Skip to main content

Posts

Showing posts from December, 2011

SAT Collision Part 2

In this collision tutorial, we will take more in detail with how exact we get the normals and how we get the intervals.  However, I will not be going in detail regarding vector math needed to understand this, although it is simple and I will eventually post blogs regarding them. Down to business.  Our shape is composed of vertices.  In the case of this rectangle, there is four vertices, in red, and four normals, in brown.  The vertices are self explanatory and the normals describe the orientation or the way a side of the triangle is facing.  Take note that the vertices are defined such that the center of the triangle, not indicated in the picture, is at position(0,0) and all vertices defining the vertex is relative to this location; just like in a normal coordinate system. Now, to get the normal for a side of the rectangle we take two vertices defining an edge of the rectangle and subtract them.  Further, we swap the x, and y components and negate the new y component.  Then we norma

Introduction to SAT

When writing games, collision detection is important, especially one that is fast and robust.  True, you can get away with having a simple rectangular collision detection where your checking if two squares overlay, but that becomes less reliable when objects in your application/game are moving fast and many I good collision detection system is SAT or  Separating axis theorem.  It says that if two convex shapes' (shapes that do not invaginate) projections along their respective normals does not overlap then the shapes do not overlay.  More clearly, if there is any project that separates the two shapes, then there is a collision. That is it. However, this requires further explanation.  A convex shape is like a rectangle, an octagon, or any shape that does not fold into itself.  When using SAT, we use its normals, denoted by brown lines, to project two convex shapes while comparing to see if the two's intervals overlap. If an overlap exist, then a collision is occurring. Her

C++ Interface

In this tutorial we will discuss interfaces in C++ and why one would be of benefit.  First off, an interface serves as a means to have a commonality of usage for varies objects.  What I mean by that is that say you have a class representing a basketball and a class that represents a soccer ball, it is understood that both are used for playing but how they are played with is different.  That difference of how they are used for playing is where interfaces come in. An Interface provides a common way of using a class of type basketball and a class of type soccer ball without having will being able to refer to each different object(basketball or soccer ball) with the same interface. Okay okay, this is confusing so let us take a couple of examples. Without an interface, to have an object of basketball and soccer ball perform the same behavior, playing, you could do this: class BasketBall{ public:      void play(){           cout << "playing with basketball" << end