• Concave Polygon Working

    Separation of Axis Theorem (SAT) for Collision Detection

    The Separation of Axis Theorem(SAT) is a technique to test whether two convex polygons are colliding. The SAT theorem: "given two convex shapes, there exists a line onto which their projections will be separate if and only if they are not intersecting." The line where the shapes have disjoint projections is called the separating axis. A separating line is the line that can be drawn between the two shapes,...
  • PointInPoly

    AS3 2D Ray Casting For Collision Detection

    Ray casting is a technique usually used in 3D worlds (often for rendering). Ray casting is exactly what it implies a ray is cast from a start point until it hits something (or a max length, so the computer doesn't die). Ray casting in 2D is great for collision detections, especially fast-moving objects (bullets). In this post, we will learn the basics of ray casting in 2D, then we will apply it to bullets in a...
  • AStar

    A* Pathfinding Basics

    A* (A-star) is an algorithm used for pathfinding. Pathfinding is where a computer computes the shortest (or best) path from a start point to an end point through a grid or nodes. We will be using a grid to find a path. The green cell is the start point and the red cell is the end point. The computer must find the shortest route from start to finish without going through the walls. We are using a grid because...
  • Sierpinski triangle

    Sierpinski Triangle

    The Sierpinski Triangle is a famous fractal named after the mathematician who discovered it. It is made up of nested triangles that get smaller and smaller. If you were to zoom in, you would see the same image (though it may be translated) and you could zoom forever and never find the end. So, how do you create the Sierpinski Triangle in AS3? First you have to know how to do recursion. Recursion is...
  • Vehicle Following the Path

    A* and Pathfollowing Steering Behavior

    In the last three posts, we explored the how A* works, then we put A-star into code, then we looked at different heuristics for A*. Now we will combine A* pathfinding with the path following steering behavior. We have already done most of the work to do this. But we'll do a quick review in case you missed those posts. A* Pathfinding In A* we take a grid of cells and find a path from start to finish. Each...

  • Using the Separation of Axis Theorem

    A few months ago, I posted on the separation of axis theorem. You can learn all about SAT and how it works here. What that post failed to do was use the SAT. We will explore using SAT for collision detection in this post. In the post on SAT, we created the code to detect collisions, however use of the code was not covered. (A download of all the classes used in the post is available at the bottom). The Shape...

  • Detecting Collisions with SAT

    Today we will finally be detecting a collision with SAT. We know how SAT works, we've built classes to work with SAT, now we can use all of this to detect a real, live collision! Using the classes we created last time, this is quite simple. First create a shape: var shape1:Polygon = Polygon.rectangle(530, 30, new Vector2D(270, 360)); It's a simple polygon created using the static function of the rectangle...

Posts tagged SWF

Flee

Steering Behavior: Fleeing

Jun 12th

Posted by rocketman in AI

No comments

This entry is part of 9 in the series Steering Behaviors

Time for the next steering behavior, fleeing. This will use the same Vehicle.as class and will be built off what we did in the seeking behavior. It is based on Craig Reynolds’ article, Steering Behaviors For Autonomous Characters.

Fleeing Behavior

Fleeing is very similar to seeking. It is actually the inverse of seeking. Instead of going towards the target, fleeing goes away from the target. It works like this:

1. desiredVelocity = target – position

2. desiredVelocity is normalized and multiplied by maxSpeed.

3. desiredVelocity is multiplied by -1 to go away from the target

4. steeringForce More >

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Steering Behaviors: Seeking

Jun 11th

Posted by rocketman in AI

1 comment

This entry is part of 9 in the series Steering Behaviors

Steering behaviors are used to create intelligent movements on a computer. These posts will be an AS3 version of the principles illustrated in Craig Reynolds’ article located at http://www.red3d.com/cwr/steer/gdc99/.

Before we can start using steering behaviors, we need a few classes. First we will be using, yet again, the Vector2D.as class. Steering behaviors rely on vector math, so you should be familiar with it.

If you need more information on vector mathematics, you can look here:

https://users.cs.jmu.edu/bernstdh/web/common/lectures/slides_vector-math-2d.php

http://en.wikipedia.org/wiki/Vector_%28mathematics%29

Next we will need a vehicle class to hold all the vehicle’s properties. The properties each vehicle will More >

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SAT in Action

May 22nd

Posted by rocketman in AS3

2 comments

In a previous post, I explained the Separation of Axis Theorem. Now it’s time to see SAT in action.

Click on a shape to move it. It both will turn red when they are touching. The shapes will turn black again when they are not colliding. Use the drop down lists to change the shapes.

Click here to see SAT in action!

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