Why is hardware acceleration not working on my View?

I've figured it out by going through the framework source code.

TL;DR: add WindowManager.LayoutParams.FLAG_HARDWARE_ACCELERATED to the layout flags when you manually attach a View to a Window / WindowManager; setting android:hardwareAccelerated=true in the manifest won't work.

I'm manually attaching my View to the WindowManager (because I need to create my UI in a Service to emulate chat heads) like so:

    // 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);

Let's go digging...

Welcome to the Android framework

I started debugging at View#draw(...), then went up the call stack to ViewRootImpl#draw(boolean). Here I came across this piece of code:

    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;            }        }    }

In my case ViewRootImpl#drawSoftware() was being called, which uses the software renderer. Hmm... that means the HardwareRenderer is null. So I went searching for the point of construction of the HardwareRenderer, which is in ViewRootImpl#enableHardwareAcceleration(WindowManager.LayoutParams):

    // 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);        // ...    }

Aha! There's our culprit!

Back to the problem at hand

In this case Android does not automatically set FLAG_HARDWARE_ACCELERATED for this Window, even though I've set android:hardwareAccerelated=true in the manifest. So the fix is simply:

    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);

Although the animation is still not as smooth as Facebook's. I wonder why... (before anyone asks: no, there are no copious logs during the animation; and yes, I've tried with a release build)