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# 2D Vector Acceleration: Trying to make an object stay on the center line.

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2 replies to this topic

### #1asperatology  Members

Posted 04 October 2012 - 01:12 AM

I have an object that stays in one place on one of the two inclines, or pipes, however you want to call it. Below shows a top and side view of what's currently going on. In my 2D game, I use the top view for everything. I added the side view so that you may understand the top view's actual design and what it should be like in the game. The game itself uses vectors entirely for all of the entities.

The left side is what the end results should look like, and the right side is what's currently happening im my current build. The right side of the ball may also be on the other side of the incline (pipe), basically meaning that in the game, the ball isn't aligned like the left part of the diagram show above.

Thus, I wanted to add a vector acceleration, so that whenever the ball is off-centered, I can trigger the acceleration, so that the ball moves itself towards the center and align itself.

Problem is, I don't know the ball's acceleration at run-time (the ball could be accelerating outwards, away from the inclines (pipes)), so I would like to ask what vector calculations should I use and how should I use it? Thanks in advance!!

### #2Freya  Members

Posted 04 October 2012 - 02:00 AM

Suggestion: use some kind of destination point. If the ball has it's destination point in the center between two pipes, you can set acceleration vector as a difference between destination point and current position:
vec acc = (destination - currentPosition).normalied();

### #3asperatology  Members

Posted 04 October 2012 - 04:29 AM

This! Yes! This works. Now, I can continue to flesh out some more incline (pipe) collisions. Thanks!

Code for those curious:

float dax = (p.dstRect.left + p.dstRect.width() / 2) - position[0];
float day = (p.dstRect.top + p.dstRect.height() / 2) - position[1];
float dan = FloatMath.sqrt(dax * dax + day * day);
dax /= dan;
this.acceleration[0] -= dax;

Edited by tom_mai78101, 29 December 2012 - 01:41 AM.

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