Move touch CTM from X into Chrome

ui/events/touch_ctm.h

+// 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.
+
+#ifndef UI_EVENTS_TOUCH_CTM_H_
+#define UI_EVENTS_TOUCH_CTM_H_
+
+#include "ui/events/events_base_export.h"
+
+namespace ui {
+
+// Touch coordinate transformation matrix (CTM) is used to map touch events
+// coordinate from screen space to root window space.
+// When touch events are reported from kernel, its coordinate is in device
+// space. After passing through X, its coordinate gets mapped to screen
+// space, e.g. the framebuffer space that is the combination of multiple
+// display output.
+// In Chrome, we use TouchCTM to remap the touch event's location from
+// the screen space to the root window space if the touch event is targeting
+// that root window.
+class EVENTS_BASE_EXPORT TouchCTM {

[sadrul, 2014/03/15 19:32:51]

Do we need this? Could we use a gfx::Transform instead?

[Yufeng Shen (Slow to review), 2014/04/29 20:34:18]

Looking at  Transform::TransformPointInternal() there is some
rounding happening which worries me. I don't want the event that's close to the
boundary gets unexpectedly rounded up and gets out of
the boundary.
While if we just use the plain float operation when applying TouchCTM, we can
rely on the static_cast<int> in EventLocationFromeNative() to truncate the event
position so it won't get out of bound.

+ public:
+  TouchCTM();
+
+  float x_scale;
+  float x_offset;
+  float y_scale;
+  float y_offset;
+};
+
+}  // namespace ui
+
+#endif  // UI_EVENTS_TOUCH_CTM_H_