java填充多边形,Java如何绘制和填充有孔的多边形

I am currently trying to draw and fill a Polygon which has a hole in it in Java. Normally this would not be a big problem, since I would draw the exterior ring and then draw the interior ring with the color of the background.

But the problem is, that the polygon is displayed above a image which should be "seen" through the hole.

I am writing the code in Java and am using JTS Topology Suite for my geometry data.

This is my current code, which just paints the border and fills the polygon with a color.

private void drawPolygon(com.vividsolutions.jts.geom.Polygon gpoly, Color color, Graphics2D g2d){

java.awt.Polygon poly = (java.awt.Polygon)gpoly;

for(Coordinate co : gpoly.getExteriorRing().getCoordinates() {

poly.addPoint(co.x, co.y);

}

g2d.setColor(col);

g2d.fill(poly);

g2d.setColor(Color.BLACK);

g2d.draw(poly);

}

Sadly java.awt.Polygon does not support Polygons with holes.

解决方案

Use the Polygon as the basis for an Area (e.g. called polygonShape).

Create an Ellipse2D for the 'hole', then establish an Area for it (ellipseShape).

Area polygonWithHole = polygonShape.subtract(ellipseShape);