New Control Behavior: Platformer

I just added a behavior for platformer style games. Find it here.

Like the article says, the code follows the design found in the MiniPlatformerTutorial. As such it is prone to several things:

1) For things to work properly, physics and collision must be set up as in the tutorial.
2) There is "bug" in the code that can sometimes get your character stuck on a wall and can lead to wall scaling (using jump). "Bug" is in quotes because it is unclear as to whether its a script bug or an engine bug. It is present in 1.1.3 and 1.5 Beta 3. One way to solve this would be to look into the collision information returned by the multiple calls to castCollision() and by using the onCollision() callback. Another way would be to use pickLine()/pickRect to determine the orientation of the player with respect to obstacles (note that you must be very careful if you include sloped surfaces in your level design).

(The above bug appears in rare cases where the code doesn't call %this.owner.setLinearVelocityX(0); until after the character is actually colliding with the wall. This then causes subsequent castCollision() calls to return a collision, pushing control flow into the final else-statement in the updateVertical() call, stopping all downward movement.)

Pre-Post [heh] Update:
The following code modification will fix the wall sticking bug with a special stipulation:
* This code was only checked when the character's Collision mode was set to Full or Polygon using a custom fitted 5-point polygon.
The script based fix [hack?] is located in the updateVertical() function. Change:

else if(%yVelocity < 0 && %this.airborne)
{
     %this.setConstantForceY(100);
}

to

else if((%yVelocity < 0 || mAbs(getWord(%collision, 5)) < 0.05) && %this.airborne)
{
     %this.setConstantForceY(100);
}

The behavior version would look like this:

else if((%yVelocity < 0 || mAbs(getWord(%collision, 5)) < 0.05) && %this.owner.airborne)
{
     %this.owner.setConstantForceY(100);
}

This uses the y-component of the collision normal returned by the castCollision() call to determine where the collision occurred. If you have only 100% vertical and horizontal surfaces, you can change "< 0.05" to "== 0". The more you increase that number (ie "< 0.10"), the more you limit the incline that the player can jump onto (adding functionality for running along inclines may require changes to the updateHorizontal() function, depending on your implementation). Keep in mind that you must play-test this value. The code above was checked using a custom polygon. Further testing with the default, square-polygon revealed a few inconsistencies with "< 0.05". Note that if you have any sloped surfaces, you may need to define your own non-square collision polygon to achieve the desired effect.

I recommend testing the value using "echo([playerNameField].castCollision(1));". If you are having trouble timing your calls, you can bind a key to that function or make it a global function in script and schedule() it in the command console. Good stuff!

Mountain Dew at the Vending Machine: $5
Ticket to Spiderman 3: $10
Adding platformer controls to an object in the engine in under 5 seconds: Priceless*

Test and enjoy!

Note:
This fix is not included in the behavior download for two reasons:
1) It is unclear if this bug is due to a bug in the source or an issue with the script (if a collision occurs, is the engine supposed to leave it there or push it just beyond the collision point?).
2) The code in the behavior attempts to remain as close to the code in the tutorial as possible. If the tutorial gets updated with this fix, so then too should the behavior.

* Actual cost depends on your hourly income and the number of hours it would take to implement the controls without Behaviors.