我作为一个ArrayList点存放的路径，我想检查线段相交。对于一些未知的原因，它不工作！我不明白，在LogCat中的任何消息，尽管我画相交的形状。 preciate如果有人可以看到我做错了，或有任何建议如何提高code。

  //路口监控
    如果（touchActionUp）{

        //循环抛出的所有点除了最后3
        的for（int i = 0; I＆LT; points.size（） -  3;我++）{
            线一号线=新线（points.get（I），points.get第（i + 1））;

            //开始上面的行之后，之后检查所有点
            对于（INT J = + 2; J＆LT; points.size（） -  1; J ++）{
                线2号线=新线（points.get（J），points.get（J + 1））;

                //调用方法检查路口
                如果（checkIntersection（一号线，2号线））{
                    Log.i（路口，是的！）;
                }
            }
        }
    }
 

和方法：

  //方法来检查线的交点
私人布尔interceptionControl（线一号线，线2号线）{
    INT X1 = line1.pointX1;
    INT X2 = line1.pointX2;
    INT X3 = line2.pointX1;
    INT X4 = line2.pointX2;

    INT Y1 = line1.pointY1;
    INT Y2 = line1.pointY2;
    INT Y3 = line2.pointY1;
    INT Y4 = line2.pointY2;

    //检查线平行

    INT DENOM =（Y4  -  Y3）*（X2  -  X1） - （X4  -  X3）*（Y2  -  Y1）;

    如果（DENOM == 0）{//线是平行的
        //？
    }

    双A =（（X4  -  X3）*（Y1  -  Y3） - （Y4  -  Y3）*（X1  -  X3））/ DENOM;
    双B =（（2次 -  1次）*（Y1  -  Y3） - （Y2  -  Y1）*（X1  - ×3））/ DENOM;

    //检查交集
    如果（A＆GT; = 0.0＆功放;＆安培; A＆LT; = 1.0F和放大器;和B＆GT; = 0.0＆功放;和B＆LT; = 1.0F）{
        返回true;
    }
    返回false;
}
 

解决方案

正在使用 INT 的坐标，它确实是这样的整数除法（即3/2 = 1 ）。这可能是原因，当你被 DENOM 分裂。您可以通过分（（双）DENOM）而不是简单地修复它 DENOM 。

I have a path stored as points in an arraylist and I want to check if the line segments are intersecting. For some unknown reason it's not working! I don't get any message in the LogCat despite that I'm drawing a shape that intersects. Preciate if someone could see what I have done wrong or have suggestions how to improve code.

    // Intersection control
    if(touchActionUp) {

        // Loop throw all points except the last 3
        for (int i = 0; i < points.size()-3; i++) {
            Line line1 = new Line(points.get(i), points.get(i+1));

            // Begin after the line above and check all points after that
            for (int j = i + 2; j < points.size()-1; j++) {
                Line line2 = new Line(points.get(j), points.get(j+1));

                // Call method to check intersection
                if(checkIntersection(line1, line2)) {
                    Log.i("Intersection", "Yes!");
                }
            }
        }
    }

And the method:

    // Method to check for intersection between lines
private boolean interceptionControl(Line line1, Line line2) {
    int x1 = line1.pointX1;
    int x2 = line1.pointX2;
    int x3 = line2.pointX1;
    int x4 = line2.pointX2;

    int y1 = line1.pointY1;
    int y2 = line1.pointY2;
    int y3 = line2.pointY1;
    int y4 = line2.pointY2;

    // Check if lines are parallel

    int denom = (y4 - y3) * (x2 - x1) - (x4 - x3) * (y2 - y1);

    if(denom == 0) { // Lines are parallel
        // ??
    }

    double a = ((x4 - x3) * (y1 - y3) - (y4 - y3) * (x1 - x3)) / denom;
    double b = ((x2 - x1) * (y1 - y3) - (y2 - y1) * (x1 - x3)) / denom;

    // Check for intersection
    if( a >= 0.0f && a <= 1.0f && b >= 0.0f && b <= 1.0f) {
        return true;
    }
    return false;
}

You are using int for coordinates and so it does integer division (i.e., 3/2 = 1). This might be the reason when you are dividing by denom. You can fix it by dividing by ((double)denom) instead of simply denom.