Thanks.
So here is the deal for my general implementation:
The user will input a set of 8 vertices . As in, "vertex0 = 85, 30, 94" etc.
Then, based upon a set of defined relationships, these input vertex components will be split up and used to provide the values of the components of the triangles and line segments that make up the cube.
As in:
Triangle0 = vertex0 vertex1 vertex3
Triangle1 = vertex0 vertex2 vertex3
...etc...
LineSegment0 = vertex0 vertex1
LineSegment1 = vertex0 vertex2
(This of course has to be able to access the components of each vertex)
Now that Triangles and LineSegments have values (from the user input), I need to run a check for intersections between each Triangle with each LineSegment.
I would like to define the intersection check function as an autonomous object so that later in the program, I can pass this function a particular Triangle and a particular LineSegment to check against each other.
Here is a C++ implementation of the intersection checker that I found at http://geometryalgorithms.com/Archiv...rithm_0105.htm
Code:
// Copyright 2001, softSurfer (www.softsurfer.com)
// This code may be freely used and modified for any purpose
// providing that this copyright notice is included with it.
// SoftSurfer makes no warranty for this code, and cannot be held
// liable for any real or imagined damage resulting from its use.
// Users of this code must verify correctness for their application.
// Assume that classes are already given for the objects:
// Point and Vector with
// coordinates {float x, y, z;}
// operators for:
// == to test equality
// != to test inequality
// (Vector)0 = (0,0,0) (null vector)
// Point = Point ± Vector
// Vector = Point - Point
// Vector = Scalar * Vector (scalar product)
// Vector = Vector * Vector (cross product)
// Line and Ray and Segment with defining points {Point P0, P1;}
// (a Line is infinite, Rays and Segments start at P0)
// (a Ray extends beyond P1, but a Segment ends at P1)
// Plane with a point and a normal {Point V0; Vector n;}
// Triangle with defining vertices {Point V0, V1, V2;}
// Polyline and Polygon with n vertices {int n; Point *V;}
// (a Polygon has V[n]=V[0])
//===================================================================
#define SMALL_NUM 0.00000001 // anything that avoids division overflow
// dot product (3D) which allows vector operations in arguments
#define dot(u,v) ((u).x * (v).x + (u).y * (v).y + (u).z * (v).z)
// intersect_RayTriangle(): intersect a ray with a 3D triangle
// Input: a ray R, and a triangle T
// Output: *I = intersection point (when it exists)
// Return: -1 = triangle is degenerate (a segment or point)
// 0 = disjoint (no intersect)
// 1 = intersect in unique point I1
// 2 = are in the same plane
int
intersect_RayTriangle( Ray R, Triangle T, Point* I )
{
Vector u, v, n; // triangle vectors
Vector dir, w0, w; // ray vectors
float r, a, b; // params to calc ray-plane intersect
// get triangle edge vectors and plane normal
u = T.V1 - T.V0;
v = T.V2 - T.V0;
n = u * v; // cross product
if (n == (Vector)0) // triangle is degenerate
return -1; // do not deal with this case
dir = R.P1 - R.P0; // ray direction vector
w0 = R.P0 - T.V0;
a = -dot(n,w0);
b = dot(n,dir);
if (fabs(b) < SMALL_NUM) { // ray is parallel to triangle plane
if (a == 0) // ray lies in triangle plane
return 2;
else return 0; // ray disjoint from plane
}
// get intersect point of ray with triangle plane
r = a / b;
if (r < 0.0) // ray goes away from triangle
return 0; // => no intersect
// for a segment, also test if (r > 1.0) => no intersect
*I = R.P0 + r * dir; // intersect point of ray and plane
// is I inside T?
float uu, uv, vv, wu, wv, D;
uu = dot(u,u);
uv = dot(u,v);
vv = dot(v,v);
w = *I - T.V0;
wu = dot(w,u);
wv = dot(w,v);
D = uv * uv - uu * vv;
// get and test parametric coords
float s, t;
s = (uv * wv - vv * wu) / D;
if (s < 0.0 || s > 1.0) // I is outside T
return 0;
t = (uv * wu - uu * wv) / D;
if (t < 0.0 || (s + t) > 1.0) // I is outside T
return 0;
return 1; // I is in T
}
Thanks for all your help so far. I am wondering if you could help me make sense of this so that I can do as I've described above (either in C or Objective-C). It is most important that the intersection check can be called in the program for the intersection of any particular Triangle and LineSegment.
Thanks again!
Originally Posted by Bjarne Stroustrup (2000-10-14)
