Treat composition frames with no layers as using GLES composition

When there are no window layers for a display, SurfaceFlinger clears
the undefined region using GLES. Some of the places that check for
GLES composition weren't considering this special case, in particular:

- We were skipping the eglSwapBuffers() on these frames.
- We were putting VirtualDisplaySurface in HWC-only composition mode.

This change centralizes the logic for this special case.

Bug: 10957068
Change-Id: I2deaf2ed101e8ea76708862a6bb67751b6078794

2 files changed, 10 insertions, 1 deletions

diff --git a/services/surfaceflinger/DisplayHardware/HWComposer.cpp b/services/surfaceflinger/DisplayHardware/HWComposer.cpp
index c851a2c067..7132b2f1b0 100644
--- a/services/surfaceflinger/DisplayHardware/HWComposer.cpp
+++ b/services/surfaceflinger/DisplayHardware/HWComposer.cpp
@@ -611,6 +611,10 @@ status_t HWComposer::prepare() {
         // here we're just making sure that "skip" layers are set
         // to HWC_FRAMEBUFFER and we're also counting how many layers
         // we have of each type.
+        //
+        // If there are no window layers, we treat the display has having FB
+        // composition, because SurfaceFlinger will use GLES to draw the
+        // wormhole region.
         for (size_t i=0 ; i<mNumDisplays ; i++) {
             DisplayData& disp(mDisplayData[i]);
             disp.hasFbComp = false;
@@ -632,6 +636,11 @@ status_t HWComposer::prepare() {
                         disp.hasOvComp = true;
                     }
                 }
+                if (disp.list->numHwLayers == (disp.framebufferTarget ? 1 : 0)) {
+                    disp.hasFbComp = true;
+                }
+            } else {
+                disp.hasFbComp = true;
             }
         }
     }
diff --git a/services/surfaceflinger/SurfaceFlinger.cpp b/services/surfaceflinger/SurfaceFlinger.cpp
index 4f139feda4..b5b0f2c00c 100644
--- a/services/surfaceflinger/SurfaceFlinger.cpp
+++ b/services/surfaceflinger/SurfaceFlinger.cpp
@@ -1524,7 +1524,7 @@ void SurfaceFlinger::doComposeSurfaces(const sp<const DisplayDevice>& hw, const
     HWComposer::LayerListIterator cur = hwc.begin(id);
     const HWComposer::LayerListIterator end = hwc.end(id);
 
-    const bool hasGlesComposition = hwc.hasGlesComposition(id) || (cur==end);
+    bool hasGlesComposition = hwc.hasGlesComposition(id);
     if (hasGlesComposition) {
         if (!hw->makeCurrent(mEGLDisplay, mEGLContext)) {
             ALOGW("DisplayDevice::makeCurrent failed. Aborting surface composition for display %s",