Killer Game Programming in Java

Managing the Ribbons

RibbonsManager is mainly a router, sending move method calls and update() and display() calls to the multiple Ribbon objects under its charge. Initially, it creates the Ribbon objects, so it acts as a central storage for their GIFs and move factors.

The initialization phase is carried out in the constructor:

    // globals
    private String ribImages[] = {"mountains", "houses", "trees"};
    private double moveFactors[] = {0.1, 0.5, 1.0};
       // applied to moveSize
       // a move factor of 0 would make a ribbon stationary

    private Ribbon[] ribbons;
    private int numRibbons;
    private int moveSize;
       // standard distance for a ribbon to 'move' each tick


    public RibbonsManager(int w, int h, int brickMvSz, ImagesLoader imsLd)
    { moveSize = brickMvSz;
            // the basic move size is the same as the bricks map

      numRibbons = ribImages.length;
      ribbons = new Ribbon[numRibbons];

      for (int i = 0; i < numRibbons; i++)
         ribbons[i] = new Ribbon(w, h, imsLd.getImage( ribImages[i] ),
                                    (int) (moveFactors[i]*moveSize));
    }  // end of RibbonsManager()

The choice of GIFs is hardwired into ribImages[], and the constructor loops through the array creating a Ribbon object for each one.

The basic move size is the same as that used by the bricks layer but multiplied by a fixed moveFactors[] value to get a size suitable for each Ribbon.

Tip

A move size is the amount that a background layer moves in each animation period.

A move factor will usually be less than one, to reduce the move size for a Ribbon in comparison to the bricks ...