void vec4_transform(struct vec4 *dst, const struct vec4 *v,
const struct matrix4 *m)
{
struct vec4 temp;
struct matrix4 transpose;
matrix4_transpose(&transpose, m);
temp.x = vec4_dot(&transpose.x, v);
temp.y = vec4_dot(&transpose.y, v);
temp.z = vec4_dot(&transpose.z, v);
temp.w = vec4_dot(&transpose.t, v);
vec4_copy(dst, &temp);
}
/* tests if ray intersects a given polygon */
int ray_intersect_polygon(const ray_t *ray, const polygon_t* poly,
point_t *pt, float *distance)
{
float num = -1.0f * (
vec4_dot((vector4_t *)&poly->plane, &ray->origin) +
poly->plane.F);
float den = vec4_dot((vector4_t *)&poly->plane, &ray->direction);
float w;
unsigned int i = 0; /* counter variable for loop */
double angleTotal = 0.0; /* running total of angle */
double angleTmp = 0.0; /* angle between current two vectors */
vector4_t tmp;
vector4_t tmp2;
#ifdef __SPU__
vector float vTmp;
#endif
/* if denomenator = 0, ray is parallel to plane */
if(den == 0.0f)
{ /* return no intersection */
return 0;
}
w = num / den; /* distance to intersection */
/* if w < 0, intersection point is behind ray */
if(w < 0.0f)
{ /* return no intersection */
return 0;
}
/* 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 */
/* at this point we at least know the ray intersects the plane.
* let's figure out if the point is actually inside the confined
* polygonal area */
for(i = 0; i < poly->nVerticies; ++i)
{
if(i == (poly->nVerticies - 1))
{ /* last vertex, compare with first */
/* calculate two vectors */
vec4_sub(&tmp, &poly->vertex[i], pt);
vec4_sub(&tmp2, &poly->vertex[0], pt);
/* find angle between them - between normal vectors, dot
* product is cos of angle between them */
#ifdef __SPU__
vTmp[0] = vec4_costheta(&tmp, &tmp2);
vTmp = _acosf4(vTmp);
angleTotal += vTmp[0];
#else
angleTmp = vec4_costheta(&tmp, &tmp2);
/* arccos to get theta */
angleTmp = acos(angleTmp);
angleTotal += angleTmp;
#endif
}
else
{
/* calculate two vectors */
vec4_sub(&tmp, &poly->vertex[i], pt);
vec4_sub(&tmp2, &poly->vertex[i+1], pt);
/* find angle between them - between normal vectors, dot
* product is cos of angle between them */
#ifdef __SPU__
vTmp[0] = vec4_costheta(&tmp, &tmp2);
vTmp = _acosf4(vTmp);
angleTotal += vTmp[0];
#else
angleTmp = vec4_costheta(&tmp, &tmp2);
/* arccos to get theta */
angleTmp = acos(angleTmp);
angleTotal += angleTmp;
#endif
}
}
/* TODO: this comparison is weak, should be refined */
if((angleTotal + .001) > (2.0 * M_PI))
{
return 1;
}
else
{
return 0;
}
}