Weblog: Pieter Vanderwerff Visualisations

I have made this tutorial to help make it clearer how to do line collisions using my Bounding Shape action in Flint. This tutorial is not necessarily the best or most efficient way of doing this, it is just the way I have found to work well for me.

First you will need to download and extract the Flintcollide.rar file that I have put together, contained within this archive is the Flint code from the Lines and Collisions Branch of the SVN with the addition of my own BoundingShape.as file in the twoD/actions folder. Within the flint source code I have removed the flintparticles/threeD folder to reduce file size since this technique is 2D only. Also within this archive I have included the flash file of the line collisions example shown above.

Now with the above file extracted, open the Flash/collide.fla file in flash. If you have not changed the file structure of the downloaded archive you should be able to publish (F12) the file without errors and see the example swf above.

To get line collisions to work in your own projects you will first need to make sure that the flint collide library source code you previously download is in the classpath for the project, this webpage documents how to do this. If you have been using the SWC version of the Flint code previously you will need to unlink this from the project.

Now within your action script code you will need the following two lines, the first line creates a new LineZone, this is the line you want the particles to bounce off. The second line creates a new BoundingShape instance and adds the action to the emitter. You will also need the respective import declarations.

var collideLine:LineZone = new LineZone( new Point(150, 400), new Point(300, 250) );
    
emitter.addAction( new BoundingShape( collideLine, 1 ) );

The BoundingShape class accepts two variables when creating it, the first is the LineZone you want the particles to collide with and the second is the Bounce coefficient of restitution when the particles bounce off the line, this should be a number from 0 to 1, this is that same as with the BoundingBox class (See documentation here).
These lines of code can be simplified to this:

emitter.addAction( new BoundingShape( new LineZone( new Point(150, 400), new Point(300, 250) ), 1 ) );

This code is not perfect and has problems in the same way the collide particle action does as it is designed for speed over accuracy. It should also be noted that I did not create the code which calculates the collisions this was created by Richard Lord the author of flint and was in the SVN, I simply created a 2D action that implemented this code.

When the particles are travelling at a high speed it becomes more likely for the particles to travel through the line and not collide, to reduce the likeness I suggest you try to keep your frame rate as high as possible as the longer between calculations the more likely it is the particle will jump over the line. Also increasing the collision radius helps stop particles going through, but it should be noted that with a high collision radius some particles instead of jumping over the line get stuck on it and bounce inside it till they reach the end.

emitter.addInitializer( new CollisionRadiusInit( 5 ) );

All credit should go to Richard Lord at Flint for creating this amazing action script library. If you have any problems leave a comment.