Johan van Mol .org - Collision detection & bouncing part 3: bouncing balls

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Collision detection & bouncing part 3: bouncing balls

Sunday, 10 September 2006

Article Index
Collision detection & bouncing part 3: bouncing balls
More about the dot product
demo 1: basic bouncing
demo 2: finding the closest wall
demo 3: recursive collision detection
demo4: rethinking the algorithm
demo5: bouncing off sloped walls
demo6: the last bug

Page 1 of 8

This is the third article on collision detection and bouncing in Flash. This article will explain how collision works between a light object and a much heavier object, such as a ball and a wall. In this case the collision response is quite simple because the heavy object is not affected by the collision.
This article builds on the algortihms explained in the first and second article.
The flash movie below will give you a taste of what you'll be able to do after reading this tutorial.

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Comments

Its a gr8 tutorial for how can we use vectors instead of trigonometry for motions and collisions
Posted by poonam sheth, Whose homepage is http://smspoonam.blogspot.com on Wednesday, 11 October 2006 at 10:17

There's a typo on step 3bis:
...the Y-component of Y...
instead of
...the Y-component of v...
but great work ;).
Posted by Fugus, on Thursday, 19 October 2006 at 12:47

I fixed the typo. Thanx.
Posted by Johan van Mol, on Thursday, 19 October 2006 at 3:06

Thanks for the great set of tutorials, very helpful!

One issue I've been trying to solve is dealing with walls that the ball can hit from either side. The direction of the normal throws things off. What I did was added an else after the 'if (this.walls[i].n.dot(speedVec) < 0) { ' block in move().

Instead of var vec:Vector = this.walls[i].n.getInverted().cross(this.radius); in the else I have it as var vec:Vector = this.walls[i].n.cross(this.radius);

This seems to work, but I'm worried I've recreated the bugs you addressed in demo4, and I'm guessing there might be a better solution out there.
Posted by peter, Whose homepage is http://www.thup.com/ on Thursday, 07 December 2006 at 11:17

do you got a tool to convert a drawed wallshape to this wall array that needed?
Posted by Peter, Whose homepage is http://index.hu on Wednesday, 30 May 2007 at 4:03

First I draw the shape in Illustrator and save the file in Illustrator 8 format. Open the file in a text editor, scroll to the bottom and you'll find something like
(Layer 1) Ln
... more stuff here ...
24 803 m
69 828 l
108 775 l
31 757 l
24 803 l
The numbers in front are the X and Y coordinates. 'm' means moveTo, 'l' means lineTo. I copy and paste these codes, save them as a string in actionscript and parse the string.
Posted by Johan van Mol, on Wednesday, 30 May 2007 at 5:20

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