RetroArch/libretro.h

#ifndef LIBRETRO_H__
#define LIBRETRO_H__

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

// Hack applied for MSVC when compiling in C89 mode as it isn't C99 compliant.
#ifdef __cplusplus
extern "C" {
#else
#if defined(_MSC_VER) && !defined(SN_TARGET_PS3) && !defined(__cplusplus)
#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

// Libretro's fundamental device abstractions.
#define RETRO_DEVICE_MASK         0xff
#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.
#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, PRESSED will usually correspond to the left mouse button.
// 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

// These device types are specializations of the base types above.
// They should only be used in retro_set_controller_type() to inform libretro implementations
// about use of a very specific device type.
//
// In input state callback, however, only the base type should be used in the 'device' field.
#define RETRO_DEVICE_JOYPAD_MULTITAP        ((1 << 8) | RETRO_DEVICE_JOYPAD)
#define RETRO_DEVICE_LIGHTGUN_SUPER_SCOPE   ((1 << 8) | RETRO_DEVICE_LIGHTGUN)
#define RETRO_DEVICE_LIGHTGUN_JUSTIFIER     ((2 << 8) | RETRO_DEVICE_LIGHTGUN)
#define RETRO_DEVICE_LIGHTGUN_JUSTIFIERS    ((3 << 8) | RETRO_DEVICE_LIGHTGUN)

// 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 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

// Special memory types.
#define RETRO_MEMORY_SNES_BSX_RAM             ((1 << 8) | RETRO_MEMORY_SAVE_RAM)
#define RETRO_MEMORY_SNES_BSX_PRAM            ((2 << 8) | RETRO_MEMORY_SAVE_RAM)
#define RETRO_MEMORY_SNES_SUFAMI_TURBO_A_RAM  ((3 << 8) | RETRO_MEMORY_SAVE_RAM)
#define RETRO_MEMORY_SNES_SUFAMI_TURBO_B_RAM  ((4 << 8) | RETRO_MEMORY_SAVE_RAM)
#define RETRO_MEMORY_SNES_GAME_BOY_RAM        ((5 << 8) | RETRO_MEMORY_SAVE_RAM)
#define RETRO_MEMORY_SNES_GAME_BOY_RTC        ((6 << 8) | RETRO_MEMORY_RTC)

// Special game types passed into retro_load_game_special().
// Only used when multiple ROMs are required.
#define RETRO_GAME_TYPE_BSX             0x101
#define RETRO_GAME_TYPE_BSX_SLOTTED     0x102
#define RETRO_GAME_TYPE_SUFAMI_TURBO    0x103
#define RETRO_GAME_TYPE_SUPER_GAME_BOY  0x104

// 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)
};


// 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.
                                           //
#define RETRO_ENVIRONMENT_GET_VARIABLE  4  // struct retro_variable * --
                                           // Interface to aquire user-defined information from environment
                                           // that cannot feasibly be supported in a multi-system way.
                                           // Mostly used for obscure,
                                           // specific features that the user can tap into when neseccary.
                                           //
#define RETRO_ENVIRONMENT_SET_VARIABLES 5  // const struct retro_variable * --
                                           // Allows an implementation to signal the environment
                                           // which variables it might want to check for later using GET_VARIABLE.
                                           // 'data' points to an array of retro_variable structs terminated by a { NULL, NULL } element.
                                           // retro_variable::value should contain a human readable description of the key.
                                           //
#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 to 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.
                                           //
#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.


// 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.
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;
};

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'.
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