Calculate display bounds for all available displays

The hwcomposer module for Android doesn't support multi-monitor well
enough for our use case yet so we give Android a large enough primary
display. This may have negative effects performance wise for the until
we disabled all non freeform stack and wallpaper related rendering on
the Android side so that only visible windows are drawn to not waste
any GPU cycles on things we don't render anyway.

src/anbox/ubuntu/platform_policy.cpp

@@ -39,16 +39,26 @@ PlatformPolicy::PlatformPolicy(
   if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_EVENTS) < 0)
     BOOST_THROW_EXCEPTION(std::runtime_error("Failed to initialize SDL"));
 
-  event_thread_ = std::thread(&PlatformPolicy::process_events, this);
+  auto display_frame = graphics::Rect::Invalid;
+  for (auto n = 0; n < SDL_GetNumVideoDisplays(); n++) {
+    SDL_Rect r;
+    if (SDL_GetDisplayBounds(n, &r) != 0)
+      continue;
+
+    graphics::Rect frame{r.x, r.y, r.x + r.w, r.y + r.h};
 
-  SDL_DisplayMode display_mode;
-  // FIXME statically just check the first (primary) display for its mode;
-  // once we get multi-monitor support we need to do this better.
-  if (SDL_GetCurrentDisplayMode(0, &display_mode) == 0) {
-    display_info_.horizontal_resolution = display_mode.w;
-    display_info_.vertical_resolution = display_mode.h;
+    if (display_frame == graphics::Rect::Invalid)
+      display_frame = frame;
+    else
+      display_frame.merge(frame);
   }
 
+  if (display_frame == graphics::Rect::Invalid)
+    BOOST_THROW_EXCEPTION(std::runtime_error("No valid display configuration found"));
+
+  display_info_.horizontal_resolution = display_frame.width();
+  display_info_.vertical_resolution = display_frame.height();
+
   pointer_ = input_manager->create_device();
   pointer_->set_name("anbox-pointer");
   pointer_->set_driver_version(1);
@@ -70,6 +80,8 @@ PlatformPolicy::PlatformPolicy(
   keyboard_->set_physical_location("none");
   keyboard_->set_key_bit(BTN_MISC);
   keyboard_->set_key_bit(KEY_OK);
+
+  event_thread_ = std::thread(&PlatformPolicy::process_events, this);
 }
 
 PlatformPolicy::~PlatformPolicy() {