - text is rendered by drawing and filling
  glyphs.
• paint - determines colors, patterns, gradients
  for filling and outlining a shape.
• rendering hints - techniques can be specified to
  help optimize drawing.
• stroke - determines the outline of the shape to
  be drawn.
• transforms - ways to perform linear
  transformations.

6
Graphics2D - continued

• Interface Paint determines the color of a shape
  that is drawn.  It can be a predefined Color, a
  GradientPaint, SystemColor or TexturePaint.
• GradientPaint takes 7 arguments starting
  coordinate, starting Color, ending coordinate,
  ending Color, and whether it's cyclic (true) or
  acyclic (false).   The two coordinates determine
  the direction of the gradient.
• Method fill draws a filled shape. 

7
Graphics2D - continued

• Interface Stroke provides options for the outline
  of a shape.  BasicStroke provides constructors to
  set the line width, specify how the line ends
  (end caps CAP_BUTT, CAP_ROUND, CAP_SQUARE), how
  lines join together (line joins JOIN_BEVEL,
  JOIN_MITER, JOIN_ROUND) and optional dash
  attributes (determined by array of lengths)

8
Graphics2D - continued

• A BufferedImage describes an Image with an
  accessible buffer of image data.  It is comprised
  of a ColorModel and a Raster of image data. The
  first two parameters are the width and height in
  pixels, the third parameter determines whether
  the image will be in color or gray scale. 
  createGraphics creates a graphics2D that can be
  used for drawing on the BufferedImage (e.g., with
  fillRect, etc.).

9
Graphics2D - continued

• The TexturePaint object uses the image stored in
  its BufferedImage as the fill texture for a
  shape.  The second argument is the area from the
  BufferedImage that will be replicated. 
• Many shapes (such as Arc2D.Double) are drawn
  within a bounding rectangle.  Arc2D is determined
  by upper left, upper right, width, height, start
  angle in degrees, arc angle and a closing option
  (Arc2D.PIE, Arc2D.CHORD and Arc2D.OPEN).

10
Graphics2D - continued

• Shapes.java output

Rectangle2D
Arc2D
Gradient
Lines (Strokes)
BufferedImage
11
Transformations

• Not covered in our text
• AffineTransform can be applied to an individual
  shape or can be set for a graphics context and
  applied to all shapes.
• Allows you to rotate, translate, shear, and
  scale. createInverse can be used to get a
  transform to undo the transformation.

12
Graphics 2D - continued

• Graphics2D extends the Graphics class to provide
  more sophisticated control over geometry,
  coordinate transformations, color management, and
  text layout.
• Coordinates passed to a Graphics2D object are
  specified in device-independent coordinate system
  called User Space.  By default, when drawing to a
  screen or image, user space is the same as device
  space.
• The Graphics2D contains methods that allow you to
  modify the coordinate system. For example,
  translate moves the origin of the coordinate
  system.
• Every Graphics2D object is associated with a
  target that defines where rendering takes place.
  A GraphicsConfiguration object defines the
  characteristics of the rendering target, such as
  pixel format and resolution. The same rendering
  target is used throughout the life of a
  Graphics2D object.
• The Rendering Process can be broken down into
  four phases that are controlled by the Graphics2D
  rendering attributes. The renderer can optimize
  many of these steps, either by caching the
  results for future calls, by collapsing multiple
  virtual steps into a single operation, or by
  recognizing various attributes as common simple
  cases that can be eliminated by modifying other
  parts of the operation.

13
Graphics 2D - continued

• The steps are
• Determine what to render.
• Constrain the rendering operation to the current
  Clip.
• The Clip is specified by a Shape in user space
  and is controlled by the program using the
  various clip manipulation methods of Graphics and
  Graphics2D.
• This user clip is transformed into device space
  by the current Transform and combined with the
  device clip, which is defined by the visibility
  of windows and device extents.
• The combination of the user clip and device clip
  defines the composite clip, which determines the
  final clipping region. The user clip is not
  modified by the rendering system to reflect the
  resulting composite clip.
• Determine what colors to render.
• Apply the colors to the destination drawing
  surface using the current Composite attribute in
  the Graphics2D context.

14
Graphics2D - continued

• Class GeneralPath represents a shape constructed
  from lines and complex curves.
• The x- and y-coordinates are represented by two
  int arrays.
• The moveTo method specifies the first point
  (could be first two points in arrays, or could be
  shifted).
• The lineTo method draws a line to the next point
  in the star.
• The closePath method draws a line from the last
  point to the target of moveTo.
• The translate method moves the drawing origin.
• The rotate method rotates around an origin.

15
Graphics2D - continued

• Shapes2.java output

16
Exercises

• Update shapes to make figure
• Update shapes2 to display 4 triangles, change
  center

17
Image Processing

• Image processing is the manipulation of digital
  images by applying filters - mathematical
  operations that change images.
• Java 2D API shields developers from underlying
  mathematics
• Compression filters reduce a digital image's
  memory usage, for reduced storage size and faster
  transmission.  Used in HDTV, video phones and
  virtual reality.
• Measurement filters collect data from digital
  images.  They are used in image recognition and
  machine vision (e.g., for use with robots).
• Enhancement filters alter certain physical
  aspects of an image, often to restore corrupted
  images.  They can remove noise, sharpen edges and
  brighten colors. 

18
Image Processing

• Filters operate on BufferedImage objects. 
  Contains a Raster and a ColorModel. 
• A Raster is composed of a DataBuffer and a
  SampleModel.  The DataBuffer stores the raw data
  for an image.  The SampleModel organizes the data
  that determines a pixel's color components.  Each
  pixel is composed of samples, which are number
  values that represent the pixel's color
  components. 
• The SampleModel accesses the sample values in the
  DataBuffer for any given pixel. 
• The ColorModel is an interpreter for the Raster,
  converting the sample values for each pixel to
  the appropriate color. 
• The ColorModel's operation depends on the color
  scale of the image.  Two common color scales are
  grayscale and RGB.
• TYPE_INT_RGB uses three 8-bit segments to
  represent red, green and blue color components.
• Method createGraphics creates a Graphics2D, which
  can be used to draw into this BufferedImage.

19
Background
e.g., RGB has 3 bands per image one band has
all red, one has all blue, one has all red. 2
options all samples from a particular band can
be stored contiguously or all samples from a
single pixel can be stored contiguously.
Raster rectangular array of pixels
encapsulates dataBuffer (stores image data)
sampleMode (describes how pixels are stored in
dataBuffer) ExSinglePixelPackedSampleModel bit
masks 016711680, 165280, 2255 bitSizes
8
Raster includes height, width, minX, minY
(bounding rectangle) numBands, numDataElements
(per pixel)
20
Background cont.
image
colorModel
Raster
alphaMask, blueMask, greenMask, redMask (nBits,
maskOffsets etc.) is_sRGB colorSpace (type,
minVal, maxVal, etc.)
21
Image Processing
22
Image Processing - application

• Deitel example creates interface
  Java2DImageFilter with just one method,
  processImage.
• processImage is used to deliver data from an
  ImageProducer to an ImageConsumer.
• Create subclasses that implement various filters

23
Image Processing - application

• MediaTracker is a utility class to track the
  status of a number of media objects. Currently
  only images are supported.
• Use addImage to add an image.  Image can have a
  unique id that controls the priority order that
  images are fetched. 
• Constructor takes a reference to the component
  (e.g., a JPanel) using the tracker's services. 
• After images have been added, use waitForAll to
  start loading all images.  Could do waitForID
  with a parameter to wait for a particular image
  to load.

24
Image Processing - application

• Toolkit is the abstract superclass of all actual
  implementations of the Abstract Window Toolkit.
  Subclasses of Toolkit are used to bind the
  various components to particular native toolkit
  implementations.  Includes methods to create
  various components, such as buttons, checkboxes,
  images etc.
• createImage creates an image which decodes the
  image stored in the specified byte array.
• The data must be in some image format, such as
  GIF or JPEG, that is supported by this toolkit.
• The ImagePanel creates an image via the call
• Toolkit.getDefaultToolkit().createImage( imageURL
  )

25
ImageObserver

• Images may take awhile to load
• An object can register itself as an imageObserver
  and do a call such as getWidth.
• getWidth can be asynchronous. Will return the
  value once the file is loaded.
• Can also use null for ImageObserver parameter,
  indicating image is already loaded (thats done
  in Java2DExample).

26
Exercise
Sepia details // tint shadows darker if (red lt
60) red 0.9 green 0.9 blue 0.9
else if (red lt 190) // tint midtones light
brown by // reducing the blue blue 0.8 else
// tint highlights a light yellow // by reducing
the blue blue 0.9 Use BufferedImage methods
such as getRaster, getData, getCompatibleWritableR
aster etc. to access pixels. getWidth, getHeight
of image for loop indices.

• Update Java2DExample to include
• Sepia
• Grayscale (ColorConvertOp)
• Light Grayscale (RescaleOp, ColorConvertOp)
• Emboss (ConvolveOp)
• Flip Vertical (AffineTransform)
• Flip Horizontal (AffineTransform)