[JAVA][Beginning Java 8 Games Development]

Chapter 16 ■ Collision Detection: Creating SVG Polygons for the Game Actors and Writing Code to Detect Collision
An example of an “unknown” class would be one of your own customized Bounds subclasses, if you were to write
one, that is. The Java 8 class hierarchy for the javafx.geometry.Bounds class would look like the following:
java.lang.Object
> javafx.geometry.Bounds
The Bounds class is used to create Bounds objects. These are used to describe the Bounds of a Node object,
which as we know are JavaFX Scene Graph Node objects. An important characteristic of a Bounds object is that it can
have a negative width, height, or depth. A negative value for any of the Bounds object attributes (properties) is used
to indicate that the Bounds object is empty. We will be using this in our code later on to ascertain when a collision has
not occurred. As I pointed out earlier in this book, sometimes you have to take the “opposite” approach to finding the
solution, or the proper work process, for achieving your game design and programming objectives.
Using Node Local Bounds: The .getBoundsInLocal() Method
One of the important methods in the JavaFX Scene Graph Node class is the public final Bounds .getBoundsInLocal()
method. This method is the getter method that retrieves the value of the boundsInLocal property. The boundsInLocal
property is “read-only” and holds a rectangular Bounds object for the Node it is contained in. The data that it contains
represents untransformed (original) local coordinate space for a Node. Untransformed means the Node coordinates
prior to their being rotated, translated, or scaled, which represents the Node object’s original (default) coordinates.
For a Node class (object) that extends the Shape class (which our ImageView Node does not), the local Bounds
will also include the space required to implement a non-zero Shape (or Path) stroke, as this might extend “outside” of
the Shape geometry, which is being defined by these position and size attributes. A local Bounds object also includes
any clipping path areas that you may have set, as well as the extents of any special effects that you may have set.
The boundsInLocal property will always have a non-null value, and it is important to note that this method does
not take the Node object’s visibility into account, so the computation is based on the geometry of the Node only. The
boundsInLocal property is automatically computed whenever the geometry of a Node object changes.
We will be using the .getBoundsInLocal() method on an intersection of our InvinciBagel SVGPath Shape data
with our other Scene Actor Prop SVGPath collision Shape data, in order to ascertain if the width of the intersection is
negative one, as -1 in a Bounds object, as we have learned, is empty, or no intersection, which signifies no collision.
Next, let’s take a look at the boundsInParent property, which contains the boundsInLocal data plus transformations.
Using Node Parent Bounds: The .getBoundsInParent() Method
Another one of those important methods to understand in the JavaFX Scene Graph Node class is the public
final Bounds .getBoundsInParent() method. This method is the getter method that retrieves the value of the
boundsInParent property. The boundsInParent property is a “read-only” property that holds the rectangular Bounds
object for the Node it is contained in. The data that it contains represents the transformed (modified) coordinate
space for a Node. Transformed means the Node coordinates plus any transforms that have taken place since the Node
object’s default, initial or original state. It is named “boundsInParent” because the Bounds object rectangle data will
need to be relative to the Parent Node object’s coordinate system. This represents the ’visual’ bounds of the Node
object, as in what you see on the screen, after the Node has been moved, rotated, scaled, skewed, and so on.
The boundsInParent property is calculated by taking a local Bounds, defined by the boundsInLocal property,
and applying all of the transforms that have taken place, including any calls to .set() methods for the following Node
properties: scaleX, scaleY, rotate, layoutX, layoutY, translateX, translateY, and transforms (the Java ObservableList).
Just like the boundsInLocal property, this boundsInParent property will always contain a non-null value.
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