Stabilize empty rect handling in EnclosingRect.

ui/gfx/geometry/size_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.
 
 #ifndef UI_GFX_GEOMETRY_SIZE_F_H_
 #define UI_GFX_GEOMETRY_SIZE_F_H_
 
 #include <iosfwd>
 #include <string>
 
 #include "base/compiler_specific.h"
 #include "ui/gfx/geometry/size.h"
 #include "ui/gfx/gfx_export.h"
 
 namespace gfx {
 
 // A floating version of gfx::Size.
 class GFX_EXPORT SizeF {
  public:
   constexpr SizeF() : width_(0.f), height_(0.f) {}
   constexpr SizeF(float width, float height)
-      : width_(width >= 0 ? width : 0), height_(height >= 0 ? height : 0) {}
+      : width_(clamp(width)), height_(clamp(height)) {}
 
   constexpr explicit SizeF(const Size& size)
       : SizeF(static_cast<float>(size.width()),
               static_cast<float>(size.height())) {}
 
   constexpr float width() const { return width_; }
   constexpr float height() const { return height_; }
 
-  void set_width(float width) { width_ = fmaxf(0, width); }
-  void set_height(float height) { height_ = fmaxf(0, height); }
+  void set_width(float width) { width_ = clamp(width); }
+  void set_height(float height) { height_ = clamp(height); }
 
   float GetArea() const;
 
   void SetSize(float width, float height) {
     set_width(width);
     set_height(height);
   }
 
   void Enlarge(float grow_width, float grow_height);
 
   void SetToMin(const SizeF& other);
   void SetToMax(const SizeF& other);
 
-  bool IsEmpty() const { return !width() || !height(); }
+  bool IsEmpty() const { return !height_ || !width_; }
 
   void Scale(float scale) {
     Scale(scale, scale);
   }
 
   void Scale(float x_scale, float y_scale) {
     SetSize(width() * x_scale, height() * y_scale);
   }
 
   std::string ToString() const;
 
  private:
   float width_;
   float height_;
+  static constexpr float kTrivial = 8.f * std::numeric_limits<float>::epsilon();
+  static constexpr float clamp(float f) { return f > kTrivial ? f : 0.f; }
+  friend float SizeFPrivateMatch();  // Test access to the kTrivial constant.

[danakj, 2017/03/28 18:00:20]

make friends the first thing in the private block and whitespace below. you can
use FRIEND_TEST to friend access to the constant
https://cs.chromium.org/chromium/src/testing/gtest/include/gtest/gtest_prod.h...

[Peter Mayo, 2017/03/28 20:11:21]

Done.

 };
 
 inline bool operator==(const SizeF& lhs, const SizeF& rhs) {
   return lhs.width() == rhs.width() && lhs.height() == rhs.height();
 }
 
 inline bool operator!=(const SizeF& lhs, const SizeF& rhs) {
   return !(lhs == rhs);
 }
 
 GFX_EXPORT SizeF ScaleSize(const SizeF& p, float x_scale, float y_scale);
 
 inline SizeF ScaleSize(const SizeF& p, float scale) {
   return ScaleSize(p, scale, scale);
 }
 
 // This is declared here for use in gtest-based unit tests but is defined in
 // the //ui/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 SizeF& size, ::std::ostream* os);
 
 }  // namespace gfx
 
 #endif  // UI_GFX_GEOMETRY_SIZE_F_H_