tabstrip: Use a PaintRecorder to access the Canvas for painting.

Don't use the canvas() from the PaintContext so that we can have the
PaintContext be backed by a DisplayItemList instead in the future.
Access to the Canvas should be done through a PaintRecorder.

For compositing effects (opacity) we use a CompositingRecorder to
provide a scoped opacity change.

R=pkasting
BUG=466426

Review URL: https://codereview.chromium.org/1062293003

Cr-Commit-Position: refs/heads/master@{#324173}

chrome/browser/ui/views/autofill/card_unmask_prompt_views.cc

@@ -463,10 +463,8 @@ CardUnmaskPromptViews::FadeOutView::~FadeOutView() {
 
 void CardUnmaskPromptViews::FadeOutView::PaintChildren(
     const ui::PaintContext& context) {
-  if (opacity_ > 0.99)
-    return views::View::PaintChildren(context);
-
-  ui::CompositingRecorder recorder(context, opacity_);
+  uint8_t alpha = static_cast<uint8_t>(255 * opacity_);
+  ui::CompositingRecorder recorder(context, alpha);
   views::View::PaintChildren(context);
 }
 

chrome/browser/ui/views/tabs/tab_strip.cc

@@ -38,7 +38,8 @@
 #include "ui/base/l10n/l10n_util.h"
 #include "ui/base/models/list_selection_model.h"
 #include "ui/base/resource/resource_bundle.h"
-#include "ui/compositor/paint_context.h"
+#include "ui/compositor/compositing_recorder.h"
+#include "ui/compositor/paint_recorder.h"
 #include "ui/gfx/animation/animation_container.h"
 #include "ui/gfx/animation/throb_animation.h"
 #include "ui/gfx/canvas.h"
@@ -74,14 +75,14 @@ namespace {
 
 static const int kTabStripAnimationVSlop = 40;
 // Inactive tabs in a native frame are slightly transparent.
-static const int kGlassFrameInactiveTabAlpha = 200;
+static const uint8_t kGlassFrameInactiveTabAlpha = 200;
 // If there are multiple tabs selected then make non-selected inactive tabs
 // even more transparent.
 static const int kGlassFrameInactiveTabAlphaMultiSelection = 150;
 
 // Alpha applied to all elements save the selected tabs.
-static const int kInactiveTabAndNewTabButtonAlphaAsh = 230;
-static const int kInactiveTabAndNewTabButtonAlpha = 255;
+static const uint8_t kInactiveTabAndNewTabButtonAlphaAsh = 230;
+static const uint8_t kInactiveTabAndNewTabButtonAlpha = 255;
 
 // Inverse ratio of the width of a tab edge to the width of the tab. When
 // hovering over the left or right edge of a tab, the drop indicator will
@@ -458,10 +459,11 @@ gfx::ImageSkia NewTabButton::GetImageForState(
   canvas.DrawImageInt(GetBackgroundImage(state, scale), 0, 0);
 
   // Draw the button border with a slight alpha.
-  const int kGlassFrameOverlayAlpha = 178;
-  const int kOpaqueFrameOverlayAlpha = 230;
-  uint8 alpha = ShouldWindowContentsBeTransparent() ?
-      kGlassFrameOverlayAlpha : kOpaqueFrameOverlayAlpha;
+  const uint8_t kGlassFrameOverlayAlpha = 178;
+  const uint8_t kOpaqueFrameOverlayAlpha = 230;
+  uint8_t alpha = ShouldWindowContentsBeTransparent()
+                      ? kGlassFrameOverlayAlpha
+                      : kOpaqueFrameOverlayAlpha;
   canvas.DrawImageInt(*overlay, 0, 0, alpha);
 
   return gfx::ImageSkia(canvas.ExtractImageRep());
@@ -1242,7 +1244,6 @@ void TabStrip::Layout() {
 }
 
 void TabStrip::PaintChildren(const ui::PaintContext& context) {
-  gfx::Canvas* canvas = context.canvas();
   // The view order doesn't match the paint order (tabs_ contains the tab
   // ordering). Additionally we need to paint the tabs that are closing in
   // |tabs_closing_map_|.
@@ -1255,12 +1256,13 @@ void TabStrip::PaintChildren(const ui::PaintContext& context) {
 
   const chrome::HostDesktopType host_desktop_type =
       chrome::GetHostDesktopTypeForNativeView(GetWidget()->GetNativeView());
-  const int inactive_tab_alpha =
-      (host_desktop_type == chrome::HOST_DESKTOP_TYPE_ASH) ?
-      kInactiveTabAndNewTabButtonAlphaAsh : kInactiveTabAndNewTabButtonAlpha;
+  const uint8_t inactive_tab_alpha =
+      (host_desktop_type == chrome::HOST_DESKTOP_TYPE_ASH)
+          ? kInactiveTabAndNewTabButtonAlphaAsh
+          : kInactiveTabAndNewTabButtonAlpha;
 
-  if (inactive_tab_alpha < 255)
-    canvas->SaveLayerAlpha(inactive_tab_alpha);
+  {
+    ui::CompositingRecorder opacity_recorder(context, inactive_tab_alpha);
 
     PaintClosingTabs(tab_count(), context);
 
@@ -1302,17 +1304,17 @@ void TabStrip::PaintChildren(const ui::PaintContext& context) {
         tab->Paint(context);
       }
     }
-  if (inactive_tab_alpha < 255)
-    canvas->Restore();
+  }
 
   if (GetWidget()->ShouldWindowContentsBeTransparent()) {
+    ui::PaintRecorder recorder(context);
     // Make sure non-active tabs are somewhat transparent.
     SkPaint paint;
     // If there are multiple tabs selected, fade non-selected tabs more to make
     // the selected tabs more noticable.
-    int alpha = selected_tab_count > 1 ?
-        kGlassFrameInactiveTabAlphaMultiSelection :
-        kGlassFrameInactiveTabAlpha;
+    uint8_t alpha = selected_tab_count > 1
+                        ? kGlassFrameInactiveTabAlphaMultiSelection
+                        : kGlassFrameInactiveTabAlpha;
     paint.setColor(SkColorSetARGB(alpha, 255, 255, 255));
     paint.setXfermodeMode(SkXfermode::kDstIn_Mode);
     paint.setStyle(SkPaint::kFill_Style);
@@ -1324,7 +1326,7 @@ void TabStrip::PaintChildren(const ui::PaintContext& context) {
     // overlap the avatar button, leading to visual artifacts.
     const int kTopOffset = 4;
     // The tabstrip area overlaps the toolbar area by 2 px.
-    canvas->DrawRect(
+    recorder.canvas()->DrawRect(
         gfx::Rect(0, kTopOffset, width(), height() - kTopOffset - 2), paint);
   }
 
@@ -1338,11 +1340,10 @@ void TabStrip::PaintChildren(const ui::PaintContext& context) {
     active_tab->Paint(context);
 
   // Paint the New Tab button.
-  if (inactive_tab_alpha < 255)
-    canvas->SaveLayerAlpha(inactive_tab_alpha);
+  {
+    ui::CompositingRecorder opacity_recorder(context, inactive_tab_alpha);
     newtab_button_->Paint(context);
-  if (inactive_tab_alpha < 255)
-    canvas->Restore();
+  }
 
   // And the dragged tabs.
   for (size_t i = 0; i < tabs_dragging.size(); ++i)

ui/compositor/compositing_recorder.cc

@@ -10,12 +10,14 @@
 namespace ui {
 
 CompositingRecorder::CompositingRecorder(const PaintContext& context,
-                                         float opacity)
-    : canvas_(context.canvas()) {
-  canvas_->SaveLayerAlpha(0xff * opacity);
+                                         uint8_t alpha)
+    : canvas_(context.canvas()), saved_(alpha < 255) {
+  if (saved_)
+    canvas_->SaveLayerAlpha(alpha);
 }
 
 CompositingRecorder::~CompositingRecorder() {
+  if (saved_)
     canvas_->Restore();
 }
 

ui/compositor/compositing_recorder.h

@@ -5,6 +5,7 @@
 #ifndef UI_COMPOSITOR_COMPOSITING_RECORDER_H_
 #define UI_COMPOSITOR_COMPOSITING_RECORDER_H_
 
+#include "base/basictypes.h"
 #include "base/macros.h"
 #include "ui/compositor/compositor_export.h"
 
@@ -22,11 +23,14 @@ class PaintContext;
 // be filtered by the effect.
 class COMPOSITOR_EXPORT CompositingRecorder {
  public:
-  CompositingRecorder(const PaintContext& context, float opacity);
+  // |alpha| is a value between 0 and 255, where 0 is transparent and 255 is
+  // opaque.
+  CompositingRecorder(const PaintContext& context, uint8_t alpha);
   ~CompositingRecorder();
 
  private:
   gfx::Canvas* canvas_;
+  bool saved_;
 
   DISALLOW_COPY_AND_ASSIGN(CompositingRecorder);
 };