Accumulate wheel ticks client-side and prefer ticks to pixels when scrolling on Linux.

BUG=180715

Review URL: https://chromiumcodereview.appspot.com/20540003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@214096 0039d316-1c4b-4281-b951-d872f2087c98

4 files changed, 40 insertions, 8 deletions

diff --git a/remoting/client/plugin/pepper_input_handler.cc b/remoting/client/plugin/pepper_input_handler.cc
index dba438a..1b67ba25 100644
--- a/remoting/client/plugin/pepper_input_handler.cc
+++ b/remoting/client/plugin/pepper_input_handler.cc
@@ -16,7 +16,9 @@ namespace remoting {
 PepperInputHandler::PepperInputHandler(protocol::InputStub* input_stub)
     : input_stub_(input_stub),
       wheel_delta_x_(0),
-      wheel_delta_y_(0) {
+      wheel_delta_y_(0),
+      wheel_ticks_x_(0),
+      wheel_ticks_y_(0) {
 }
 
 PepperInputHandler::~PepperInputHandler() {
@@ -107,12 +109,17 @@ bool PepperInputHandler::HandleInputEvent(const pp::InputEvent& event) {
       if (pp_wheel_event.GetScrollByPage())
         return false;
 
-      // Add this event to our accumulated sub-pixel deltas.
+      // Add this event to our accumulated sub-pixel deltas and clicks.
       pp::FloatPoint delta = pp_wheel_event.GetDelta();
       wheel_delta_x_ += delta.x();
       wheel_delta_y_ += delta.y();
+      pp::FloatPoint ticks = pp_wheel_event.GetTicks();
+      wheel_ticks_x_ += ticks.x();
+      wheel_ticks_y_ += ticks.y();
 
-      // If there is at least a pixel's movement, emit an event.
+      // If there is at least a pixel's movement, emit an event. We don't
+      // ever expect to accumulate one tick's worth of scrolling without
+      // accumulating a pixel's worth at the same time, so this is safe.
       int delta_x = static_cast<int>(wheel_delta_x_);
       int delta_y = static_cast<int>(wheel_delta_y_);
       if (delta_x != 0 || delta_y != 0) {
@@ -122,6 +129,18 @@ bool PepperInputHandler::HandleInputEvent(const pp::InputEvent& event) {
         mouse_event.set_wheel_delta_x(delta_x);
         mouse_event.set_wheel_delta_y(delta_y);
 
+        // Always include the ticks in the event, even if insufficient pixel
+        // scrolling has accumulated for a single tick. This informs hosts
+        // that can't inject pixel-based scroll events that the client will
+        // accumulate them into tick-based scrolling, which gives a better
+        // overall experience than trying to do this host-side.
+        int ticks_x = static_cast<int>(wheel_ticks_x_);
+        int ticks_y = static_cast<int>(wheel_ticks_y_);
+        wheel_ticks_x_ -= ticks_x;
+        wheel_ticks_y_ -= ticks_y;
+        mouse_event.set_wheel_ticks_x(ticks_x);
+        mouse_event.set_wheel_ticks_y(ticks_y);
+
         input_stub_->InjectMouseEvent(mouse_event);
       }
       return true;
diff --git a/remoting/client/plugin/pepper_input_handler.h b/remoting/client/plugin/pepper_input_handler.h
index 2983b07a..0e63e0f 100644
--- a/remoting/client/plugin/pepper_input_handler.h
+++ b/remoting/client/plugin/pepper_input_handler.h
@@ -28,9 +28,11 @@ class PepperInputHandler {
  private:
   protocol::InputStub* input_stub_;
 
-  // Accumulated sub-pixel deltas from wheel events.
+  // Accumulated sub-pixel and sub-tick deltas from wheel events.
   float wheel_delta_x_;
   float wheel_delta_y_;
+  float wheel_ticks_x_;
+  float wheel_ticks_y_;
 
   DISALLOW_COPY_AND_ASSIGN(PepperInputHandler);
 };
diff --git a/remoting/host/input_injector_linux.cc b/remoting/host/input_injector_linux.cc
index 45221d1..6054cc5 100644
--- a/remoting/host/input_injector_linux.cc
+++ b/remoting/host/input_injector_linux.cc
@@ -340,8 +340,15 @@ void InputInjectorLinux::Core::InjectMouseEvent(const MouseEvent& event) {
                          CurrentTime);
   }
 
+  // Older client plugins always send scroll events in pixels, which
+  // must be accumulated host-side. Recent client plugins send both
+  // pixels and ticks with every scroll event, allowing the host to
+  // choose the best model on a per-platform basis. Since we can only
+  // inject ticks on Linux, use them if available.
   int ticks_y = 0;
-  if (event.has_wheel_delta_y()) {
+  if (event.has_wheel_ticks_y()) {
+    ticks_y = event.wheel_ticks_y();
+  } else if (event.has_wheel_delta_y()) {
     wheel_ticks_y_ += event.wheel_delta_y() * kWheelTicksPerPixel;
     ticks_y = static_cast<int>(wheel_ticks_y_);
     wheel_ticks_y_ -= ticks_y;
@@ -352,7 +359,9 @@ void InputInjectorLinux::Core::InjectMouseEvent(const MouseEvent& event) {
   }
 
   int ticks_x = 0;
-  if (event.has_wheel_delta_x()) {
+  if (event.has_wheel_ticks_x()) {
+    ticks_x = event.wheel_ticks_x();
+  } else if (event.has_wheel_delta_x()) {
     wheel_ticks_x_ += event.wheel_delta_x() * kWheelTicksPerPixel;
     ticks_x = static_cast<int>(wheel_ticks_x_);
     wheel_ticks_x_ -= ticks_x;
diff --git a/remoting/proto/event.proto b/remoting/proto/event.proto
index e5ec135..8f28f07 100644
--- a/remoting/proto/event.proto
+++ b/remoting/proto/event.proto
@@ -52,10 +52,12 @@ message MouseEvent {
   optional bool button_down = 6;
 
   // Mouse wheel information.
-  // These values encode the number of pixels of movement that would result
-  // from the wheel event on the client system.
+  // These values encode the number of pixels and 'ticks' of movement that
+  // would result from the wheel event on the client system.
   optional float wheel_delta_x = 7;
   optional float wheel_delta_y = 8;
+  optional float wheel_ticks_x = 9;
+  optional float wheel_ticks_y = 10;
 }
 
 // Defines an event that sends clipboard data between peers.