vector float
sqrtf4 (vector float x)
{
return _sqrtf4( x );
}
/* tests if ray intersects a given sphere */
int ray_intersect_sphere(const ray_t *ray, const sphere_t* sphere,
point_t *pt, float *distance)
{
vector4_t tmp; /* used to hold scale of ray direction */
float A = 1; /* since we know ray direction is normalized */
float dx = ray->origin.x - sphere->center.x;
float dy = ray->origin.y - sphere->center.y;
float dz = ray->origin.z - sphere->center.z;
float B = 2 * (
ray->direction.x * (dx) +
ray->direction.y * (dy) +
ray->direction.z * (dz));
float C = (dx * dx + dy * dy + dz * dz)
- (sphere->radius * sphere->radius);
float det = (B*B) - (4 * A * C);
float wOne; /* distance to first intersection */
float wTwo; /* distance to second intersection */
float w = 0.0f; /* least positive w */
#ifdef __SPU__
vector float vTmp;
float scalarTmp;
#endif
if(det < 0.0f)
{ /* intersection is behind ray so none at all*/
return 0;
}
else
{ /* no need to use A since it's 1 */
#ifdef __SPU__
vTmp = spu_promote(det, 0);
scalarTmp = spu_extract(
_sqrtf4(vTmp), 0);
wOne = (-B - scalarTmp) / (2.0f * A);
wTwo = (-B + scalarTmp) / (2.0f * A);
#else
wOne = (-B - sqrt(det)) / (2.0f * A);
wTwo = (-B + sqrt(det)) / (2.0f * A);
#endif
if(det == 0.0f)
{ /* one root, wOne and wTwo should be equal */
vec4_add(pt, &ray->origin,
vec4_scale(&tmp, &ray->direction, wOne));
*distance = wOne; /* pass back distance to intersection */
return 1;
}
else
{
if(wOne > 0.0f)
w = wOne;
if(wTwo > 0.0f && wTwo < w)
w = wTwo;
/* now w is least positive root */
/* use it to calculate where intersection point is */
vec4_add(pt, &ray->origin,
vec4_scale(&tmp, &ray->direction, w));
*distance = w; /* pass back distance to intersection */
return 1;
}
}
/* all code paths above this point should have returned something
* but if we've gotten here anyways, assume no intersection occured */
#if defined(_DEBUG)
printf("Ray-Sphere intersection test failed!!!\n");
#endif
return 0;
}
