Hardware Sprites

Section 7 of this User Guide concentrates on the moving image. You will learn how to create, edit and control moving objects and backgrounds, how to make them react to one another and how to create professional animations.

AMOS Professional offers ,a choice of two moving-object systems, each with its own characteristics and benefits. Objects stored as part of the current screen are featured in the next Chapter. These blitter objects (Bobs) are easy to use, very fast and incredibly flexible. Unfortunately, they consume a lot of memory and tend to slow down on 32 or 64-colour displays.

By contrast, this Chapter deals with those graphical objects that exist independently from the screen, known as Sprites. You will discover how AMOS Professional shatters the limitations imposed by the Amiga on the number, size and colours of Sprites, and how to fully exploit their potential.

Normal hardware Sprites
Sprites are directly generated by the Amiga's hardware. Because they are completely independent from the screen, they can be moved at very high speeds over any type of screen, including the 4096-colour screens achieved in HAM mode. This makes hardware Sprites ideal for use in arcade games.

The Amiga offers up to eight hardware Sprites for instant display over any position on screen. They are supposed to be exactly 16 units wide, up to 270 scan lines high and feature three colours, with colour zero "transparent", allowing the background screen to show through. The computer's hardware can also combine pairs of Sprites, increasing the range of colours to 15, but halving the number of available Sprites to just four.

A choice between eight 3-colour and four 15-colour Sprites on screen is very limited, and quite unacceptable to the AMOS Professional programmer, so the old Rule Book has been torn up and rewritten for your benefit.

AMOS Professional computed Sprites
The AMOS Professional system takes the original hardware Sprites and combines them in a revolutionary way. The new "computed Sprites" are extremely powerful, they are perfect for the games programmer and they offer the following advantages:

• 56 computed Sprites are allowed on screen at once.
• Each Sprite can feature up to 15 colours.
• Each Sprite may be up to 64 units wide.
• Each Sprite may be up to 270 lines high.

In order to take full advantage of computed Sprites in practice, you will need some working knowledge of the theory behind them.

AMOS Professional computed Sprites rely on the fact that each original Amiga hardware Sprite is up to 270 units high. So if your required image is smaller than this, most of the Sprite area is effectively wasted. Look at the diagram below, which shows a single hardware Sprite positioned at the centre of a typical screen.