Matthias      2011-03-20 23:07:02 PDT

On X11, SDL 1.3 does not generate a mouse wheel event. Instead, button
down/buttton up events are generated by SDL. After looking at the code in
SDL_x11events.c, I assume this is due to the fact that X11 does not have a
dedicated mouse wheel event.

I did a little research on the behavior of mouse wheel events on X11 systems.
Apparently, mouse wheel events generate a button down/button up event with the
same time, i.e. with exact same timestamp.

Attached you can find my changes to SDL_x11events.c, which generates SDL mouse
wheel events for those button down events that have a button release event
immediately following it (for the same button, and with the same timestamp).

I did have to make an assumption: As standard X11 implementations know only 5
buttons, I have mapped Button4 to "wheel up" (i.e. +1), and Button5 to "wheel
down" (i.e. -1).

Note that if you include this patch, no SDL button down/up events will be
generated on X11 platforms for mouse wheel events (which is probably a
significant change for those that have programmed their code to work with
them).