java – 这个奇怪的区域减法问题是什么原因造成的？
作者：互联网
当我编写一个碰撞检测算法时,我已经提出了这个问题.这是一种奇怪的东西,超出了我的理解范围.
这里的问题是,如果在我的算法中,在函数tryMove()中呈现,我将potentialArea添加到moveLineArea并且我在减去所有单位占用的区域后检测spaceTestArea(从moveLineArea创建)中的变化,我有与一个甚至不接近x = 280,y = 120的单位的碰撞,其中移动单位在x = 1880,y = 120,并且它移动到x = 1914,y = 126.
我想知道这个问题可能是什么原因以及为了将来避免它该怎么做.
我必须说我有一个临时解决方案(tryMove2()),但请不要让它影响你的想法,即我不喜欢这个解决方案,我坚信第一个解决方案(tryMove())应该工作,它一定是我谁忘记了什么.
请参阅下面显示问题的代码.
import java.awt.Point;
import java.awt.Polygon;
import java.awt.geom.Area;
import java.awt.geom.Ellipse2D;
import java.util.ArrayList;
import java.util.List;
/**
* Test showing some unexpected and weird behaviour of area subtraction.
* @author Konrad Borowiecki
*/
public class TestTryMove {
private static final List<Point> unitCenterPoints = new ArrayList<Point>();
static{
unitCenterPoints.add(new Point(1720, 120));
unitCenterPoints.add(new Point(1880, 120));
unitCenterPoints.add(new Point(1800, 200));
unitCenterPoints.add(new Point(1720, 280));
unitCenterPoints.add(new Point(1880, 280));
unitCenterPoints.add(new Point(120, 120));
unitCenterPoints.add(new Point(280, 120));
unitCenterPoints.add(new Point(200, 200));
unitCenterPoints.add(new Point(120, 280));
unitCenterPoints.add(new Point(280, 280));
unitCenterPoints.add(new Point(120, 1720));
unitCenterPoints.add(new Point(280, 1720));
unitCenterPoints.add(new Point(200, 1800));
unitCenterPoints.add(new Point(120, 1880));
unitCenterPoints.add(new Point(280, 1880));
}
public static void main(String[] args) {
int[] xpointsOK = new int[]{1876, 1884, 1918, 1910};//for Move OK
int[] ypointsOK = new int[]{139, 101, 108, 146};//for Move OK
Polygon lineOK = new Polygon(xpointsOK, ypointsOK, xpointsOK.length);
int[] xpointsFAIL = new int[]{1877, 1883, 1917, 1911};//for problem no move
int[] ypointsFAIL = new int[]{139, 101, 107, 145};//for problem no move
Polygon lineFAIL = new Polygon(xpointsFAIL, ypointsFAIL, xpointsFAIL.length);
Point endPointCPOK = new Point(1914, 127);//Move OK
Point endPointCPFAIL = new Point(1914, 126);//problem no move
//where in both cases it should be move OK
System.out.println("******TEST for method tryMove()******");
System.out.println("TEST 1: this will FAIL");
System.out.println("Result="+tryMove(endPointCPFAIL, lineFAIL));
System.out.println("\nTEST 2: this will be OK");
System.out.println("Result="+tryMove(endPointCPOK, lineOK));
System.out.println("******TEST for method tryMove2()******");
System.out.println("TEST 1: this will be OK");
System.out.println("Result="+tryMove2(endPointCPFAIL, lineFAIL));
System.out.println("\nTEST 2: this will be OK");
System.out.println("Result="+tryMove2(endPointCPOK, lineOK));
}
/**
* Tests if a unit represented by point of index 1 in the list of
* unitCenterPoints (i.e. [1880, 120]) can make a move to the given endPointCP.
* (Please notice we are ignoring this unit in the algorithm
* i.e. if(i != movingUnitIndexInTheArray)).
* @param endPointCP the point where the unit moves to.
* @param line the line of the move of the thickness equal to units width (mod=40),
* drawn between the current unit's center point and the endPointCP,
* represented as a polygon object.
* @return true if move possible; false otherwise.
*/
private static boolean tryMove(Point endPointCP, Polygon line){
Area potentialArea = getArea(endPointCP);
Area moveLineArea = new Area(line);
moveLineArea.add(potentialArea);
//this area is used for testing if nothing stays on the way of the move
Area spaceTestArea = new Area(moveLineArea);
//the index of the unit making the move in the unitCenterPoints list
int movingUnitIndexInTheArray = 1;
//we are subtracting from spaceTestArea all areas of units
for(int i = 0; i < unitCenterPoints.size(); i++)
if(i != movingUnitIndexInTheArray) {
Point p = unitCenterPoints.get(i);
Area uArea = getArea(p);
spaceTestArea.subtract(uArea);
//we have intersection then return false, we cannot make this move
if(spaceTestArea.isEmpty() || !spaceTestArea.equals(moveLineArea)) {
System.out.println("No move --- a unit is on the way. "
+ "Conflicting point is="+p +"; for i="+i);
return false;
}
}
System.out.println("Move OK.");
return true;
}
private static boolean tryMove2(Point endPointCP, Polygon line){
Area potentialArea = getArea(endPointCP);
Area moveLineArea = new Area(line);
//test if unit can move to the new position
Area potentialTestArea = new Area(potentialArea);
//this area is used for testing if nothing stays on the way of the move
Area spaceTestArea = new Area(moveLineArea);
//the index of the unit making the move in the unitCenterPoints list
int movingUnitIndexInTheArray = 1;
//we are subtracting from spaceTestArea all areas of units
for(int i = 0; i < unitCenterPoints.size(); i++)
if(i != movingUnitIndexInTheArray) {
Point p = unitCenterPoints.get(i);
Area uArea = getArea(p);
spaceTestArea.subtract(uArea);
potentialTestArea.subtract(uArea);
//we have intersection then return false, we cannot make this move
if(spaceTestArea.isEmpty() || !spaceTestArea.equals(moveLineArea)
|| potentialTestArea.isEmpty() || !potentialTestArea.equals(potentialArea)) {
System.out.println("No move --- a unit is on the way. "
+ "Conflicting point is="+p +"; for i="+i);
return false;
}
}
System.out.println("Move OK.");
return true;
}
/**
* Gets the area taken by a unit given the unit's center point.
* @param p the center point of a unit.
* @return circle area.
*/
private static Area getArea(Point p) {
int mod = 40;//this is width and height of a unit
Ellipse2D circle = new Ellipse2D.Double(p.x - mod / 2, p.y - mod / 2, mod, mod);
return new Area(circle);
}
}
这是它产生的输出：
******TEST for method tryMove()******
TEST 1: this will FAIL
No move --- a unit is on the way. Conflicting point is=java.awt.Point[x=280,y=120]; for i=6; where moving unit point is=java.awt.Point[x=1880,y=120]; the unit is moving to=java.awt.Point[x=1914,y=126]
Result=false
TEST 2: this will be OK
Move OK.
Result=true
******TEST for method tryMove2()******
TEST 1: this will be OK
Move OK.
Result=true
TEST 2: this will be OK
Move OK.
Result=true
为了让你更好地看到这个问题,我有两个图像呈现两个endPoints,第一个1914,126当方法失败时,第二个1914,127就可以了.
如果需要更多描述,我会尽快回答.谢谢大家.
EDIT1：
正如@trashgod所建议的那样,我尝试并实现了一个使用intersect()方法的解决方案.我不喜欢你必须创建一个新对象的每个测试.你能为这个算法建议一些优化吗？
private static boolean tryMove3(Point endPointCP, Polygon line){
Area potentialArea = getArea(endPointCP);
Area moveLineArea = new Area(line);
moveLineArea.add(potentialArea);
//this area is used for testing if nothing stays on the way of the move
//the index of the unit making the move in the unitCenterPoints list
int movingUnitIndexInTheArray = 1;
//we are subtracting from spaceTestArea all areas of units
for(int i = 0; i < unitCenterPoints.size(); i++)
if(i != movingUnitIndexInTheArray) {
Point p = unitCenterPoints.get(i);
Area uArea = getArea(p);
Area spaceTestArea = new Area(moveLineArea);
spaceTestArea.intersect(uArea);
//we have intersection then return false, we cannot make this move
if(!spaceTestArea.isEmpty()) {
System.out.println("No move --- a unit is on the way. "
+ "Conflicting point is="+p +"; for i="+i
+ "; where moving unit point is="
+unitCenterPoints.get(movingUnitIndexInTheArray)
+"; the unit is moving to="+endPointCP
+"; spaceTestArea.isEmpty()="+spaceTestArea.isEmpty());
return false;
}
}
System.out.println("Move OK.");
return true;
}
解决方法:
我猜你正在与java.awt.geom.Area变空的方式发生冲突.如果它有帮助,我在下面拍了一张照片.或者,你可以使用createTransformedShape()和contains()吗？
附录：tryMove3()显示正确.如果真的变得更糟,我会看到几种可能性：
> Cache任何静态区域,也许是与每个中心点相关的区域.
>根据getBounds()或quadtree进行粗略的邻近检查,并跳过远程对.
JFrame f = new JFrame();
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.add(new JPanel(){
@Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g;
g2d.scale(10, 10);
g2d.translate(-1875, -100);
g2d.setColor(Color.green);
g2d.draw(lineOK);
g2d.setColor(Color.green.darker());
g2d.drawRect(endPointCPOK.x, endPointCPOK.y, 1, 1);
g2d.setColor(Color.red);
g2d.draw(lineFAIL);
g2d.setColor(Color.red.darker());
g2d.drawRect(endPointCPFAIL.x, endPointCPFAIL.y, 1, 1);
}
});
f.pack();
f.setSize(450, 500);
f.setLocationRelativeTo(null);
f.setVisible(true);
标签：java,collision-detection,area 来源： https://codeday.me/bug/20190903/1796170.html