Displaying Graphics with Graphics2D

Constructing Complex Shapes from Geometry Primitives

Constructive Area Geometry (CAG) is the process of creating new geometric shapes by performing boolean operations on existing ones. In the Java 2D API, a special type of Shape called an Area supports boolean operations. You can construct an Area from any Shape .

Areas support the following boolean operations:

	Union
	Intersection
	Subtraction
	Exclusive OR (XOR)

Example: Areas

In the Pear example, Area objects are used to construct a pear shape from several different ellipses.

The leaves are each created by performing an intersection on two overlapping circles.

leaf = new Ellipse2D.Double();
...
leaf1 = new Area(leaf);
leaf2 = new Area(leaf);
...
leaf.setFrame(ew-16, eh-29, 15.0, 15.0);
leaf1 = new Area(leaf);
leaf.setFrame(ew-14, eh-47, 30.0, 30.0);
leaf2 = new Area(leaf); 
leaf1.intersect(leaf2);
g2.fill(leaf1);
...
leaf.setFrame(ew+1, eh-29, 15.0, 15.0);
leaf1 = new Area(leaf);
leaf2.intersect(leaf1);
g2.fill(leaf2);

Overlapping circles are also used to construct the stem through a subtraction operation.

stem = new Ellipse2D.Double();
...
st1 = new Area(stem);
st2 = new Area(stem);
...
leaf1 = new Area(leaf);
leaf2 = new Area(leaf);
st1 = new Area(stem);
st2 = new Area(stem);
stem.setFrame(ew, eh-42, 40.0, 40.0);
st1 = new Area(stem);
stem.setFrame(ew+3, eh-47, 50.0, 50.0);
st2 = new Area(stem);
st1.subtract(st2);
g2.fill(st1);

The body of the pear is constructed by performing a union operation on a circle and an oval:

circle = new Ellipse2D.Double();
oval = new Ellipse2D.Double();
circ = new Area(circle);
ov = new Area(oval);
...
circle.setFrame(ew-25, eh, 50.0, 50.0);
oval.setFrame(ew-19, eh-20, 40.0, 70.0);
circ = new Area(circle);
ov = new Area(oval);
circ.add(ov);
g2.fill(circ);

You can find the complete code for this program in Pear.java and an HTML file that includes the applet in Pear.html.

Displaying Graphics with Graphics2D