[Android] Select text when stylus first button is pressed.

content/browser/renderer_host/input/gesture_text_selector.cc

+// Copyright (c) 2014 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 "content/browser/renderer_host/input/gesture_text_selector.h"
+
+#include "ui/events/event_constants.h"
+#include "ui/events/gesture_detection/gesture_event_data.h"
+#include "ui/events/gesture_detection/motion_event.h"
+
+namespace content {
+
+GestureTextSelector::GestureTextSelector(GestureTextSelectorClient* client)
+    : client_(client),
+      text_selection_triggered_(false),
+      anchor_x_(0.0f),
+      anchor_y_(0.0f) {
+}
+
+GestureTextSelector::~GestureTextSelector() {
+}
+
+bool GestureTextSelector::OnTouchEvent(const ui::MotionEvent& event) {
+  if (event.GetAction() == ui::MotionEvent::ACTION_DOWN) {
+    // Only trigger selection on ACTION_DOWN to prevent partial touch or gesture
+    // sequences from being forwarded.
+    text_selection_triggered_ = ShouldStartTextSelection(event);
+  }
+  return text_selection_triggered_;
+}
+
+bool GestureTextSelector::OnGestureEvent(const ui::GestureEventData& gesture) {
+  if (!text_selection_triggered_)
+    return false;
+
+  switch (gesture.type()) {
+    case ui::ET_GESTURE_TAP: {
+      client_->Unselect();
+      break;
+    }
+    case ui::ET_GESTURE_SCROLL_BEGIN: {
+      client_->Unselect();
+      anchor_x_ = gesture.x;
+      anchor_y_ = gesture.y;
+      break;
+    }
+    case ui::ET_GESTURE_SCROLL_UPDATE: {
+      client_->ShowSelectionHandlesAutomatically();

[jdduke (slow), 2014/06/26 00:33:21]

I'm curious how the handles look while you're dragging the selection? Do they
pop in and out or interfere with the stylus? If they look OK, then let's move
the |client_->ShowSelectionHandlesAutomatically();| call to
|ET_GESTURE_SCROLL_BEGIN|.  Otherwise, we may need to figure out another way to
show them, perhaps by hooking into ET_GESTURE_SCROLL_END?

[Changwan Ryu, 2014/06/26 02:54:10]

Moved ShowSelectionHandlesAutomatically to GESTURE_SCROLL_BEGIN.
But the current implementation of ShowSelectionHandlesAutomatically() only shows
handles when it's called before we change the selection, so I couldn't do it for
now (added a TODO). Please consider this use case when you work on the
composited selection handles.

+      client_->SelectRange(anchor_x_, anchor_y_, gesture.x, gesture.y);
+      break;
+    }
+    default:
+      // Suppress all other gestures when we are selecting text.
+      break;
+  }
+  return true;
+}
+
+// static
+bool GestureTextSelector::ShouldStartTextSelection(
+    const ui::MotionEvent& event) {
+  DCHECK_GT(event.GetPointerCount(), 0u);
+  // Currently we are supporting stylus-only cases.
+  const bool is_stylus =
+      event.GetToolType(0) == ui::MotionEvent::TOOL_TYPE_STYLUS;
+  const bool is_only_secondary_button_pressed =
+      event.GetButtonState() == ui::MotionEvent::BUTTON_SECONDARY;
+  return is_stylus && is_only_secondary_button_pressed;
+}
+
+}  // namespace content