Graphics Object : Java Glossary

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Graphics Object
The Graphics class is abstract. It is just a collection of specifications for low-level drawing methods. The graphics object also contains a reference to the area of ram where the bit image will be constructed and it also contains the current clipping region. It is used for all types of painting including placing components, canvas drawing and laying out text.

The most often use the Graphics object is as a parameter to your paint, paintComponent or print method. You often cast the abstract Graphics to an actual Graphics2D object to access additional methods. Have a look at the Screws application to understand the basics of drawing.

Learning More

Round Polygons

Graphics has methods drawRoundRect and drawRoundRect to draw rectangles with rounded corners, but there are no built-in methods to do the same for arbitrary polygons, including triangles. Here is the code taken from the connectors downloadable package to do it:

view

The math behind that program may be a bit baffling. This diagram might help. The technique for computing the rounding uses elementary geometry, the Pythagorean theorem and elementary trigonometry.

Round corner math

Operations on the Entire Image

Oracle’s Javadoc on Graphics class : available:
Oracle’s Javadoc on Graphics2D class : available:
Oracle’s Javadoc on Graphics2D.setTransform : Beware, cascaded transforms are specified in reverse order. : available:
Oracle’s Javadoc on Graphics2D.addRenderingHints : available:
Oracle’s Javadoc on setClip class : Graphics.setClip replaces the clip region. clip merges/intersecs this clip with the existing clip region. : available:
Oracle’s Javadoc on Graphics2D.clip : setClip replaces the clip region. clip merges/intersecs this clip with the existing clip region. : available:
Oracle’s Javadoc on Graphics.create : Used to prevent permanently modifying your caller’s AffineTransform or clip region. : available:
Oracle’s Javadoc on Area class : Useful to create drop cloths — odd shaped clip regions. : available:
Oracle’s Javadoc on Composite class : Controls how new painting interacts with what is already painted. : available:
Oracle’s Javadoc on AlphaComposite class : Controls how new painting interacts with what is already painted. : available:

Lines

Oracle’s Javadoc on Graphics.drawLine : available:
Oracle’s Javadoc on BasicStroke class : available:

Rectangles

Oracle’s Javadoc on Graphics.clearRect : available:
Oracle’s Javadoc on Graphics.drawRect} : available:
Oracle’s Javadoc on Graphics.fillRect : available:
Oracle’s Javadoc on Rectangle class : available:
Oracle’s Javadoc on RoundRectangle2D.Double : available:

Text

Oracle’s Javadoc on Graphics.drawString : the Graphics. drawString method behaves differently from other drawing methods. Usually the x,y is the upper left corner. For drawString, it is the left end of the string baseline. : available:
Oracle’s Javadoc on FontRenderContext class : available:
Oracle’s Javadoc on LineMetrics class : available:

Ovals, Ellipse and Circles

Oracle’s Javadoc on Graphics.drawArc : Beware. Angles are measured in degrees counter clockwise from 3 o’clock. It does not take start and end angle but start angle and arc size in degrees (end-start). Angles may be negative. : available:
Oracle’s Javadoc on Graphics.fillArc : Beware. Angles are measured in degrees counter clockwise from 3 o’clock. It does not take start and end angle but start angle and arc size in degrees (end-start). Angles may be negative. : available:
Oracle’s Javadoc on Arc2D.Double : available:
Oracle’s Javadoc on Graphics.fillOval : available:
Oracle’s Javadoc on Ellipse2D.Double : This is an inner class to describe an ellipse or circle. Note that you specify the upper left corner of the enclosing rectangle, not the centre. : available:

Images

Oracle’s Javadoc on Graphics.drawImage : available:
Oracle’s Javadoc on BufferedImage class : available:
Oracle’s Javadoc on ImageIO class : Used to read and write png, jpg and gif files. : available:
Oracle’s Javadoc on BufferedImage.getRaster : Used to manipulate individual pixels. : available:

Arbitrary Shapes

Oracle’s Javadoc on Shape class : Interface you can pass to draw for drawing arbitrary shape outlines, solids and clip regions. Check out the long list of implementors. : available:
Oracle’s Javadoc on Path2D.Double : Path2D is available in Java 1.6+. It replaces the legacy GeneralPath. : available:
Oracle’s Javadoc on Graphics2D.draw(Shape) : Draw a line around an arbitrary shape. : available:
Oracle’s Javadoc on Graphics.drawPolygon : Draws outline of a closed polygon. : available:
Oracle’s Javadoc on Graphics.drawPolyline : Draws open polygon, series of line segments. : available:
Oracle’s Javadoc on Polygon class : available:

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