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[simd] Indicate when the circumsphere is degenerate

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CircumSphere_vf sets the sphere radius to -1 when the points are
degenerate (co-linear for three points, co-planar for four points).
This commit is contained in:
Bill Currie 2021-12-13 15:13:19 +09:00
parent eee25d21ba
commit 854c92d10e
2 changed files with 33 additions and 12 deletions
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38
libs/util/simd.c
View file

@ -36,6 +36,7 @@
#define IMPLEMENT_VEC4D_Funcs
#define IMPLEMENT_MAT4F_Funcs
#include "QF/mathlib.h"
#include "QF/simd/vec4d.h"
#include "QF/simd/vec4f.h"
#include "QF/simd/mat4f.h"
@ -91,8 +92,8 @@ BarycentricCoords_vf (const vec4f_t **points, int num_points, const vec4f_t p)
Sys_Error ("Not enough points to project or enclose the point");
}
static vec4f_t
circum_circle (const vec4f_t points[], int num_points)
static int
circum_circle (const vec4f_t points[], int num_points, vec4f_t *center)
{
vec4f_t a, c, b;
vec4f_t bc, ca, ab;
@ -102,9 +103,11 @@ circum_circle (const vec4f_t points[], int num_points)
switch (num_points) {
case 1:
return points[0];
*center = points[0];
return 1;
case 2:
return (points[0] + points[1]) / 2;
*center = (points[0] + points[1]) / 2;
return 1;
case 3:
a = points[0] - points[1];
b = points[0] - points[2];
@ -114,10 +117,15 @@ circum_circle (const vec4f_t points[], int num_points)
cc = dotf (c, c);
div = dotf (a, c);
div = 2 * (aa * cc - div * div);
if (fabs (div[0]) < EQUAL_EPSILON) {
// degenerate
return 0;
}
alpha = cc * dotf (a, b) / div;
beta = -bb * dotf (a, c) / div;
gamma = aa * dotf (b, c) / div;
return alpha * points[0] + beta * points[1] + gamma * points[2];
*center = alpha * points[0] + beta * points[1] + gamma * points[2];
return 1;
case 4:
a = points[1] - points[0];
b = points[2] - points[0];
@ -126,13 +134,17 @@ circum_circle (const vec4f_t points[], int num_points)
ca = crossf (c, a);
ab = crossf (a, b);
div = 2 * dotf (a, bc);
if (fabs (div[0]) < EQUAL_EPSILON) {
// degenerate
return 0;
}
aa = dotf (a, a) / div;
bb = dotf (b, b) / div;
cc = dotf (c, c) / div;
return bc * aa + bb * ca + cc * ab + points[0];
*center = bc * aa + bb * ca + cc * ab + points[0];
return 1;
}
vec4f_t zero = {};
return zero;
return 0;
}
vspheref_t
@ -140,9 +152,13 @@ CircumSphere_vf (const vec4f_t *points, int num_points)
{
vspheref_t sphere = {};
if (num_points > 0 && num_points <= 4) {
sphere.center = circum_circle (points, num_points);
vec4f_t d = sphere.center - points[0];
sphere.radius = sqrt(dotf (d, d)[0]);
if (circum_circle (points, num_points, &sphere.center)) {
vec4f_t d = sphere.center - points[0];
sphere.radius = sqrt(dotf (d, d)[0]);
} else {
// degenerate
sphere.radius = -1;
}
}
return sphere;
}

7
libs/util/test/test-csvf.c
View file

@ -105,13 +105,18 @@ main (int argc, const char **argv)
VectorSet (rnd (&mt), rnd (&mt), rnd (&mt), cloud[j]);
}
cc = CircumSphere_vf (cloud, 4);
if (cc.radius < 0) {
// degenerate
continue;
}
r2 = cc.radius * cc.radius;
for (j = 0; j < 4; j++) {
vec4f_t d = cloud[j] - cc.center;
fr = dotf (d, d)[0];
if (fabs (fr - r2) < 1e-3 * r2)
continue;
printf ("%d %.9g - %.9g = %.9g %.9g\n", j, fr, r2, fr - r2, fabs(fr - r2));
printf ("%zd %d %.9g - %.9g = %.9g %.9g\n",
i, j, fr, r2, fr - r2, fabs(fr - r2));
printf ("[%.9g %.9g %.9g] - [%.9g %.9g %.9g] = %.9g != %.9g\n",
VectorExpand (cloud[j]), VectorExpand (cc.center), fr, r2);
res = 1;