Re: SDL_Controller design

Hi Daniel,

On Thu, 1 Dec 2016, Daniel Gibson wrote:

> 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.

Okay, so this basically provides a way for a game using SDL to turn every 
device into an ABXY input device, hide the details from the user and have 
them plug it in and figure out on their own which controls act like "A", 
"RT", "RS", etc.  That's certainly useful.

> 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)

That's useful too.  I'm porting some code that has it's own "action" 
mapping system that maps the SDL joystick number (v1.2) + control changes 
(button 0 down, axis 0 right, hat left) to game actions... so to work with 
this I need to still use the SDL_Joystickxxxx() calls but I'm trying to 
take advantage of the knowledge available in the SDL_GameController 
mappings to respond to "button A down" instead of "button n down" (where X 
varies depending on device).  Also, when setting up the mappings, if I 
have a game controller mapping in SDL, I'd like to display "button A" in 
the mapping GUI instead of "button 0", at least for XINPUT devices.  I'm 
thinking that, for DINPUT devices, showing the game controller mapped 
names will just add to the confusion for non-XINPUT devices that might 
have a button named X on them, but it's not anywhere near where the X 
button is on an XBox gamepad.

> 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.

Yeah, I'm a bit confused regarding the BPM controller mapping GUI.  With a 
Steam Controller, it seems to allow me to remap things even for a game 
that has no Steam game "action map" file published.  For other 
controllers, on SteamOS, it seems to not let me do ANY remapping for even, 
say, a Wireless XB360 controller.  This weirdness makes it difficult to 
test, and makes me feel like I'm missing something basic.

That aside, the environment variable mapping string... doesn't it include 
mappings for ALL the game controllers that have configs for the game?  Or 
does it include all connected game controllers that have configs for the 
game?  If I don't have my controller plugged in, and I fire up the game 
and connect my controller, will there be a config for it, or will the user 
have to restart the game?

> 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.

Steam configuration of a controller allows the user to map "actions" (the 
things in the actions file like "strafe left", "fire missle", "toggle 
shield mode", etc.) to controls on their device.  The game sees no input 
controls... only triggered actions and readings from axis/mouse 
inputs/trackpad inputs.  However, for games without an "actions" file, I'm 
not sure what it's supposed to do... the Steam Controller is obviously 
special, it can be set up like an XBox gamepad with or without a mouse 
control via the right trackpad and DPAD control via the left trackpad, 
etc.  It doesn't seem to let me do this kind of thing for any other type 
of device tho'.

So, the fact that the BPM controller config stuff can't deal with ALL 
devices leads me to needing to keep my game's controller mapping GUI, and 
try to at least make things work automatically as best as possible for 
XBox Gamepad-like devices (or those with SDL mappings to make it seem like 
an XBox Gamepad), and let them "deep dive" and customize mappings if they 
want.

Players these days will connect a device and start pressing buttons, 
expecting it to work just like the game they were just playing, even if 
that makes no logical sense.

> 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).

YES!  That is a complete hoot to read!  I've been dealing with all of that 
kind of stuff for years, and the guy is right, most of it has never made 
a lick of sense.

 	Ed

Ed Phillips <[email protected]> University of Delaware (302) 831-6082
Systems Programmer IV, Network and Systems Services