[JAVA][Beginning Java 8 Games Development]

Chapter 16 ■ Collision Detection: Creating SVG Polygons for the Game Actors and Writing Code to Detect Collision
Chapter 8. Off of the Actor object we pass into the .collide() method we will method chain the .getBoundsInParent()
method call, resulting in the object.getSpriteFrame().getBoundsInParent() structure, which is then placed on the
inside of an .intersect() method call. The complete conditional if() construct looks like this:
if( invinciBagel.iBagel.spriteFrame.getBoundsInParent().intersects(
object.getSpriteFrame().getBoundsInParent() ) ){second level of collision detection in here}
This first level of collision detection code will check for the intersection of the iBagel spriteFrame ImageView
Node with the spriteFrame ImageView Node object that is contained in each Actor object that will be passed into this
.collide(Actor object) method call that we are coding currently.
This part of the code will check for a “top level” ImageView Node proximity (collision) before we call a more
“expensive” Shape intersection algorithm, which we are going to implement next, in order to confirm more definitive
collision occurrence (SVGPath collision polygon intersection). Remember that the code we’re putting into place
inside of this .collide() method will be processed for each iteration of the for loop (for each cast member) that is
calling this collide(Actor object) method.
The Java code inside of this first conditional if() statement creates a Shape object, named intersection, and sets
it equal to the result of an SVGPath.intersect() method call that references the iBagel SVGPath Shape object and an
SVGPath Shape object passed into the collide(Actor object) method. Both objects call a .getSpriteBound() method,
which we created back in Chapter 8, to access the SVGPath Shape objects needed for the .intersect(Shape1, Shape2)
method call format. Your Java code, formatted using two lines of code, for readability, should look like the following:
Shape intersection = SVGPath.intersect( invinciBagel.iBagel.getSpriteBound(),
object.getSpriteBound() );
After we have this intersection data, we will use another conditional if() statement to see if that intersection
Shape object contains any collision data, and if it does (that is, if it doesn’t contain a -1 value) a collision has occurred.
The second nested if() statement will utilize the .getBoundsInLocal().getWidth() method chain, called off of
the intersection Shape object, and will check to see if it is empty (returns a -1 value), or if a collision has occurred. The
collision detection will occur if the intersection Shape object’s Bounds object contains any data value other than -1. In
the body of the if() statement, collisionDetect Boolean flag is set to true of any data is present ( signified by != -1). The
Java code for the conditional if() statement should look like the following:
if(intersection.getBoundsInLocal().getWidth() != -1) { collisionDetect = true; }
To test the collision code, I put the invinciBagel.playiSound0() method call inside of the if(collisionDetect){}
conditional statement. This is why I commented out that .playAudioClip() method call in the .update() method, so
that the only thing that I will hear during a collision is the audio playback. This is a quick, easy, and effective way
to test the collision code, at least for now. Since this is the public boolean collide(Actor object) method, I am also
going to put a return true; line of code at the end of the if() body, that returns a true value from the method call.
I am placing the statement inside of this conditional if() construct, so that if needed, we can use this true Boolean
value returned from the .collide() method call in the .update() method for other processing, if we want to. The
very nature of this .collide() method is to detect if a collision has occurred and then return a value, so we could do
further processing inside of the .collide() method, or more efficiently do this on-collision processing inside of the
.checkCollision() method, using an if(collide(object)=true){invinciBagel.playiSound0();} construct, instead
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