Add support for taking partial screenshot using touch

ash/wm/partial_screenshot_view.cc

 // 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.
 
 #include "ash/wm/partial_screenshot_view.h"
 
 #include <algorithm>
 
 #include "ash/display/mouse_cursor_event_filter.h"
 #include "ash/screenshot_delegate.h"
@@ skipping 122 matching lines @@
 }
 
 gfx::Rect PartialScreenshotView::GetScreenshotRect() const {
   int left = std::min(start_position_.x(), current_position_.x());
   int top = std::min(start_position_.y(), current_position_.y());
   int width = ::abs(start_position_.x() - current_position_.x());
   int height = ::abs(start_position_.y() - current_position_.y());
   return gfx::Rect(left, top, width, height);
 }
 
+void PartialScreenshotView::OnSelectionStarted(const gfx::Point& position) {
+  start_position_ = position;
+}
+
+void PartialScreenshotView::OnSelectionChanged(const gfx::Point& position) {
+  current_position_ = position;

[sky, 2013/03/25 23:42:29]

Can this early out if is_dragging_ and current_position_ == position?

[Yufeng Shen (Slow to review), 2013/03/26 01:24:03]

Done.

+  SchedulePaint();
+  is_dragging_ = true;
+}
+
+void PartialScreenshotView::OnSelectionFinished() {
+  overlay_delegate_->Cancel();
+  if (!is_dragging_)
+    return;
+
+  is_dragging_ = false;
+  if (screenshot_delegate_) {
+    aura::RootWindow *root_window =
+        GetWidget()->GetNativeWindow()->GetRootWindow();
+    screenshot_delegate_->HandleTakePartialScreenshot(
+        root_window,
+        gfx::IntersectRects(root_window->bounds(), GetScreenshotRect()));
+  }
+}
+
 gfx::NativeCursor PartialScreenshotView::GetCursor(
     const ui::MouseEvent& event) {
   // Always use "crosshair" cursor.
   return ui::kCursorCross;
 }
 
 void PartialScreenshotView::OnPaint(gfx::Canvas* canvas) {
   if (is_dragging_) {
     // Screenshot area representation: black rectangle with white
     // rectangle inside.  To avoid capturing these rectangles when mouse
     // release, they should be outside of the actual capturing area.
     gfx::Rect screenshot_rect = GetScreenshotRect();
     screenshot_rect.Inset(-1, -1, -1, -1);
     canvas->DrawRect(screenshot_rect, SK_ColorWHITE);
     screenshot_rect.Inset(-1, -1, -1, -1);
     canvas->DrawRect(screenshot_rect, SK_ColorBLACK);
   }
 }
 
 bool PartialScreenshotView::OnMousePressed(const ui::MouseEvent& event) {
   // Prevent moving across displays during drag. Capturing a screenshot across
   // the displays is not supported yet.
   // TODO(mukai): remove this restriction.
   internal::MouseCursorEventFilter* mouse_cursor_filter =
       Shell::GetInstance()->mouse_cursor_filter();
   mouse_cursor_filter->set_mouse_warp_mode(
       internal::MouseCursorEventFilter::WARP_NONE);
-  start_position_ = event.location();
+  OnSelectionStarted(event.location());
   return true;
 }
 
 bool PartialScreenshotView::OnMouseDragged(const ui::MouseEvent& event) {
-  current_position_ = event.location();
-  SchedulePaint();
-  is_dragging_ = true;
+  OnSelectionChanged(event.location());
   return true;
 }
 
 bool PartialScreenshotView::OnMouseWheel(const ui::MouseWheelEvent& event) {
   // Do nothing but do not propagate events futhermore.
   return true;
 }
 
 void PartialScreenshotView::OnMouseReleased(const ui::MouseEvent& event) {
-  overlay_delegate_->Cancel();
-  if (!is_dragging_)
-    return;
+  OnSelectionFinished();

[sky, 2013/03/25 23:42:29]

What about if capture is lost?

[Yufeng Shen (Slow to review), 2013/03/26 01:24:03]

Added OnMouseCaptureLost() which basically cancels the screenshot.

+}
 
-  is_dragging_ = false;
-  if (screenshot_delegate_) {
-    aura::RootWindow *root_window =
-        GetWidget()->GetNativeWindow()->GetRootWindow();
-    screenshot_delegate_->HandleTakePartialScreenshot(
-        root_window,
-        gfx::IntersectRects(root_window->bounds(), GetScreenshotRect()));
+void PartialScreenshotView::OnGestureEvent(ui::GestureEvent* event) {
+  gfx::Point position = event->location();

[sky, 2013/03/25 23:42:29]

const gfx::Point&, although you only use this in two branches, maybe move it to
where needed (meaning 217 and 220).

[Yufeng Shen (Slow to review), 2013/03/26 01:24:03]

Done.

+  switch(event->type()) {
+    case ui::ET_GESTURE_TAP_DOWN:
+      OnSelectionStarted(position);
+      break;
+    case ui::ET_GESTURE_SCROLL_UPDATE:
+      OnSelectionChanged(position);
+      break;
+    case ui::ET_GESTURE_SCROLL_END:
+    case ui::ET_SCROLL_FLING_START:
+      OnSelectionFinished();
+      break;
+    default:
+      break;
   }
+
+  event->SetHandled();
 }
 
 }  // namespace ash