Displaying Graphics with Graphics2D |
By changing the stroke and paint attributes in theGraphics2D
context before rendering, you can easily apply fancy line styles and fill patterns to graphics primitives.For example, to draw a dashed line, you create an appropriate
Stroke
object and callsetStroke
to add it to theGraphics2D
context before you render the line. Similarly, to apply a gradient fill to aShape
, you create aGradientPaint
object and add it to theGraphics2D
context by callingsetPaint
before rendering theShape
.The
ShapesDemo2D
applet introduced in the overview demonstrates how you can render basic geometries using theGraphics2D
draw
andfill
methods. Each of the shapes is constructed from one of the geometries and then rendered throughGraphics2D
. TherectHeight
andrectWidth
variables define the dimensions of the space where each shape is drawn in, in pixels. The x and y variables change for each shape so that they are drawn in a grid formation:
// draw Line2D.Double g2.draw(new Line2D.Double(x, y+rectHeight-1, x + rectWidth, y)); // draw Rectangle2D.Double g2.setStroke(stroke); g2.draw(new Rectangle2D.Double(x, y, rectWidth, rectHeight)); // draw RoundRectangle2D.Double g2.setStroke(dashed); g2.draw(new RoundRectangle2D.Double(x, y, rectWidth, rectHeight, 10, 10)); // draw Arc2D.Double g2.setStroke(wideStroke); g2.draw(new Arc2D.Double(x, y, rectWidth, rectHeight, 90, 135, Arc2D.OPEN)); // draw Ellipse2D.Double g2.setStroke(stroke); g2.draw(new Ellipse2D.Double(x, y, rectWidth, rectHeight)); // draw GeneralPath (polygon) int x1Points[] = {x, x+rectWidth, x, x+rectWidth}; int y1Points[] = {y, y+rectHeight, y+rectHeight, y}; GeneralPath polygon = new GeneralPath(GeneralPath.WIND_EVEN_ODD, x1Points.length); polygon.moveTo(x1Points[0], y1Points[0]); for (int index = 1; index < x1Points.length; index++) { polygon.lineTo(x1Points[index], y1Points[index]); }; polygon.closePath(); g2.draw(polygon); // draw GeneralPath (polyline) int x2Points[] = {x, x+rectWidth, x, x+rectWidth}; int y2Points[] = {y, y+rectHeight, y+rectHeight, y}; GeneralPath polyline = new GeneralPath(GeneralPath.WIND_EVEN_ODD, x2Points.length); polyline.moveTo (x2Points[0], y2Points[0]); for (int index = 1; index < x2Points.length; index++) { polyline.lineTo(x2Points[index], y2Points[index]); }; g2.draw(polyline); // fill Rectangle2D.Double (red) g2.setPaint(red); g2.fill(new Rectangle2D.Double(x, y, rectWidth, rectHeight)); // fill RoundRectangle2D.Double g2.setPaint(redtowhite); g2.fill(new RoundRectangle2D.Double(x, y, rectWidth, rectHeight, 10, 10)); // fill Arc2D g2.setPaint(red); g2.fill(new Arc2D.Double(x, y, rectWidth, rectHeight, 90, 135, Arc2D.OPEN)); // fill Ellipse2D.Double g2.setPaint(redtowhite); g2.fill (new Ellipse2D.Double(x, y, rectWidth, rectHeight)); // fill and stroke GeneralPath int x3Points[] = {x, x+rectWidth, x, x+rectWidth}; int y3Points[] = {y, y+rectHeight, y+rectHeight, y}; GeneralPath filledPolygon = new GeneralPath(GeneralPath.WIND_EVEN_ODD, x3Points.length); filledPolygon.moveTo(x3Points[0], y3Points[0]); for (int index = 1; index < x3Points.length; index++) { filledPolygon.lineTo(x3Points[index], y3Points[index]); }; filledPolygon.closePath(); g2.setPaint(red); g2.fill(filledPolygon);Note that this example uses the double-precision implementations of the geometries classes. Where applicable, float and double precision implementations of each of the geometries are provided as inner classes.
You can find the complete code for this example in
ShapesDemo2D.java
and an HTML file that includes the applet inShapesDemo2D.html
.Defining Fancy Line Styles and Fill Patterns
You probably noticed that in the previous example, some of the shapes have thicker outline or are filled with a two-color gradient. Using the Java 2DStroke
andPaint
classes, you can easily define fancy line styles and fill patterns.Line Styles
Line styles are defined by the stroke attribute in the
Graphics2D
rendering context. To set the stroke attribute, you create aBasicStroke
object and pass it into theGraphics2D
setStroke
method.A
BasicStroke
object holds information about the line width, join style, endcap style, and dash style. This information is used when aShape
is rendered with thedraw
method.The line width is the thickness of the line measured perpendicular to its trajectory. The line width is specified as a float value in user coordinate units, which are roughly equivalent to 1/72 of an inch.
The join style is the decoration that is applied where two line segments meet.
BasicStroke
supports three join styles:
JOIN_BEVEL JOIN_MITER JOIN_ROUND The endcap style is the decoration that is applied where a line segment ends.
BasicStroke
supports three endcap styles:The dash style defines the pattern of opaque and transparent sections applied along the length of the line. The dash style is defined by a dash array and a dash phase. The dash array defines the dash pattern--alternating elements in the array represent the dash length and the length of the space between dashes in user coordinate units. Element 0 represents the first dash, element 1 represents the first space, and so on. The dash phase is an offset into the dash pattern, also specified in user coordinate units. It indicates what part of the dash pattern is applied to the beginning of the line.
CAP_BUTT CAP_ROUND CAP_SQUARE Fill Patterns
Fill patterns are defined by the paint attribute in the
Graphics2D
rendering context. To set the paint attribute, you create an instance of an object that implements thePaint
interface and pass it into theGraphics2D
setPaint
method.Three classes implement the
Paint
interface:Color
,GradientPaint
, andTexturePaint
.GradientPaint
andTexturePaint
are new in JDK 1.2.To create a
The pattern for aGradientPaint
, you specify a beginning position and color, and an ending position and color. The gradient changes proportionally from one color to the other along the line connecting the two positions.TexturePaint
is defined by aBufferedImage
. To create aTexturePaint
, you specify the image that contains the pattern and a rectangle that is used to replicate and anchor the pattern:Example: StrokeAndFill
The
How rendering is performed depends on which rendering option is selected:StrokeAndFill
program allows the user to select a graphics primitive, line style, and paint style and then either stroke the object's outline, fill it with the selected paint, or stroke the object in black and then fill it with the selected paint.
- When the user selects stroke ,
Graphics2D.draw
is called to perform the rendering. If text is selected as the primitive, the glyph outlines are retrieved and then rendered with thedraw
method.- When the user selects fill ,
Graphics2D.fill
orGraphics2D.drawString
is called to perform the rendering.- When the user selects stroke and fill ,
fill
ordrawString
is called to fill theShape
and thendraw
is called to stroke its outline.
Note: To both fill and stroke a graphics primitive, you need to make two separate method calls:fill
ordrawString
to fill its interior anddraw
to stroke its outline.
The three line styles used in this example--thin, thick, and dashed--are instances of
BasicStroke
:The dash style in this example has 10 unit dashes alternating with 10 unit spaces. The beginning of the dash pattern is applied to the beginning of the line--the dash phase is set to 0.0.// Sets the Stroke. ... case 0 : g2.setStroke(new BasicStroke(3.0f)); break; case 1 : g2.setStroke(new BasicStroke(8.0f)); break; case 2 : float dash[] = {10.0f}; g2.setStroke(new BasicStroke(3.0f, BasicStroke.CAP_BUTT, BasicStroke.JOIN_MITER, 10.0f, dash, 0.0f)); break;Three paint styles are used in this example--solid, gradient, and polka. The solid color paint style is an instance of
Color
, the gradient is an instance ofGradientPaint
, and the pattern is an instance ofTexturePaint
:Here's the code for the// Sets the Paint. ... case 0 : g2.setPaint(Color.blue); break; case 1 : g2.setPaint(new GradientPaint(0, 0, Color.lightGray, w-250, h, Color.blue, false)); break; case 2 : BufferedImage bi = new BufferedImage(5, 5, BufferedImage.TYPE_INT_RGB); Graphics2D big = bi.createGraphics(); big.setColor(Color.blue); big.fillRect(0, 0, 5, 5); big.setColor(Color.lightGray); big.fillOval(0, 0, 5, 5); Rectangle r = new Rectangle(0,0,5,5); g2.setPaint(new TexturePaint(bi, r)); break;StrokeAndFill.java
program and an HTML file that includes the appletStrokeAndFill.html
.
Displaying Graphics with Graphics2D