Implements core logic for Pixel Canvas

ui/views/paint_info.h

Index: ui/views/paint_info.h
diff --git a/ui/views/paint_info.h b/ui/views/paint_info.h
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index 0000000000000000000000000000000000000000..ee9dbe9e07f3cb8ea4362417df0871b6df443a0f
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+++ b/ui/views/paint_info.h
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+// Copyright 2017 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_PAINT_INFO_H_
+#define UI_VIEWS_PAINT_INFO_H_
+
+#include "ui/compositor/paint_context.h"
+#include "ui/gfx/geometry/rect.h"
+#include "ui/views/views_export.h"
+
+namespace views {
+
+// This class manages the context required during View::Paint(). It is
+// responsible for setting the paint recording size and the paint recording
+// scale factors for an individual View.
+// Each PaintInfo instance has paint recording offset relative to a root
+// PaintInfo.
+// All coordinates are in paint recording space. If pixel canvas is enabled this
+// essentially becomes pixel coordinate space.
+class VIEWS_EXPORT PaintInfo {
+ public:
+  enum class ScaleType {
+    // Scale the recordings by the default dsf. Use this if you don't want any
+    // form of distortion during scaling.
+    kScaleToScaleFactor = 0,
+
+    // Scale the recordings based on the effective dsf. This may lead to minor
+    // distortion during scaling due to edge snapping.
+    kScaleToFit
+  };
+
+  // Instantiates a root PaintInfo. This should only be initialized at the Paint
+  // root, ie., a layer or the root of a widget.
+  static PaintInfo CreateRootPaintInfo(const ui::PaintContext& root_context,

[sky, 2017/07/28 16:02:12]

Thanks for the improved names, they make it much easier to understand the
context.

+                                       const gfx::Size& size);
+
+  // Instantiate a child PaintInfo instance. All bounds for this object are
+  // relative to its root PaintInfo.
+  static PaintInfo CreateChildPaintInfo(const PaintInfo& other,

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

other -> parent_paint_info.

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

Done

+                                        const gfx::Rect& bounds,
+                                        const gfx::Size& parent_size,
+                                        ScaleType scale_type);
+
+  PaintInfo(const PaintInfo& other);

[sky, 2017/07/28 16:02:12]

The way you have this class set up the assignment operator is also generated.
Are you sure you want that?

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

You are right, this will create a PaintContext clone without the invalidation at
every assignment operator.

Creating a factory method for cloning in that case.

Also creating a copy constructor for all the factory function assignments to
work.

+  ~PaintInfo();
+
+  const ui::PaintContext& context() const {
+    return root_context_ ? *root_context_ : context_;
+  }
+
+  gfx::Vector2d offset_from_root() const {
+    return paint_recording_bounds_.OffsetFromOrigin();
+  }
+
+  // Returns true if all paint commands are recorded at pixel size.
+  bool IsPixelCanvas() const;
+
+  const gfx::Vector2d& offset_from_parent() const {
+    return offset_from_parent_;
+  }
+
+  gfx::PointF paint_recording_scale() const {

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

Why are you using a Point for something that isn't a point but a scale? Instead
expose getters for the scales, for example:
float paint_recording_scale_x() const { return ... };

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

Done

+    return gfx::PointF(paint_recording_scale_x_, paint_recording_scale_y_);
+  }
+
+  const gfx::Size& paint_recording_size() const {
+    return paint_recording_bounds_.size();
+  }
+
+  const gfx::Rect& paint_recording_bounds() const {
+    return paint_recording_bounds_;
+  }
+
+ private:
+  friend class PaintInfoTest;
+
+  PaintInfo(const ui::PaintContext& root_context, const gfx::Size& size);
+  PaintInfo(const PaintInfo& other,
+            const gfx::Rect& bounds,
+            const gfx::Size& parent_size,
+            ScaleType scale_type);
+
+  // Given the DIP |size|, this function updates the paint recording scales.
+  void ComputePaintRecordingScales(const gfx::Size& size, ScaleType scale_type);
+
+  // Scales the |child_bounds| to its recording bounds based on the
+  // |context.device_scale_factor()|. The recording bounds are snapped to the
+  // parent's right and/or bottom edge if required.
+  // If pixel canvas is disabled, this function returns |child_bounds| as is.
+  gfx::Rect GetSnappedRecordingBounds(const gfx::Size& parent_size,
+                                      const gfx::Rect& child_bounds) const;
+
+  // The scale at which the paint commands are recorded at. Due to the decimal
+  // rounding and snapping to edges during the scale operation, the effective
+  // paint recording scale may end up being slightly different between the x and
+  // y axis.
+  float paint_recording_scale_x_;
+  float paint_recording_scale_y_;
+
+  // Paint Recording bounds of the view. The offset is relative to the root
+  // PaintInfo.
+  const gfx::Rect paint_recording_bounds_;
+
+  // Offset relative to the parent view's paint recording bounds. Returns 0
+  // offset if this is the root.
+  gfx::Vector2d offset_from_parent_;
+
+  // Compositor PaintContext associated with the view this object belongs to.
+  ui::PaintContext context_;
+  const ui::PaintContext* root_context_;
+};
+
+}  // namespace views
+
+#endif  // UI_VIEWS_PAINT_INFO_H_