为什么硬件加速在我的视图上不起作用？

我在用着Facebook 的 Rebound 库 http://facebook.github.io/rebound/复制聊天头实现中看到的弹性动画。问题是，大多数时候动画都会断断续续。几张图片会更好地解释这一点。这是黄油般流畅的聊天头动画：

这是我的尝试（注意白色的动画如何View跳过几乎所有帧）：

偶尔它会顺利运行：

下面是我当前使用的代码（整个项目是在 Github 上 https://github.com/vickychijwani/BubbleNote/tree/eb708e3910a7279c5490f614a7150009b59bad0b如果您想快速设置）。我猜这与我的硬件加速未正确启用有关View。有2个Springs in my SpringSystem，一个代表“气泡”（Android 图标），另一个代表内容（白色View点击气泡时显示）。任何有关如何解决此问题的帮助将不胜感激。谢谢。

AndroidManifest.xml:

    <application android:hardwareAccelerated="true" ...>
        ...
    </application>

AppService.java:

    // the following code is in AppService#onCreate()
    // AppService extends android.app.Service
    // full code at https://github.com/vickychijwani/BubbleNote

    mContent.setLayerType(View.LAYER_TYPE_HARDWARE, null);

    final Spring bubbleSpring = system.createSpring();
    bubbleSpring.setCurrentValue(1.0);
    bubbleSpring.addListener(new SpringListener() {
        @Override
        public void onSpringUpdate(Spring spring) {
            float value = (float) spring.getCurrentValue();
            params.x = (int) (mPos[0] * value);
            params.y = (int) (mPos[1] * value);
            mWindowManager.updateViewLayout(mBubble, params);
            // fire the second animation when this one is about to end
            if (spring.isOvershooting() && contentSpring.isAtRest()) {
                contentSpring.setEndValue(1.0);
            }
        }

        // ...
    });

    final Spring contentSpring = system.createSpring();
    contentSpring.setCurrentValue(0.0);
    contentSpring.addListener(new SpringListener() {
        @Override
        public void onSpringUpdate(Spring spring) {
            // always prints false?!
            Log.d(TAG, "hardware acc = " + mContent.isHardwareAccelerated());
            float value = (float) spring.getCurrentValue();
            // clamping is required to prevent flicker
            float clampedValue = Math.min(Math.max(value, 0.0f), 1.0f);
            mContent.setScaleX(value);
            mContent.setScaleY(value);
            mContent.setAlpha(clampedValue);
        }

        // ...
    });

我通过查看框架源代码已经弄清楚了。

TL;DR: add WindowManager.LayoutParams.FLAG_HARDWARE_ACCELERATED当您手动附加一个布局标志时View to a Window / WindowManager;环境android:hardwareAccelerated=true在清单中将不起作用。

I'm 手动附加我的View to the WindowManager https://github.com/vickychijwani/BubbleNote/blob/eb708e3910a7279c5490f614a7150009b59bad0b/app/src/main/java/io/github/vickychijwani/bubblenote/BubbleNoteService.java#L54（因为我需要在Service模拟聊天头），如下所示：

    // code at https://github.com/vickychijwani/BubbleNote/blob/eb708e3910a7279c5490f614a7150009b59bad0b/app/src/main/java/io/github/vickychijwani/bubblenote/BubbleNoteService.java#L54
    mWindowManager = (WindowManager) getSystemService(WINDOW_SERVICE);
    LayoutInflater inflater = (LayoutInflater) getSystemService(LAYOUT_INFLATER_SERVICE);
    mBubble = (LinearLayout) inflater.inflate(R.layout.bubble, null, false);
    // ...
    final WindowManager.LayoutParams params = new WindowManager.LayoutParams(
            WindowManager.LayoutParams.WRAP_CONTENT,
            WindowManager.LayoutParams.WRAP_CONTENT,
            WindowManager.LayoutParams.TYPE_PHONE,
            WindowManager.LayoutParams.FLAG_LAYOUT_NO_LIMITS | WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE,
            PixelFormat.TRANSLUCENT);
    // ...
    mWindowManager.addView(mBubble, params);

我们去挖吧...

欢迎使用 Android 框架

我开始调试View#draw(...) http://grepcode.com/file/repository.grepcode.com/java/ext/com.google.android/android/4.4.4_r1/android/view/View.java?av=f#14069，然后向上调用堆栈ViewRootImpl#draw(boolean) http://grepcode.com/file/repository.grepcode.com/java/ext/com.google.android/android/4.4.4_r1/android/view/ViewRootImpl.java?av=f#2280。在这里我遇到了这段代码：

    if (!dirty.isEmpty() || mIsAnimating) {
        if (attachInfo.mHardwareRenderer != null && attachInfo.mHardwareRenderer.isEnabled()) {
            // Draw with hardware renderer.
            mIsAnimating = false;
            mHardwareYOffset = yoff;
            mResizeAlpha = resizeAlpha;

            mCurrentDirty.set(dirty);
            dirty.setEmpty();

            attachInfo.mHardwareRenderer.draw(mView, attachInfo, this,
                    animating ? null : mCurrentDirty);
        } else {
            // If we get here with a disabled & requested hardware renderer, something went
            // wrong (an invalidate posted right before we destroyed the hardware surface
            // for instance) so we should just bail out. Locking the surface with software
            // rendering at this point would lock it forever and prevent hardware renderer
            // from doing its job when it comes back.
            // Before we request a new frame we must however attempt to reinitiliaze the
            // hardware renderer if it's in requested state. This would happen after an
            // eglTerminate() for instance.
            if (attachInfo.mHardwareRenderer != null &&
                    !attachInfo.mHardwareRenderer.isEnabled() &&
                    attachInfo.mHardwareRenderer.isRequested()) {

                try {
                    attachInfo.mHardwareRenderer.initializeIfNeeded(mWidth, mHeight,
                            mHolder.getSurface());
                } catch (OutOfResourcesException e) {
                    handleOutOfResourcesException(e);
                    return;
                }

                mFullRedrawNeeded = true;
                scheduleTraversals();
                return;
            }

            if (!drawSoftware(surface, attachInfo, yoff, scalingRequired, dirty)) {
                return;
            }
        }
    }

就我而言ViewRootImpl#drawSoftware() http://grepcode.com/file/repository.grepcode.com/java/ext/com.google.android/android/4.4.4_r1/android/view/ViewRootImpl.java?av=f#2420被调用，它使用软件渲染器。嗯……这意味着HardwareRenderer is null。所以我去寻找建造的点HardwareRenderer，这是在ViewRootImpl#enableHardwareAcceleration(WindowManager.LayoutParams) http://grepcode.com/file/repository.grepcode.com/java/ext/com.google.android/android/4.4.4_r1/android/view/ViewRootImpl.java?av=f#681:

    // Try to enable hardware acceleration if requested
    final boolean hardwareAccelerated =
            (attrs.flags & WindowManager.LayoutParams.FLAG_HARDWARE_ACCELERATED) != 0;
    if (hardwareAccelerated) {
        // ...
        mAttachInfo.mHardwareRenderer = HardwareRenderer.createGlRenderer(2, translucent);
        // ...
    }

啊哈！我们的罪魁祸首就在这里！

回到手头的问题

在这种情况下Android不会自动设置FLAG_HARDWARE_ACCELERATED为了这Window，尽管我已经设置了android:hardwareAccerelated=true在清单中。所以修复方法很简单：

    mWindowManager = (WindowManager) getSystemService(WINDOW_SERVICE);
    LayoutInflater inflater = (LayoutInflater) getSystemService(LAYOUT_INFLATER_SERVICE);
    mBubble = (LinearLayout) inflater.inflate(R.layout.bubble, null, false);
    // ...
    final WindowManager.LayoutParams params = new WindowManager.LayoutParams(
            WindowManager.LayoutParams.WRAP_CONTENT,
            WindowManager.LayoutParams.WRAP_CONTENT,
            WindowManager.LayoutParams.TYPE_PHONE,
            // NOTE
            WindowManager.LayoutParams.FLAG_HARDWARE_ACCELERATED | WindowManager.LayoutParams.FLAG_LAYOUT_NO_LIMITS | WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE,
            PixelFormat.TRANSLUCENT);
    // ...
    mWindowManager.addView(mBubble, params);

虽然动画还是不如Facebook的流畅。我想知道为什么......（在有人问之前：不，动画期间没有大量日志；是的，我尝试过发布版本）