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#2745 TkAqua MouseWheel wrong delta step size
open-wont-fix
7
2011-01-07
2010-01-13
No
The delta value %D for MouseWheel events on in TkAqua is 1 or -1 or small integers.
On Mac X11, Linux and Windows the delta value is 120 or -120 or small multiples of these.
This means any MouseWheel tcl code has to be special-cased for TkAqua. I believe the 120
value is intended to allow future mouse wheel devices that provide finer granularity.
The TkAqua MouseWheel events should produce 120 and -120 delta values to avoid special-case
code in applications. Maybe this change could be introduced into the new TkAqua 8.6 Cocoa
implementation.
Use the following Wish script to see the delta values produced by mouse wheel events:
bind . <MouseWheel> { puts %D }
The mousewheel handling in Aqua has had its own platform-specific implementation for a number of years, most likely for reasons of performance and platform integration. Rather than change it for cross-platform compatibility, some additional documentation in the man pages would be appropriate.
The choice here is whether to leave the historical mistake as is where Mac mouse wheel events produce single step increments of +/- 1 while other platforms produce increments of +/- 120 and document it, or to fix it so that all platforms use the +/- 120 scale so that new cross-platform apps get correct mouse wheel behavior. The latter choice would break some existing apps when used with a new fixed Tk. I think the latter choice is better for the future of Tk.
The reason the values are in +- 120 steps except on Mac is because the widely used standard (outside Tk) is that the mouse wheel integer step represents 1/8th degree rotations of the mouse wheel. Most mouse wheels measure smallest steps of 15 degrees and 15 * 8 = 120.
If mice with smaller than 15 degree steps come into use the finer sensitivity will be available for applications based on the 1/8 degree steps, while the current Mac Tk behavior where an integer +/- 1 value represents a step of 15 degrees cannot handle finer granularity. The strongest reason to use the 1/8 degree steps is simply that that scale is used everywhere (except Mac Tk).