mSphere.cpp

Detailed Description

 1
 2//-----------------------------------------------------------------------------
 3// Copyright (c) 2012 GarageGames, LLC
 4//
 5// Permission is hereby granted, free of charge, to any person obtaining a copy
 6// of this software and associated documentation files (the "Software"), to
 7// deal in the Software without restriction, including without limitation the
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 9// sell copies of the Software, and to permit persons to whom the Software is
10// furnished to do so, subject to the following conditions:
11//
12// The above copyright notice and this permission notice shall be included in
13// all copies or substantial portions of the Software.
14//
15// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
16// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
17// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
18// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
19// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
20// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
21// IN THE SOFTWARE.
22//-----------------------------------------------------------------------------
23
24#include "platform/platform.h"
25#include "math/mSphere.h"
26
27#include "math/mMatrix.h"
28
29
30bool SphereF::intersectsRay( const Point3F &start, const Point3F &end ) const
31{
32   MatrixF worldToObj( true );
33   worldToObj.setPosition( center );
34   worldToObj.inverse();
35
36   VectorF dir = end - start;
37   dir.normalize();
38
39   Point3F tmpStart = start;
40   worldToObj.mulP( tmpStart ); 
41
42   //Compute A, B and C coefficients
43   F32 a = mDot(dir, dir);
44   F32 b = 2 * mDot(dir, tmpStart);
45   F32 c = mDot(tmpStart, tmpStart) - (radius * radius);
46
47   //Find discriminant
48   F32 disc = b * b - 4 * a * c;
49
50   // if discriminant is negative there are no real roots, so return 
51   // false as ray misses sphere
52   if ( disc < 0 )
53      return false;
54
55   // compute q as described above
56   F32 distSqrt = mSqrt( disc );
57   F32 q;
58   if ( b < 0 )
59      q = (-b - distSqrt)/2.0;
60   else
61      q = (-b + distSqrt)/2.0;
62
63   // compute t0 and t1
64   F32 t0 = q / a;
65   F32 t1 = c / q;
66
67   // make sure t0 is smaller than t1
68   if ( t0 > t1 )
69   {
70      // if t0 is bigger than t1 swap them around
71      F32 temp = t0;
72      t0 = t1;
73      t1 = temp;
74   }
75
76   // This function doesn't use it
77   // but t would be the interpolant
78   // value for getting the exact
79   // intersection point, by interpolating
80   // start to end by t.
81
82   /*
83   F32 t = 0;
84   TORQUE_UNUSED(t);
85   */
86
87   // if t1 is less than zero, the object is in the ray's negative direction
88   // and consequently the ray misses the sphere
89   if ( t1 < 0 )
90      return false;
91
92   // if t0 is less than zero, the intersection point is at t1
93   if ( t0 < 0 ) // t = t1;     
94      return true;
95   else // else the intersection point is at t0
96      return true; // t = t0;
97}
98