Point-Line Distance

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HoboBen	Created : 11 July 2008 Edited : 11 July 2008 Language : Cobra Point-Line Distance
Needed this for my shmup, I figured I may as well post it in case it comes in handy. function DistancePointLine(px: Real, py: Real, x1: Real, y1: Real, x2: Real, y2: Real): Real Returns the smallest distance between a point and a line Unit { Cobra Unit to find the shortest distance between a point and a line Theory by Paul Bourke https://local.wasp.uwa.edu.au/~pbourke/geometry/pointline/ Ported from a Pascal (Delphi v7) implementation by Graham O'Brien https://local.wasp.uwa.edu.au/~pbourke/geometry/pointline/DistancePointLine.delphi With a few modifications of my own. } Const EPS = 0.000001 // smallest positive value: less than that to be considered zero EPSEPS = EPS * EPS // and its square Function SqLineMagnitude(x1 : Real, y1: Real, x2: Real, y2: Real) : Real Begin result = (x2 - x1) * (x2 - x1) + (y2 - y1) * (y2 - y1) End function DistancePointLine(px: Real, py: Real, x1: Real, y1: Real, x2: Real, y2: Real): Real { px, py is the point to test. x1, y1, x2, y2 is the line to check distance. Returns distance from the line, or if the intersecting point on the line nearest the point tested is outside the endpoints of the line, the distance to the nearest endpoint. On zero-valued denominator conditions (this seems to be when the Line is infinitely short, e.g. the Line is a dot), returns the distance between the two points (e.g. a^2 + b^2 = c^2). } Var SqLineMag : integer u : Real ix : Real iy : Real Begin SqLineMag = SqLineMagnitude(x1, y1, x2, y2) If SqLineMag < EPS then result = Sqrt(((px - x1)^2) + ((py - y1)^2)) exit Endif u = ( (px - x1)(x2 - x1) + (py - y1)(y2 - y1) ) / SqLineMag If (u < EPS) or (u > 1) then ix = SqLineMagnitude(px, py, x1, y1) iy = SqLineMagnitude(px, py, x2, y2) result = min(ix, iy) Else ix = x1 + u * (x2 - x1) iy = y1 + u * (y2 - y1) result = SqlineMagnitude(px, py, ix, iy) Endif result = Sqrt(result) End Begin End --v

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