Constructing Complex Shapes from Geometry Primitives从几何图元构造复杂形状

Constructive area geometry (CAG) is the process of creating new geometric shapes by performing boolean operations on existing ones.构造区域几何（CAG）是通过对现有几何图形执行布尔运算来创建新几何图形的过程。In the Java 2D API the Area class implements the Shape interface and supports the following boolean operations.在Java2D API中，Area类实现了Shape接口并支持以下布尔操作。

	Union并集		Subtraction减集
	Intersection交集		Exclusive-or排他或 (XOR)

Example: Areas示例：区域

In this example Area objects construct a pear shape from several ellipses.在本例中，区域对象从几个椭圆构造梨形。

Pear.java contains the complete code for this applet.包含此小程序的完整代码。

The leaves are each created by performing an intersection on two overlapping circles.每个叶子都是通过在两个重叠的圆上执行相交来创建的。

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.重叠圆也用于通过减法运算构造杆。

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.梨体是通过在一个圆和一个椭圆形上执行并集操作来构建的。

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);