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import { pointFrom } from "./point";
import type { GlobalPoint, Line, LocalPoint } from "./types";
/**
* Create a line from two points.
*
* @param points The two points lying on the line
* @returns The line on which the points lie
*/
export function line<P extends GlobalPoint | LocalPoint>(a: P, b: P): Line<P> {
return [a, b] as Line<P>;
}
/**
* Determines the intersection point (unless the lines are parallel) of two
* lines
*
* @param a
* @param b
* @returns
*/
export function linesIntersectAt<Point extends GlobalPoint | LocalPoint>(
a: Line<Point>,
b: Line<Point>,
): Point | null {
const A1 = a[1][1] - a[0][1];
const B1 = a[0][0] - a[1][0];
const A2 = b[1][1] - b[0][1];
const B2 = b[0][0] - b[1][0];
const D = A1 * B2 - A2 * B1;
if (D !== 0) {
const C1 = A1 * a[0][0] + B1 * a[0][1];
const C2 = A2 * b[0][0] + B2 * b[0][1];
return pointFrom<Point>((C1 * B2 - C2 * B1) / D, (A1 * C2 - A2 * C1) / D);
}
return null;
}
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