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/display_item_list.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 ScaleType {

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

enum class.

[malaykeshav, 2017/07/07 22:57:10]

Done

+    // Scales the context by the default dsf. Use this if you dont want any form
+    // of distortion during scaling.
+    SCALE_TO_SCALE_FACTOR = 0,

[danakj, 2017/06/27 16:28:36]

Why is this a property of a PaintContext? A view can set up a transform as it
wants when inserting commands into the recording. PaintContext seems like the
wrong place for this to me.

[malaykeshav, 2017/07/07 22:57:10]

These are the scales that set the recording bounds for the paint recorder.
Depending on the enum type, when the recording bounds for the given PaintContext
is computed, the bounds may or may not be snapped.

This can also be moved to PaintRecorder if PaintContext does not look like the
right place for it.

+
+    // 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. |scale_type| should be from |ScaleType|.
+  PaintContext(const PaintContext& other,
+               const gfx::Rect& bounds,
+               int 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 |pixel_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(gfx::Rect(pixel_size()) + offset_);
   }
 
 #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_; }
 #endif
 
   const gfx::Rect& InvalidationForTesting() const { return invalidation_; }
 
+  bool IsPixelCanvas() const { return list_ && list_->pixel_canvas_enabled(); }
+
+  const gfx::Size& pixel_size() const { return pixel_bounds_.size(); }
+  const gfx::Rect& pixel_bounds() const { return pixel_bounds_; }
+
+  // Scales the given DIP measurement to their corresponding canvas measurement
+  // using the effective scale factors and corner point scaling logic.
+  // Returns the measurements as is, if pixel canvas is disabled.
+  gfx::Size ScaleToCornerScaledPixelSize(const gfx::Size& size) const;
+
+  // A tranform that converts a given cooridinate from local DIP coordinates to
+  // the parent pixel coordinates.
+  gfx::Transform TransformToParentPixelSpace() 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;
 
+  // Scales the |child_bounds| to its pixel bounds based on the
+  // |device_scale_factor_|. The pixel 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 GetSnappedPixelBounds(const gfx::Rect& child_bounds) const;
+
+  // Due to decimal rounding during scaling operations the effective device
+  // scale factor ends up being different from |device_scale_factor_|. To
+  // convert any DIP measurement to its corresponding measurement on the canvas,
+  // the following scales must be used.
+  float effective_scale_factor_x() const;
+  float effective_scale_factor_y() 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_;
   // 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_;
+  // Bounds of the paint context.
+  const gfx::Rect bounds_;
+  // Bounds of paint context in exact pixel size. This will have the same value
+  // as |bounds_| if pixel canvas is disabled.
+  const gfx::Rect pixel_bounds_;
   // Offset from the PaintContext to the space of the paint root and the
-  // |invalidation_|.
+  // |invalidation_|. This is in pixels if pixel canvas is enabled.
   gfx::Vector2d offset_;
+  // The |scale_type| tells the context how it needs to perform scaling when
+  // pixel canvas is enabled.
+  int scale_type_ = 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_