ash: Add basic prediction code to the laser pointer.

ash/laser/laser_pointer_controller.cc

Index: ash/laser/laser_pointer_controller.cc
diff --git a/ash/laser/laser_pointer_controller.cc b/ash/laser/laser_pointer_controller.cc
index ac8de4ebc5d5032e9334efa4a98ec40f26bda418..0aaac213fd6a5098fbfc274dfad6bab1d4acf8de 100644
--- a/ash/laser/laser_pointer_controller.cc
+++ b/ash/laser/laser_pointer_controller.cc
@@ -4,9 +4,12 @@
 
 #include "ash/laser/laser_pointer_controller.h"
 
+#include "ash/common/ash_switches.h"
 #include "ash/common/system/chromeos/palette/palette_utils.h"
 #include "ash/laser/laser_pointer_view.h"
 #include "ash/shell.h"
+#include "base/command_line.h"
+#include "base/strings/string_number_conversions.h"
 #include "ui/display/screen.h"
 #include "ui/views/widget/widget.h"
 
@@ -26,6 +29,11 @@ const int kPointLifeDurationMs = 200;
 // TODO(reveman): Use real VSYNC interval instead of a hard-coded delay.
 const int kAddStationaryPointsDelayMs = 16;
 
+// The default amount of time used to estimate time from VSYNC event to when
+// visible light can be noticed by the user. This is used when a device
+// specific estimate was not provided using --estimated-presentation-delay.
+const int kDefaultPresentationDelayMs = 18;
+
 }  // namespace
 
 LaserPointerController::LaserPointerController()
@@ -34,8 +42,24 @@ LaserPointerController::LaserPointerController()
           base::TimeDelta::FromMilliseconds(kAddStationaryPointsDelayMs),
           base::Bind(&LaserPointerController::AddStationaryPoint,
                      base::Unretained(this)),
-          true /* is_repeating */)) {
+          true /* is_repeating */)),
+      presentation_delay_(
+          base::TimeDelta::FromMilliseconds(kDefaultPresentationDelayMs)) {
   Shell::GetInstance()->AddPreTargetHandler(this);
+
+  // Use device specific presentation delay if specified.
+  const base::CommandLine* command_line =
+      base::CommandLine::ForCurrentProcess();
+  if (command_line->HasSwitch(switches::kAshEstimatedPresentationDelay)) {

[Daniele Castagna, 2017/03/15 19:07:28]

nit: you can get rid of this line and the code should behave the same way.
If the flag is not passed the string will be "" and StringToInt64 will return
false.

[reveman, 2017/03/16 12:57:28]

Done.

+    std::string presentation_delay_string = command_line->GetSwitchValueASCII(
+        switches::kAshEstimatedPresentationDelay);
+    int64_t presentation_delay_time_ms;
+    if (base::StringToInt64(presentation_delay_string,
+                            &presentation_delay_time_ms)) {
+      presentation_delay_ =
+          base::TimeDelta::FromMilliseconds(presentation_delay_time_ms);
+    }
+  }
 }
 
 LaserPointerController::~LaserPointerController() {
@@ -106,7 +130,8 @@ void LaserPointerController::SwitchTargetRootWindowIfNeeded(
 
   if (!laser_pointer_view_ && enabled_) {
     laser_pointer_view_.reset(new LaserPointerView(
-        base::TimeDelta::FromMilliseconds(kPointLifeDurationMs), root_window));
+        base::TimeDelta::FromMilliseconds(kPointLifeDurationMs),
+        presentation_delay_, root_window));
   }
 }
 
@@ -116,7 +141,8 @@ void LaserPointerController::UpdateLaserPointerView(
     ui::Event* event) {
   SwitchTargetRootWindowIfNeeded(current_window);
   current_stylus_location_ = event_location;
-  laser_pointer_view_->AddNewPoint(current_stylus_location_);
+  laser_pointer_view_->AddNewPoint(current_stylus_location_,
+                                   event->time_stamp());
   event->StopPropagation();
 }
 
@@ -136,10 +162,12 @@ void LaserPointerController::RestartTimer() {
 }
 
 void LaserPointerController::AddStationaryPoint() {
-  if (is_fading_away_)
+  if (is_fading_away_) {
     laser_pointer_view_->UpdateTime();
-  else
-    laser_pointer_view_->AddNewPoint(current_stylus_location_);
+  } else {
+    laser_pointer_view_->AddNewPoint(current_stylus_location_,
+                                     base::TimeTicks::Now());
+  }
 
   // We can stop repeating the timer once the stylus has been stationary for
   // longer than the life of a point.