39 lines
1.8 KiB
JavaScript
39 lines
1.8 KiB
JavaScript
exports.intersection = function (line1StartX, line1StartY, line1EndX, line1EndY, line2StartX, line2StartY, line2EndX, line2EndY) {
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// if the lines intersect, the result contains the x and y of the intersection (treating the lines as infinite) and booleans for whether line segment 1 or line segment 2 contain the point
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var denominator, a, b, numerator1, numerator2, result = {
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x: null,
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y: null,
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onLine1: false,
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onLine2: false
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};
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denominator = ((line2EndY - line2StartY) * (line1EndX - line1StartX)) - ((line2EndX - line2StartX) * (line1EndY - line1StartY));
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if (Math.abs(denominator) <= 0.000000001) {
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return result;
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}
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a = line1StartY - line2StartY;
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b = line1StartX - line2StartX;
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numerator1 = ((line2EndX - line2StartX) * a) - ((line2EndY - line2StartY) * b);
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numerator2 = ((line1EndX - line1StartX) * a) - ((line1EndY - line1StartY) * b);
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a = numerator1 / denominator;
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b = numerator2 / denominator;
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// if we cast these lines infinitely in both directions, they intersect here:
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result.x = line1StartX + (a * (line1EndX - line1StartX));
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result.y = line1StartY + (a * (line1EndY - line1StartY));
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/*
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// it is worth noting that this should be the same as:
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x = line2StartX + (b * (line2EndX - line2StartX));
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y = line2StartX + (b * (line2EndY - line2StartY));
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*/
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// if line1 is a segment and line2 is infinite, they intersect if:
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if (a > 0 && a < 1) {
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result.onLine1 = true;
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}
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// if line2 is a segment and line1 is infinite, they intersect if:
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if (b > 0 && b < 1) {
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result.onLine2 = true;
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}
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// if line1 and line2 are segments, they intersect if both of the above are true
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return result;
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};
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