在我编写碰撞检测算法时，我遇到了这个问题。这是一件很奇怪的事情，超出了我的理解。
这里的问题是，如果在我的算法中，在 function 中提出，tryMove()我添加并在减去所有单元占用的区域后检测（由甚至没有靠近，移动单元所在的位置，它正在移动到。potentialAreamoveLineAreaspaceTestAreamoveLineAreax=280,y=120x=1880,y=120x=1914,y=126
我想知道这个问题的原因可能是什么，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()) 应该有效，而且一定是我忘记了一些事情。
请参阅下面出现问题的代码。
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
为了让您更好地看到问题，我有两个图像为两个端点呈现它，第一个1914, 126是方法失败时，第二个1914, 127是正常时。
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，我确实尝试并实现了一个使用intersect()方法的解决方案。我不喜欢每次测试都必须创建一个新对象。你能为这个算法提出一些优化建议吗？
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;
}
