Layout Traversals (Droidcon Turin 2015)

Presented at Droidcon Turin 2015

Transcript

1. LAYOUT TRAVERSALS Droidcon Turin, 2015
2. LUCAS ROCHA +LucasRocha | @lucasratmundo
4. BE DELIBERATE Less handwavy UI code
5. THE BASICS From inside out.
6. UI TOOLKITS Layout + Rendering + Input Events
7. OLD SCHOOL Nested boxes, rudimentary motion API.
8. PRE-JELLY BEAN public final class ViewRoot extends Handler ... { ... public void scheduleTraversals() { if (!mTraversalScheduled) { mTraversalScheduled = true; sendEmptyMessage(DO_TRAVERSAL); } } ... public void handleMessage(Message msg) { ... case DO_TRAVERSAL: performTraversals(); ... } } ViewRoot.java
9. MODERNIZE Predictable notion of time that drives input, layout, and motion.
10. TICK TOCK VSYNC sets the pace. No tearing, no extra work.
11. CHOREOGRAPHER f1 f2 f3 f4 f5 . . . . . . VSYNC (60fps) Resize view Redraw view Input Events
12. CHOREOGRAPHER public void onVsync(long timestampNanos, int builtInDisplayId, int frame) { ... scheduleVsync(); ... } ... void doFrame(long frameTimeNanos, int frame) { ... if (!mFrameScheduled) { return; } ... doCallbacks(Choreographer.CALLBACK_INPUT, frameTimeNanos); doCallbacks(Choreographer.CALLBACK_ANIMATION, frameTimeNanos); doCallbacks(Choreographer.CALLBACK_TRAVERSAL, frameTimeNanos); ... } Choreographer.java
13. ViewRootImpl Connects WindowManager with the View framework
14. THE ROOT * * SurfaceFlinger ViewRootImpl
15. VIEWS Measure + Layout + Draw
16. TRAVERSAL * performTraversals() f2 performTraversals()
17. MEASURE * measure(int, int) f2 M M M M M M → onMeasure(int, int) measureHierarchy(...)
18. LAZY MEASURE Multi-MeasureSpec cache, invalidated in requestLayout()
19. LAZY MEASURE public final void measure(int widthMeasureSpec, int heightMeasureSpec) { ... int cacheIndex = mMeasureCache.indexOfKey(key); if (cacheIndex < 0 || sIgnoreMeasureCache) { onMeasure(widthMeasureSpec, heightMeasureSpec); mPrivateFlags3 &= ~PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT; } else { long value = mMeasureCache.valueAt(cacheIndex); setMeasuredDimensionRaw((int) (value >> 32), (int) value); mPrivateFlags3 |= PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT; } ... } View.java
20. LAZY MEASURE public void layout(int l, int t, int r, int b) { if ((flags & PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT) != 0) { onMeasure(mOldWidthMeasureSpec, mOldHeightMeasureSpec); mPrivateFlags3 &= ~PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT; } ... } View.java
21. LAYOUT * f2 M L M L M L M L M L M L layout(int, int, int, int) → onLayout(boolean, int, int, int, int) performLayout()
22. FRAME IT public void layout(int l, int t, int r, int b) { ... boolean changed = isLayoutModeOptical(mParent) ? setOpticalFrame(l, t, r, b) : setFrame(l, t, r, b); ... } View.java
23. DRAW * f2 M L D M L D M L D M L D M L D M L D draw(Canvas) → onDraw(Canvas) performDraw()
24. DISPLAY LISTS private DisplayList getDisplayList(...) { ... final HardwareCanvas canvas = displayList.start(width, height); ... draw(canvas); ... displayList.end(); ... } View.java
25. INVARIANTS Layout means measurement is done. Drawing means layout is done.
26. SMELLS 1. getMeasured*() calls outside onLayout() 2. New allocations during traversal · onLayout: ok-ish · onMeasure: avoid · onDraw: nope 3. post(Runnable) to mean “after layout”
27. HAPPENS TO WORK public final class MyActivity extends Activity { ... @Override public void onCreate() { final View myView = findViewById(R.id.some_id); myView.post(new Runnable() { @Override public void run() { Log.d(“LOGTAG”, myView.getWidth()); } }); } ... }
28. LOOPER BARRIERS void scheduleTraversals() { ... mTraversalBarrier = mHandler.getLooper().postSyncBarrier(); ... } ViewRootImpl.java
29. TREE OBSERVER Use OnPreDrawListener!
30. TRANSITIONS http://lucasr.org/?p=3902
31. OnPreDrawListener // 1. Save layout state and wait for next frame. getViewTreeObserver().addOnPreDrawListener(new OnPreDrawListener() { @Override public boolean onPreDraw() { getViewTreeObserver().removeOnPreDrawListener(this); // 2. Restore original layout state. // 3. Trigger animators towards new layout state. } }
32. CHANGES Resize, redraw & animate.
33. * requestLayout() f1 f2 f3 f4 f5 . . . . . .
34. requestLayout() public void requestLayout() { ... if (mParent != null && !mParent.isLayoutRequested()) { mParent.requestLayout(); } ... } void scheduleTraversals() { ... mChoreographer.postCallback( Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null); ... } View.java ViewRootImpl.java
35. * Invalidate(...) f1 f2 f3 f4 f5 . . . . . .
36. invalidate(...) public void invalidateInternal(...) { ... mPrivateFlags |= PFLAG_INVALIDATED; ... if (mParent != null && mAttachInfo != null && l < r && t < b) { final Rect damage = mAttachInfo.mTmpInvalRect; damage.set(l, t, r, b); mParent.invalidateChild(this, damage); } ... } boolean draw(...) { ... mRecreateDisplayList = (mPrivateFlags & PFLAG_INVALIDATED) == PFLAG_INVALIDATED; ... } View.java
37. * postOnAnimation() f1 f2 f3 f4 f5 . . . . . . ValueAnimator ...
38. postOnAnimation() public void postOnAnimation(Runnable action) { ... attachInfo.mViewRootImpl.mChoreographer.postCallback( Choreographer.CALLBACK_ANIMATION, action, null); ... } void doFrame(long frameTimeNanos, int frame) { ... doCallbacks(Choreographer.CALLBACK_INPUT, frameTimeNanos); doCallbacks(Choreographer.CALLBACK_ANIMATION, frameTimeNanos); doCallbacks(Choreographer.CALLBACK_TRAVERSAL, frameTimeNanos); ... } View.java Choreographer.java
39. BASIC TIPS 1. No layout requests during layout 2. No layout requests during animations 3. Invalidate regions when possible
40. PERFORMANCE 1. Simplify your view hierarchy 2. Avoid multi-pass measurement
41. GO CUSTOM Simplify view hierarchy, performance, missing features. http://lucasr.org/?p=3920
42. PROBE IT! Intercept view methods. Dissect layout traversals. https://github.com/lucasr/probe
43. WRAP VIEW METHODS public class LogRequestLayout extends Interceptor { @Override public void requestLayout(View view) { super.requestLayout(view); Log.d(LOGTAG, “requestLayout() on ” + view); } }
44. DEPLOY public final class MainActivity extends Activity { @Override protected void onCreate(Bundle savedInstanceState) { Probe.deploy(this, new DrawGreen(), new Filter.ViewId(R.id.view2)); super.onCreate(savedInstanceState); setContentView(R.id.main_activity); } }
45. FANCY HACKING ON DEEP LAYOUT STUFF? We're hiring :-)
46. QUESTIONS? +LucasRocha | @lucasratmundo