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Bug 382

Summary: Support horizontal mouse scrolling
Product: SDL Reporter: Jonas Koelker <jonaskoelker>
Component: eventsAssignee: Ryan C. Gordon <icculus>
Status: RESOLVED FIXED QA Contact: Sam Lantinga <slouken>
Severity: enhancement    
Priority: P2    
Version: 2.0.0   
Hardware: All   
OS: Linux   

Description Jonas Koelker 2007-01-17 16:39:46 UTC 
I posted the below to the mailing list (january 2007) and got silence back:

Hi.  I'm new to the list, so that's why you don't know me.

My agenda is the following:  to have horizontal mouse scrolling (with EmulateWheel) in Battle for Wesnoth (wesnoth.org; a libsdl-using turn-based strategy game).  I wrote a patch which got rejected more or less because horizontal mouse scrolling wasn't a standard feature of sdl (see patch 644 on https://gna.org/patch/?group=wesnoth).

So, I figure that I should convince you to support horizontal mouse scrolling.

Last time you discussed this, the following points were made:
(1) On OS X, when you hold shift and scroll, the vertical scroll events become horizontal.  What should SDL do about this?
(2) We could define SDL_BUTTON_WHEEL(LEFT|RIGHT)
(3) We shouldn't, because it would not work on more than one platform
(4) Yes it would

And that's why you don't support horizontal mouse scrolling, AFAICT.  See for
yourself: http://www.libsdl.org/pipermail/sdl/2005-March/thread.html#67970

To actually quote something:
> Microsoft also sells (and Windows supports) a USB mouse with both vertical
> and horizontal wheels, so it's not necessarily a Mac-specific thing.

And xorg has EmulateWheel:  pick a button.  When you hold that button, pointer movement gets converted into scroll events (in both directions); and you get to decide which button events they get converted into.  Common wisdom is that vert=4,5 and horz=6,7.

So, every major platform can generate horizontal scroll events.  I think libsdl should provide a uniform interface to it, because there's demand for it from application developers:  I want to use horizontal scrolling, the wesnoth devs would like to be able to accept the patch, and horizontal scrolling is already used in many non-sdl applications (konqueror and firefox, to name two).

In summary: support horizontal scrolling in SDL!
Comment 1 Sam Lantinga 2007-07-06 02:22:58 UTC 
I agree!  This has been added to SDL 1.2.12, subversion revision 3156
Comment 2 Ryan C. Gordon 2007-07-06 03:02:02 UTC 
Buttons 6 and 7 are likely to be real mouse buttons (see the WM_XBUTTON patch in Bug #311)...I know we picked 4 and 5 for the vertical wheel because it matched XFree86's nasty hack, but can we select something that isn't likely to map to a real button, like, 44 and 45?

(and in 1.3, can we have these not map to buttons at all?)

--ryan.
Comment 3 Sam Lantinga 2007-07-06 06:30:45 UTC 
We could, although I picked 6 and 7 because it looks like that's what horizontal scrolling usually maps to in xorg.  At this point I don't think there's any way to tell in X11 whether buttons 4/5/6/7 are actual buttons or mouse wheel, which is a shame...

In 1.3 there's a real scrolling event, and the mousewheel button events are only there for backwards compatibility.
Comment 4 Sam Lantinga 2007-07-06 06:36:49 UTC 
The only problem with this is that if we use buttons 6 and 7 to represent mousewheel, then that actually changes the buttons that applications will see.  That's probably not acceptable for SDL 1.2 which is supposed to be binary compatible between revisions.
Comment 5 Sam Lantinga 2007-07-06 06:40:01 UTC 
Okay, this has been reverted in 1.2 with subversion revision 3159, and horizontal scrolling support is now in SDL 1.3.