Ball collision and sweep test

Programming Questions

allonestr..

Ball collision and sweep test

in Programming Questions • 2 years ago

I've been relearning vectors by rewriting my cartesian/trig-based ball collisions as PVectors (like you do).

The result with balls colliding with

- other balls

- stationary balls (here called rings)

- lines

is here. And I'm really quite chuffed!

I'm considering adding sweep tests (nicely descirbed here), but am struggling with getting my head round how to do so when the ball colliding with a moving object - in this case a rotating line. The ball "knows" its velocity, but the line's position and rotation are passed to it. So I can tell where the ball will be in the next frame, but I won't (necessarily) be able to tell where the line will be.

Do I

- pretend that the line is stationary and call that good enough

- store its previous position and rotation just in case it's going to hit a ball in the next frame

- rewrite it (though that doesn't really make sense given the type of beast it is)

- or what?

Thanks

Replies(2)

owaunz

Re: Ball collision and sweep test

2 years ago

You have two (2) options in my opinion

Option 1
Draw lines using just dots. That way when the collision occurs you know where on the line it occurs, and you can draw the points with vectors so you can store the velocity at witch that particular point on the line is moving in the z-axis in the vector. You can store whatever you like in the x and y since you already have a way to decide where the two collide.

Option 2
Since you are using large line-strokes, you can either draw a shape of the line or increase the strokeweight(). I prefer the shape of the line where instead of a straight line of dots in option 1 it is more of a line of dots to form a shape. Plus if you want to have a solid line just draw lines from one corresponding points to the adjacent side.

There is probably a better way but that's just off the top of my head.

allonestr..

Re: Ball collision and sweep test

2 years ago

Thanks, but I think that you've misunderstood my question.

My code, as it is, can deal with any positive line width, correcting the ball's position on collision according to that line width.

At the moment I am waiting for a collision then repositioning the ball and sending it on its way.

The sweep test looks to see if the ball's about to collide with an object between the current frame and the next frame, and repositions it before they overlap. I can see how to work this out when the ball hits a stationary object and when the ball hits another ball because I know the relative velocities, but can't see how best to deal with a ball moving according to its velocity and a line which isn't necessarily obeying any particular rules.

I think then that I've answered my own question; if the line's movement is unpredictable then I can't predict it, so I should pretend that either it's going to move from this frame to the next exactly as it did from the previous frame to this, or that it's stationary, and so live with either error.

Mm, thoughts still welcome.

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