Detect output state at startup to avoid changes

chromeos/monitor/output_configurator.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROMEOS_MONITOR_OUTPUT_CONFIGURATOR_H_
 #define CHROMEOS_MONITOR_OUTPUT_CONFIGURATOR_H_
 #pragma once
 
 #include <X11/Xlib.h>
 #include <X11/extensions/dpms.h>
@@ skipping 85 matching lines @@
   // A helper to re-cache instance variable state and transition into the
   // appropriate default state for the observed displays.
   bool RecacheAndUseDefaultState();
 
   // Checks the |primary_output_index_|, |secondary_output_index_|, and
   // |mirror_supported_| to see how many displays are currently connected and
   // returns the state which is most appropriate as a default state for those
   // displays.
   State GetDefaultState() const;
 
+  // Called during start-up to determine what the current state of the displays
+  // appears to be, by investigating how the outputs compare to the data stored
+  // in |output_cache_|.  Returns STATE_INVALID if the current display state
+  // doesn't match any supported state.  |output_cache_| must be up-to-date with
+  // regards to the state of X or this method may return incorrect results.
+  State InferCurrentState(Display* display, XRRScreenResources* screen) const;
+
   // This is detected by the constructor to determine whether or not we should
   // be enabled.  If we aren't running on ChromeOS, we can't assume that the
   // Xrandr X11 extension is supported.
   // If this flag is set to false, any attempts to change the output
   // configuration to immediately fail without changing the state.
   bool is_running_on_chrome_os_;
 
   // The number of outputs in the output_cache_ array.
   int output_count_;
 
@@ skipping 20 matching lines @@
   // The display state as derived from the outputs observed in |output_cache_|.
   // This is used for rotating display modes.
   State output_state_;
 
   DISALLOW_COPY_AND_ASSIGN(OutputConfigurator);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROMEOS_MONITOR_OUTPUT_CONFIGURATOR_H_