don't call eglSwapBufferss() when its not needed.

eglSwapBuffers() copies the previous backbuffer, which consumes
power and bandwidth. If there are no framebuffer layers there is
no reason to do this.

this should save power with full-screen videos.

Change-Id: I7feb5a3f2d7d426dd93d2203849a6d591ce377db

1 files changed, 8 insertions, 3 deletions

diff --git a/libhwcomposer/SecHWC.cpp b/libhwcomposer/SecHWC.cpp
index 6fe39a0..0f81277 100644
--- a/libhwcomposer/SecHWC.cpp
+++ b/libhwcomposer/SecHWC.cpp
@@ -293,6 +293,8 @@ static int hwc_set(hwc_composer_device_t *dev,
     struct sec_rect dst_rect;
 
 
+    bool need_swap_buffers = ctx->num_of_fb_layer > 0;
+
     /*
      * H/W composer documentation states:
      * There is an implicit layer containing opaque black
@@ -312,13 +314,16 @@ static int hwc_set(hwc_composer_device_t *dev,
         glClearColor(0, 0, 0, 0);
         glClear(GL_COLOR_BUFFER_BIT);
         glEnable(GL_SCISSOR_TEST);
+        need_swap_buffers = true;
     }
 
     ctx->num_of_fb_layer_prev = ctx->num_of_fb_layer;
 
-    EGLBoolean sucess = eglSwapBuffers((EGLDisplay)dpy, (EGLSurface)sur);
-    if (!sucess) {
-        return HWC_EGL_ERROR;
+    if (need_swap_buffers || !list) {
+        EGLBoolean sucess = eglSwapBuffers((EGLDisplay)dpy, (EGLSurface)sur);
+        if (!sucess) {
+            return HWC_EGL_ERROR;
+        }
     }
 
     if (!list) {