[JAVA][Beginning Java 8 Games Development]

Chapter 16
Collision Detection: Creating SVG
Polygons for the Game Actors and
Writing Code to Detect Collision
Now that we have implemented digital audio for our game sound effects and short-loop music, as well as
implemented our digital imaging related classes that create motion sprites (characters) and fixed sprites (props),
we will now delve into the other major genre or area of new media: vectors. Vectors are utilized in 2D illustration
software (InkScape) as well as 3D modeling and animation software (Blender), and use math to define the shapes that
are used to create the 2D or 3D artwork. This makes vectors the perfect solution for defining custom collision shapes
that perfectly encase our sprites, so that instead of using a complex array of pixels to detect collision, we use a far
simpler (and far more memory and processor efficient) collision polygon, that will perfectly surround our sprite.
Fortunately for us, the JavaFX SVGPath class in the javafx.scene.shape package allows us to use custom SVG
Path (Shape) data to define our sprite collision boundaries. Not only that, but this SVGPath class (object) is also
highly efficient, as it has zero properties, only a few methods, and a simple SVGPath() constructor method, as you
have seen already in Chapter 8. This means that using the SVGPath class (object) is relatively memory and processor
efficient. In fact, the only method that we will need to use is the .setContent() method that we used in our Actor class
constructor method in Chapter 8. Since we’ll do this once, at game start-up, the SVG Path collision data will be loaded
into system memory and will be used in our collision detection routines, which we will be putting into place later in
this chapter.
In this chapter we’ll take a detailed look at how the SVG Path data can be defined. This is specified by World
Wide Web (W3) Consortium (also known as W3C), the body who defines HTML5. This specification is on their w3.org
website, and is located at the http://www.w3.org/TR/SVG/paths.html URL, if you want to view it in further detail.
After we look at the SVG or Scalable Vector Graphics (in case you are wondering what this stands for) data
format in detail, we will get into using the popular GIMP 2.8 digital image editing software, which you installed
in Chapter 1, and learn how to create collision polygons. We will also take a look at how to use the PhysEd
(PhysicsEditor) collision polygon generation software. This is from a company called CodeAndWeb GmbH, who
makes professional, and affordable, game assets creation software.
We will go through a collision polygon vector asset creation and optimization process using GIMP 2.8, using both
the quick and dirty work process, which allows GIMP to 100% create the collision polygon shape for you, as well as
a more “involved” work process, where you create your own collision polygon yourself, by hand, using GIMP’s Path
tools. After we have learned how to create collision polygons that are compatible with the JavaFX SVGPath class, we
will spend the remainder of the chapter on Java 8 game programming, creating the collision detection engine (code)
that will allow us to detect when our InvinciBagel character comes into contact with any of the other Actor objects in
the game environment (Scene and Stage objects). This is where the book will start to become more advanced (useful).
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