Make various gfx classes more amenable to use as compile-time constants.

ui/gfx/geometry/box_f.h

 // Copyright 2013 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_GFX_GEOMETRY_BOX_F_H_
 #define UI_GFX_GEOMETRY_BOX_F_H_
 
 #include <iosfwd>
 #include <string>
 
 #include "ui/gfx/geometry/point3_f.h"
 #include "ui/gfx/geometry/vector3d_f.h"
 
 namespace gfx {
 
 // A 3d version of gfx::RectF, with the positive z-axis pointed towards
 // the camera.
 class GFX_EXPORT BoxF {
  public:
-  BoxF()
+  constexpr BoxF()
       : width_(0.f),
         height_(0.f),
         depth_(0.f) {}
 
-  BoxF(float width, float height, float depth)
+  constexpr BoxF(float width, float height, float depth)
       : width_(width < 0 ? 0 : width),
         height_(height < 0 ? 0 : height),
         depth_(depth < 0 ? 0 : depth) {}
 
-  BoxF(float x, float y, float z, float width, float height, float depth)
+  constexpr BoxF(float x,
+                 float y,
+                 float z,
+                 float width,
+                 float height,
+                 float depth)
       : origin_(x, y, z),
         width_(width < 0 ? 0 : width),
         height_(height < 0 ? 0 : height),
         depth_(depth < 0 ? 0 : depth) {}
 
-  BoxF(const Point3F& origin, float width, float height, float depth)
+  constexpr BoxF(const Point3F& origin, float width, float height, float depth)
       : origin_(origin),
         width_(width < 0 ? 0 : width),
         height_(height < 0 ? 0 : height),
         depth_(depth < 0 ? 0 : depth) {}
 
-  ~BoxF() {}
-
   // Scales all three axes by the given scale.
   void Scale(float scale) {
     Scale(scale, scale, scale);
   }
 
   // Scales each axis by the corresponding given scale.
   void Scale(float x_scale, float y_scale, float z_scale) {
     origin_.Scale(x_scale, y_scale, z_scale);
     set_size(width_ * x_scale, height_ * y_scale, depth_ * z_scale);
   }
 
   // Moves the box by the specified distance in each dimension.
   void operator+=(const Vector3dF& offset) {
     origin_ += offset;
   }
 
   // Returns true if the box has no interior points.
   bool IsEmpty() const;
 
   // Computes the union of this box with the given box. The union is the
   // smallest box that contains both boxes.
   void Union(const BoxF& box);
 
   std::string ToString() const;
 
-  float x() const { return origin_.x(); }
+  constexpr float x() const { return origin_.x(); }

[danakj, 2016/06/10 00:36:47]

is this constexpr and const not redundant? Why is it not placed where "const" is
currently?

[vmpstr, 2016/06/10 00:46:15]

I think in C++14, non-static constexpr member function does not have to be
implicitly const, so maybe keep it as future proofing? 

[Peter Kasting, 2016/06/10 05:50:06]

No, they're not redundant.  Originally, constexpr implied const as you expect
(and as I expected originally).  This was removed in N3598.  More detail is
available at http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3598.html
.

MSVC 2015 will actually warn you that you've written a constexpr-but-not-const
function and ask if that's really what you intend.

   void set_x(float x) { origin_.set_x(x); }
 
-  float y() const { return origin_.y(); }
+  constexpr float y() const { return origin_.y(); }
   void set_y(float y) { origin_.set_y(y); }
 
-  float z() const { return origin_.z(); }
+  constexpr float z() const { return origin_.z(); }
   void set_z(float z) { origin_.set_z(z); }
 
-  float width() const { return width_; }
+  constexpr float width() const { return width_; }
   void set_width(float width) { width_ = width < 0 ? 0 : width; }
 
-  float height() const { return height_; }
+  constexpr float height() const { return height_; }
   void set_height(float height) { height_ = height < 0 ? 0 : height; }
 
-  float depth() const { return depth_; }
+  constexpr float depth() const { return depth_; }
   void set_depth(float depth) { depth_ = depth < 0 ? 0 : depth; }
 
-  float right() const { return x() + width(); }
-  float bottom() const { return y() + height(); }
-  float front() const { return z() + depth(); }
+  constexpr float right() const { return x() + width(); }
+  constexpr float bottom() const { return y() + height(); }
+  constexpr float front() const { return z() + depth(); }
 
   void set_size(float width, float height, float depth) {
     width_ = width < 0 ? 0 : width;
     height_ = height < 0 ? 0 : height;
     depth_ = depth < 0 ? 0 : depth;
   }
 
-  const Point3F& origin() const { return origin_; }
+  constexpr const Point3F& origin() const { return origin_; }
   void set_origin(const Point3F& origin) { origin_ = origin; }
 
   // Expands |this| to contain the given point, if necessary. Please note, even
   // if |this| is empty, after the function |this| will continue to contain its
   // |origin_|.
   void ExpandTo(const Point3F& point);
 
   // Expands |this| to contain the given box, if necessary. Please note, even
   // if |this| is empty, after the function |this| will continue to contain its
   // |origin_|.
@@ skipping 51 matching lines @@
 }
 
 // This is declared here for use in gtest-based unit tests but is defined in
 // the gfx_test_support target. Depend on that to use this in your unit test.
 // This should not be used in production code - call ToString() instead.
 void PrintTo(const BoxF& box, ::std::ostream* os);
 
 }  // namespace gfx
 
 #endif  // UI_GFX_GEOMETRY_BOX_F_H_