Implements core logic for Pixel Canvas

ui/compositor/paint_context.h

Index: ui/compositor/paint_context.h
diff --git a/ui/compositor/paint_context.h b/ui/compositor/paint_context.h
index bc17c50f46bd3b00cee3ce9e83229b04704d12a9..78e5e1209c07f11ea9c2f89709974409636efe43 100644
--- a/ui/compositor/paint_context.h
+++ b/ui/compositor/paint_context.h
@@ -9,6 +9,7 @@
 
 #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"
@@ -25,14 +26,28 @@ class TransformRecorder;
 
 class COMPOSITOR_EXPORT PaintContext {
  public:
-  // Construct a PaintContext that may only re-paint the area in the
-  // |invalidation|.
+  enum 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. |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 {
@@ -42,16 +57,15 @@ class COMPOSITOR_EXPORT PaintContext {
 
   ~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(); }
-
-  // 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_);
+  bool CanCheckRepaint() const { return !invalidation_.IsEmpty(); }
+
+  // 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()
@@ -65,6 +79,23 @@ class COMPOSITOR_EXPORT PaintContext {
 
   const gfx::Rect& InvalidationForTesting() const { return invalidation_; }
 
+  bool IsPixelCanvas() const { return list_ && list_->pixel_canvas_enabled(); }
+
+  // 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;
+
+  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 ScaleToCorneredPixelSize(const gfx::Size& size) 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
@@ -84,16 +115,31 @@ class COMPOSITOR_EXPORT PaintContext {
   // 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;
+
   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.
+  gfx::Rect bounds_;
+  // Bounds of paint context in exact pixel size. This will have the same value
+  // as |bounds_| if pixel canvas is disabled.
+  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