Implements core logic for Pixel Canvas

ui/compositor/paint_context.h

 // Copyright 2015 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_COMPOSITOR_PAINT_CONTEXT_H_
 #define UI_COMPOSITOR_PAINT_CONTEXT_H_
 
 #include <memory>
 
 #include "base/logging.h"
 #include "base/macros.h"
 #include "cc/paint/paint_recorder.h"
 #include "ui/compositor/compositor_export.h"
 #include "ui/gfx/geometry/rect.h"
 
 namespace cc {
 class DisplayItemList;
 }
 
 namespace ui {
 class ClipRecorder;
 class CompositingRecorder;
 class PaintRecorder;
 class TransformRecorder;
 
 class COMPOSITOR_EXPORT PaintContext {
  public:
-  // Construct a PaintContext that may only re-paint the area in the
-  // |invalidation|.
+  enum class ScaleType {
+    // Scales the context by the default dsf. Use this if you dont want any form
+    // of distortion during scaling.
+    SCALE_TO_SCALE_FACTOR = 0,
+
+    // Scales the context based on the effective dsf. This may lead to minor
+    // distortion during scaling.
+    SCALE_TO_FIT
+  };
+
+  // Construct a PaintContext of given size that may only re-paint the area in
+  // the |invalidation|.
   PaintContext(cc::DisplayItemList* list,
                float device_scale_factor,
-               const gfx::Rect& invalidation);
+               const gfx::Rect& invalidation,
+               const gfx::Size& size);
 
-  // Clone a PaintContext with an additional |offset|.
-  PaintContext(const PaintContext& other, const gfx::Vector2d& offset);
+  // Clone a PaintContext with different |bounds| that has some offset from its
+  // parent.
+  PaintContext(const PaintContext& other,
+               const gfx::Rect& bounds,
+               const gfx::Rect& parent_bounds,
+               ScaleType scale_type);
 
   // Clone a PaintContext that has no consideration for invalidation.
   enum CloneWithoutInvalidation {
     CLONE_WITHOUT_INVALIDATION,
   };
   PaintContext(const PaintContext& other, CloneWithoutInvalidation c);
 
   ~PaintContext();
 
-  // When true, IsRectInvalid() can be called, otherwise its result would be
+  // When true, ShouldRepaint() can be called, otherwise its result would be
   // invalid.
-  bool CanCheckInvalid() const { return !invalidation_.IsEmpty(); }
+  bool CanCheckRepaint() const { return !invalidation_.IsEmpty(); }
 
-  // When true, the |bounds| touches an invalidated area, so should be
-  // re-painted. When false, re-painting can be skipped. Bounds should be in
-  // the local space with offsets up to the painting root in the PaintContext.
-  bool IsRectInvalid(const gfx::Rect& bounds) const {
-    DCHECK(CanCheckInvalid());
-    return invalidation_.Intersects(bounds + offset_);
+  // When true, the |paint_recording_bounds_| touches an invalidated area, so
+  // should be re-painted. When false, re-painting can be skipped.
+  bool ShouldRepaint() const {
+    DCHECK(CanCheckRepaint());
+    return invalidation_.Intersects(paint_recording_bounds_);
   }
 
 #if DCHECK_IS_ON()
   void Visited(void* visited) const {
     if (!root_visited_)
       root_visited_ = visited;
   }
   void* RootVisited() const { return root_visited_; }
-  const gfx::Vector2d& PaintOffset() const { return offset_; }
+  const gfx::Point& PaintOffset() const {
+    return paint_recording_bounds_.origin();
+  }
 #endif
 
   const gfx::Rect& InvalidationForTesting() const { return invalidation_; }
 
+  bool IsPixelCanvas() const;
+
+  const gfx::Size& paint_recording_size() const {
+    return paint_recording_bounds_.size();
+  }
+  const gfx::Rect& paint_recording_bounds() const {
+    return paint_recording_bounds_;
+  }
+
+  // A tranform that converts a given cooridinate from local DIP coordinates to
+  // the parent paint recording coordinates.
+  gfx::Transform TransformToParentRecordingSpace(

[vmpstr, 2017/07/11 17:37:22]

Just some general thoughts:

- It feels like ui::PaintContext is becoming more of transport for things that
seem to be specific to ui::View. PaintContext is also used in a bunch of places
outside of views that don't need any of this functionality. Is that correct?
- Can some of the functionality like this one move to ui::View? What I'm trying
to do is to limit the exposure of the pixel canvas and this new recording mode
to the place where it's used (ie views). 
- Some of this functionality can be moved to views I think, and some maybe to
the recording canvas. 

FWIW, I think the code looks reasonable, it's just it seems that PaintContext is
becoming a places where a bunch of unrelated concepts live, and I think we
should avoid that. 

[malaykeshav, 2017/07/12 00:55:35]

Done.
Moving this to views::View() and exposing paint_recording_scale_

+      const gfx::Vector2d& offset_from_parent) const;
+
  private:
   // The Recorder classes need access to the internal canvas and friends, but we
   // don't want to expose them on this class so that people must go through the
   // recorders to access them.
   friend class ClipRecorder;
   friend class CompositingRecorder;
   friend class PaintRecorder;
   friend class TransformRecorder;
   // The Cache class also needs to access the DisplayItemList to append its
   // cache contents.
   friend class PaintCache;
 
   // Returns a rect with the given size in the space of the context's
   // containing layer.
   gfx::Rect ToLayerSpaceBounds(const gfx::Size& size_in_context) const;
 
-  // Returns the given rect translated by the layer space offset.
-  gfx::Rect ToLayerSpaceRect(const gfx::Rect& rect) const;
+  // Given the DIP |size|, this function updates the paint recording scales.
+  void ComputePaintRecordingScales(const gfx::Size& size);
+
+  // Scales the |child_bounds| to its recording bounds based on the
+  // |device_scale_factor_|. The recording bounds are snapped to the
+  // |parent bound|'s right and/or bottom edge if required.
+  // This function returns |child_bounds| as is if pixel canvas is disabled.
+  gfx::Rect GetSnappedRecordingBounds(const gfx::Rect& parent_bounds,
+                                      const gfx::Rect& child_bounds) const;
 
   cc::DisplayItemList* list_;
   // The device scale of the frame being painted. Used to determine which bitmap
   // resources to use in the frame.
   float device_scale_factor_;
+  // The scale at which the paint commands are recorded at. Due to the decimal
+  // rounding and snapping to edges during scaling operations, 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_;
   // Invalidation in the space of the paint root (ie the space of the layer
-  // backing the paint taking place).
+  // backing the paint taking place). This is in pixel size if pixel canvas is
+  // enabled.
   gfx::Rect invalidation_;
-  // Offset from the PaintContext to the space of the paint root and the
-  // |invalidation_|.
-  gfx::Vector2d offset_;
+  // Paint Recording bounds for this paint context. The offset is relative to
+  // the paint root.
+  const gfx::Rect paint_recording_bounds_;
+  // The |scale_type| tells the context how it needs to perform scaling when
+  // pixel canvas is enabled.
+  ScaleType scale_type_ = ScaleType::SCALE_TO_SCALE_FACTOR;
 
 #if DCHECK_IS_ON()
   // Used to verify that the |invalidation_| is only used to compare against
   // rects in the same space.
   mutable void* root_visited_;
   // Used to verify that paint recorders are not nested. True while a paint
   // recorder is active.
   mutable bool inside_paint_recorder_;
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(PaintContext);
 };
 
 }  // namespace ui
 
 #endif  // UI_COMPOSITOR_PAINT_CONTEXT_H_