Trail: 2D Graphics
Lesson: Advanced Topics in Java2D
Constructing Complex Shapes from Geometry Primitives
Home Page > 2D Graphics > Advanced Topics in Java2D

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 the Area class implements the Shape interface and supports the following boolean operations.

Venn diagram showing Union Union Venn diagram showing Subtraction Subtraction
Venn diagram showing Intersection Intersection Venn diagram showing Exclusive-or operation Exclusive-or (XOR)

Example: Areas

In this example Area objects construct a pear shape from several ellipses.


Note:  If you don't see the applet running, you need to install at least the Java SE Development Kit (JDK) 7 release.

Pear.java contains the complete code for this applet.

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();
...
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);

Problems with the examples? Try Compiling and Running the Examples: FAQs.
Complaints? Compliments? Suggestions? Give us your feedback.

Previous page: Controlling Rendering Quality
Next page: Supporting User Interaction