the visible region sent to HWC was garbage

we used to have a visibleRegion object per layer, but now
it's per screen; so at somepoint the code got changed to
calculate the per-screen visible region on the stack and that's
what got passed to HWC.

we're now setting the visibleRegionScreen at each frame and
freeing at after the HWC set() call. We use the underlaying
SharedBuffer so that in most cases we don't have to allocate,
free or copy memory around.

Bug: 7089478
Change-Id: I24fa556c76613a225d9fe7a6c6b727bb476144d8

services/surfaceflinger/DisplayHardware/HWComposer.cpp

@@ -573,9 +573,12 @@ public:
         reinterpret_cast<Rect&>(getLayer()->sourceCrop) = crop;
     }
     virtual void setVisibleRegionScreen(const Region& reg) {
-        getLayer()->visibleRegionScreen.rects =
-                reinterpret_cast<hwc_rect_t const *>(
-                        reg.getArray(&getLayer()->visibleRegionScreen.numRects));
+        // Region::getSharedBuffer creates a reference to the underlying
+        // SharedBuffer of this Region, this reference is freed
+        // in onDisplayed()
+        hwc_region_t& visibleRegion = getLayer()->visibleRegionScreen;
+        SharedBuffer const* sb = reg.getSharedBuffer(&visibleRegion.numRects);
+        visibleRegion.rects = reinterpret_cast<hwc_rect_t const *>(sb->data());
     }
     virtual void setBuffer(const sp<GraphicBuffer>& buffer) {
         if (buffer == 0 || buffer->handle == 0) {
@@ -586,6 +589,16 @@ public:
             getLayer()->handle = buffer->handle;
         }
     }
+    virtual void onDisplayed() {
+        hwc_region_t& visibleRegion = getLayer()->visibleRegionScreen;
+        SharedBuffer const* sb = SharedBuffer::bufferFromData(visibleRegion.rects);
+        if (sb) {
+            sb->release();
+            // not technically needed but safer
+            visibleRegion.numRects = 0;
+            visibleRegion.rects = NULL;
+        }
+    }
 };
 
 /*

services/surfaceflinger/DisplayHardware/HWComposer.h

@@ -130,6 +130,7 @@ public:
         virtual void setVisibleRegionScreen(const Region& reg) = 0;
         virtual void setBuffer(const sp<GraphicBuffer>& buffer) = 0;
         virtual void setAcquireFenceFd(int fenceFd) = 0;
+        virtual void onDisplayed() = 0;
     };
 
     /*

services/surfaceflinger/Layer.cpp

@@ -72,6 +72,7 @@ Layer::Layer(SurfaceFlinger* flinger, const sp<Client>& client)
 
 void Layer::onLayerDisplayed(const sp<const DisplayDevice>& hw,
         HWComposer::HWCLayerInterface* layer) {
+    LayerBaseClient::onLayerDisplayed(hw, layer);
     if (layer) {
         mSurfaceTexture->setReleaseFence(layer->getAndResetReleaseFenceFd());
     }

services/surfaceflinger/LayerBase.cpp

@@ -288,12 +288,16 @@ void LayerBase::setGeometry(
     // scaling is already applied in transformedBounds
     layer.setFrame(transformedBounds);
     layer.setCrop(transformedBounds.getBounds());
-    layer.setVisibleRegionScreen(tr.transform(visibleRegion));
 }
 
 void LayerBase::setPerFrameData(const sp<const DisplayDevice>& hw,
         HWComposer::HWCLayerInterface& layer) {
     layer.setBuffer(0);
+    // we have to set the visible region on every frame because
+    // we currently free it during onLayerDisplayed(), which is called
+    // after HWComposer::commit() -- every frame.
+    const Transform& tr = hw->getTransform();
+    layer.setVisibleRegionScreen(tr.transform(visibleRegion));
 }
 
 void LayerBase::setAcquireFence(const sp<const DisplayDevice>& hw,
@@ -301,6 +305,13 @@ void LayerBase::setAcquireFence(const sp<const DisplayDevice>& hw,
     layer.setAcquireFenceFd(-1);
 }
 
+void LayerBase::onLayerDisplayed(const sp<const DisplayDevice>& hw,
+        HWComposer::HWCLayerInterface* layer) {
+    if (layer) {
+        layer->onDisplayed();
+    }
+}
+
 void LayerBase::setFiltering(bool filtering)
 {
     mFiltering = filtering;

services/surfaceflinger/LayerBase.h

@@ -218,7 +218,7 @@ public:
     /** called after page-flip
      */
     virtual void onLayerDisplayed(const sp<const DisplayDevice>& hw,
-            HWComposer::HWCLayerInterface* layer) { }
+            HWComposer::HWCLayerInterface* layer);
 
     /** called before composition.
      * returns true if the layer has pending updates.