// Collision detection of two boxs with arbitrary angles.
// Does only one side (a->b) of the collision.
// -- If no collision, then no collision..
// -- If returns collision, check the other side (b<-a)
// -- A vector will be returned to displace 'a' so that there is no
// no collision anymore. The vector returned is one of the normals of 'b'.
static vec_t box_o_o_collision(box_t a, box_t b) {
// We will perform the collision using b's point of view and axes because
// those will be consided the surface normals, and we want to return 'a's'
// displacement in terms of 'a's' orientation vectors. -- So this may at times look reveresed.
vec_t dist = vec_diff(b.pos, a.pos);
// Normalized axis of box b. One of those axes will be the surface normal.
vec_t axn[2]; // = { b.axis0, b.axis1 };
float axl[2]; // Half axis length.
// Half axis.
vec_t ahx0 = vec_scale(a.axis0, a.size.x);
vec_t ahx1 = vec_scale(a.axis1, a.size.y);
// Distance we need to displace 'a' to remove the collision.
// -- (0, 0) => no collision.
float col_vec[2] = { 0.0, 0.0 };
int i = 2;
axn[0] = b.axis0;
axn[1] = b.axis1;
axl[0] = b.size.x;
axl[1] = b.size.y;
while(i--) {
float a1, a2, d;
// We check if the distance from center to center is smaller
// than the sum of the distance from center to box edge
// and that projection along each vector normal.
// If it is false for one normal, we have no collision.
// Otherwise we have the displacement distance to remove the collision.
a1 = vec_absdot(axn[i], ahx0);
a2 = vec_absdot(axn[i], ahx1);
d = vec_absdot(axn[i], dist);
col_vec[i] = a1 + a2 + axl[i] - d;
if(col_vec[i] <= 0) {
// Then there was no intersection.
return vec_new(0, 0);
}
}
if(col_vec[0] < col_vec[1]) {
if(vec_dot(dist, axn[0]) > 0) {
return vec_scale(axn[0], col_vec[0]);
} else {
return vec_scale(axn[0], -col_vec[0]);
}
} else {
if(vec_dot(dist, axn[1]) > 0) {
return vec_scale(axn[1], col_vec[1]);
} else {
return vec_scale(axn[1], -col_vec[1]);
}
}
}
/**
* Collision detection of two box with arbitrary angles. Does
* only one side (a->b) of the collision.
* if it returns no collision -> no collision
* if it returns a collision -> check the other side (b<-a)
* It will return a vector to displace a so that there is no collision
* anymore. the vector returned is one of the normals of b.
*/
static vec_t box_o_o_collision(box_t a, box_t b){
/* we will perform the collision using b point of view and axis
* because those will be considered the surface normals, and we
* want to return 'a' displacement in terms of 'b' surface normals
* and not in terms of 'a' orientation vectors.
* that's why the logic looks reverse at times
* */
vec_t dist = vec_diff(b.pos,a.pos);
/* normalized axis of the box b. One of those axis will be the
* surface normal. */
vec_t axn[2]; /* = {b.axis0, b.axis1}; */
float axl[2]; /* half axis length */
/* a half axis */
vec_t ahx0 = vec_scale(a.axis0,a.size.x);
vec_t ahx1 = vec_scale(a.axis1,a.size.y);
/*distance we need to displace a to remove the collision.
* (0,0) => no collision*/
float col_vec[2] = { 0.0, 0.0 };
int i = 2;
axn[0] = b.axis0;
axn[1] = b.axis1;
axl[0] = b.size.x;
axl[1] = b.size.y;
while(i--){
float a1,a2,d;
/* we check if the distance from center to center is smaller
* than the sum of the distance from center to box edges.
* and that projected along each vector normal.
* If it is false for one normal, we have no collision.
* otherwise we have the displacement distance to remove
* the collision.
*/
a1 = vec_absdot(axn[i],ahx0);
a2 = vec_absdot(axn[i],ahx1);
d = vec_absdot(axn[i],dist);
col_vec[i] = a1 + a2 + axl[i] - d;
if(col_vec[i] <= 0){ /* No intersection ! */
return vec_new(0,0);
}
/*printf("a1:%f\t,a2:%f\t,b1:%f\t,d:%f\tr:%f\n",
a1,a2,axl[i],d,col_vec[i] );*/
}
/* col_vec has the distance we need to displace 'a' along axn[0],axn[1]
* to remove the collision. We now need to pick the shortest
* distance and the right direction.
* This is just choosing smallest dist and flipping normals if
* necessary.
*/
if(col_vec[0] < col_vec[1]){
if(vec_dot(dist,axn[0]) > 0 ){
return vec_scale(axn[0], col_vec[0]);
}else{
return vec_scale(axn[0],-col_vec[0]);
}
}else{
if(vec_dot(dist,axn[1]) > 0){
return vec_scale(axn[1], col_vec[1]);
}else{
return vec_scale(axn[1],-col_vec[1]);
}
}
}
