Re: SDL_Controller design

Hi Ed,

SDL_GameController is for game controllers aka gamepads, which tend to 
be similar to the xbox360 or PS2/3/4 pad (one DPAD on the left, two 
analog sticks, 4 buttons for the right thumb, 2 shoulder buttons on each 
side that may be trigger axes and those "back" and "start" buttons in 
the middle, maybe even an "xbox" button or similar).
I think the main purposes are
1. making it easy(er) to port XInput code to SDL, esp. for Linux/Mac
2. allowing game developers to set default bindings for gamepads that 
make sense with most gamepads.

Usually you use SDL_GameController with the corresponding events 
(SDL_CONTROLLER*), I think, but you *can* also use it to set the 
displayed names etc of normal SDL_Joystick buttons, if the joystick 
happens to be a known game controller.
SDL_IsGameController(joystick) tells you if a joystick is a know game 
controller, SDL_GameControllerGetBindForAxis() and 
SDL_GameControllerGetBindForButton() tell you how things are mapped.
(I've used it that way so I don't have to handle game controller events 
separately, but still get the mapping)

Regarding Steam: The documentation is referring to the gamepad 
configuration in the Steam (Linux?) Big Picture settings, that lets you 
create a mapping from your gamepad's buttons/axes to the xbox controller 
model. I think Steam then sets the SDL_GAMECONTROLLERCONFIG environment 
variable with the mapping string, which SDL2 then uses for games that 
use SDL2 and are launched from Steam.

So "mapping" refers to "Button 3 corresponds to SDL_CONTROLLER_BUTTON_A, 
Axis 2 corresponds to SDL_CONTROLLER_AXIS_RIGHTX" and so on, not to 
standard actions.
No idea if standard action mappings are available on Steam/Linux, but if 
they are that's something provided by Steamworks SDK, not by SDL2.

BTW: 
https://joostdevblog.blogspot.de/2012/08/the-craziness-that-is-joysticks-on-pc.html 
is an interesting read about how handling joysticks and similar input 
devices sucks (only difference is that now with SDL2 it's a a bit better 
for gamepads).

Cheers,
Daniel

On 01.12.2016 18:22, Ed Phillips wrote:
> Hello,
>
> I think I'm missing something when it comes to the basic reasoning
> behind the design of the SDL_Controller stuff, and the documentation on
> the Wiki that I can see doesn't go into any discussion on the design
> decisions.
>
> When I first looked at the "mapping" capabilities of SDL_Controller, I
> thought, HEY!, this was a way to give names to each of the buttons/axes
> on any device, so you can pass them through to the application/game and
> it can present these names to the user when they are setting up their
> controller configuration.  Cool!  Oh look, they already have a database
> of these name mappings!  Great!
>
> However, the more I started looking at it, I began to see that this is
> not the case at all.  It seems to be a way to turn the raw button/axis
> numbers on a non-XInput device into an XInput control like
> "leftshoulder" or "righty"?
>
> So really, this is just a way to make every controller work like an XBox
> controller (even if it doesn't have the same physical controls or the
> same names on the buttons, etc.), and doesn't really address the issue
> of mapping the names of the actual physical controls on a particular
> device to the button/axis numbers normally received in SDL_Joystick calls?
>
> I guess if you don't want your game/application to treat every device
> like an XBox 360 Controller, then the SDL_Controller stuff is not for you?
>
> How does Steam's controller API play into things?  There is mention of
> Steam here (and nowhere else I can find):
>
> http://wiki.libsdl.org/CategoryGameController
>
> It states:
>
> "If you are running your game from Steam, the game controller mapping is
> automatically provided for your game."
>
> I'm not sure what that means.  Steam controller mappings take a list of
> "actions" defined for a game, and allow the developer and/or user to
> configure which controls on their devices will invoke these actions.  A
> game using the controller API will see "actions" and not raw inputs...
> so I'm not sure how the SDL_Controller stuff plays into this.  Also, in
> order to use the Steam controller API, you have to call functions in the
> Steam runtime, and I'm not sure if SDL can/would be doing that, and it
> won't provide an SDL_Controller mapping.
>
> Any help regarding these concepts would be greatly appreciated!
>
> Thanks,
>
>     Ed
>
> Ed Phillips <[email protected]> University of Delaware (302) 831-6082
> Systems Programmer IV, Network and Systems Services
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