[CG] Convex Hull
// from https://observablehq.com/@d3/polygonclip
// y is up, > 0 when left turn (in svg, y is down)
function lineOrient(ax, ay, bx, by, cx, cy) {
return (ax - cx) * (by - cy) - (ay - cy) * (bx - cx);
}
function normalizedSqrOrient(ax, ay, bx, by, cx, cy){
// cx -> bx+(cx-bx)/Math.sqrt((cx-bx)**2+(cy-by)**2)
// const m = (ax - bx)*(by-cy)-(ay-by)*(bx-cx) // = (ax - cx) * (by - cy) - (ay - cy) * (bx - cx)
const m = lineOrient(ax, ay, bx, by, cx, cy)
const s = Math.sign(m)
const n = (cx-bx)**2+(cy-by)**2
return m**2*s/n
}
// close to 1 when c is at the extension of ab
// can we replace the division? better not to bother though
function signedSquaredNormalizedDot(ax, ay, bx, by, cx, cy) {
const dot = (bx-ax)*(cx-bx) + (by-ay)*(cy-by)
const s = Math.sign(dot)
const lensqr = ((bx-ax)**2+(by-ay)**2)*((cx-bx)**2+(cy-by)**2)
return dot**2*s/lensqr
}
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