MPC spam#1

float angle180(vector a, b){
    return cos(clamp(dot(normalize(a), normalize(b)),-1,1)) ;
}
vector crossM(vector a, b){
    return {1,0,0} * lookat(0,-a,b) ;
}
vector alignrot(vector pos, a, b ; float lerp){
    return qrotate(quaternion(angle180(a,b) * lerp, crossM(a,b)), pos);
}

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vector b = {1,0,0} ;
vector e = {-1,0,0} ;


vector axis = {1,0,0} * lookat(0,-b,e) ;
float angle = acos(clamp(dot(normalize(b), normalize(e)),-1,1)) ;
vector4 quat = quaternion(angle*ch("blend"), axis) ;

vector pos = @P ;
pos = qrotate(quat, pos) ;

@P = pos ;