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Gravité 2.0

© 1999, Sylvain Demongeot

What is Gravité?

Gravité makes Macintosh Drag & Drop look and feel more like the real thing. When Gravité is installed, dragged objects (Finder icons, image clips...) behave according to laws of mechanics such as gravity, inertia and friction.

* Gravité 2.0 is designed for PowerPC Macintoshes running MacOS 7.5.3 through 9.
* To install, just put the Gravité control panel into the 'Control Panels' folder of your system folder and reboot your Macintosh.
* Gravité 2.0 is free.

If you like Gravité, send an e-mail to -- or better, a postcard to the following address:

Sylvain Demongeot
34 Chemin Latéral
94140 Alfortville

Visit the Gravité Page: <>

Control Panel Reference

* Toggled by Caps Lock: If this is checked, you can activate or deactivate Gravité through Caps Lock (without opening the control panel).

* Gravity: This controls the gravity field intensity.

* Mouse Friction: This controls the intensity of the friction force at the end of the arrow.

* Air Friction: This controls the intensity of the air friction force.

* Sounds: This allows sounds to be played.

* Free Flight: If this is checked, the object can be dropped by pressing the ctrl key and releasing the mouse button. The object will fly freely until you release the ctrl key.

* Quality: This controls the display quality (anti-aliasing level). Better quality may yield poorer animation if your machine isn't fast enough.

* Solid Drag: If this is checked, the dragged object will appear solid, not transparent.

Technical Insight

* Gravité 2.0 was completely rewritten for PowerPC, the Drag Manager and tranparency. No code from Gravité 1.5 was used.
* Gravité 2.0 patches the 'SetDragImage' system call to install its own custom DragDrawingProc.
* Gravité 2.0 also patches 'OSEventAvail' to allow proper free flight. This patch is 'fat' to prevent instruction set architecture switches.
* Gravité 2.0 implements 11 optimized bitmap rotation routines - one for each combination of screen depth (8, 15 and 24-bit modes) and oversampling (1x, 2x, 4x, 8x and 16x). Oversampling is not available in 8-bit mode.

Other Things that Need to be Written

* Gravité comes with no technical support. I don't commit to fixing bugs either. However, bug reports are welcome at
* Although Gravité is believed to be safe and harmless, Gravité comes with no guarantee of any kind. Use it at your own risk.
* Gravité 2.0 may be distributed freely. If you distribute Gravité on a CD-ROM, it would be nice to let me know and even nicer to send me a copy. Thanks! :^)
* 68K users: Gravité 2.0 won't run on your machine (transparent dragging isn't implemented on 68K machines anyway). However, if you use system 6.0.3 trough 7.5, you can probably use Gravité 1.5 (to be downloaded at the Gravité page).

Released 12/25/1999

Gravité 2.0 © Sylvain Demongeot, 1999.
Slider CDEF by Jim Stout.

Original file name: Quick note about Gravité 2.0 - converted on Monday, 6 March 2000, 21:57

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