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  Plane Class
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This is a simple plane class that allows you to calculate the equation of a plane given three points, determine a points orientation to the plane and determine if a line from point1 to point2 intersects the plane.

Download Associated File: planeflip.h (2,264 bytes)

#ifndef __PLANEH__
#define __PLANEH__

#include "mathlib.h"

static const float Epsilon = 1.0e-05f;

struct plane_t { plane_t() {d = 0;} virtual ~plane_t() { } void Reset(void) {n.Set(0, 0, 0); d = 0;}

// Returns 1 if the point, 'pt', is in front of the plane bool IsFront(vec3_t &pt) {return (GetPointDistance(pt) > 0.0f) ? 1 : 0;}

// Returns 1 if the point, 'pt', is behind the plane bool IsBack(vec3_t &pt) {return !(IsFront(pt));}

// Returns 1 if the point, 'pt', is on the plane inline bool IsOn(vec3_t &pt);

// Calculates the plane equation given three points inline void CalcPlane(vec3_t &pta, vec3_t &ptb, vec3_t &ptc);

// Returns 1 if the line from 'start' to 'end' intersects the plane. // 'point' is a point on the plane and 'result' is the point of // intersection if there is one, if there is no intersection 'result' is // not modified. inline bool LineIntersect(vec3_t &start, vec3_t &end, vec3_t &point, vec3_t &result);

// Returns the distance that a point, 'pt', is from the plane float GetPointDistance(vec3_t &pt) {return n.Dot(pt) + d;}

// Returns the normal, A B and C in the plane equation const vec3_t &GetNormal(void) {return n;} // Returns the D component of the plane equation const float &GetD(void) {return d;}

protected: vec3_t n; float d; };

inline bool plane_t::IsOn(vec3_t &pt) { float d = GetPointDistance(pt); return (d > -Epsilon && d < Epsilon) ? 1 : 0; }

inline void plane_t::CalcPlane(vec3_t &pta, vec3_t &ptb, vec3_t &ptc) { n.Cross(ptb - pta, ptc - pta); n.Normalize(); d = -ptc.Dot(n); }

inline bool plane_t::LineIntersect(vec3_t &start, vec3_t &end, vec3_t &point, vec3_t &result) { float denom, numer, u; vec3_t dir;

dir = end - start;

denom = n.Dot(dir);

// No divide by zero! if (denom > -Epsilon && denom < Epsilon) return 0; // Line is parallel to the plane numer = n.Dot(point - start);

u = numer / denom;

// Is there an intersection along the line? if (u <= 0.0f || u > 1.0f) return 0;

result = start + dir * u; // point of intersection return 1; }


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