HowToC:FollowAnObject
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How to follow an object with the camera
Using handles, you can easily detect when an object has been right-clicked. With two pretty simple bits of code, you can then make the camera keep focussed on that object.
1. use a handle callback to register the most recently selected handle:
int camfollow; // initialised to -1 in main
unsigned char *selected; // array storing selected state of all handles
void pickcb(int *id) {
// ...
// toggle state:
selected[*id] = (selected[*id] + 1) % 2;
if (selected[*id]) {
camfollow = *id;
} else {
camfollow = -1;
}
s2togglehandle(*id);
}
2. in the standard dynamic callback, set the camera position if required XYZ *iP; // array storing positions of all handles
void callback(double *t, int *kc) {
// ...
if (camfollow >= 0) {
// a. fetch current camera position, up and view direction vectors
XYZ position, up, vdir;
ss2qc(&position, &up, &vdir, 1);
// b. calculate new right vector
XYZ vright = CrossProduct(vdir, up);
// c. calculate new view direction vector
vdir = VectorSub(position, iP[camfollow]);
Normalise(&vdir);
// d. calculate new up vector and set new camera position
up = CrossProduct(vright, vdir);
ss2sc(position, up, vdir, 1);
}
// ...
}
