Add a boardconfig to force HWC composition of virtual displays

When this boardconfig is defined, even when all virtual display
composition is done by GLES, the HWC will be forced to copy from the
GLES framebuffer to the output buffer. On some hardware this allows
HWC to do format conversions that would otherwise have to be done by
the consumer, with worse power and/or performance.

Bug: 8316155
Change-Id: If980ecc589f138cef063eafa757f7f748196713e

2 files changed, 20 insertions, 0 deletions

diff --git a/services/surfaceflinger/Android.mk b/services/surfaceflinger/Android.mk
index c3daa64..1a8f243 100644
--- a/services/surfaceflinger/Android.mk
+++ b/services/surfaceflinger/Android.mk
@@ -51,6 +51,12 @@ ifeq ($(TARGET_DISABLE_TRIPLE_BUFFERING),true)
 	LOCAL_CFLAGS += -DTARGET_DISABLE_TRIPLE_BUFFERING
 endif
 
+ifneq ($(TARGET_FORCE_HWC_FOR_VIRTUAL_DISPLAYS),)
+    LOCAL_CFLAGS += -DFORCE_HWC_COPY_FOR_VIRTUAL_DISPLAYS=false
+else
+    LOCAL_CFLAGS += -DFORCE_HWC_COPY_FOR_VIRTUAL_DISPLAYS=true
+endif
+
 ifneq ($(NUM_FRAMEBUFFER_SURFACE_BUFFERS),)
   LOCAL_CFLAGS += -DNUM_FRAMEBUFFER_SURFACE_BUFFERS=$(NUM_FRAMEBUFFER_SURFACE_BUFFERS)
 endif
diff --git a/services/surfaceflinger/DisplayHardware/VirtualDisplaySurface.cpp b/services/surfaceflinger/DisplayHardware/VirtualDisplaySurface.cpp
index 29e9d40..0d6cbb4 100644
--- a/services/surfaceflinger/DisplayHardware/VirtualDisplaySurface.cpp
+++ b/services/surfaceflinger/DisplayHardware/VirtualDisplaySurface.cpp
@@ -22,6 +22,8 @@
 namespace android {
 // ---------------------------------------------------------------------------
 
+static bool sForceHwcCopy = FORCE_HWC_COPY_FOR_VIRTUAL_DISPLAYS;
+
 #define VDS_LOGE(msg, ...) ALOGE("[%s] "msg, \
         mDisplayName.string(), ##__VA_ARGS__)
 #define VDS_LOGW_IF(cond, msg, ...) ALOGW_IF(cond, "[%s] "msg, \
@@ -96,6 +98,18 @@ status_t VirtualDisplaySurface::prepareFrame(CompositionType compositionType) {
     mDbgState = DBG_STATE_PREPARED;
 
     mCompositionType = compositionType;
+    if (sForceHwcCopy && mCompositionType == COMPOSITION_GLES) {
+        // Some hardware can do RGB->YUV conversion more efficiently in hardware
+        // controlled by HWC than in hardware controlled by the video encoder.
+        // Forcing GLES-composed frames to go through an extra copy by the HWC
+        // allows the format conversion to happen there, rather than passing RGB
+        // directly to the consumer.
+        //
+        // On the other hand, when the consumer prefers RGB or can consume RGB
+        // inexpensively, this forces an unnecessary copy.
+        mCompositionType = COMPOSITION_MIXED;
+    }
+
     if (mCompositionType != mDbgLastCompositionType) {
         VDS_LOGV("prepareFrame: composition type changed to %s",
                 dbgCompositionTypeStr(mCompositionType));