Android bootanimation學習

一、bootanimation啓動和結束

bootanimation的啓動和結束受surfaceflinger控制
bootanimation進程啓動在android/frameworks/native/services/surfaceflinger/StartPropertySetThread.cpp

bool StartPropertySetThread::threadLoop() {
    // Set property service.sf.present_timestamp, consumer need check its readiness
    property_set(kTimestampProperty, mTimestampPropertyValue ? "1" : "0");
    // Clear BootAnimation exit flag
    property_set("service.bootanim.exit", "0");//啓動開機動畫進程

    char value[PROPERTY_VALUE_MAX];
    property_get("debug.sf.nobootanimation", value, "0");
    if (atoi(value) == 0) {
        // Start BootAnimation if not started
        property_set("ctl.start", "bootanim");
    }

    // Exit immediately
    return false;
}

bootanimation進程結束在
android/frameworks/native/services/surfaceflinger/SurfaceFlinger.cpp

void SurfaceFlinger::bootFinished()
{
    if (mStartPropertySetThread->join() != NO_ERROR) {
        ALOGE("Join StartPropertySetThread failed!");
    }
    const nsecs_t now = systemTime();
    const nsecs_t duration = now - mBootTime;
    ALOGI("Boot is finished (%ld ms)", long(ns2ms(duration)) );

    // wait patiently for the window manager death
    const String16 name("window");
    sp<IBinder> window(defaultServiceManager()->getService(name));
    if (window != 0) {
        window->linkToDeath(static_cast<IBinder::DeathRecipient*>(this));
    }

    if (mVrFlinger) {
      mVrFlinger->OnBootFinished();
    }

    // stop boot animation
    // formerly we would just kill the process, but we now ask it to exit so it
    // can choose where to stop the animation.
    property_set("service.bootanim.exit", "1");//退出開機動畫

    const int LOGTAG_SF_STOP_BOOTANIM = 60110;
    LOG_EVENT_LONG(LOGTAG_SF_STOP_BOOTANIM,
                   ns2ms(systemTime(SYSTEM_TIME_MONOTONIC)));

    sp<LambdaMessage> readProperties = new LambdaMessage([&]() {
        readPersistentProperties();
    });
    postMessageAsync(readProperties);
}

二、bootanimation源碼

開機動畫源碼在android/frameworks/base/cmds/bootanimation目錄。
修改開機動畫，收到退出消息後晚維持最後一幀4秒然後退出(一擋遮百醜):

void BootAnimation::checkExit() {
    // Allow surface flinger to gracefully request shutdown
    char value[PROPERTY_VALUE_MAX];
    property_get(EXIT_PROP_NAME, value, "0");
    int exitnow = atoi(value);
    if (exitnow) {
        usleep(4000 * 1000);//增加4s延時
        requestExit();
        mCallbacks->shutdown();
    }
}

三、bootanimation資源

開機動畫資源在android/vendor/XXX/hmi/bootanimation目錄(XXX和平臺有關)
是一個或多個存儲格式的zip文件。(zip -r -0 xxx.zip [file])
在android/frameworks/base/cmds/bootanimation下有一份文檔FORMAT.md，裏面非常詳細的說明。

# bootanimation format

## zipfile paths

The system selects a boot animation zipfile from the following locations, in order:

    /system/media/bootanimation-encrypted.zip (if getprop("vold.decrypt") = '1')
    /system/media/bootanimation.zip
    /oem/media/bootanimation.zip

## zipfile layout

The `bootanimation.zip` archive file includes:

    desc.txt - a text file
    part0  \
    part1   \  directories full of PNG frames
    ...     /
    partN  /

## desc.txt format

The first line defines the general parameters of the animation:

    WIDTH HEIGHT FPS

  * **WIDTH:** animation width (pixels)
  * **HEIGHT:** animation height (pixels)
  * **FPS:** frames per second, e.g. 60

It is followed by a number of rows of the form:

    TYPE COUNT PAUSE PATH [#RGBHEX CLOCK]

  * **TYPE:** a single char indicating what type of animation segment this is:
      + `p` -- this part will play unless interrupted by the end of the boot
      + `c` -- this part will play to completion, no matter what
  * **COUNT:** how many times to play the animation, or 0 to loop forever until boot is complete
  * **PAUSE:** number of FRAMES to delay after this part ends
  * **PATH:** directory in which to find the frames for this part (e.g. `part0`)
  * **RGBHEX:** _(OPTIONAL)_ a background color, specified as `#RRGGBB`
  * **CLOCK:** _(OPTIONAL)_ the y-coordinate at which to draw the current time (for watches)

There is also a special TYPE, `$SYSTEM`, that loads `/system/media/bootanimation.zip`
and plays that.

## loading and playing frames

Each part is scanned and loaded directly from the zip archive. Within a part directory, every file
(except `trim.txt` and `audio.wav`; see next sections) is expected to be a PNG file that represents
one frame in that part (at the specified resolution). For this reason it is important that frames be
named sequentially (e.g. `part000.png`, `part001.png`, ...) and added to the zip archive in that
order.

## trim.txt

To save on memory, textures may be trimmed by their background color.  trim.txt sequentially lists
the trim output for each frame in its directory, so the frames may be properly positioned.
Output should be of the form: `WxH+X+Y`. Example:

    713x165+388+914
    708x152+388+912
    707x139+388+911
    649x92+388+910

If the file is not present, each frame is assumed to be the same size as the animation.

## audio.wav

Each part may optionally play a `wav` sample when it starts. To enable this, add a file
with the name `audio.wav` in the part directory.

## exiting

The system will end the boot animation (first completing any incomplete or even entirely unplayed
parts that are of type `c`) when the system is finished booting. (This is accomplished by setting
the system property `service.bootanim.exit` to a nonzero string.)

## protips

### PNG compression

Use `zopflipng` if you have it, otherwise `pngcrush` will do. e.g.:

    for fn in *.png ; do
        zopflipng -m ${fn}s ${fn}s.new && mv -f ${fn}s.new ${fn}
        # or: pngcrush -q ....
    done

Some animations benefit from being reduced to 256 colors:

    pngquant --force --ext .png *.png
    # alternatively: mogrify -colors 256 anim-tmp/*/*.png

### creating the ZIP archive

    cd <path-to-pieces>
    zip -0qry -i \*.txt \*.png \*.wav @ ../bootanimation.zip *.txt part*

Note that the ZIP archive is not actually compressed! The PNG files are already as compressed
as they can reasonably get, and there is unlikely to be any redundancy between files.