User-agent: Mozilla Thunderbird 1.0 (Windows/20041206)
Hi,
I'm interested in comparing the Mac OS X and Windows XP mouse
acceleration curves. The Windows XP acceleration curve is well
documented (http://www.microsoft.com/whdc/device/input/pointer-bal.mspx)
whereas it's very difficult to find any information on the Mac OS X one.
Looks like Microsoft copied the Mac OS X curve in some way.
I've found some code from the Darwin project that handles the mouse:
http://darwinsource.opendarwin.org/10.3/IOHIDFamily-86/IOHIDSystem/IOHIPointing.cpp
I'm not familiar with Darwin so I would to know:
1°) Is that code used to handle the mouse on Mac OS X?
2°) Where is stored the pointing acceleration curve and what are the
coordinates of the points used?
For question 2, I've found three device key entries using a developer
utility on Mac OS X to dump the device tree info.
Here is one of those:
CFBundleIdentifier = "com.apple.driver.AppleUSBOpticalMouse";
HIDDefaultBehavior = Mouse;
HIDPointerAccelerationTable = <00008000 5553422a 00070000
00000001 00010000 00010000 00002000 00100000 713b0000 4ce30004...>;
IOClass = AppleUSBOpticalMouse;
IOProviderClass = IOUSBInterface;
IOUserClientClass = IOUSBHIDDriverUserClient;
SwitchTo2000FPS = 1;
bConfigurationValue = 1;
bInterfaceNumber = 0;
idProduct = 775;
idVendor = 1452;
Look like the curve is stored in the HIDPointerAccelerationTable. To try
to understand that, I divided all the value by 2^16 and among a lot of
mysterous values, I found 3 set of points that look like to correspond
to acceleration curves (values from 41 to 77, 120 to 154 and 193 to
225). When I plot the curves, the X axis seems to correspond to the
mouse speed in inch/s (it goes up to 40 inch/s, which is the maximum
speed of the mouse). For the Y axis, I have no idea to what it
corresponds. Also, why is there three curves and how are they used?
Any help to understand how the pointing acceleration is done on Mac OS X
would be very much appreciated.
Thank you in advance.
Géry
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