Low-level Audio in R/S - Githubissues

API详细说明参考：http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1386r2.pdf

目前我们只支持 Sample Type float32! 就行。三大平台应该都支持这个格式。

各平台使用的框架：

Windows (via WASAPI)
macOS (via CoreAudio)
Linux (via ALSA)

计划支持的功能：

Enumerate all available audio devices.
Get the current default input and output devices.
Enumerate known supported input and output stream formats for a device.
Get the current default input and output stream formats for a device.
Build and run input and output PCM streams on a chosen device with a given stream format

;-- implementation-defined type
#case [
    OS = 'Windows [
        #define audio-buffer-size! xxx
        #define audio-sample-rate! xxx
        #define audio-device-id! xxx
        audio-clock!: alias struct! [xxx]
    ]
    OS = ...
]

#define MAX_NUM_CHANNELS        16

#enum audio-sample-type! [
    SAMPLE_TYPE_F32
    SAMPLE_TYPE_I16
]

#enum audio-device-event! [
    DEVICE_CHANGED
    DEFAULT_INPUT_CHANGED
    DEFAULT_OUTPUT_CHANGED
]

audio-buffer!: alias struct! [
    contiguous?     [logic!]
    frames-count    [integer!]
    channels-count  [integer!]
    sample-type     [audio-sample-type!]
    stride          [integer!]
    channels        [ptr-ptr!]
]

audio-device-io!: alias struct! [
    input-buffer    [audio-buffer!]
    input-time      [audio-clock!]
    output-buffer   [audio-buffer!]
    output-time     [audio-clock!]
]

audio-io-callback!: alias function! [
    dev     [audio-device!]
    io      [audio-device-io!]
]

audio-device-callback!: alias function! [
    dev     [audio-device!]
]

audio-changed-callback!: alias function! []

audio-device!: alias struct! [
    ;-- implementation-defined
    ;-- 每个实现自己定里面需要的字段
]

audio: context [
    all-devices: func [
        count   [int-ptr!]          ;-- number of devices
        return: [audio-device!]     ;-- an array of audio-device!
    ]

    input-devices: func [
        count   [int-ptr!]          ;-- number of input devices
        return: [audio-device!]     ;-- an array of audio-device!
    ]

    output-devices: func [
        count   [int-ptr!]          ;-- number of output devices
        return: [audio-device!]     ;-- an array of audio-device!
    ]

    default-input-device: func [
        return: [audio-device!]
    ]

    default-output-device: func [
        return: [audio-device!]
    ]

    set-device-changed-callback: func [
        event   [audio-device-event!]
        cb      [int-ptr!]          ;-- audio-changed-callback!
    ]

    free-device: func [
        dev     [audio-device!]
    ]

    free-devices: func [
        devs    [audio-device!]     ;-- an array of audio-device!
        count   [integer!]          ;-- number of devices
        /local
            p   [byte-ptr!]
    ][
        p: as byte-ptr! devs
        loop count [
            free-device devs
            devs: devs + 1
        ]
        free p
    ]
]

audio-device: context [
    name: func [
        dev     [audio-device!]
        return: [c-string!]
    ]

    id: func [
        dev     [audio-device!]
        return: [audio-device-id!]
    ]

    input-channels-count: func [
        dev     [audio-device!]
        return: [integer!]
    ]

    output-channels-count: func [
        dev     [audio-device!]
        return: [integer!]
    ]

    buffer-size: func [
        dev     [audio-device!]
        return: [audio-buffer-size!]
    ]

    set-buffer-size: func [
        dev     [audio-device!]
        size    [audio-buffer-size!]
        return: [logic!]
    ]

    sample-rate: func [
        dev     [audio-device!]
        return: [audio-sample-rate!]
    ]

    set-sample-rate: func [
        dev     [audio-device!]
        rate    [audio-sample-rate!]
        return: [logic!]
    ]

    input?: func [
        dev     [audio-device!]
        return: [logic!]
    ]

    output?: func [
        dev     [audio-device!]
        return: [logic!]
    ]

    running?: func [
        dev     [audio-device!]
        return: [logic!]
    ]

    sample-type-support?: func [
        dev     [audio-device!]
        return: [logic!]
    ]

    can-connect?: func [
        dev     [audio-device!]
        return: [logic!]
    ]

    can-process?: func [
        dev     [audio-device!]
        return: [logic!]
    ]

    has-unprocessed-io?: func [
        dev     [audio-device!]
        return: [logic!]
    ]

    process: func [
        dev     [audio-device!]
        type    [audio-sample-rate!]
        io-cb   [int-ptr!]      ;-- audio-io-callback!
    ]

    connect: func [
        dev     [audio-device!]
        type    [audio-sample-rate!]
        io-cb   [int-ptr!]      ;-- audio-io-callback!
    ]

    start: func [
        dev      [audio-device!]
        start-cb [int-ptr!]     ;-- audio-device-callback!
        stop-cb  [int-ptr!]     ;-- audio-device-callback!
    ]

    stop: func [
        dev     [audio-device!]
        return: [logic!]
    ]

    wait: func [
        dev     [audio-device!]     
    ]
]

audio-buffer: context [
    frames-count: func [
        buf         [audio-buffer!]
        return:     [ulong!]
    ]

    channels-count: func [
        buf         [audio-buffer!]
        return:     [ulong!]
    ]

    samples-count: func [
        buf         [audio-buffer!]
        return:     [ulong!]
    ]

    contiguous?: func [
        buf         [audio-buffer!]
        return:     [logic!]
    ]

    channels-contiguous?: func [
        buf         [audio-buffer!]
        return:     [logic!]
    ]

    frames-contiguous?: func [
        buf         [audio-buffer!]
        return:     [logic!]
    ]

    data: func [
        buf         [audio-buffer!]
        return:     [float32-ptr!]  
    ]

    write: func [
        buf         [audio-buffer!]
        frame-idx   [integer!]
        channel-idx [integer!]
        value       [float32!]
    ]

    read: func [
        buf         [audio-buffer!]
        frame-idx   [integer!]
        channel-idx [integer!]
        return:     [float32!]
    ]

    ;@@ implements those functions onces we have int16! in R/S
    ;data-i16: func [
    ;   buf         [audio-buffer!]
    ;   return:     [int16!]    
    ;]

    ;write-i16: func [
    ;   buf         [audio-buffer!]
    ;   frame-idx   [integer!]
    ;   channel-idx [integer!]
    ;   value       [int16!]
    ;]

    ;read-i16: func [
    ;   buf         [audio-buffer!]
    ;   frame-idx   [integer!]
    ;   channel-idx [integer!]
    ;   return:     [int16!]
    ;]
]

示例代码： Ports from: https://github.com/stdcpp-audio/libstdaudio/blob/master/examples/level_meter.cpp

#define COND_CC [#if OS <> 'Windows [[cdecl]]]

audio-io-cb: func [
    COND_CC
    dev     [audio-device!]
    io      [audio-device-io!]
][
    ...
]

test: func [return: [integer!]][
    device: audio/default-input-device
    if null? device [return 1]

    audio-device/connect device SAMPLE_TYPE_F32 as int-ptr! :audio-io-cb
    audio-device/start device null null

    while [audio-device/running? device][
        ;sleep 250ms

    ]

]

后续需要在这个库的基础上实现Sound API。因此在实现的过程中，在查阅系统API的文档时，可以对相关的系统API留个心眼。

Sound API大致如下：

Load-WAV
Load-MP3
Play-Sound
Stop-Sound
Pause-Sound
Loop-Sound
Set-Volume
Set-Pan
Set-Delay

qtxie / notes

Low-level Audio in R/S #5