Generic Tile Engine

GTE (Generic Tile Engine) is a 2D tile engine developed for the Apple IIGS personal computer and written in 65816 assembly language.

History

The underlying technology was developed for a recreational port of Super Mario Bros for the Apple IIGS platform. At this point the engine only supported single-layer backgrounds, a single non-standard tile size and limited sprite support. After the release of the unfinished SMB GS, the core graphics engine was modularized and released as a GS/OS Tool Set.

Features

GTE provides graphical capabilities that lie roughly between the third and fourth generation of video game consoles. The technical capabilities of the engine are contrasted with the NES and SNES consoles, which share the same CPU family as the Apple IIGS

Implementation

The memory bandwidth of the Apple IIGS is 1 MiB/s, which is too slow to update the 32 KiB graphics memory at a full 60 frames per second. In fact, the theoretical maximum frame rate for full-screen animation is 31.25 frames per second. Thus, GTE focuses on achieving a reasonable frame rate given the limitations of the hardware.

Tile engine

A tile engine is a computer graphics technique which generates a larger graphic from re-using a number of smaller graphics to save RAM and increase real-time rendering performance.

Basic tile map history

In the early days of video game development, proper RAM economy was a must for a successful game engine, much more so than it is today. One of the largest problems, graphics rendering performance, came down to the amount of RAM dedicated to storing graphics for the game worlds and characters, and fetching these graphics and displaying them on screen in as rapid and smooth a way as possible. An early hack which not only stored larger game worlds in less RAM, but also made use of fewer, smaller sized pieces of graphics rather than the full scale overall image was the tile map, a technique taking the stance that if you are rendering a grassy field, chances are most of that field is going to look the same anyway, hence the smart approach would be to re-use one small graphic over and over to shape the grassy field. This approach became widely used in specific game genres such as platformers and role-playing video games, and reached its peak during the 8-bit and 16-bit eras of consoles, with games such as Mega Man (NES), The Legend of Zelda: A Link to the Past (SNES) and Shining Force (Mega Drive) being prime examples of tile-based games, producing a highly recognizable look and feel.