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[diderot] View of /trunk/doc/probe/code/c3dgrad.c
 [diderot] / trunk / doc / probe / code / c3dgrad.c

# View of /trunk/doc/probe/code/c3dgrad.c

Revision 296 - (download) (as text) (annotate)
Sun Aug 15 23:06:00 2010 UTC (8 years, 11 months ago) by glk
File size: 2446 byte(s)
`for gradient code`
```#include <stdio.h>
#include <math.h>

#define IMG_SZ 11

double V[IMG_SZ][IMG_SZ][IMG_SZ];		// image data
double h[4][4] = {		// bspln3
{ 1.33333,   2.0,  1.0,  0.166667 },   // -2 .. -1
{ 0.666667,  0.0, -1.0, -0.5 },        // -1 .. 0
{ 0.666667,  0.0, -1.0,  0.5 },        //  0 .. 1
{ 1.33333,  -2.0,  1.0, -0.166667 },   //  1 .. 2
};
const int s = 2;       // kernel support

typedef double vec3[3];

void
probe (double grad[3], const double x[3])
{
/* double x[3] = transform(p);	// image-space position */
double nxd, nyd, nzd, fx, fy, fz;
int nx, ny, nz;

fx = modf (x[0], &nxd); nx = (int)nxd;
fy = modf (x[1], &nyd); ny = (int)nyd;
fz = modf (x[2], &nzd); nz = (int)nzd;

// compute kernel values for each axis
double hx[4], dhx[4], hy[4], dhy[4], hz[4], dhz[4];
for (int i = 1-s;  i <= s;  i++) {
double t;
t = fx - i;
hx[i+s-1] = h[s-i][0] + t*(h[s-i][1] + t*(h[s-i][2] + t*h[s-i][3]));
dhx[i+s-1] = h[s-i][1] + t*(2*h[s-i][2] + t*3*h[s-i][3]);
t = fy - i;
hy[i+s-1] = h[s-i][0] + t*(h[s-i][1] + t*(h[s-i][2] + t*h[s-i][3]));
dhy[i+s-1] = h[s-i][1] + t*(2*h[s-i][2] + t*3*h[s-i][3]);
t = fz - i;
hz[i+s-1] = h[s-i][0] + t*(h[s-i][1] + t*(h[s-i][2] + t*h[s-i][3]));
dhz[i+s-1] = h[s-i][1] + t*(2*h[s-i][2] + t*3*h[s-i][3]);
}

vec3 vx = {0, 0, 0};
for (int i = 1-s;  i <= s;  i++) {
vec3 vy = {0, 0, 0};
for (int j = 1-s;  j <= s;  j++) {
vec3 vz = {0, 0, 0};
for (int k = 1-s;  k <= s;  k++) {
double v = V[nx+i][ny+j][nz+k];
vz[0] += v * hz[k+s-1];
vz[1] += v * hz[k+s-1];
vz[2] += v * dhz[k+s-1];
}
vy[0] += vz[0] * hy[j+s-1];
vy[1] += vz[1] * dhy[j+s-1];
vy[2] += vz[2] * hy[j+s-1];
}
vx[0] += vy[0] * dhx[i+s-1];
vx[1] += vy[1] * hx[i+s-1];
vx[2] += vy[2] * hx[i+s-1];
}

return;
}

#define AIR_AFFINE(i,x,I,o,O) ( \
((double)(O)-(o))*((double)(x)-(i)) / ((double)(I)-(i)) + (o))

int
main() {
int I, J, K, N;

V[5][5][5] = 1.0;
N=60;
for (I=0; I<N; I++) {
P[0] = AIR_AFFINE(0, I, N, 2.0001, 7.9999);
for (J=0; J<N; J++) {
P[1] = AIR_AFFINE(0, J, N, 2.0001, 7.9999);
for (K=0; K<N; K++) {
P[2] = AIR_AFFINE(0, K, N, 2.0001, 7.9999);