/** Compute the Z-order */
void getZOrder() {
// transform the coordinates
if (!transformed) {
mat.transform(realXYZ, screenXYZ, np);
transformed = true;
}
// bubble sort z-order
// zOrder[0] is the fartherest from the viewer
// zOrder[np - 1] is the nearest to the viewer
for (int i = 0; i < np; i++) zOrder[i] = i;
for (int i = 0; i < np; i++) {
// find the particle with the smallest z
int jm = i, k;
for (int j = i + 1; j < np; j++)
if (screenXYZ[zOrder[j]][2] < screenXYZ[zOrder[jm]][2]) jm = j;
if (jm != i) {
k = zOrder[i];
zOrder[i] = zOrder[jm];
zOrder[jm] = k;
}
}
}
