[英]Android Canvas Check if Point is on Line
我有一個自定義視圖,它繪制線條並將它們保存到ArrayList。 我想要做的是檢查指定點是否在Arraylist內的一行上並返回該行。 通過使用if (l.startX == l.stopX && l.startY < l.stopY
但是如果線條處於某個角度,這不起作用,我已經能夠做到這一點。我也想用drawText和drawCircle做這個。有沒有一些簡單的方法可以做到這一點,我錯過了?
DrawView.java
class Line {
float startX, startY, stopX, stopY;
public Line(float startX, float startY, float stopX, float stopY) {
this.startX = startX;
this.startY = startY;
this.stopX = stopX;
this.stopY = stopY;
}
public Line(float startX, float startY) { // for convenience
this(startX, startY, startX, startY);
}
}
public class DrawView extends View {
Paint paint = new Paint();
ArrayList<Line> lines = new ArrayList<Line>();
public DrawView(Context context, AttributeSet attrs) {
super(context, attrs);
paint.setAntiAlias(true);
paint.setStrokeWidth(6f);
paint.setColor(Color.BLACK);
paint.setStyle(Paint.Style.STROKE);
paint.setStrokeJoin(Paint.Join.ROUND);
}
@Override
protected void onDraw(Canvas canvas) {
for (Line l : lines) {
canvas.drawLine(l.startX, l.startY, l.stopX, l.stopY, paint);
}
}
@Override
public boolean onTouchEvent(MotionEvent event) {
if (event.getAction() == MotionEvent.ACTION_DOWN) {
lines.add(new Line(event.getX(), event.getY()));
return true;
}
else if ((event.getAction() == MotionEvent.ACTION_MOVE ||
event.getAction() == MotionEvent.ACTION_UP) &&
lines.size() > 0) {
Line current = lines.get(lines.size() - 1);
current.stopX = event.getX();
current.stopY = event.getY();
Invalidate();
return true;
}
else {
return false;
}
}
}
我不知道是否有一個畫布庫,但手動你可以:
經過幾個小時的嘗試,我設法得出一個算法來檢查一個點是否在給定的線上使用if (x = startX && y > startY && y < stopY)
公式的混合和if (x = startX && y > startY && y < stopY)
下面是代碼,如果點在線則返回true,否則為false,希望這可以節省一些時間!
public boolean checkPosition(float x, float y, float sx, float sy, float ex, float ey) {
float mX = ex - sx;
float mY = ey - sy;
float smX = sx - ex;
float smY = sy - ey;
float pmX = mX;
float pmY = mY;
float psmX = smX;
float psmY = smY;
float yY = ey - y;
float xX = ex - x;
float sX = sx - x;
float sY = sy - y;
float m = mY / mX;
float b = sy - (m * sx);
if (mX < 0) {
pmX = mX * - 1;
}
if (mY < 0) {
pmY = mY * - 1;
}
if (smX < 0) {
psmX = smX * - 1;
}
if (smY < 0) {
psmY = smY * - 1;
}
if (yY < 0) {
yY = yY * - 1;
}
if (xX < 0) {
xX = xX * - 1;
}
if (sX < 0) {
sX = sX * - 1;
}
if (sY < 0) {
sY = sY * - 1;
}
if (sy == ey && y == sy) {
if (sx >= ex) {
if (x <= sx && x >= ex) return true;
else return false;
}
else if (ex >= sx) {
if (x <= ex && x >= sx) return true;
else return false;
}
else return false;
}
else if (sx == ex && x == sx) {
if (sy >= ey) {
if (y <= sy && y >= ey) return true;
else return false;
}
else if (ey >= sy) {
if (y <= ey && y >= sy) return true;
else return false;
}
else return false;
}
else if (xX <= pmX && sX <= psmX && yY <= pmY && sY <= psmY) {
if (y == (m * x) + b) return true;
else return false;
}
else return false;
}
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