RetroArch/libretro.h

/* Copyright (C) 2010-2014 The RetroArch team
 *
 * ---------------------------------------------------------------------------------------
 * The following license statement only applies to this libretro API header (libretro.h).
 * ---------------------------------------------------------------------------------------
 *
 * Permission is hereby granted, free of charge,
 * to any person obtaining a copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation the rights to
 * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software,
 * and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
 * INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
 * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

#ifndef LIBRETRO_H__
#define LIBRETRO_H__

#include <stdint.h>
#include <stddef.h>
#include <limits.h>

#ifdef __cplusplus
extern "C" {
#endif

#ifndef __cplusplus
#if defined(_MSC_VER) && !defined(SN_TARGET_PS3)
/* Hack applied for MSVC when compiling in C89 mode as it isn't C99 compliant. */
#define bool unsigned char
#define true 1
#define false 0
#else
#include <stdbool.h>
#endif
#endif

// Used for checking API/ABI mismatches that can break libretro implementations.
// It is not incremented for compatible changes to the API.
#define RETRO_API_VERSION         1

//
// Libretros fundamental device abstractions.
/////////
//
// Libretros input system consists of some standardized device types such as a joypad (with/without analog),
// mouse, keyboard, lightgun and a pointer. The functionality of these devices are fixed, and individual cores map
// their own concept of a controller to libretros abstractions.
// This makes it possible for frontends to map the abstract types to a real input device,
// and not having to worry about binding input correctly to arbitrary controller layouts.


#define RETRO_DEVICE_TYPE_SHIFT         8
#define RETRO_DEVICE_MASK               ((1 << RETRO_DEVICE_TYPE_SHIFT) - 1)
#define RETRO_DEVICE_SUBCLASS(base, id) (((id + 1) << RETRO_DEVICE_TYPE_SHIFT) | base)

// Input disabled.
#define RETRO_DEVICE_NONE         0

// The JOYPAD is called RetroPad. It is essentially a Super Nintendo controller,
// but with additional L2/R2/L3/R3 buttons, similar to a PS1 DualShock.
#define RETRO_DEVICE_JOYPAD       1

// The mouse is a simple mouse, similar to Super Nintendo's mouse.
// X and Y coordinates are reported relatively to last poll (poll callback).
// It is up to the libretro implementation to keep track of where the mouse pointer is supposed to be on the screen.
// The frontend must make sure not to interfere with its own hardware mouse pointer.
#define RETRO_DEVICE_MOUSE        2

// KEYBOARD device lets one poll for raw key pressed.
// It is poll based, so input callback will return with the current pressed state.
// For event/text based keyboard input, see RETRO_ENVIRONMENT_SET_KEYBOARD_CALLBACK.
#define RETRO_DEVICE_KEYBOARD     3

// Lightgun X/Y coordinates are reported relatively to last poll, similar to mouse.
#define RETRO_DEVICE_LIGHTGUN     4

// The ANALOG device is an extension to JOYPAD (RetroPad).
// Similar to DualShock it adds two analog sticks.
// This is treated as a separate device type as it returns values in the full analog range
// of [-0x8000, 0x7fff]. Positive X axis is right. Positive Y axis is down.
// Only use ANALOG type when polling for analog values of the axes.
#define RETRO_DEVICE_ANALOG       5

// Abstracts the concept of a pointing mechanism, e.g. touch.
// This allows libretro to query in absolute coordinates where on the screen a mouse (or something similar) is being placed.
// For a touch centric device, coordinates reported are the coordinates of the press.
//
// Coordinates in X and Y are reported as:
// [-0x7fff, 0x7fff]: -0x7fff corresponds to the far left/top of the screen,
// and 0x7fff corresponds to the far right/bottom of the screen.
// The "screen" is here defined as area that is passed to the frontend and later displayed on the monitor.
// The frontend is free to scale/resize this screen as it sees fit, however,
// (X, Y) = (-0x7fff, -0x7fff) will correspond to the top-left pixel of the game image, etc.
//
// To check if the pointer coordinates are valid (e.g. a touch display actually being touched),
// PRESSED returns 1 or 0.
// If using a mouse on a desktop, PRESSED will usually correspond to the left mouse button, but this is a frontend decision.
// PRESSED will only return 1 if the pointer is inside the game screen.
//
// For multi-touch, the index variable can be used to successively query more presses.
// If index = 0 returns true for _PRESSED, coordinates can be extracted
// with _X, _Y for index = 0. One can then query _PRESSED, _X, _Y with index = 1, and so on.
// Eventually _PRESSED will return false for an index. No further presses are registered at this point.
#define RETRO_DEVICE_POINTER      6

// Buttons for the RetroPad (JOYPAD).
// The placement of these is equivalent to placements on the Super Nintendo controller.
// L2/R2/L3/R3 buttons correspond to the PS1 DualShock.
#define RETRO_DEVICE_ID_JOYPAD_B        0
#define RETRO_DEVICE_ID_JOYPAD_Y        1
#define RETRO_DEVICE_ID_JOYPAD_SELECT   2
#define RETRO_DEVICE_ID_JOYPAD_START    3
#define RETRO_DEVICE_ID_JOYPAD_UP       4
#define RETRO_DEVICE_ID_JOYPAD_DOWN     5
#define RETRO_DEVICE_ID_JOYPAD_LEFT     6
#define RETRO_DEVICE_ID_JOYPAD_RIGHT    7
#define RETRO_DEVICE_ID_JOYPAD_A        8
#define RETRO_DEVICE_ID_JOYPAD_X        9
#define RETRO_DEVICE_ID_JOYPAD_L       10
#define RETRO_DEVICE_ID_JOYPAD_R       11
#define RETRO_DEVICE_ID_JOYPAD_L2      12
#define RETRO_DEVICE_ID_JOYPAD_R2      13
#define RETRO_DEVICE_ID_JOYPAD_L3      14
#define RETRO_DEVICE_ID_JOYPAD_R3      15

// Index / Id values for ANALOG device.
#define RETRO_DEVICE_INDEX_ANALOG_LEFT   0
#define RETRO_DEVICE_INDEX_ANALOG_RIGHT  1
#define RETRO_DEVICE_ID_ANALOG_X         0
#define RETRO_DEVICE_ID_ANALOG_Y         1

// Id values for MOUSE.
#define RETRO_DEVICE_ID_MOUSE_X      0
#define RETRO_DEVICE_ID_MOUSE_Y      1
#define RETRO_DEVICE_ID_MOUSE_LEFT   2
#define RETRO_DEVICE_ID_MOUSE_RIGHT  3

// Id values for LIGHTGUN types.
#define RETRO_DEVICE_ID_LIGHTGUN_X        0
#define RETRO_DEVICE_ID_LIGHTGUN_Y        1
#define RETRO_DEVICE_ID_LIGHTGUN_TRIGGER  2
#define RETRO_DEVICE_ID_LIGHTGUN_CURSOR   3
#define RETRO_DEVICE_ID_LIGHTGUN_TURBO    4
#define RETRO_DEVICE_ID_LIGHTGUN_PAUSE    5
#define RETRO_DEVICE_ID_LIGHTGUN_START    6

// Id values for POINTER.
#define RETRO_DEVICE_ID_POINTER_X         0
#define RETRO_DEVICE_ID_POINTER_Y         1
#define RETRO_DEVICE_ID_POINTER_PRESSED   2

// Returned from retro_get_region().
#define RETRO_REGION_NTSC  0
#define RETRO_REGION_PAL   1

// Passed to retro_get_memory_data/size().
// If the memory type doesn't apply to the implementation NULL/0 can be returned.
#define RETRO_MEMORY_MASK        0xff

// Regular save ram. This ram is usually found on a game cartridge, backed up by a battery.
// If save game data is too complex for a single memory buffer,
// the SAVE_DIRECTORY (preferably) or SYSTEM_DIRECTORY environment callback can be used.
#define RETRO_MEMORY_SAVE_RAM    0

// Some games have a built-in clock to keep track of time.
// This memory is usually just a couple of bytes to keep track of time.
#define RETRO_MEMORY_RTC         1

// System ram lets a frontend peek into a game systems main RAM.
#define RETRO_MEMORY_SYSTEM_RAM  2

// Video ram lets a frontend peek into a game systems video RAM (VRAM).
#define RETRO_MEMORY_VIDEO_RAM   3

// Keysyms used for ID in input state callback when polling RETRO_KEYBOARD.
enum retro_key
{
   RETROK_UNKNOWN        = 0,
   RETROK_FIRST          = 0,
   RETROK_BACKSPACE      = 8,
   RETROK_TAB            = 9,
   RETROK_CLEAR          = 12,
   RETROK_RETURN         = 13,
   RETROK_PAUSE          = 19,
   RETROK_ESCAPE         = 27,
   RETROK_SPACE          = 32,
   RETROK_EXCLAIM        = 33,
   RETROK_QUOTEDBL       = 34,
   RETROK_HASH           = 35,
   RETROK_DOLLAR         = 36,
   RETROK_AMPERSAND      = 38,
   RETROK_QUOTE          = 39,
   RETROK_LEFTPAREN      = 40,
   RETROK_RIGHTPAREN     = 41,
   RETROK_ASTERISK       = 42,
   RETROK_PLUS           = 43,
   RETROK_COMMA          = 44,
   RETROK_MINUS          = 45,
   RETROK_PERIOD         = 46,
   RETROK_SLASH          = 47,
   RETROK_0              = 48,
   RETROK_1              = 49,
   RETROK_2              = 50,
   RETROK_3              = 51,
   RETROK_4              = 52,
   RETROK_5              = 53,
   RETROK_6              = 54,
   RETROK_7              = 55,
   RETROK_8              = 56,
   RETROK_9              = 57,
   RETROK_COLON          = 58,
   RETROK_SEMICOLON      = 59,
   RETROK_LESS           = 60,
   RETROK_EQUALS         = 61,
   RETROK_GREATER        = 62,
   RETROK_QUESTION       = 63,
   RETROK_AT             = 64,
   RETROK_LEFTBRACKET    = 91,
   RETROK_BACKSLASH      = 92,
   RETROK_RIGHTBRACKET   = 93,
   RETROK_CARET          = 94,
   RETROK_UNDERSCORE     = 95,
   RETROK_BACKQUOTE      = 96,
   RETROK_a              = 97,
   RETROK_b              = 98,
   RETROK_c              = 99,
   RETROK_d              = 100,
   RETROK_e              = 101,
   RETROK_f              = 102,
   RETROK_g              = 103,
   RETROK_h              = 104,
   RETROK_i              = 105,
   RETROK_j              = 106,
   RETROK_k              = 107,
   RETROK_l              = 108,
   RETROK_m              = 109,
   RETROK_n              = 110,
   RETROK_o              = 111,
   RETROK_p              = 112,
   RETROK_q              = 113,
   RETROK_r              = 114,
   RETROK_s              = 115,
   RETROK_t              = 116,
   RETROK_u              = 117,
   RETROK_v              = 118,
   RETROK_w              = 119,
   RETROK_x              = 120,
   RETROK_y              = 121,
   RETROK_z              = 122,
   RETROK_DELETE         = 127,

   RETROK_KP0            = 256,
   RETROK_KP1            = 257,
   RETROK_KP2            = 258,
   RETROK_KP3            = 259,
   RETROK_KP4            = 260,
   RETROK_KP5            = 261,
   RETROK_KP6            = 262,
   RETROK_KP7            = 263,
   RETROK_KP8            = 264,
   RETROK_KP9            = 265,
   RETROK_KP_PERIOD      = 266,
   RETROK_KP_DIVIDE      = 267,
   RETROK_KP_MULTIPLY    = 268,
   RETROK_KP_MINUS       = 269,
   RETROK_KP_PLUS        = 270,
   RETROK_KP_ENTER       = 271,
   RETROK_KP_EQUALS      = 272,

   RETROK_UP             = 273,
   RETROK_DOWN           = 274,
   RETROK_RIGHT          = 275,
   RETROK_LEFT           = 276,
   RETROK_INSERT         = 277,
   RETROK_HOME           = 278,
   RETROK_END            = 279,
   RETROK_PAGEUP         = 280,
   RETROK_PAGEDOWN       = 281,

   RETROK_F1             = 282,
   RETROK_F2             = 283,
   RETROK_F3             = 284,
   RETROK_F4             = 285,
   RETROK_F5             = 286,
   RETROK_F6             = 287,
   RETROK_F7             = 288,
   RETROK_F8             = 289,
   RETROK_F9             = 290,
   RETROK_F10            = 291,
   RETROK_F11            = 292,
   RETROK_F12            = 293,
   RETROK_F13            = 294,
   RETROK_F14            = 295,
   RETROK_F15            = 296,

   RETROK_NUMLOCK        = 300,
   RETROK_CAPSLOCK       = 301,
   RETROK_SCROLLOCK      = 302,
   RETROK_RSHIFT         = 303,
   RETROK_LSHIFT         = 304,
   RETROK_RCTRL          = 305,
   RETROK_LCTRL          = 306,
   RETROK_RALT           = 307,
   RETROK_LALT           = 308,
   RETROK_RMETA          = 309,
   RETROK_LMETA          = 310,
   RETROK_LSUPER         = 311,
   RETROK_RSUPER         = 312,
   RETROK_MODE           = 313,
   RETROK_COMPOSE        = 314,

   RETROK_HELP           = 315,
   RETROK_PRINT          = 316,
   RETROK_SYSREQ         = 317,
   RETROK_BREAK          = 318,
   RETROK_MENU           = 319,
   RETROK_POWER          = 320,
   RETROK_EURO           = 321,
   RETROK_UNDO           = 322,

   RETROK_LAST,

   RETROK_DUMMY          = INT_MAX // Ensure sizeof(enum) == sizeof(int)
};

enum retro_mod
{
   RETROKMOD_NONE       = 0x0000,

   RETROKMOD_SHIFT      = 0x01,
   RETROKMOD_CTRL       = 0x02,
   RETROKMOD_ALT        = 0x04,
   RETROKMOD_META       = 0x08,

   RETROKMOD_NUMLOCK    = 0x10,
   RETROKMOD_CAPSLOCK   = 0x20,
   RETROKMOD_SCROLLOCK  = 0x40,

   RETROKMOD_DUMMY = INT_MAX // Ensure sizeof(enum) == sizeof(int)
};

// If set, this call is not part of the public libretro API yet. It can change or be removed at any time.
#define RETRO_ENVIRONMENT_EXPERIMENTAL 0x10000
// Environment callback to be used internally in frontend.
#define RETRO_ENVIRONMENT_PRIVATE 0x20000

// Environment commands.
#define RETRO_ENVIRONMENT_SET_ROTATION  1  // const unsigned * --
                                           // Sets screen rotation of graphics.
                                           // Is only implemented if rotation can be accelerated by hardware.
                                           // Valid values are 0, 1, 2, 3, which rotates screen by 0, 90, 180, 270 degrees
                                           // counter-clockwise respectively.
                                           //
#define RETRO_ENVIRONMENT_GET_OVERSCAN  2  // bool * --
                                           // Boolean value whether or not the implementation should use overscan, or crop away overscan.
                                           //
#define RETRO_ENVIRONMENT_GET_CAN_DUPE  3  // bool * --
                                           // Boolean value whether or not frontend supports frame duping,
                                           // passing NULL to video frame callback.
                                           //
// Environ 4, 5 are no longer supported (GET_VARIABLE / SET_VARIABLES), and reserved to avoid possible ABI clash.
#define RETRO_ENVIRONMENT_SET_MESSAGE   6  // const struct retro_message * --
                                           // Sets a message to be displayed in implementation-specific manner for a certain amount of 'frames'.
                                           // Should not be used for trivial messages, which should simply be logged via RETRO_ENVIRONMENT_GET_LOG_INTERFACE (or as a fallback, stderr).
#define RETRO_ENVIRONMENT_SHUTDOWN      7  // N/A (NULL) --
                                           // Requests the frontend to shutdown.
                                           // Should only be used if game has a specific
                                           // way to shutdown the game from a menu item or similar.
                                           //
#define RETRO_ENVIRONMENT_SET_PERFORMANCE_LEVEL 8
                                           // const unsigned * --
                                           // Gives a hint to the frontend how demanding this implementation
                                           // is on a system. E.g. reporting a level of 2 means
                                           // this implementation should run decently on all frontends
                                           // of level 2 and up.
                                           //
                                           // It can be used by the frontend to potentially warn
                                           // about too demanding implementations.
                                           //
                                           // The levels are "floating", but roughly defined as:
                                           // 0: Low-powered embedded devices such as Raspberry Pi
                                           // 1: 6th generation consoles, such as Wii/Xbox 1, and phones, tablets, etc.
                                           // 2: 7th generation consoles, such as PS3/360, with sub-par CPUs.
                                           // 3: Modern desktop/laptops with reasonably powerful CPUs.
                                           // 4: High-end desktops with very powerful CPUs.
                                           //
                                           // This function can be called on a per-game basis,
                                           // as certain games an implementation can play might be
                                           // particularily demanding.
                                           // If called, it should be called in retro_load_game().
                                           //
#define RETRO_ENVIRONMENT_GET_SYSTEM_DIRECTORY 9
                                           // const char ** --
                                           // Returns the "system" directory of the frontend.
                                           // This directory can be used to store system specific ROMs such as BIOSes, configuration data, etc.
                                           // The returned value can be NULL.
                                           // If so, no such directory is defined,
                                           // and it's up to the implementation to find a suitable directory.
                                           //
                                           // NOTE: Some cores used this folder also for "save" data such as memory cards, etc, for lack of a better place to put it.
                                           // This is now discouraged, and if possible, cores should try to use the new GET_SAVE_DIRECTORY.
                                           //
#define RETRO_ENVIRONMENT_SET_PIXEL_FORMAT 10
                                           // const enum retro_pixel_format * --
                                           // Sets the internal pixel format used by the implementation.
                                           // The default pixel format is RETRO_PIXEL_FORMAT_0RGB1555.
                                           // This pixel format however, is deprecated (see enum retro_pixel_format).
                                           // If the call returns false, the frontend does not support this pixel format.
                                           // This function should be called inside retro_load_game() or retro_get_system_av_info().
                                           //
#define RETRO_ENVIRONMENT_SET_INPUT_DESCRIPTORS 11
                                           // const struct retro_input_descriptor * --
                                           // Sets an array of retro_input_descriptors.
                                           // It is up to the frontend to present this in a usable way.
                                           // The array is terminated by retro_input_descriptor::description being set to NULL.
                                           // This function can be called at any time, but it is recommended to call it as early as possible.
#define RETRO_ENVIRONMENT_SET_KEYBOARD_CALLBACK 12
                                           // const struct retro_keyboard_callback * --
                                           // Sets a callback function used to notify core about keyboard events.
                                           //
#define RETRO_ENVIRONMENT_SET_DISK_CONTROL_INTERFACE 13
                                           // const struct retro_disk_control_callback * --
                                           // Sets an interface which frontend can use to eject and insert disk images.
                                           // This is used for games which consist of multiple images and must be manually
                                           // swapped out by the user (e.g. PSX).
#define RETRO_ENVIRONMENT_SET_HW_RENDER 14
                                           // struct retro_hw_render_callback * --
                                           // Sets an interface to let a libretro core render with hardware acceleration.
                                           // Should be called in retro_load_game().
                                           // If successful, libretro cores will be able to render to a frontend-provided framebuffer.
                                           // The size of this framebuffer will be at least as large as max_width/max_height provided in get_av_info().
                                           // If HW rendering is used, pass only RETRO_HW_FRAME_BUFFER_VALID or NULL to retro_video_refresh_t.
#define RETRO_ENVIRONMENT_GET_VARIABLE 15
                                           // struct retro_variable * --
                                           // Interface to acquire user-defined information from environment
                                           // that cannot feasibly be supported in a multi-system way.
                                           // 'key' should be set to a key which has already been set by SET_VARIABLES.
                                           // 'data' will be set to a value or NULL.
                                           //
#define RETRO_ENVIRONMENT_SET_VARIABLES 16
                                           // const struct retro_variable * --
                                           // Allows an implementation to signal the environment
                                           // which variables it might want to check for later using GET_VARIABLE.
                                           // This allows the frontend to present these variables to a user dynamically.
                                           // This should be called as early as possible (ideally in retro_set_environment).
                                           //
                                           // 'data' points to an array of retro_variable structs terminated by a { NULL, NULL } element.
                                           // retro_variable::key should be namespaced to not collide with other implementations' keys. E.g. A core called 'foo' should use keys named as 'foo_option'.
                                           // retro_variable::value should contain a human readable description of the key as well as a '|' delimited list of expected values.
                                           // The number of possible options should be very limited, i.e. it should be feasible to cycle through options without a keyboard.
                                           // First entry should be treated as a default.
                                           //
                                           // Example entry:
                                           // { "foo_option", "Speed hack coprocessor X; false|true" }
                                           //
                                           // Text before first ';' is description. This ';' must be followed by a space, and followed by a list of possible values split up with '|'.
                                           // Only strings are operated on. The possible values will generally be displayed and stored as-is by the frontend.
                                           //
#define RETRO_ENVIRONMENT_GET_VARIABLE_UPDATE 17
                                           // bool * --
                                           // Result is set to true if some variables are updated by
                                           // frontend since last call to RETRO_ENVIRONMENT_GET_VARIABLE.
                                           // Variables should be queried with GET_VARIABLE.
                                           //
#define RETRO_ENVIRONMENT_SET_SUPPORT_NO_GAME 18
                                           // const bool * --
                                           // If true, the libretro implementation supports calls to retro_load_game() with NULL as argument.
                                           // Used by cores which can run without particular game data.
                                           // This should be called within retro_set_environment() only.
                                           //
#define RETRO_ENVIRONMENT_GET_LIBRETRO_PATH 19
                                           // const char ** --
                                           // Retrieves the absolute path from where this libretro implementation was loaded.
                                           // NULL is returned if the libretro was loaded statically (i.e. linked statically to frontend), or if the path cannot be determined.
                                           // Mostly useful in cooperation with SET_SUPPORT_NO_GAME as assets can be loaded without ugly hacks.
                                           //
                                           //
// Environment 20 was an obsolete version of SET_AUDIO_CALLBACK. It was not used by any known core at the time,
// and was removed from the API.
#define RETRO_ENVIRONMENT_SET_AUDIO_CALLBACK 22
                                           // const struct retro_audio_callback * --
                                           // Sets an interface which is used to notify a libretro core about audio being available for writing.
                                           // The callback can be called from any thread, so a core using this must have a thread safe audio implementation.
                                           // It is intended for games where audio and video are completely asynchronous and audio can be generated on the fly.
                                           // This interface is not recommended for use with emulators which have highly synchronous audio.
                                           //
                                           // The callback only notifies about writability; the libretro core still has to call the normal audio callbacks
                                           // to write audio. The audio callbacks must be called from within the notification callback.
                                           // The amount of audio data to write is up to the implementation.
                                           // Generally, the audio callback will be called continously in a loop.
                                           //
                                           // Due to thread safety guarantees and lack of sync between audio and video, a frontend
                                           // can selectively disallow this interface based on internal configuration. A core using
                                           // this interface must also implement the "normal" audio interface.
                                           //
                                           // A libretro core using SET_AUDIO_CALLBACK should also make use of SET_FRAME_TIME_CALLBACK.
#define RETRO_ENVIRONMENT_SET_FRAME_TIME_CALLBACK 21
                                           // const struct retro_frame_time_callback * --
                                           // Lets the core know how much time has passed since last invocation of retro_run().
                                           // The frontend can tamper with the timing to fake fast-forward, slow-motion, frame stepping, etc.
                                           // In this case the delta time will use the reference value in frame_time_callback..
                                           //
#define RETRO_ENVIRONMENT_GET_RUMBLE_INTERFACE 23
                                           // struct retro_rumble_interface * --
                                           // Gets an interface which is used by a libretro core to set state of rumble motors in controllers.
                                           // A strong and weak motor is supported, and they can be controlled indepedently.
                                           //
#define RETRO_ENVIRONMENT_GET_INPUT_DEVICE_CAPABILITIES 24
                                           // uint64_t * --
                                           // Gets a bitmask telling which device type are expected to be handled properly in a call to retro_input_state_t.
                                           // Devices which are not handled or recognized always return 0 in retro_input_state_t.
                                           // Example bitmask: caps = (1 << RETRO_DEVICE_JOYPAD) | (1 << RETRO_DEVICE_ANALOG).
                                           // Should only be called in retro_run().
                                           //
#define RETRO_ENVIRONMENT_GET_SENSOR_INTERFACE (25 | RETRO_ENVIRONMENT_EXPERIMENTAL)
                                           // struct retro_sensor_interface * --
                                           // Gets access to the sensor interface.
                                           // The purpose of this interface is to allow
                                           // setting state related to sensors such as polling rate, enabling/disable it entirely, etc.
                                           // Reading sensor state is done via the normal input_state_callback API.
                                           //
#define RETRO_ENVIRONMENT_GET_CAMERA_INTERFACE (26 | RETRO_ENVIRONMENT_EXPERIMENTAL)
                                           // struct retro_camera_callback * --
                                           // Gets an interface to a video camera driver.
                                           // A libretro core can use this interface to get access to a video camera.
                                           // New video frames are delivered in a callback in same thread as retro_run().
                                           //
                                           // GET_CAMERA_INTERFACE should be called in retro_load_game().
                                           //
                                           // Depending on the camera implementation used, camera frames will be delivered as a raw framebuffer,
                                           // or as an OpenGL texture directly.
                                           //
                                           // The core has to tell the frontend here which types of buffers can be handled properly.
                                           // An OpenGL texture can only be handled when using a libretro GL core (SET_HW_RENDER).
                                           // It is recommended to use a libretro GL core when using camera interface.
                                           //
                                           // The camera is not started automatically. The retrieved start/stop functions must be used to explicitly
                                           // start and stop the camera driver.
                                           //
#define RETRO_ENVIRONMENT_GET_LOG_INTERFACE 27
                                           // struct retro_log_callback * --
                                           // Gets an interface for logging. This is useful for logging in a cross-platform way
                                           // as certain platforms cannot use use stderr for logging. It also allows the frontend to
                                           // show logging information in a more suitable way.
                                           // If this interface is not used, libretro cores should log to stderr as desired.
#define RETRO_ENVIRONMENT_GET_PERF_INTERFACE 28
                                           // struct retro_perf_callback * --
                                           // Gets an interface for performance counters. This is useful for performance logging in a
                                           // cross-platform way and for detecting architecture-specific features, such as SIMD support.
#define RETRO_ENVIRONMENT_GET_LOCATION_INTERFACE 29
                                           // struct retro_location_callback * --
                                           // Gets access to the location interface.
                                           // The purpose of this interface is to be able to retrieve location-based information from the host device,
                                           // such as current latitude / longitude.
                                           //
#define RETRO_ENVIRONMENT_GET_CONTENT_DIRECTORY 30
                                           // const char ** --
                                           // Returns the "content" directory of the frontend.
                                           // This directory can be used to store specific assets that the core relies upon, such as art assets,
                                           // input data, etc etc.
                                           // The returned value can be NULL.
                                           // If so, no such directory is defined,
                                           // and it's up to the implementation to find a suitable directory.
                                           //
#define RETRO_ENVIRONMENT_GET_SAVE_DIRECTORY 31
                                           // const char ** --
                                           // Returns the "save" directory of the frontend.
                                           // This directory can be used to store SRAM, memory cards, high scores, etc, if the libretro core
                                           // cannot use the regular memory interface (retro_get_memory_data()).
                                           //
                                           // NOTE: libretro cores used to check GET_SYSTEM_DIRECTORY for similar things before.
                                           // They should still check GET_SYSTEM_DIRECTORY if they want to be backwards compatible.
                                           // The path here can be NULL. It should only be non-NULL if the frontend user has set a specific save path.
                                           //
#define RETRO_ENVIRONMENT_SET_SYSTEM_AV_INFO 32
                                           // const struct retro_system_av_info * --
                                           // Sets a new av_info structure. This can only be called from within retro_run().
                                           // This should *only* be used if the core is completely altering the internal resolutions, aspect ratios, timings, sampling rate, etc.
                                           // Calling this can require a full reinitialization of video/audio drivers in the frontend,
                                           // so it is important to call it very sparingly, and usually only with the users explicit consent.
                                           // An eventual driver reinit will happen so that video and audio callbacks
                                           // happening after this call within the same retro_run() call will target the newly initialized driver.
                                           //
                                           // This callback makes it possible to support configurable resolutions in games, which can be useful to
                                           // avoid setting the "worst case" in max_width/max_height.
                                           //
                                           // ***HIGHLY RECOMMENDED*** Do not call this callback every time resolution changes in an emulator core if it's
                                           // expected to be a temporary change, for the reasons of possible driver reinit.
                                           // This call is not a free pass for not trying to provide correct values in retro_get_system_av_info().
                                           //
                                           // If this returns false, the frontend does not acknowledge a changed av_info struct.
#define RETRO_ENVIRONMENT_SET_PROC_ADDRESS_CALLBACK 33
                                           // const struct retro_get_proc_address_interface * --
                                           // Allows a libretro core to announce support for the get_proc_address() interface.
                                           // This interface allows for a standard way to extend libretro where use of environment calls are too indirect,
                                           // e.g. for cases where the frontend wants to call directly into the core.
                                           //
                                           // If a core wants to expose this interface, SET_PROC_ADDRESS_CALLBACK **MUST** be called from within retro_set_environment().
                                           //
#define RETRO_ENVIRONMENT_SET_SUBSYSTEM_INFO 34
                                           // const struct retro_subsystem_info * --
                                           // This environment call introduces the concept of libretro "subsystems".
                                           // A subsystem is a variant of a libretro core which supports different kinds of games.
                                           // The purpose of this is to support e.g. emulators which might have special needs, e.g. Super Nintendos Super GameBoy, Sufami Turbo.
                                           // It can also be used to pick among subsystems in an explicit way if the libretro implementation is a multi-system emulator itself.
                                           //
                                           // Loading a game via a subsystem is done with retro_load_game_special(),
                                           // and this environment call allows a libretro core to expose which subsystems are supported for use with retro_load_game_special().
                                           // A core passes an array of retro_game_special_info which is terminated with a zeroed out retro_game_special_info struct.
                                           //
                                           // If a core wants to use this functionality, SET_SUBSYSTEM_INFO **MUST** be called from within retro_set_environment().
                                           //
#define RETRO_ENVIRONMENT_SET_CONTROLLER_INFO 35
                                           // const struct retro_controller_info * --
                                           // This environment call lets a libretro core tell the frontend which
                                           // controller types are recognized in calls to retro_set_controller_port_device().
                                           //
                                           // Some emulators such as Super Nintendo
                                           // support multiple lightgun types which must be specifically selected from.
                                           // It is therefore sometimes necessary for a frontend to be able to tell
                                           // the core about a special kind of input device which is not covered by the
                                           // libretro input API.
                                           //
                                           // In order for a frontend to understand the workings of an input device,
                                           // it must be a specialized type
                                           // of the generic device types already defined in the libretro API.
                                           //
                                           // Which devices are supported can vary per input port.
                                           // The core must pass an array of const struct retro_controller_info which is terminated with
                                           // a blanked out struct. Each element of the struct corresponds to an ascending port index to retro_set_controller_port_device().
                                           // Even if special device types are set in the libretro core, libretro should only poll input based on the base input device types.

struct retro_controller_description
{
   // Human-readable description of the controller. Even if using a generic input device type, this can be
   // set to the particular device type the core uses.
   const char *desc;

   // Device type passed to retro_set_controller_port_device(). If the device type is a sub-class of a generic input device type,
   // use the RETRO_DEVICE_SUBCLASS macro to create an ID. E.g. RETRO_DEVICE_SUBCLASS(RETRO_DEVICE_JOYPAD, 1).
   unsigned id;
};

struct retro_controller_info
{
   const struct retro_controller_description *types;
   unsigned num_types;
};

struct retro_subsystem_memory_info
{
   const char *extension; // The extension associated with a memory type, e.g. "psram".
   unsigned type; // The memory type for retro_get_memory(). This should be at least 0x100 to avoid conflict with standardized libretro memory types.
};

struct retro_subsystem_rom_info
{
   const char *desc; // Describes what the ROM is (SGB bios, GB rom, etc).
   const char *valid_extensions; // Same definition as retro_get_system_info().
   bool need_fullpath; // Same definition as retro_get_system_info().
   bool block_extract; // Same definition as retro_get_system_info().
   bool required; // This is set if the ROM is required to load a game. If this is set to false, a zeroed-out retro_game_info can be passed.

   // ROMs can have multiple associated persistent memory types (retro_get_memory()).
   const struct retro_subsystem_memory_info *memory;
   unsigned num_memory;
};

struct retro_subsystem_info
{
   const char *desc; // Human-readable string of the subsystem type, e.g. "Super GameBoy"
   // A computer friendly short string identifier for the subsystem type.
   // This name must be [a-z].
   // E.g. if desc is "Super GameBoy", this can be "sgb".
   // This identifier can be used for command-line interfaces, etc.
   const char *ident;

   // Infos for each ROM. The first entry is assumed to be the "most significant" ROM for frontend purposes.
   // E.g. with Super GameBoy, the first ROM should be the GameBoy ROM, as it is the most "significant" ROM to a user.
   // If a frontend creates new file paths based on the ROM used (e.g. savestates), it should use the path for the first ROM to do so.
   const struct retro_subsystem_rom_info *roms;

   unsigned num_roms; // Number of ROMs associated with a subsystem.
   unsigned id; // The type passed to retro_load_game_special().
};

typedef void (*retro_proc_address_t)(void);
// libretro API extension functions:
// (None here so far).
//////

// Get a symbol from a libretro core.
// Cores should only return symbols which are actual extensions to the libretro API.
// Frontends should not use this to obtain symbols to standard libretro entry points (static linking or dlsym).
// The symbol name must be equal to the function name, e.g. if void retro_foo(void); exists, the symbol must be called "retro_foo".
// The returned function pointer must be cast to the corresponding type.
typedef retro_proc_address_t (*retro_get_proc_address_t)(const char *sym);
struct retro_get_proc_address_interface
{
   retro_get_proc_address_t get_proc_address;
};

enum retro_log_level
{
   RETRO_LOG_DEBUG = 0,
   RETRO_LOG_INFO,
   RETRO_LOG_WARN,
   RETRO_LOG_ERROR,

   RETRO_LOG_DUMMY = INT_MAX
};

// Logging function. Takes log level argument as well.
typedef void (*retro_log_printf_t)(enum retro_log_level level, const char *fmt, ...);

struct retro_log_callback
{
   retro_log_printf_t log;
};

// Performance related functions
//
// ID values for SIMD CPU features
#define RETRO_SIMD_SSE      (1 << 0)
#define RETRO_SIMD_SSE2     (1 << 1)
#define RETRO_SIMD_VMX      (1 << 2)
#define RETRO_SIMD_VMX128   (1 << 3)
#define RETRO_SIMD_AVX      (1 << 4)
#define RETRO_SIMD_NEON     (1 << 5)
#define RETRO_SIMD_SSE3     (1 << 6)
#define RETRO_SIMD_SSSE3    (1 << 7)
#define RETRO_SIMD_MMX      (1 << 8)
#define RETRO_SIMD_MMXEXT   (1 << 9)
#define RETRO_SIMD_SSE4     (1 << 10)
#define RETRO_SIMD_SSE42    (1 << 11)
#define RETRO_SIMD_AVX2     (1 << 12)
#define RETRO_SIMD_VFPU     (1 << 13)
#define RETRO_SIMD_PS       (1 << 14)

typedef uint64_t retro_perf_tick_t;
typedef int64_t retro_time_t;

struct retro_perf_counter
{
   const char *ident;
   retro_perf_tick_t start;
   retro_perf_tick_t total;
   retro_perf_tick_t call_cnt;

   bool registered;
};

// Returns current time in microseconds. Tries to use the most accurate timer available.
typedef retro_time_t (*retro_perf_get_time_usec_t)(void);
// A simple counter. Usually nanoseconds, but can also be CPU cycles.
// Can be used directly if desired (when creating a more sophisticated performance counter system).
typedef retro_perf_tick_t (*retro_perf_get_counter_t)(void);
// Returns a bit-mask of detected CPU features (RETRO_SIMD_*).
typedef uint64_t (*retro_get_cpu_features_t)(void);
// Asks frontend to log and/or display the state of performance counters.
// Performance counters can always be poked into manually as well.
typedef void (*retro_perf_log_t)(void);
// Register a performance counter.
// ident field must be set with a discrete value and other values in retro_perf_counter must be 0.
// Registering can be called multiple times. To avoid calling to frontend redundantly, you can check registered field first.
typedef void (*retro_perf_register_t)(struct retro_perf_counter *counter);
// Starts and stops a registered counter.
typedef void (*retro_perf_start_t)(struct retro_perf_counter *counter);
typedef void (*retro_perf_stop_t)(struct retro_perf_counter *counter);

// For convenience it can be useful to wrap register, start and stop in macros.
// E.g.:
// #ifdef LOG_PERFORMANCE
// #define RETRO_PERFORMANCE_INIT(perf_cb, name) static struct retro_perf_counter name = {#name}; if (!name.registered) perf_cb.perf_register(&(name))
// #define RETRO_PERFORMANCE_START(perf_cb, name) perf_cb.perf_start(&(name))
// #define RETRO_PERFORMANCE_STOP(perf_cb, name) perf_cb.perf_stop(&(name))
// #else
// ... Blank macros ...
// #endif
// These can then be used mid-functions around code snippets.
//
// extern struct retro_perf_callback perf_cb; // Somewhere in the core.
//
// void do_some_heavy_work(void)
// {
//    RETRO_PERFORMANCE_INIT(cb, work_1);
//    RETRO_PERFORMANCE_START(cb, work_1);
//    heavy_work_1();
//    RETRO_PERFORMANCE_STOP(cb, work_1);
//
//    RETRO_PERFORMANCE_INIT(cb, work_2);
//    RETRO_PERFORMANCE_START(cb, work_2);
//    heavy_work_2();
//    RETRO_PERFORMANCE_STOP(cb, work_2);
// }
//
// void retro_deinit(void)
// {
//    perf_cb.perf_log(); // Log all perf counters here for example.
// }

struct retro_perf_callback
{
   retro_perf_get_time_usec_t    get_time_usec;
   retro_get_cpu_features_t      get_cpu_features;

   retro_perf_get_counter_t      get_perf_counter;
   retro_perf_register_t         perf_register;
   retro_perf_start_t            perf_start;
   retro_perf_stop_t             perf_stop;
   retro_perf_log_t              perf_log;
};

// FIXME: Document the sensor API and work out behavior.
// It will be marked as experimental until then.
enum retro_sensor_action
{
   RETRO_SENSOR_ACCELEROMETER_ENABLE = 0,
   RETRO_SENSOR_ACCELEROMETER_DISABLE,

   RETRO_SENSOR_DUMMY = INT_MAX
};

// Id values for SENSOR types.
#define RETRO_SENSOR_ACCELEROMETER_X 0
#define RETRO_SENSOR_ACCELEROMETER_Y 1
#define RETRO_SENSOR_ACCELEROMETER_Z 2

typedef bool (*retro_set_sensor_state_t)(unsigned port, enum retro_sensor_action action, unsigned rate);
typedef float (*retro_sensor_get_input_t)(unsigned port, unsigned id);
struct retro_sensor_interface
{
   retro_set_sensor_state_t set_sensor_state;
   retro_sensor_get_input_t get_sensor_input;
};
////

enum retro_camera_buffer
{
   RETRO_CAMERA_BUFFER_OPENGL_TEXTURE = 0,
   RETRO_CAMERA_BUFFER_RAW_FRAMEBUFFER,

   RETRO_CAMERA_BUFFER_DUMMY = INT_MAX
};

// Starts the camera driver. Can only be called in retro_run().
typedef bool (*retro_camera_start_t)(void);
// Stops the camera driver. Can only be called in retro_run().
typedef void (*retro_camera_stop_t)(void);
// Callback which signals when the camera driver is initialized and/or deinitialized.
// retro_camera_start_t can be called in initialized callback.
typedef void (*retro_camera_lifetime_status_t)(void);
// A callback for raw framebuffer data. buffer points to an XRGB8888 buffer.
// Width, height and pitch are similar to retro_video_refresh_t.
// First pixel is top-left origin.
typedef void (*retro_camera_frame_raw_framebuffer_t)(const uint32_t *buffer, unsigned width, unsigned height, size_t pitch);
// A callback for when OpenGL textures are used.
//
// texture_id is a texture owned by camera driver.
// Its state or content should be considered immutable, except for things like texture filtering and clamping.
//
// texture_target is the texture target for the GL texture.
// These can include e.g. GL_TEXTURE_2D, GL_TEXTURE_RECTANGLE, and possibly more depending on extensions.
//
// affine points to a packed 3x3 column-major matrix used to apply an affine transform to texture coordinates. (affine_matrix * vec3(coord_x, coord_y, 1.0))
// After transform, normalized texture coord (0, 0) should be bottom-left and (1, 1) should be top-right (or (width, height) for RECTANGLE).
//
// GL-specific typedefs are avoided here to avoid relying on gl.h in the API definition.
typedef void (*retro_camera_frame_opengl_texture_t)(unsigned texture_id, unsigned texture_target, const float *affine);
struct retro_camera_callback
{
   uint64_t caps; // Set by libretro core. Example bitmask: caps = (1 << RETRO_CAMERA_BUFFER_OPENGL_TEXTURE) | (1 << RETRO_CAMERA_BUFFER_RAW_FRAMEBUFFER).

   unsigned width; // Desired resolution for camera. Is only used as a hint.
   unsigned height;
   retro_camera_start_t start; // Set by frontend.
   retro_camera_stop_t stop; // Set by frontend.

   retro_camera_frame_raw_framebuffer_t frame_raw_framebuffer; // Set by libretro core if raw framebuffer callbacks will be used.
   retro_camera_frame_opengl_texture_t frame_opengl_texture; // Set by libretro core if OpenGL texture callbacks will be used.

   // Set by libretro core. Called after camera driver is initialized and ready to be started.
   // Can be NULL, in which this callback is not called.
   retro_camera_lifetime_status_t initialized;

   // Set by libretro core. Called right before camera driver is deinitialized.
   // Can be NULL, in which this callback is not called.
   retro_camera_lifetime_status_t deinitialized;
};

// Sets the interval of time and/or distance at which to update/poll location-based data.
// To ensure compatibility with all location-based implementations, values for both
// interval_ms and interval_distance should be provided.
// interval_ms is the interval expressed in milliseconds.
// interval_distance is the distance interval expressed in meters.
typedef void (*retro_location_set_interval_t)(unsigned interval_ms, unsigned interval_distance);

// Start location services. The device will start listening for changes to the
// current location at regular intervals (which are defined with retro_location_set_interval_t).
typedef bool (*retro_location_start_t)(void);

// Stop location services. The device will stop listening for changes to the current
// location.
typedef void (*retro_location_stop_t)(void);

// Get the position of the current location. Will set parameters to 0 if no new
// location update has happened since the last time.
typedef bool (*retro_location_get_position_t)(double *lat, double *lon, double *horiz_accuracy,
      double *vert_accuracy);

// Callback which signals when the location driver is initialized and/or deinitialized.
// retro_location_start_t can be called in initialized callback.
typedef void (*retro_location_lifetime_status_t)(void);

struct retro_location_callback
{
   retro_location_start_t         start;
   retro_location_stop_t          stop;
   retro_location_get_position_t  get_position;
   retro_location_set_interval_t  set_interval;

   retro_location_lifetime_status_t initialized;
   retro_location_lifetime_status_t deinitialized;
};

enum retro_rumble_effect
{
   RETRO_RUMBLE_STRONG = 0,
   RETRO_RUMBLE_WEAK = 1,

   RETRO_RUMBLE_DUMMY = INT_MAX
};

// Sets rumble state for joypad plugged in port 'port'. Rumble effects are controlled independently,
// and setting e.g. strong rumble does not override weak rumble.
// Strength has a range of [0, 0xffff].
//
// Returns true if rumble state request was honored. Calling this before first retro_run() is likely to return false.
typedef bool (*retro_set_rumble_state_t)(unsigned port, enum retro_rumble_effect effect, uint16_t strength);
struct retro_rumble_interface
{
   retro_set_rumble_state_t set_rumble_state;
};

// Notifies libretro that audio data should be written.
typedef void (*retro_audio_callback_t)(void);

// True: Audio driver in frontend is active, and callback is expected to be called regularily.
// False: Audio driver in frontend is paused or inactive. Audio callback will not be called until set_state has been called with true.
// Initial state is false (inactive).
typedef void (*retro_audio_set_state_callback_t)(bool enabled);
struct retro_audio_callback
{
   retro_audio_callback_t callback;
   retro_audio_set_state_callback_t set_state;
};

// Notifies a libretro core of time spent since last invocation of retro_run() in microseconds.
// It will be called right before retro_run() every frame.
// The frontend can tamper with timing to support cases like fast-forward, slow-motion and framestepping.
// In those scenarios the reference frame time value will be used.
typedef int64_t retro_usec_t;
typedef void (*retro_frame_time_callback_t)(retro_usec_t usec);
struct retro_frame_time_callback
{
   retro_frame_time_callback_t callback;
   retro_usec_t reference; // Represents the time of one frame. It is computed as 1000000 / fps, but the implementation will resolve the rounding to ensure that framestepping, etc is exact.
};

// Pass this to retro_video_refresh_t if rendering to hardware.
// Passing NULL to retro_video_refresh_t is still a frame dupe as normal.
#define RETRO_HW_FRAME_BUFFER_VALID ((void*)-1)

// Invalidates the current HW context.
// Any GL state is lost, and must not be deinitialized explicitly. If explicit deinitialization is desired by the libretro core,
// it should implement context_destroy callback.
// If called, all GPU resources must be reinitialized.
// Usually called when frontend reinits video driver.
// Also called first time video driver is initialized, allowing libretro core to init resources.
typedef void (*retro_hw_context_reset_t)(void);
// Gets current framebuffer which is to be rendered to. Could change every frame potentially.
typedef uintptr_t (*retro_hw_get_current_framebuffer_t)(void);

// Get a symbol from HW context.
typedef retro_proc_address_t (*retro_hw_get_proc_address_t)(const char *sym);

enum retro_hw_context_type
{
   RETRO_HW_CONTEXT_NONE = 0,
   RETRO_HW_CONTEXT_OPENGL, // OpenGL 2.x. Latest version available before 3.x+. Driver can choose to use latest compatibility context.
   RETRO_HW_CONTEXT_OPENGLES2, // GLES 2.0
   RETRO_HW_CONTEXT_OPENGL_CORE, // Modern desktop core GL context. Use major/minor fields to set GL version.
   RETRO_HW_CONTEXT_OPENGLES3, // GLES 3.0

   RETRO_HW_CONTEXT_DUMMY = INT_MAX
};

struct retro_hw_render_callback
{
   enum retro_hw_context_type context_type; // Which API to use. Set by libretro core.

   // Called when a context has been created or when it has been reset.
   // An OpenGL context is only valid after context_reset() has been called.
   //
   // When context_reset is called, OpenGL resources in the libretro implementation are guaranteed to be invalid.
   // It is possible that context_reset is called multiple times during an application lifecycle.
   // If context_reset is called without any notification (context_destroy),
   // the OpenGL context was lost and resources should just be recreated
   // without any attempt to "free" old resources.
   retro_hw_context_reset_t context_reset;

   retro_hw_get_current_framebuffer_t get_current_framebuffer; // Set by frontend.
   retro_hw_get_proc_address_t get_proc_address; // Set by frontend.
   bool depth; // Set if render buffers should have depth component attached.
   bool stencil; // Set if stencil buffers should be attached.
   // If depth and stencil are true, a packed 24/8 buffer will be added. Only attaching stencil is invalid and will be ignored.
   bool bottom_left_origin; // Use conventional bottom-left origin convention. Is false, standard libretro top-left origin semantics are used.
   unsigned version_major; // Major version number for core GL context.
   unsigned version_minor; // Minor version number for core GL context.

   bool cache_context; // If this is true, the frontend will go very far to avoid resetting context in scenarios like toggling fullscreen, etc.
   // The reset callback might still be called in extreme situations such as if the context is lost beyond recovery.
   // For optimal stability, set this to false, and allow context to be reset at any time.

   retro_hw_context_reset_t context_destroy; // A callback to be called before the context is destroyed in a controlled way by the frontend.
   // OpenGL resources can be deinitialized cleanly at this step.
   // context_destroy can be set to NULL, in which resources will just be destroyed without any notification.
   //
   // Even when context_destroy is non-NULL, it is possible that context_reset is called without any destroy notification.
   // This happens if context is lost by external factors (such as notified by GL_ARB_robustness).
   // In this case, the context is assumed to be already dead,
   // and the libretro implementation must not try to free any OpenGL resources in the subsequent context_reset.

   bool debug_context; // Creates a debug context.
};

// Callback type passed in RETRO_ENVIRONMENT_SET_KEYBOARD_CALLBACK. Called by the frontend in response to keyboard events.
// down is set if the key is being pressed, or false if it is being released.
// keycode is the RETROK value of the char.
// character is the text character of the pressed key. (UTF-32).
// key_modifiers is a set of RETROKMOD values or'ed together.
//
// The pressed/keycode state can be indepedent of the character.
// It is also possible that multiple characters are generated from a single keypress.
// Keycode events should be treated separately from character events.
// However, when possible, the frontend should try to synchronize these.
// If only a character is posted, keycode should be RETROK_UNKNOWN.
// Similarily if only a keycode event is generated with no corresponding character, character should be 0.
typedef void (*retro_keyboard_event_t)(bool down, unsigned keycode, uint32_t character, uint16_t key_modifiers);

struct retro_keyboard_callback
{
   retro_keyboard_event_t callback;
};

// Callbacks for RETRO_ENVIRONMENT_SET_DISK_CONTROL_INTERFACE.
// Should be set for implementations which can swap out multiple disk images in runtime.
// If the implementation can do this automatically, it should strive to do so.
// However, there are cases where the user must manually do so.
//
// Overview: To swap a disk image, eject the disk image with set_eject_state(true).
// Set the disk index with set_image_index(index). Insert the disk again with set_eject_state(false).

// If ejected is true, "ejects" the virtual disk tray.
// When ejected, the disk image index can be set.
typedef bool (*retro_set_eject_state_t)(bool ejected);
// Gets current eject state. The initial state is 'not ejected'.
typedef bool (*retro_get_eject_state_t)(void);
// Gets current disk index. First disk is index 0.
// If return value is >= get_num_images(), no disk is currently inserted.
typedef unsigned (*retro_get_image_index_t)(void);
// Sets image index. Can only be called when disk is ejected.
// The implementation supports setting "no disk" by using an index >= get_num_images().
typedef bool (*retro_set_image_index_t)(unsigned index);
// Gets total number of images which are available to use.
typedef unsigned (*retro_get_num_images_t)(void);
//
// Replaces the disk image associated with index.
// Arguments to pass in info have same requirements as retro_load_game().
// Virtual disk tray must be ejected when calling this.
// Replacing a disk image with info = NULL will remove the disk image from the internal list.
// As a result, calls to get_image_index() can change.
//
// E.g. replace_image_index(1, NULL), and previous get_image_index() returned 4 before.
// Index 1 will be removed, and the new index is 3.
struct retro_game_info;
typedef bool (*retro_replace_image_index_t)(unsigned index, const struct retro_game_info *info);
// Adds a new valid index (get_num_images()) to the internal disk list.
// This will increment subsequent return values from get_num_images() by 1.
// This image index cannot be used until a disk image has been set with replace_image_index.
typedef bool (*retro_add_image_index_t)(void);

struct retro_disk_control_callback
{
   retro_set_eject_state_t set_eject_state;
   retro_get_eject_state_t get_eject_state;

   retro_get_image_index_t get_image_index;
   retro_set_image_index_t set_image_index;
   retro_get_num_images_t  get_num_images;

   retro_replace_image_index_t replace_image_index;
   retro_add_image_index_t add_image_index;
};

enum retro_pixel_format
{
   // 0RGB1555, native endian. 0 bit must be set to 0.
   // This pixel format is default for compatibility concerns only.
   // If a 15/16-bit pixel format is desired, consider using RGB565.
   RETRO_PIXEL_FORMAT_0RGB1555 = 0,

   // XRGB8888, native endian. X bits are ignored.
   RETRO_PIXEL_FORMAT_XRGB8888 = 1,

   // RGB565, native endian. This pixel format is the recommended format to use if a 15/16-bit format is desired
   // as it is the pixel format that is typically available on a wide range of low-power devices.
   // It is also natively supported in APIs like OpenGL ES.
   RETRO_PIXEL_FORMAT_RGB565   = 2,

   // Ensure sizeof() == sizeof(int).
   RETRO_PIXEL_FORMAT_UNKNOWN  = INT_MAX
};

struct retro_message
{
   const char *msg;        // Message to be displayed.
   unsigned    frames;     // Duration in frames of message.
};

// Describes how the libretro implementation maps a libretro input bind
// to its internal input system through a human readable string.
// This string can be used to better let a user configure input.
struct retro_input_descriptor
{
   // Associates given parameters with a description.
   unsigned port;
   unsigned device;
   unsigned index;
   unsigned id;

   const char *description; // Human readable description for parameters.
                            // The pointer must remain valid until retro_unload_game() is called.
};

struct retro_system_info
{
   // All pointers are owned by libretro implementation, and pointers must remain valid until retro_deinit() is called.

   const char *library_name;      // Descriptive name of library. Should not contain any version numbers, etc.
   const char *library_version;   // Descriptive version of core.

   const char *valid_extensions;  // A string listing probably rom extensions the core will be able to load, separated with pipe.
                                  // I.e. "bin|rom|iso".
                                  // Typically used for a GUI to filter out extensions.

   bool        need_fullpath;     // If true, retro_load_game() is guaranteed to provide a valid pathname in retro_game_info::path.
                                  // ::data and ::size are both invalid.
                                  // If false, ::data and ::size are guaranteed to be valid, but ::path might not be valid.
                                  // This is typically set to true for libretro implementations that must load from file.
                                  // Implementations should strive for setting this to false, as it allows the frontend to perform patching, etc.

   bool        block_extract;     // If true, the frontend is not allowed to extract any archives before loading the real ROM.
                                  // Necessary for certain libretro implementations that load games from zipped archives.
};

struct retro_game_geometry
{
   unsigned base_width;    // Nominal video width of game.
   unsigned base_height;   // Nominal video height of game.
   unsigned max_width;     // Maximum possible width of game.
   unsigned max_height;    // Maximum possible height of game.

   float    aspect_ratio;  // Nominal aspect ratio of game. If aspect_ratio is <= 0.0,
                           // an aspect ratio of base_width / base_height is assumed.
                           // A frontend could override this setting if desired.
};

struct retro_system_timing
{
   double fps;             // FPS of video content.
   double sample_rate;     // Sampling rate of audio.
};

struct retro_system_av_info
{
   struct retro_game_geometry geometry;
   struct retro_system_timing timing;
};

struct retro_variable
{
   const char *key;        // Variable to query in RETRO_ENVIRONMENT_GET_VARIABLE.
                           // If NULL, obtains the complete environment string if more complex parsing is necessary.
                           // The environment string is formatted as key-value pairs delimited by semicolons as so:
                           // "key1=value1;key2=value2;..."
   const char *value;      // Value to be obtained. If key does not exist, it is set to NULL.
};

struct retro_game_info
{
   const char *path;       // Path to game, UTF-8 encoded. Usually used as a reference.
                           // May be NULL if rom was loaded from stdin or similar.
                           // retro_system_info::need_fullpath guaranteed that this path is valid.
   const void *data;       // Memory buffer of loaded game. Will be NULL if need_fullpath was set.
   size_t      size;       // Size of memory buffer.
   const char *meta;       // String of implementation specific meta-data.
};

// Callbacks
//
// Environment callback. Gives implementations a way of performing uncommon tasks. Extensible.
typedef bool (*retro_environment_t)(unsigned cmd, void *data);

// Render a frame. Pixel format is 15-bit 0RGB1555 native endian unless changed (see RETRO_ENVIRONMENT_SET_PIXEL_FORMAT).
// Width and height specify dimensions of buffer.
// Pitch specifices length in bytes between two lines in buffer.
// For performance reasons, it is highly recommended to have a frame that is packed in memory, i.e. pitch == width * byte_per_pixel.
// Certain graphic APIs, such as OpenGL ES, do not like textures that are not packed in memory.
typedef void (*retro_video_refresh_t)(const void *data, unsigned width, unsigned height, size_t pitch);

// Renders a single audio frame. Should only be used if implementation generates a single sample at a time.
// Format is signed 16-bit native endian.
typedef void (*retro_audio_sample_t)(int16_t left, int16_t right);
// Renders multiple audio frames in one go. One frame is defined as a sample of left and right channels, interleaved.
// I.e. int16_t buf[4] = { l, r, l, r }; would be 2 frames.
// Only one of the audio callbacks must ever be used.
typedef size_t (*retro_audio_sample_batch_t)(const int16_t *data, size_t frames);

// Polls input.
typedef void (*retro_input_poll_t)(void);
// Queries for input for player 'port'. device will be masked with RETRO_DEVICE_MASK.
// Specialization of devices such as RETRO_DEVICE_JOYPAD_MULTITAP that have been set with retro_set_controller_port_device()
// will still use the higher level RETRO_DEVICE_JOYPAD to request input.
typedef int16_t (*retro_input_state_t)(unsigned port, unsigned device, unsigned index, unsigned id);

// Sets callbacks. retro_set_environment() is guaranteed to be called before retro_init().
// The rest of the set_* functions are guaranteed to have been called before the first call to retro_run() is made.
void retro_set_environment(retro_environment_t);
void retro_set_video_refresh(retro_video_refresh_t);
void retro_set_audio_sample(retro_audio_sample_t);
void retro_set_audio_sample_batch(retro_audio_sample_batch_t);
void retro_set_input_poll(retro_input_poll_t);
void retro_set_input_state(retro_input_state_t);

// Library global initialization/deinitialization.
void retro_init(void);
void retro_deinit(void);

// Must return RETRO_API_VERSION. Used to validate ABI compatibility when the API is revised.
unsigned retro_api_version(void);

// Gets statically known system info. Pointers provided in *info must be statically allocated.
// Can be called at any time, even before retro_init().
void retro_get_system_info(struct retro_system_info *info);

// Gets information about system audio/video timings and geometry.
// Can be called only after retro_load_game() has successfully completed.
// NOTE: The implementation of this function might not initialize every variable if needed.
// E.g. geom.aspect_ratio might not be initialized if core doesn't desire a particular aspect ratio.
void retro_get_system_av_info(struct retro_system_av_info *info);

// Sets device to be used for player 'port'.
// By default, RETRO_DEVICE_JOYPAD is assumed to be plugged into all available ports.
// Setting a particular device type is not a guarantee that libretro cores will only poll input based on that particular device type. It is only a hint to the libretro core when a core cannot automatically detect the appropriate input device type on its own. It is also relevant when a core can change its behavior depending on device type.
void retro_set_controller_port_device(unsigned port, unsigned device);

// Resets the current game.
void retro_reset(void);

// Runs the game for one video frame.
// During retro_run(), input_poll callback must be called at least once.
//
// If a frame is not rendered for reasons where a game "dropped" a frame,
// this still counts as a frame, and retro_run() should explicitly dupe a frame if GET_CAN_DUPE returns true.
// In this case, the video callback can take a NULL argument for data.
void retro_run(void);

// Returns the amount of data the implementation requires to serialize internal state (save states).
// Beetween calls to retro_load_game() and retro_unload_game(), the returned size is never allowed to be larger than a previous returned value, to
// ensure that the frontend can allocate a save state buffer once.
size_t retro_serialize_size(void);

// Serializes internal state. If failed, or size is lower than retro_serialize_size(), it should return false, true otherwise.
bool retro_serialize(void *data, size_t size);
bool retro_unserialize(const void *data, size_t size);

void retro_cheat_reset(void);
void retro_cheat_set(unsigned index, bool enabled, const char *code);

// Loads a game.
bool retro_load_game(const struct retro_game_info *game);

// Loads a "special" kind of game. Should not be used except in extreme cases.
bool retro_load_game_special(
  unsigned game_type,
  const struct retro_game_info *info, size_t num_info
);

// Unloads a currently loaded game.
void retro_unload_game(void);

// Gets region of game.
unsigned retro_get_region(void);

// Gets region of memory.
void *retro_get_memory_data(unsigned id);
size_t retro_get_memory_size(unsigned id);

#ifdef __cplusplus
}
#endif

#endif