Macintosh Drag and Drop GC v1.0.0 Release Notes

by jmacz on the 68kmla.org forums

May 16, 2026

Introduction

Apple's 8 * 24 GC accelerated video card is not officially compatible with Apple's Macintosh Drag and Drop extension for System 7. It is also not compatible with System 7.5+ where the Drag Manager is built in. When acceleration is enabled alongside drag and drop functionality, artifacts appear on the screen.

The 8 * 24 GC card performs asynchronous acceleration of QuickDraw via an onboard processor. This raises the possibility for a race condition during screen rendering. The Drag Manager (built in for System 7.5+ and installed as an extension on System 7) performs fast XOR based drawing during drags to show drag outlines. Normally this works fine. But if another piece of software (like the Finder) performs drawings during a drag, this can cause a race condition where the XOR fails. The Finder does draw to the screen during drags. One place is when you drag over a folder, the Finder will darken the folder. Another place is when you drag into a window, the Finder will show a hilited border in the window. These two Finder drawing operations conflict with the XOR based drawing by the Drag Manager and cause artifacts.

This Macintosh Drag and Drop GC system extension causes 8 * 24 GC acceleration to be disabled during a drag. Drags are normally fast enough to not need acceleration. By disabling acceleration during drags, the race condition is resolved and no artifacts appear.

Installation

Install the Macintosh Drag and Drop GC system extension by dropping it into the Extensions folder within your System Folder.

During boot, the Macintosh Drag and Drop GC system extension must load AFTER the standard Macintosh Drag and Drop system extension. The Macintosh Drag and Drop GC system extension does NOT replace the stock Macintosh Drag and Drop extension. They must both exist in System 7.1. For System 7.5, the stock Macintosh Drag and Drop system extension is NOT necessary as the Drag Manager is built into System 7.5.

Macintosh Drag and Drop GC is named to ensure it loads after Macintosh Drag and Drop.

Testing

I have tested this on System 7.1 on a Macintosh IIfx running the 8 * 24 GC card revision 2. I have also tested it under System 7.6.1. It should work on both revisions of the 8 * 24 GC card and should run on anything between System 7.1 and System 7.6.1.

Bugs

If you like this software or find any bugs, swing by 68Kmla.org (Macintosh Liberation Army Forums) and leave a message for user jmacz.

Licensing

No licensing. This software is free to use and distribute.


Change List

v1.0.0 Initial Public Release