我有一个问题。
如何检查Android中的路径是否与自身相交？
我有这堂课：
public class GameView extends SurfaceView implements Runnable {
Thread gameThread = null;
SurfaceHolder surfaceHolder;
volatile boolean playing;
Canvas canvas;
private final static int MAX_FPS = 60;
private final static int FRAME_PERIOD = 1000 / MAX_FPS;
ArrayList<Point> points = new ArrayList<>();
private Context ctx;
Path path;
public static final int DEFAULT_COLOR = Color.RED;
public static final int DEFAULT_BG_COLOR = Color.WHITE;
private static final float TOUCH_TOLERANCE = 4;
private float mX, mY;
private Path mPath;
private Paint mPaint;
private int backgroundColor = DEFAULT_BG_COLOR;
public GameView(Context context) {
super(context);
ctx = context;
surfaceHolder = getHolder();
surfaceHolder.setFormat(PixelFormat.RGBA_8888);
path = new Path();
playing = true;
mPaint = new Paint();
mPaint.setAntiAlias(true);
mPaint.setDither(true);
mPaint.setColor(DEFAULT_COLOR);
mPaint.setStyle(Paint.Style.STROKE);
mPaint.setStrokeJoin(Paint.Join.ROUND);
mPaint.setStrokeCap(Paint.Cap.ROUND);
mPaint.setXfermode(null);
mPaint.setAlpha(0xff);
mPaint.setStrokeWidth(12);
}
static Boolean isPathComplex(List<Point> path) {
if (path == null || path.size() <= 2) {
return false;
}
int len = path.size();
for (int i = 1; i < len; i++) {
Point lineAStart = path.get(i - 1);
Point lineAEnd = path.get(i);
for (int j = i + 1; j < len; j++) {
Point lineBStart = path.get(j - 1);
Point lineBEnd = path.get(j);
if (lineSegmentsIntersect(lineAStart.x,lineAStart.y,
lineAEnd.x,lineAEnd.y,
lineBStart.x,lineBStart.y,
lineBEnd.x,lineBEnd.y)) {
return true;
}
} // inner loop
} // outer loop
return false;
}
static Boolean lineSegmentsIntersect(float p0_x, float p0_y, float p1_x, float p1_y,
float p2_x, float p2_y, float p3_x, float p3_y) {
float s1_x, s1_y, s2_x, s2_y;
s1_x = p1_x - p0_x; s1_y = p1_y - p0_y;
s2_x = p3_x - p2_x; s2_y = p3_y - p2_y;
float s, t;
s = (-s1_y * (p0_x - p2_x) + s1_x * (p0_y - p2_y)) / (-s2_x * s1_y + s1_x * s2_y);
t = ( s2_x * (p0_y - p2_y) - s2_y * (p0_x - p2_x)) / (-s2_x * s1_y + s1_x * s2_y);
if (s >= 0 && s <= 1 && t >= 0 && t <= 1)
{
// Collision detected
return true;
}
return false; // No collision
}
public void update(){
isPathComplex(points);
}
public void draw(){
if(surfaceHolder.getSurface().isValid()){
canvas = surfaceHolder.lockCanvas();
if(canvas != null) {
canvas.drawColor(backgroundColor);
if (mPath != null) {
canvas.drawPath(mPath, mPaint);
}
surfaceHolder.unlockCanvasAndPost(canvas);
}
}
}
@Override
public void run() {
while(playing){
long started = System.currentTimeMillis();
float deltaTime = (System.currentTimeMillis() - started);
int sleepTime = (int) (FRAME_PERIOD - deltaTime);
update();
draw();
if (sleepTime > 0) {
try {
Thread.sleep(sleepTime);
}
catch (InterruptedException e) {
}
}
while (sleepTime < 0) {
update();
draw();
sleepTime += FRAME_PERIOD;
}
}
}
private void touchStart(float x, float y) {
mPath = new Path();
points.add(new Point((int)x,(int)y));
mPath.reset();
mPath.moveTo(x, y);
mX = x;
mY = y;
}
private void touchMove(float x, float y) {
float dx = Math.abs(x - mX);
float dy = Math.abs(y - mY);
points.add(new Point((int)x,(int)y));
if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) {
mPath.quadTo(mX, mY, (x + mX) / 2, (y + mY) / 2);
mX = x;
mY = y;
}
}
private void touchUp() {
mPath.lineTo(mX, mY);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
float x = event.getX();
float y = event.getY();
switch(event.getAction()) {
case MotionEvent.ACTION_DOWN :
touchStart(x, y);
break;
case MotionEvent.ACTION_MOVE :
touchMove(x, y);
break;
case MotionEvent.ACTION_UP :
touchUp();
break;
}
return true;
}
public void pause() {
playing = false;
try {
gameThread.join();
} catch (InterruptedException e) {
Log.e("Error:", "joining thread");
}
}
public void resume(Context context) {
playing = true;
gameThread = new Thread(this);
gameThread.start();
}
}
请您知道解决此问题的方法吗？
我尝试了很多，但没有任何帮助我解决我的问题。
我想要实现的是检测像this
这样的交叉我尝试使用来自Check android.graphics.path intersection with itself的积分解决方案，但似乎不适合我。
我也可能做错了，因为我是Android开发和编程的新手:)。
提前谢谢！
修改
要检测上面的解决方案后面的交叉i并修改了这个函数https://stackoverflow.com/a/1968345/9339525但是它几乎一直都返回true，即使路径没有穿过它自己。
检测交叉口的所有代码：
static Boolean isPathComplex(List<Point> path) {
if (path == null || path.size() <= 2) {
return false;
}
int len = path.size();
for (int i = 1; i < len; i++) {
Point lineAStart = path.get(i - 1);
Point lineAEnd = path.get(i);
for (int j = i + 1; j < len; j++) {
Point lineBStart = path.get(j - 1);
Point lineBEnd = path.get(j);
if (lineSegmentsIntersect(lineAStart.x,lineAStart.y,
lineAEnd.x,lineAEnd.y,
lineBStart.x,lineBStart.y,
lineBEnd.x,lineBEnd.y)) {
return true;
}
} // inner loop
} // outer loop
return false;
}
static Boolean lineSegmentsIntersect(float p0_x, float p0_y, float p1_x, float p1_y,
float p2_x, float p2_y, float p3_x, float p3_y) {
float s1_x, s1_y, s2_x, s2_y;
s1_x = p1_x - p0_x; s1_y = p1_y - p0_y;
s2_x = p3_x - p2_x; s2_y = p3_y - p2_y;
float s, t;
s = (-s1_y * (p0_x - p2_x) + s1_x * (p0_y - p2_y)) / (-s2_x * s1_y + s1_x * s2_y);
t = ( s2_x * (p0_y - p2_y) - s2_y * (p0_x - p2_x)) / (-s2_x * s1_y + s1_x * s2_y);
if (s >= 0 && s <= 1 && t >= 0 && t <= 1) {
// Collision detected
return true;
}
return false; // No collision
}
修改
我修改了我的类GameView并添加了检测交集的方法。
答案 0 :(得分：0)
我无法忍受那是那么困难，所以我打开电脑并编码了一些东西。
我只尝试了几个值，并且不知道如果段的开始 - 结束点重合会发生什么。
请试试。
static boolean lineSegmentsDoIntersect(
float Ax, float Ay
, float Bx, float By
, float Cx, float Cy
, float Dx, float Dy) {
// two line segments: AB and CD
// segment AB intersects segment CD
// if A and B on different sides of line through C and D
// AND C and D on different sides of line through A and B
// note the difference between line and segment!
if ( ! pointsOnDifferentSidesOfLineThrough(Ax, Ay, Bx, By, Cx, Cy, Dx, Dy) )
return false;
if ( ! pointsOnDifferentSidesOfLineThrough(Cx, Cy, Dx, Dy, Ax, Ay, Bx, By) )
return false;
return true;
}
static boolean pointsOnDifferentSidesOfLineThrough(
float Ax, float Ay
, float Bx, float By
, float x1, float y1
, float x2, float y2) {
// determine equation of line through C and D
// y = ax + b
// a = (y2-y1)/(x2-x1) but.. ( x2-x1) not equal to zero
// y-y1 = a (x-x1)
// y = a (x-x1) + y1
// y = ax -ax1 + y1
// b = -ax1 + y1
//but.. (x2-x1) not 0
if ( x2==x1)
{
if ( Ax > x1 && Bx > x1 )
return false;
if ( Ax < x1 && Bx < x1 )
return false;
return true;
}
float a = (y2-y1)/(x2-x1);
float b = -a * x1 + y1;
float yA = a * Ax + b;
float yB = a * Bx + b;
if ( yA > Ay && yB > By )
return false;
if ( yA < Ay && yB < By )
return false;
return true;
}