GTE Tool Set

The Generic Tile Engine (GTE) Tool Set enables tile-based games to be implemented in an efficient manner. The tool set provides support for sprites, animations, large scrolling backgrounds and special effects.

To effectively use this tool set, a user should be familiar with the following

• The IIgs Hardware Reference
• The QuickDraw II tool set
• IIgs Technical Note #70

A preview of the GTE Tool Set routines

To introduce you to the capabilities of the GTE Tool Set the routines are grouped by function and briefly described in Table 1. These routines are descibed in detail later where they are separated into housekeeping routines (discussed in routine number order) and the rest of the GTE Tool Set routines (discussed in alphabetical order).

Using the GTE Tool Set

This section discusses how the GTE Tool Set routines fit into the general flow of an application and gives you an idea of which routines you'll need to use under normal circumstances. Each routine is described in detail later in this chapter. The GTE Tool Set depends on the presence of the tool sets shown in Table 2 and requires at least the indicated version of each tool set be present.

To use the GTE Tool Set routines, your application must call the GTEStartUp routine before making any other GTE calls. To save memory, the GTE Tool Set may be started up with some features disabled. See the section GTEStartUp in this chapter for further details.

Your application should also make the GTEShutDown call when the application quits.

Sprites

Object Attibute Memory

Sprites are displayed on screen by filling in the Object Attribute Memory (OAM) table. The application may obtain a pointer to this table by using the GTEGetAddress function with the oamAddr argument. There are a toal of 32 entries in the OAM table which limits the number of onscreen sprites. Each entry of the OAM table is defined as

 typedef struct
 {
   Word xpos;            /* Signed horizontal position */
   Word ypos;            /* Signed vertical position */
   Word flags;           /* Sprite flags (see below) */
   GTESpritePtr sprite;  /* Pointer to sprite */
 } OAMEntry, *OAMEntryPtr;
 

The sprite pointer must point to a sprite returned from the GTENewSprite function. The sprite flags are defined in Table 3.

Performance considerations and limitations