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gamepad: Clarify range and direction of axes 

It would be easy to assume that all APIs that reference
SDL_JOYSTICK_AXIS_MAX work the same way, but they do not: triggers
generally use the full signed 16-bit range in the lower-level joystick
API, but are normalized to be non-negative by the higher-level gamepad
API.

We also never said explicitly which direction is positive here.
Experimentally, it's right (X), down (Y), and pressed (triggers).

Resolves: https://github.com/libsdl-org/SDL/issues/8793
Signed-off-by: Simon McVittie <smcv@collabora.com>
This commit is contained in:
Simon McVittie 2024-01-08 15:53:51 +00:00 committed by Sam Lantinga
parent 4942027117
commit 059fb560ba
1 changed files with 10 additions and 3 deletions
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13
include/SDL3/SDL_gamepad.h
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@ -149,7 +149,9 @@ typedef enum
* and are centered within ~8000 of zero, though advanced UI will allow users to set
* or autodetect the dead zone, which varies between gamepads.
*
* Trigger axis values range from 0 to SDL_JOYSTICK_AXIS_MAX.
* Trigger axis values range from 0 (released) to SDL_JOYSTICK_AXIS_MAX
* (fully pressed) when reported by SDL_GetGamepadAxis(). Note that this is not the
* same range that will be reported by the lower-level SDL_GetJoystickAxis().
*/
typedef enum
{
@ -961,8 +963,13 @@ extern DECLSPEC SDL_bool SDLCALL SDL_GamepadHasAxis(SDL_Gamepad *gamepad, SDL_Ga
*
* The axis indices start at index 0.
*
* The state is a value ranging from -32768 to 32767. Triggers, however, range
* from 0 to 32767 (they never return a negative value).
* For thumbsticks, the state is a value ranging from -32768 (up/left)
* to 32767 (down/right).
*
* Triggers range from 0 when released to 32767 when fully pressed, and
* never return a negative value. Note that this differs from the value
* reported by the lower-level SDL_GetJoystickAxis(), which normally uses
* the full range.
*
* \param gamepad a gamepad
* \param axis an axis index (one of the SDL_GamepadAxis values)