Implements core logic for Pixel Canvas

ui/gfx/geometry/rect.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 integer rectangle class.  The containment semantics
 // are array-like; that is, the coordinate (x, y) is considered to be
 // contained by the rectangle, but the coordinate (x + width, y) is not.
 // The class will happily let you create malformed rectangles (that is,
 // rectangles with negative width and/or height), but there will be assertions
 // in the operations (such as Contains()) to complain in this case.
@@ skipping 322 matching lines @@
       x : static_cast<int>(std::floor(rect.right() * x_scale));
   int b = rect.height() == 0 ?
       y : static_cast<int>(std::floor(rect.bottom() * y_scale));
   return Rect(x, y, r - x, b - y);
 }
 
 inline Rect ScaleToEnclosedRect(const Rect& rect, float scale) {
   return ScaleToEnclosedRect(rect, scale, scale);
 }
 
+// Scales |rect| by scaling its four corner points. If the corner points lie on
+// non-integral coordinate after scaling, their values are rounded to the
+// nearest integer.
+// This scheme for scaling is important to keep consistency during layout.
+// All rectangles (or any point) within the same coordinate space will

[sky, 2017/07/28 16:02:11]

I'm not sure what this last sentence means. This sentence implies it isn't
lossy, yet it is. Also, you don't give guidance on *when* this should be used vs
the others. That is the important thing to document.

[malaykeshav, 2017/07/31 18:54:29]

The relative positions _isn't_ lossy, even though the absolute position may be.
Adding a comment that this scheme of scaling should be used when performing
layout operations to give lossless relative positioning.

[sky, 2017/08/01 15:10:23]

At the end of the day you are rounding to ints, so I don't know how it can be
'not lossy.' It all depends upon how you are using this.

But again, the important thing is the comment. Thanks for adding it.

+// have the same relative positioning after scaling if this scheme is used.
+inline Rect ScaleToRoundedRect(const Rect& rect, float x_scale, float y_scale) {
+  if (x_scale == 1.f && y_scale == 1.f)
+    return rect;
+
+  DCHECK(
+      base::IsValueInRangeForNumericType<int>(std::round(rect.x() * x_scale)));
+  DCHECK(
+      base::IsValueInRangeForNumericType<int>(std::round(rect.y() * y_scale)));
+  DCHECK(base::IsValueInRangeForNumericType<int>(
+      std::round(rect.right() * x_scale)));
+  DCHECK(base::IsValueInRangeForNumericType<int>(
+      std::round(rect.bottom() * y_scale)));
+
+  int x = static_cast<int>(std::round(rect.x() * x_scale));
+  int y = static_cast<int>(std::round(rect.y() * y_scale));
+  int r = rect.width() == 0
+              ? x
+              : static_cast<int>(std::round(rect.right() * x_scale));
+  int b = rect.height() == 0
+              ? y
+              : static_cast<int>(std::round(rect.bottom() * y_scale));
+
+  return Rect(x, y, r - x, b - y);
+}
+
+inline Rect ScaleToRoundedRect(const Rect& rect, float scale) {
+  return ScaleToRoundedRect(rect, 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 Rect& rect, ::std::ostream* os);
 
 }  // namespace gfx
 
 #endif  // UI_GFX_GEOMETRY_RECT_H_