JavaFX: Mapping pixels on screen to a 2D matrix

Question

I'm making an animation in which I need to keep track of explored/unexplored pixels on the screen.Initially the screen is black colored,then as the node(a circle) moves(over defined path) the explored pixels are set to white.For doing this task(color change) I'm using Canvas class of JavaFX as background and painting the path using an object of GraphicsContext class(see the createPathAnimation method),now I want to update the int 2D matrix as 0-unexplored,1-explored. How can I use the changed() function inside createPathAnimation to update my matrix as that function is updating the pixel color to white and I need to update the same set of explored pixels to 1 in my matrix? sample translation

I'm trying to use the inbuilt function because even if I know the initial and final pixel coordinates,its not easy to determine which all pixels will be set while the circle moves between them(for ex along one of the diagonals),since circle is a like a blob of tiny squares on a pixel level. My motive is to find the number of white colored pixels after a diagonal translation.

public void start(Stage primaryStage)throws Exception{
    Pane root=new Pane();
    Path path1=createPath();

    canvas=new Canvas(800,600);

    root.getChildren().addAll(path1,canvas);

    primaryStage.setScene(new Scene(root,800,600,Color.BLACK));
    primaryStage.show();

    Animation animation1=createPathAnimation(path1,Duration.seconds(10));

    pt.getChildren().addAll(animation1);
    pt.play();
}


private Path createPath(){
    Path path=new Path();
    path.setStroke(Color.BLACK);
    path.setStrokeWidth(10);
    path.getElements().add(new MoveTo(400,300));
    path.getElements().add(new LineTo(600,500));
    return path;
}
public int a,b;
private Animation createPathAnimation(Path path,Duration duration){
    GraphicsContext gc=canvas.getGraphicsContext2D();
    Circle pen=new Circle(0,0,10);
    PathTransition pathTransition=new PathTransition(duration,path,pen);
    pathTransition.currentTimeProperty().addListener(new ChangeListener<Duration>(){

        Location oldLocation = null;

        /**
         * Draw a line from the old location to the new location
         */
        @Override
        public void changed(ObservableValue<? extends Duration> observable, Duration oldValue, Duration newValue) {


            if( oldValue == Duration.ZERO)
                return;

            // get current location
            double x = pen.getTranslateX();
            double y = pen.getTranslateY();

            // initialize the location
            if( oldLocation == null) {
                oldLocation = new Location();
                oldLocation.x = x;
                oldLocation.y = y;
                return;
            }

            // draw line
            gc.setStroke(Color.WHITE);
            gc.setLineWidth(30);
            gc.strokeLine(oldLocation.x, oldLocation.y, x, y);

            // update old location with current one
            oldLocation.x = x;
            oldLocation.y = y;
        }
    });

    return pathTransition;
}

public static class Location {
    double x;
    double y;