Killer Game Programming in Java

Creating Ground Cover

Ground cover is the 2D scenery that decorates a landscape. An item of ground cover is represented by a transparent GIF pasted onto a quad that stands on the terrain's surface and is always oriented towards the viewer. The quad is implemented as a four-sided QuadArray inside a GroundShape object (a subclass of OrientedShape3D). The pasting uses blended transparency so the quad is invisible and only the opaque parts of the GIF are rendered.

Typical ground cover includes trees, bushes, and road signs. Such elements will appear many times inside a scene, and it would be inefficient to create a separate shape for each one. Instead, the GroundShape object (e.g., a tree) is embedded in a SharedGroup node, which allows the geometry to be shared by multiple TransformGroups. Each TransfromGroup specifies a location for a particular ground cover element, but the object is a shared node.

The approach is illustrated by Figure 27-19.

Figure 27-19. A subgraph using a shared GroundShape object

Since a GroundShape object is attached to landBG, terrain coordinates can be used to set its position inside the landscape.

The constructor for Landscape() adds ground cover by calling:

    GroundCover gc = new GroundCover(fname);
    landBG.addChild( gc.getCoverBG() );

The GroundCover object, gc, manages the creation of the subgraph holding the ground cover items. The call to getCoverBG() returns the ...