mirror of https://github.com/encounter/SDL.git
2be75c6a61
David Ludwig I have created a new driver for SDL's Joystick and Game-Controller subsystem: a Virtual driver. This driver allows one to create a software-based joystick, which to SDL applications will look and react like a real joystick, but whose state can be set programmatically. A primary use case for this is to help enable developers to add touch-screen joysticks to their apps. The driver comes with a set of new, public APIs, with functions to attach and detach joysticks, set virtual-joystick state, and to determine if a joystick is a virtual-one. Use of virtual joysticks goes as such: 1. Attach one or more virtual joysticks by calling SDL_JoystickAttachVirtual. If successful, this returns the virtual-device's joystick-index. 2. Open the virtual joysticks (using indicies returned by SDL_JoystickAttachVirtual). 3. Call any of the SDL_JoystickSetVirtual* functions when joystick-state changes. Please note that virtual-joystick state will only get applied on the next call to SDL_JoystickUpdate, or when pumping or polling for SDL events (via SDL_PumpEvents or SDL_PollEvent). Here is a listing of the new, public APIs, at present and subject to change: ------------------------------------------------------------ /** * Attaches a new virtual joystick. * Returns the joystick's device index, or -1 if an error occurred. */ extern DECLSPEC int SDLCALL SDL_JoystickAttachVirtual(SDL_JoystickType type, int naxes, int nballs, int nbuttons, int nhats); /** * Detaches a virtual joystick * Returns 0 on success, or -1 if an error occurred. */ extern DECLSPEC int SDLCALL SDL_JoystickDetachVirtual(int device_index); /** * Indicates whether or not a virtual-joystick is at a given device index. */ extern DECLSPEC SDL_bool SDLCALL SDL_JoystickIsVirtual(int device_index); /** * Set values on an opened, virtual-joystick's controls. * Returns 0 on success, -1 on error. */ extern DECLSPEC int SDLCALL SDL_JoystickSetVirtualAxis(SDL_Joystick * joystick, int axis, Sint16 value); extern DECLSPEC int SDLCALL SDL_JoystickSetVirtualBall(SDL_Joystick * joystick, int ball, Sint16 xrel, Sint16 yrel); extern DECLSPEC int SDLCALL SDL_JoystickSetVirtualButton(SDL_Joystick * joystick, int button, Uint8 value); extern DECLSPEC int SDLCALL SDL_JoystickSetVirtualHat(SDL_Joystick * joystick, int hat, Uint8 value); ------------------------------------------------------------ Miscellaneous notes on the initial patch, which are also subject to change: 1. no test code is present in SDL, yet. This should, perhaps, change. Initial development was done with an ImGui-based app, which potentially is too thick for use in SDL-official. If tests are to be added, what kind of tests? Automated? Graphical? 2. virtual game controllers can be created by calling SDL_JoystickAttachVirtual with a joystick-type of SDL_JOYSTICK_TYPE_GAME_CONTROLLER, with naxes (num axes) set to SDL_CONTROLLER_AXIS_MAX, and with nbuttons (num buttons) set to SDL_CONTROLLER_BUTTON_MAX. When updating their state, values of type SDL_GameControllerAxis or SDL_GameControllerButton can be casted to an int and used for the control-index (in calls to SDL_JoystickSetVirtual* functions). 3. virtual joysticks' guids are mostly all-zeros with the exception of the last two bytes, the first of which is a 'v', to indicate that the guid is a virtual one, and the second of which is a SDL_JoystickType that has been converted into a Uint8. 4. virtual joysticks are ONLY turned into virtual game-controllers if and when their joystick-type is set to SDL_JOYSTICK_TYPE_GAMECONTROLLER. This is controlled by having SDL's default list of game-controllers have a single entry for a virtual game controller (of guid, "00000000000000000000000000007601", which is subject to the guid-encoding described above). 5. regarding having to call SDL_JoystickUpdate, either directly or indirectly via SDL_PumpEvents or SDL_PollEvents, before new virtual-joystick state becomes active (as specified via SDL_JoystickSetVirtual* function-calls), this was done to match behavior found in SDL's other joystick drivers, almost all of which will only update SDL-state during SDL_JoystickUpdate. 6. the initial patch is based off of SDL 2.0.12 7. the virtual joystick subsystem is disabled by default. It should be possible to enable it by building with SDL_JOYSTICK_VIRTUAL=1 Questions, comments, suggestions, or bug reports very welcome! |
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| .. | ||
| atomic | ||
| audio | ||
| core | ||
| cpuinfo | ||
| dynapi | ||
| events | ||
| file | ||
| filesystem | ||
| haptic | ||
| hidapi | ||
| joystick | ||
| libm | ||
| loadso | ||
| main | ||
| power | ||
| render | ||
| sensor | ||
| stdlib | ||
| test | ||
| thread | ||
| timer | ||
| video | ||
| SDL.c | ||
| SDL_assert.c | ||
| SDL_assert_c.h | ||
| SDL_dataqueue.c | ||
| SDL_dataqueue.h | ||
| SDL_error.c | ||
| SDL_error_c.h | ||
| SDL_hints.c | ||
| SDL_hints_c.h | ||
| SDL_internal.h | ||
| SDL_log.c | ||