Generic Tile Engine for the Apple IIgs

A high-performance library for writing tile-based games for the Apple IIgs personal computer in 65816 assembly langugage. Unlock the full, 16-bit potential of the last machine of the Apple ][ line.

Introduction

The Generic Tile Engine (GTE) project is a tile engine built to exploit the unique hardware capabilities of the Apple IIgs personal computer. It supports the Apple IIgs super hires graphics mode (320x200, 16/256 colors) and provides two full-screen independent scrolling layers along with software sprites. The API and core functionality of the library is inspired by the graphics hardware of the NES/SMS/SNES/Genesis console era.

Getting Started

Initialization

Starting up GTE only requires a single subroutine call to GTEStartUp. This subroutine will take care of starting up the necessary Toolboxes and allocating any necessary memory. GTE heavily leverages memory for its speed. A total of 4MB is RAM is recommended, with a 2MB as the minimum.

; Initialize the graphics engine
        jsl      EngineStartUp
        bcs      exit

; Main code here...

; When finished, shut down the engine

        jsl      EngineShutDown

exit    _QuitGS  qtRec
qtRec   adrl     $0000
        da       $00

Setting up the play field

Once the engine is initialized, the play field must be set up. The play field defines a rectangular area of the physical graphics screen that is managed by the Tile Engine.

The size of the play field can be set directly by passing the width and height in the x and y registers. Also, there are 9 predefined¹ screen sizes that correspond to well-known Apple IIgs software titles and hardware of the era which can be selected by the x register argument.

; Main code here...

        ldx      #WIDTH
        ldy      #HEIGHT
        jsl      SetScreenMode

; Alternatively, pick a predefined size

        ldx      #0                   ; 0 = full screen (320x200)
        jsl      SetScreenMode

; When finished, shut down the engine

        jsl      EngineShutDown

By default, the play field will be centered on the graphics screen. If a custom placement of the play field is desired, then the SetScreenRect subroutine can be used directly to set a specific area of the graphics screen as the managed area.

API

GTE provides the following capabilities

References

• Apple IIgs Tech Note #70: Fast Graphics Hints
• Super Merryo Trolls
• Coding Secrets of Wolfenstein IIgs
• Apple IIgs Graphics and Sound College

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1. Table of predefined SetScreenMode sizes

   Play Field Id	Width	Height		Size (bytes)	Percent of Full Screen
   0	320	200	Full Screen	32,000	100%
   1	272	192	Sword of Sodan	26,112	81.6%
   2	256	200	NES (approx.)	25,600	80.0%
   3	256	176	Task Force	22,528	70.4%
   4	280	160	Defender of the World	22,400	70.0%
   5	256	160	Rastan	20,480	64.0%
   6	240	160	Game Boy Advanced	19,200	60.0%
   7	288	128	Ancient Land of Y's	18,432	57.6%
   8	160	144	Game Boy Color	11,520	36.0%

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