2 個線段是否截獲

如果兩個線段相交，則此示例中的函式返回 true，否則返回 false。

該示例是為效能而設計的，並使用閉包來儲存工作變數

    // point object: {x:, y:}
    // p0 & p1 form one segment, p2 & p3 form the second segment
    // Returns true if lines segments are intercepting
    var lineSegmentsIntercept = (function(){ // function as singleton so that closure can be used
        
        var v1, v2, v3, cross, u1, u2;  // working variable are closed over so they do not need creation 
                                   // each time the function is called. This gives a significant performance boost.
        v1 = {x : null, y : null}; // line p0, p1 as vector
        v2 = {x : null, y : null}; // line p2, p3 as vector
        v3 = {x : null, y : null}; // the line from p0 to p2 as vector
        
        function lineSegmentsIntercept (p0, p1, p2, p3) {
            v1.x = p1.x - p0.x; // line p0, p1 as vector
            v1.y = p1.y - p0.y; 
            v2.x = p3.x - p2.x; // line p2, p3 as vector
            v2.y = p3.y - p2.y; 
            if((cross = v1.x * v2.y - v1.y * v2.x) === 0){  // cross prod 0 if lines parallel
                return false; // no intercept
            }
            v3 = {x : p0.x - p2.x, y : p0.y - p2.y};  // the line from p0 to p2 as vector
            u2 = (v1.x * v3.y - v1.y * v3.x) / cross; // get unit distance along line p2 p3 
            // code point B
            if (u2 >= 0 && u2 <= 1){                   // is intercept on line p2, p3
                u1 = (v2.x * v3.y - v2.y * v3.x) / cross; // get unit distance on line p0, p1;
                // code point A
                return (u1 >= 0 && u1 <= 1);           // return true if on line else false.
                // code point A end
            }
            return false; // no intercept;
            // code point B end
        }
        return lineSegmentsIntercept;  // return function with closure for optimisation.
    })();

用法示例

var p1 = {x: 100, y: 0};   // line 1
var p2 = {x: 120, y: 200};
var p3 = {x: 0,   y: 100}; // line 2
var p4 = {x: 100, y: 120};
var areIntersepting = lineSegmentsIntercept (p1, p2, p3, p4); // true

該示例很容易修改以返回截距點。替換 code point A 和 A end 之間的程式碼

if(u1 >= 0 && u1 <= 1){
    return {
        x : p0.x + v1.x * u1,
        y : p0.y + v1.y * u1,
    };
}

或者如果你想獲得線上的攔截點，忽略線段的開始和結束替換 code point B 和 B end 之間的程式碼

return {
    x : p2.x + v2.x * u2,
    y : p2.y + v2.y * u2,
};

如果沒有攔截，則兩個修改都將返回 false，或者將截距點作為 {x : xCoord, y : yCoord} 返回