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

ui/gfx/vector2d.cc

Index: ui/gfx/vector2d.cc
diff --git a/ui/gfx/vector2d.cc b/ui/gfx/vector2d.cc
new file mode 100644
index 0000000000000000000000000000000000000000..49dfbd2c47d785b6038f9daa0bf0976162851e9a
--- /dev/null
+++ b/ui/gfx/vector2d.cc
@@ -0,0 +1,55 @@
+// 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 "ui/gfx/vector2d.h"
+
+#include <cmath>
+
+#include "base/stringprintf.h"
+
+namespace gfx {
+
+Vector2d::Vector2d()
+    : x_(0),
+      y_(0) {

[Peter Kasting, 2012/10/30 01:14:14]

Nit: Could also put these first three lines all on one line (2 places)

+}
+
+Vector2d::Vector2d(int x, int y)
+    : x_(x),
+      y_(y) {
+}
+
+bool Vector2d::IsZero() const {
+  return x_ == 0 && y_ == 0;
+}
+
+void Vector2d::Grow(int x, int y) {
+  x_ += x;
+  y_ += y;
+}
+
+void Vector2d::Add(const Vector2d& other) {
+  x_ += other.x_;
+  y_ += other.y_;
+}
+
+void Vector2d::Subtract(const Vector2d& other) {
+  x_ -= other.x_;
+  y_ -= other.y_;
+}
+
+int64 Vector2d::LengthSquared() const {
+  return x_ * x_ + y_ * y_;
+}
+
+float Vector2d::Length() const {
+  return static_cast<float>(std::sqrt(
+      static_cast<double>(x_) * x_ + static_cast<double>(y_) * y_));

[Peter Kasting, 2012/10/30 01:14:14]

Nit: Would this be more efficient as

      static_cast<double>(x_ * x_) + y_ * y_));

?  Then we'd do all but the sqrt() step as integer math...

[danakj, 2012/10/30 19:21:21]

But we'd also lose some range, as x*x doesn't fit in the same integer size as x.

[Peter Kasting, 2012/10/30 20:24:37]

What about this then:

  return static_cast<float>(std::sqrt(static_cast<double>(LengthSquared())));

And actually, now that I think about it -- doesn't LengthSquared() maybe need to
explicitly upcast in the multiplication, for the same reason you complained
about here?  Otherwise it does everything as int and then promotes the final
result, doesn't it?

(I never remember the fine details of the promotion/conversion rules, so I could
be wrong.  But an explicit cast like that would be obvious and safe.)

[danakj, 2012/10/30 21:14:52]

Ya, I like that!
Yep, good catch.

+}
+
+std::string Vector2d::ToString() const {
+  return base::StringPrintf("[%d %d]", x_, y_);
+}
+
+}  // namespace gfx