Motivation for SDL backend mouse wheel handling

[Grieverheart]

I'm wondering what the motivation is for handling the mouse wheel in SDL like this:

        case SDL_MOUSEWHEEL:
        {
            float wheel_x = (event->wheel.x > 0) ? 1.0f : (event->wheel.x < 0) ? -1.0f : 0.0f;
            float wheel_y = (event->wheel.y > 0) ? 1.0f : (event->wheel.y < 0) ? -1.0f : 0.0f;
            io.AddMouseWheelEvent(wheel_x, wheel_y);
            return true;
        }

why are increments clipped to +-1?

[PathogenDavid]

Whatever motivation there was has probably been lost to time. It's changed shape a few times over the years, but the general logic has been the same since the SDL backend was originally introduced back in 2015:

imgui/examples/opengl_sdl_example/imgui_impl_sdl.cpp

Lines 220 to 229 in 2acdafe

	case SDL_MOUSEWHEEL:
	if (event.wheel.y>0 )
	{
	g_MouseWheel = 1;
	}
	if (event.wheel.y<0 )
	{
	g_MouseWheel = -1;
	}
	break;

It might just be that it was inspired by the example code from the SDL documentation, which does the same thing: https://wiki.libsdl.org/SDL2/SDL_MouseWheelEvent

[ocornut]

I'm wondering what the motivation is for handling the mouse wheel in SDL like this:

Knowing which values are you getting and on what system may be useful to know. Thanks!

[Grieverheart]

Ah, sorry, I didn't see a question mark so I thought it was a general statement, with which I agreed :D . Anyway, on MacOS mouse wheel values can be way above 1 or below -1.

[ocornut]

Could you log the values for a typical scroll wheel flick and share that log?

[Grieverheart]

wheel.txt
I recorded two flicks. A slow and a fast one.

[ocornut]

Thanks. Linking to our work on #3795

[ocornut]

Do you have smooth scrolling disabled?
Could you try other backends: GLFW, OSX and compare the values you are getting?
Thanks a lot!

[ocornut]

See #4019 (comment) for a sneak peak at some messy the "mouse wheeling" landscape. Although I don't REMEMBER why we clamped it is apparent this is needed until we can unf*ckify this mess.

[ocornut]

See #4019 (comment) for a full document about this
(TL;DR; can't clamp just yet but when we figure out what to do to replace the GLFW scale we will try to apply same logic to SDL backend)