这个奇怪的区域减法问题是什么原因造成的？
当我编写碰撞检测算法时，我已经解决了这个问题。这是一种奇怪的东西，超出了我的理解范围。
这里的问题如果在我的算法中，在函数tryMove()中显示，我将potentialArea添加到moveLineArea，我正在检测减去所有单位所占区域后，spaceTestArea（由moveLineArea创建），我与一个甚至不接近x=280,y=120的单位发生碰撞，其中移动单位为{ {1}}，它正在转移到x=1880,y=120。
我想知道这个问题可能是什么原因以及为了避免以后该怎么做。
我必须说我有一个临时解决方案（x=1914,y=126），但请不要让它影响你的想法，即我不喜欢这个解决方案而且我坚信第一个解决方案（tryMove2()）应该工作，忘记某事必须是我。
请参阅以下显示问题的代码。
tryMove()这是它产生的输出：
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);
}
}
为了让您更好地看到问题，我有两个图像为两个endPoints呈现它，当方法失败时首先******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
，当它正常时第二个1914, 126。
如果需要更多描述，我会尽快回答。提前谢谢大家。
EDIT1：
正如@trashgod所建议的那样，我尝试并实现了一种使用1914, 127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？
intersect()2 个答案:
答案 0 :(得分：3)
我猜你正在与java.awt.geom.Area变空的方式之一发生冲突。如果它有帮助，我在下面拍了一张照片。或者，您可以使用createTransformedShape()和contains()吗？
附录：tryMove3()似乎正确无误。如果真的变得更糟，我会看到几种可能性：
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);
答案 1 :(得分：2)
不知何故，第6个减法正在改变spaceTestArea的几何形状，因此它不等于moveLineArea，这可以通过exlusiveOr'ing这两个来直观地看到。如果两个几何相等，则Area API仅表示等于测试，但遗憾的是没有详细说明。例如，如果您向程序添加调试代码，您将看到此exclusiveOr区域仅在第6个减法中弹出。我还没弄清楚为什么，但也许如果你创建一个你会看到的excluxiveOr图像的图像。
你的代码包含我的调试语句（有些多余，对不起）：
import java.awt.*;
import java.awt.geom.*;
import java.util.ArrayList;
import java.util.Formatter;
import java.util.List;
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));
}
private static boolean tryMove(Point endPointCP, Polygon line) {
Area potentialArea = getArea(endPointCP);
Area moveLineArea = new Area(line);
System.out.println(showBounds("moveLine before add", moveLineArea));
moveLineArea.add(potentialArea);
System.out.println(showBounds("moveLine after add ", moveLineArea));
// this area is used for testing if nothing stays on the way of the move
Area spaceTestArea = new Area(moveLineArea);
System.out.println(showBounds("spaceTest", spaceTestArea));
Area xOr = (Area)spaceTestArea.clone();
xOr.exclusiveOr(moveLineArea);
System.out.printf("Pre %s %s %s%n", showBounds("STA", spaceTestArea), showBounds("MLA", moveLineArea),
showBounds("xOr", xOr));
// 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);
xOr = (Area)spaceTestArea.clone();
xOr.exclusiveOr(moveLineArea);
System.out.printf("i: %02d %s %s %s %s%n", i,
showBounds("STA", spaceTestArea),
showBounds("MLA", moveLineArea),
showBounds("uA", uArea),
showBounds("xOr", xOr));
// we have intersection then return false, we cannot make this move
if (spaceTestArea.isEmpty() || !spaceTestArea.equals(moveLineArea)) {
System.out.println("spaceTestArea.isEmpty()? " + spaceTestArea.isEmpty());
System.out.println("!spaceTestArea.equals(moveLineArea)? " + !spaceTestArea.equals(moveLineArea));
System.out.println("moveLineArea bounds: " + moveLineArea.getBounds());
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;
}
public static String showBounds(String name, Area area) {
Rectangle rect = area.getBounds();
StringBuilder resultSB = new StringBuilder();
Formatter formatter = new Formatter(resultSB);
formatter.format("%5s [%04d, %04d, %04d, %04d]", name, rect.x, rect.y, rect.width, rect.height);
return resultSB.toString();
}
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);
}
}
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