Closest distance at which a missile passes by your hero

Teachers
1

Maybe some people might be interested in this formula when trying to dodge missiles.
Knowing a missile position and velocity via appropriate methods .pos & .velocity.

p stands for position
v stands for velocity
d stands for the closest distance the missile will pass by your hero.

p = missile.pos ;
p0 = this.pos ;
v = missile.velocity ;
vNorm = Math.sqrt( v.x * v.x + v.y * v.y ) ;    

d = Math.abs( ( v.x * ( p.y - p0.y ) )   -   ( v.y * ( p.x - p0.x ) ) )   /  vNorm ;

In explicit wording, d is equal to the positive ( cross product of ( (the missile velocity) and (the vector “missile -> me”) ) ) divided by the norm of the missile velocity. (This definition would also work in 3D btw, as long as the trajectories are still linear)

A for-loop across the missiles that are close to your hero will provide you a list of dangerous missiles (if d < colisionRadius ). You might want to dodge those missiles.

For more documentation, I invite you to check Wikipedia
Edit : added 3 handwritten lines of explainations.

Explaination

7 Likes
2

I’m guessing this is the code you used for you apocalypse auto dodge code
Am I right?

3

Nah, it’s (mainly) for Sarven treasure 5, in order to dodge razor disks from HeadHunters.

My apocalypse code is more a swisscheese problem, where I define holes where I should not be at a given time. I get positions of the explosions with missile.targetPos (X,Y) and the timing is 3.6sec after a missile appears (T). So I find the safest path through this cheese, by checking the space-time distance from the explosion. Here is the idea :

// When a missile appears, I record the 3 parameters of the shell in an array.
X = missile.targetPos.x ;
Y = missile.targetPos.y ; // in meters.
T = this.now() + 3.6 ; // in seconds

In order to know if a position (x,y) is safe at a given time t, you can check if this position (x,y,t) is far enough from the explosion.

dX = X - x ;
dY = Y - y ;
dT = T - t ;
v = this.velocity

distanceFromExplosion = Math.sqrt( dX*dX + dY*dY + v*v*dT*dT ) ;

If distanceFromExplosion > explosionRadius (which is 10, but using 11 or 12 is safer), then the position (x,y,t) is safe.

So when I detect the position of my hero isn’t safe anymore, I compute several path around me (in a star pattern) to check that every steps (x,y) on my way to a safe position are safe (t is a future time. It is computed via t = distance / velocity). If I find one fully safe path, I do take this path. Rince and repeat.

Sometimes, there isn’t a path and the hero dies horribly. But that’s part of the fun :smile:

PM me if you want more info on Apocalypse.

4 Likes
4

I just have to say that eventually you have to pass over some x’s because at one point there in not place on the map that will not be in the radius of a projectile