SurfaceFlinger: Cache updateInputWindows call

This is a conservative but safe cache. We invalidate it if
any layer with InputInfo, or any layer whose children/relative-children
have input info updates their drawing state. Not all these drawing state
updates will result in Input changes, but we can be confident that
without some drawing state change there wont be any Input changes,
and thus it seems the cache is safe. This will solve the case of
moving layers that don't have any InputInfo assosciated generating
setInputWindows calls.

Bug: 148675756
Test: Existing tests pass. go/wm-smoke
Change-Id: Ie5979b25370c2d5c3d8a55f187fc6fda1cc75b27
diff --git a/services/surfaceflinger/BufferLayer.cpp b/services/surfaceflinger/BufferLayer.cpp
index d7ec868..e4d754c 100644
--- a/services/surfaceflinger/BufferLayer.cpp
+++ b/services/surfaceflinger/BufferLayer.cpp
@@ -485,6 +485,10 @@
         }
     }
 
+    if (recomputeVisibleRegions == true) {
+        maybeDirtyInput();
+    }
+
     return true;
 }
 
diff --git a/services/surfaceflinger/Layer.cpp b/services/surfaceflinger/Layer.cpp
index 64cfb3d..3765d0d 100644
--- a/services/surfaceflinger/Layer.cpp
+++ b/services/surfaceflinger/Layer.cpp
@@ -993,6 +993,9 @@
     commitTransaction(c);
     mPendingStatesSnapshot = mPendingStates;
     mCurrentState.callbackHandles = {};
+
+    maybeDirtyInput();
+
     return flags;
 }
 
@@ -2472,6 +2475,32 @@
     }
 }
 
+bool Layer::maybeDirtyInput() {
+    // No sense redirtying input.
+    if (mFlinger->inputDirty()) return true;
+
+    if (hasInput()) {
+        mFlinger->dirtyInput();
+        return true;
+    }
+
+    // If a child or relative dirties the input, no sense continuing to traverse
+    // so we return early and halt the recursion. We traverse ourselves instead
+    // of using traverse() so we can implement this early halt.
+    for (const sp<Layer>& child : mDrawingChildren) {
+        if (child->maybeDirtyInput()) {
+            return true;
+        }
+    }
+    for (const wp<Layer>& weakRelative : mDrawingState.zOrderRelatives) {
+        sp<Layer> relative = weakRelative.promote();
+        if (relative && relative->maybeDirtyInput()) {
+            return true;
+        }
+    }
+    return false;
+}
+
 // ---------------------------------------------------------------------------
 
 }; // namespace android
diff --git a/services/surfaceflinger/Layer.h b/services/surfaceflinger/Layer.h
index 20d7232..e21a866 100644
--- a/services/surfaceflinger/Layer.h
+++ b/services/surfaceflinger/Layer.h
@@ -997,6 +997,10 @@
     // Window types from WindowManager.LayoutParams
     const int mWindowType;
 
+    // Called when mDrawingState has changed. If we or one of our children/relatives hasInput()
+    // then we will dirty the setInputWindows cache.
+    bool maybeDirtyInput();
+
 private:
     /**
      * Returns an unsorted vector of all layers that are part of this tree.
diff --git a/services/surfaceflinger/SurfaceFlinger.cpp b/services/surfaceflinger/SurfaceFlinger.cpp
index c995db4..6f49c7a 100644
--- a/services/surfaceflinger/SurfaceFlinger.cpp
+++ b/services/surfaceflinger/SurfaceFlinger.cpp
@@ -2769,6 +2769,19 @@
 void SurfaceFlinger::updateInputWindowInfo() {
     std::vector<InputWindowInfo> inputHandles;
 
+    // We use a simple caching algorithm here. mInputDirty begins as true,
+    // after we call setInputWindows we set it to false, so
+    // in the future we wont call it again.. We set input dirty to true again
+    // when any layer that hasInput() has a transaction performed on it
+    // or when any parent or relative parent of such a layer has a transaction
+    // performed on it. Not all of these transactions will really result in
+    // input changes but all input changes will spring from these transactions
+    // so the cache is safe but not optimal. It seems like it might be annoyingly
+    // costly to cache and comapre the actual InputWindowHandle vector though.
+    if (!mInputDirty) {
+        return;
+    }
+
     mDrawingState.traverseInReverseZOrder([&](Layer* layer) {
         if (layer->hasInput()) {
             // When calculating the screen bounds we ignore the transparent region since it may
@@ -2780,6 +2793,8 @@
     mInputFlinger->setInputWindows(inputHandles,
                                    mInputWindowCommands.syncInputWindows ? mSetInputWindowsListener
                                                                          : nullptr);
+
+    mInputDirty = false;
 }
 
 void SurfaceFlinger::commitInputWindowCommands() {
diff --git a/services/surfaceflinger/SurfaceFlinger.h b/services/surfaceflinger/SurfaceFlinger.h
index 83f0131..e162da6 100644
--- a/services/surfaceflinger/SurfaceFlinger.h
+++ b/services/surfaceflinger/SurfaceFlinger.h
@@ -1236,6 +1236,11 @@
     // janky frames there are.
     nsecs_t mMissedFrameJankStart = 0;
     int32_t mMissedFrameJankCount = 0;
+
+    // See updateInputWindowInfo() for details
+    std::atomic<bool> mInputDirty = true;
+    void dirtyInput() { mInputDirty = true; }
+    bool inputDirty() { return mInputDirty; }
 };
 
 } // namespace android