client/plugin/normalizing_input_filter_cros.cc

// Copyright 2013 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.

#include "remoting/client/plugin/normalizing_input_filter_cros.h"

#include "base/logging.h"

namespace remoting {

namespace {

// Returns true for OSKey codes.
static bool IsOsKey(unsigned int code) {
  const unsigned int kUsbLeftOsKey = 0x0700e3;
  const unsigned int kUsbRightOsKey = 0x0700e7;
  return code == kUsbLeftOsKey || code == kUsbRightOsKey;
}

// Returns true for the left-hand Alt key.
static bool IsLeftAltKey(unsigned int code) {
  const unsigned int kUsbLeftAltKey = 0x0700e2;
  return code == kUsbLeftAltKey;
}

// Returns true for codes generated by EventRewriter::RewriteFunctionKeys().
static bool IsRewrittenFunctionKey(unsigned int code) {
  const unsigned int kUsbFunctionKeyMin = 0x07003a;
  const unsigned int kUsbFunctionKeyMax = 0x070045;
  return code >= kUsbFunctionKeyMin && code <= kUsbFunctionKeyMax;
}

// Returns true for codes generated by EventRewriter::RewriteExtendedKeys().
static bool IsRewrittenExtendedKey(unsigned int code) {
  const unsigned int kUsbExtendedKeyMin = 0x070049;
  const unsigned int kUsbExtendedKeyMax = 0x07004e;
  return code >= kUsbExtendedKeyMin && code <= kUsbExtendedKeyMax;
}

// Returns true for codes generated by EventRewriter::Rewrite().
static bool IsRewrittenKey(unsigned int code) {
  return IsRewrittenExtendedKey(code) || IsRewrittenFunctionKey(code);
}

}  // namespace

// The input filter tries to avoid sending keydown/keyup events for OSKey
// (aka Search, WinKey, Cmd, Super) when it is used to rewrite other key events.
// Rewriting via other combinations is not currently handled.
//
// OSKey events can be categorised as one of three kinds:
// - Modifying - Holding the key down while executing other input modifies the
//     effect of that input, e.g. OSKey+L causes the workstation to lock, e.g.
//     OSKey + mouse-move performs an extended selection.
// - Rewriting (ChromeOS only) - Holding the key down while pressing certain
//     keys causes them to be treated as different keys, e.g. OSKey causes the
//     Down key to behave as PageDown.
// - Normal - Press & release of the key trigger an action, e.g. showing the
//     Start menu.
//
// The input filter has four states:
// 1. No OSKey has been pressed.
//    - When an OSKey keydown is received, the event is deferred, and we move to
//      State #2.
// 2. An OSKey is pressed, but may be Normal, Rewriting or Modifying.
//    - If the OSKey keyup is received, the key is Normal, both events are sent
//      and we return to State #1.
//    - If a Rewritten event is received we move to State #3.
//    - If a Modified event is received the OSKey keydown is sent and we enter
//      State #4.
// 3. An OSKey is pressed, and is being used to Rewrite other key events.
//    - If the OSKey keyup is received then it is suppressed, and we move to
//      State #1.
//    - If a Modified event is received the OSKey keydown is sent and we enter
//      State #4.
//    - If a Rewritten event is received then we stay in State #3.
// 4. An OSKey is pressed, and is Modifying.
//    - If the OSKey keyup is received then we send it and we move to State #1.
//    - All other key event pass through the filter unchanged.
//
// ChromeOS also maps Alt+LeftClick to RightClick (even for an external mouse).
// As with the OSKey remapping described above, this is fed into this filter
// as Alt followed by RightClick. However, because there are other ways to
// generate RightClick (two-finger tap, for example), rather than suppressing
// the Alt key as we do for the OSKey (which would allow Alt+LeftClick to be
// interpreted as interpreted as RightClick as per the ChromeOS idiom), the
// filter maps RightClick to LeftClick while LeftAlt is held, which allows
// Alt+LeftClick to be injected. The equivalent mapping using RightAlt is
// unchanged, allowing Alt+RightClick also to be injected, as long as the
// target application doesn't distinguish between left and right Alt keys.
//
// This file must be kept up-to-date with changes to
// chrome/browser/chromeos/events/event_rewriter.cc


NormalizingInputFilterCros::NormalizingInputFilterCros(
    protocol::InputStub* input_stub)
    : protocol::InputFilter(input_stub),
      deferred_key_is_rewriting_(false),
      modifying_key_(0),
      left_alt_is_pressed_(false) {
}

NormalizingInputFilterCros::~NormalizingInputFilterCros() {}

void NormalizingInputFilterCros::InjectKeyEvent(
    const protocol::KeyEvent& event) {
  DCHECK(event.has_usb_keycode());
  DCHECK(event.has_pressed());

  if (event.pressed()) {
    ProcessKeyDown(event);
  } else {
    ProcessKeyUp(event);
  }
}

void NormalizingInputFilterCros::InjectMouseEvent(
    const protocol::MouseEvent& event) {
  if (deferred_keydown_event_.has_usb_keycode())
    SwitchRewritingKeyToModifying();
  protocol::MouseEvent newEvent = event;
  if (left_alt_is_pressed_ &&
      event.has_button() &&
      event.button() == protocol::MouseEvent::BUTTON_RIGHT) {
    newEvent.set_button(protocol::MouseEvent::BUTTON_LEFT);
  }
  InputFilter::InjectMouseEvent(newEvent);
}

void NormalizingInputFilterCros::ProcessKeyDown(
    const protocol::KeyEvent& event) {
  // If |event| is |deferred_keydown_event_| repeat then assume that the user is
  // holding the key down rather than using it to Rewrite.
  if (deferred_keydown_event_.has_usb_keycode() &&
      deferred_keydown_event_.usb_keycode() == event.usb_keycode()) {
    SwitchRewritingKeyToModifying();
  }

  // If |event| is a |modifying_key_| repeat then let it pass through.
  if (modifying_key_ == event.usb_keycode()) {
    InputFilter::InjectKeyEvent(event);
    return;
  }

  // If |event| is for an OSKey and we don't know whether it's a Normal,
  // Rewriting or Modifying use, then hold the keydown event.
  if (IsOsKey(event.usb_keycode())) {
    deferred_keydown_event_ = event;
    deferred_key_is_rewriting_ = false;
    return;
  }

  // If |event| is for a Rewritten key then set a flag to prevent any deferred
  // OSKey keydown from being sent when keyup is received for it. Otherwise,
  // inject the deferred OSKey keydown, if any, and switch that key into
  // Modifying mode.
  if (IsRewrittenKey(event.usb_keycode())) {
    // Note that there may not be a deferred OSKey event if there is a full
    // PC keyboard connected, which can generate e.g. PageDown without
    // rewriting.
    deferred_key_is_rewriting_ = true;
  } else {
    if (deferred_keydown_event_.has_usb_keycode())
      SwitchRewritingKeyToModifying();
  }

  if (IsLeftAltKey(event.usb_keycode()))
    left_alt_is_pressed_ = true;

  InputFilter::InjectKeyEvent(event);
}

void NormalizingInputFilterCros::ProcessKeyUp(const protocol::KeyEvent& event) {
  if (deferred_keydown_event_.has_usb_keycode() &&
      deferred_keydown_event_.usb_keycode() == event.usb_keycode()) {
    if (deferred_key_is_rewriting_) {
      // If we never sent the keydown then don't send a keyup.
      deferred_keydown_event_ = protocol::KeyEvent();
      return;
    }

    // If the OSKey hasn't Rewritten anything then treat as Modifying.
    SwitchRewritingKeyToModifying();
  }

  if (modifying_key_ == event.usb_keycode())
    modifying_key_ = 0;

  if (IsLeftAltKey(event.usb_keycode()))
    left_alt_is_pressed_ = false;

  InputFilter::InjectKeyEvent(event);
}

void NormalizingInputFilterCros::SwitchRewritingKeyToModifying() {
  DCHECK(deferred_keydown_event_.has_usb_keycode());
  modifying_key_ = deferred_keydown_event_.usb_keycode();
  InputFilter::InjectKeyEvent(deferred_keydown_event_);
  deferred_keydown_event_ = protocol::KeyEvent();
}

}  // namespace remoting