Add Vector2d classes that represent offsets, instead of using Point.

ui/gfx/vector2d_f.h

+// 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.
+
+// Defines a simple float vector class.  This class is used to indicate a

[tfarina, 2012/10/26 22:22:30]

I generally prefer to put this kind of comment right before the class
declaration. I don't know if Scott or Peter has similar preferences, nor if they
care about or not.

[Peter Kasting, 2012/10/26 22:44:50]

Google style actually talks about both file- and class-level comments.  In a
case like this, most people end up just writing a class-level comment that says
much of the same thing.  It's not wrong to do it this way.  I would probably
very very weakly prefer the other way just because it allows the comment to be
slightly shorter (e.g. the beginning can be condensed to "A distance in two
dimensions between points." or something).

Though to be totally honest, the meaning of "vector" is so clear that this
comment could probably be omitted entirely...

+// distance in two dimentions between two points. Subtracting two points should
+// produce a vector, and adding a vector to a point produces the point at the
+// vector's distance from the original point.
+
+#ifndef UI_GFX_VECTOR2D_F_H_
+#define UI_GFX_VECTOR2D_F_H_
+
+#include <cmath>
+#include <string>
+
+#include "ui/base/ui_export.h"
+
+namespace gfx {
+
+class UI_EXPORT Vector2dF {
+ public:
+  Vector2dF();
+  Vector2dF(float x, float y);
+
+  float x() const { return x_; }
+  void set_x(float x) { x_ = x; }
+
+  float y() const { return y_; }
+  void set_y(float y) { y_ = y; }
+
+  bool IsZero() const { return x_ == 0 && y_ == 0; }
+
+  void Grow(float x, float y) {
+    x_ += x;
+    y_ += y;
+  }
+
+  void Add(const Vector2dF& other) {
+    x_ += other.x_;
+    y_ += other.y_;
+  }
+
+  void Scale(float scale) {
+    Scale(scale, scale);
+  }
+
+  void Scale(float x_scale, float y_scale) {
+    x_ *= x_scale;
+    y_ *= y_scale;
+  }
+
+  float LengthSquared() const {
+    return x_ * x_ + y_ * y_;
+  }
+
+  float Length() const {

[tfarina, 2012/10/26 22:22:30]

Could you deinline all the implementations, i.e, move all the
definitions/implementations of these "may be" not trivial functions to the
source file instead?

[danakj, 2012/10/26 22:24:52]

I can, though I'm following the lead of point_base.h for instance, which has
them inline. So, should this differ?

[Peter Kasting, 2012/10/26 22:44:50]

As Thiago noted, we're forced to inline there due to templates.  When you don't
have that constraint, you should move all the non-unix_hacker()-style-accessors
to a .cc file.

+    return static_cast<float>(std::sqrt(
+        static_cast<double>(x_) * x_ + static_cast<double>(y_) * y_));
+  }
+
+  std::string ToString() const;
+
+ private:

[tfarina, 2012/10/26 22:22:30]

Do we allow copy and assign, right? Just checking, I think this is similar to
what done with Point class?

[danakj, 2012/10/26 22:24:52]

Right, we do.

+  float x_;
+  float y_;
+};
+
+inline bool operator==(const Vector2dF& lhs, const Vector2dF& rhs) {
+  return lhs.x() == rhs.x() && lhs.y() == rhs.y();
+}
+
+inline Vector2dF operator-(const Vector2dF& v) {
+  return Vector2dF(-v.x(), -v.y());
+}
+
+inline Vector2dF operator+(const Vector2dF& lhs, const Vector2dF& rhs) {
+  Vector2dF result = lhs;
+  result.Add(rhs);
+  return result;
+}
+
+inline Vector2dF operator-(const Vector2dF& lhs, const Vector2dF& rhs) {
+  Vector2dF result = lhs;
+  result.Add(-rhs);
+  return result;
+}
+
+}  // namespace gfx
+
+#endif // UI_GFX_VECTOR2D_F_H_