Implements core logic for Pixel Canvas

ui/views/view.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_VIEWS_VIEW_H_
 #define UI_VIEWS_VIEW_H_
 
 #include <stddef.h>
 
 #include <algorithm>
@@ skipping 1250 matching lines @@
   static int GetHorizontalDragThreshold();
   static int GetVerticalDragThreshold();
 
   // NativeTheme ---------------------------------------------------------------
 
   // Invoked when the NativeTheme associated with this View changes, including
   // when one first becomes available (after the view is added to a widget
   // hierarchy).
   virtual void OnNativeThemeChanged(const ui::NativeTheme* theme) {}
 
+  // Pixel Canvas --------------------------------------------------------------
+
+  // Returns the type of scaling to be done for this View. Values should be from
+  // ui::PaintContext::ScaleType.
+  virtual int GetContextScaleType() const;

[sky, 2017/06/23 23:40:23]

Why is this virtual? Why would it need to be overriden? And why is the return
type int instead of ScaleType?

[malaykeshav, 2017/06/24 00:30:03]

The ScaleType can vary depending on whether we are scaling to fit/snap (default)
or 
if we are simply scaling with no snapping.

With scaling by fractional scale factors, the effective scale factor is
different 
from the original scale factor due to rounding. 

 - In Scale to Fit/Snap, all the draw commands are scaled via the effective
scale 
   factor.
 - But this leads to some undesired scaling in terms of images or vector icons, 
   that require consistent scaling along x and y axis. (effective scale along x 
   may not be equal to effective scale along y). For such cases we use Scale To 
   Scale Factor. Which scales all draw commands with device_scale_factor_. But
the 
   canvas is still bounded with the scale to fit bounds (For any child snapping
and
   FillCanvas() like commands).

By default this function returns SCALE_TO_FIT. In case a view wants to
SCALE_TO_SCALE_FACTOR, it can
override accordingly and return the correct enum.
This can also be made a member variable along with a setter.

I was using int as the return type to prevent including paint_context.h files in
all the header files that were overriding this function.

+
   // Debugging -----------------------------------------------------------------
 
 #if !defined(NDEBUG)
   // Returns string containing a graph of the views hierarchy in graphViz DOT
   // language (http://graphviz.org/). Can be called within debugger and save
   // to a file to compile/view.
   // Note: Assumes initial call made with first = true.
   virtual std::string PrintViewGraph(bool first);
 
   // Some classes may own an object which contains the children to displayed in
@@ skipping 28 matching lines @@
 
   // Schedules a paint on the parent View if it exists.
   void SchedulePaintOnParent();
 
   // Returns whether this view is eligible for painting, i.e. is visible and
   // nonempty.  Note that this does not behave like IsDrawn(), since it doesn't
   // check ancestors recursively; rather, it's used to prune subtrees of views
   // during painting.
   bool ShouldPaint() const;
 
-  // Returns the offset that should be used when constructing the paint context
+  // Returns the bounds that should be used when constructing the paint context
   // for this view.
-  gfx::Vector2d GetPaintContextOffset() const;
+  gfx::Rect GetPaintContextBounds() const;
 
   // Adjusts the transform of |recorder| in advance of painting.
-  void SetupTransformRecorderForPainting(ui::TransformRecorder* recorder) const;
+  void SetupTransformRecorderForPainting(ui::TransformRecorder* recorder,
+                                         const ui::PaintContext& context) const;
 
   // Recursively calls the painting method |func| on all non-layered children,
   // in Z order.
   void RecursivePaintHelper(void (View::*func)(const ui::PaintContext&),
                             const ui::PaintContext& context);
 
   // Invokes Paint() and, if necessary, PaintDebugRects().  Should be called
   // only on the root of a widget/layer.  PaintDebugRects() is invoked as a
   // separate pass, instead of being rolled into Paint(), so that siblings will
   // not obscure debug rects.
@@ skipping 374 matching lines @@
   // Observers -------------------------------------------------------------
 
   base::ObserverList<ViewObserver> observers_;
 
   DISALLOW_COPY_AND_ASSIGN(View);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_VIEW_H_