[WIP: not for review] Reduce re-layout

ui/views/examples/multiline_example.cc

 // Copyright 2013 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.
 
 #include "ui/views/examples/multiline_example.h"
 
 #include <stddef.h>
 
 #include "base/macros.h"
 #include "base/strings/utf_string_conversions.h"
 #include "ui/events/event.h"
-#include "ui/gfx/render_text.h"
 #include "ui/views/background.h"
 #include "ui/views/border.h"
 #include "ui/views/controls/button/checkbox.h"
 #include "ui/views/controls/label.h"
 #include "ui/views/controls/textfield/textfield.h"
 #include "ui/views/layout/grid_layout.h"
 #include "ui/views/view.h"
 
 using base::ASCIIToUTF16;
 
@@ skipping 18 matching lines @@
   gfx::Size GetPreferredSize() const override {
     return gfx::Size(50, Label::GetPreferredSize().height());
   }
 
  private:
   DISALLOW_COPY_AND_ASSIGN(PreferredSizeLabel);
 };
 
 }  // namespace
 
-// A simple View that hosts a RenderText object.
-class MultilineExample::RenderTextView : public View {
- public:
-  RenderTextView() : render_text_(gfx::RenderText::CreateInstanceForEditing()) {
-    render_text_->SetHorizontalAlignment(gfx::ALIGN_TO_HEAD);
-    render_text_->SetColor(SK_ColorBLACK);
-    render_text_->SetMultiline(true);
-    SetBorder(Border::CreateSolidBorder(2, SK_ColorGRAY));
-  }
-
-  void OnPaint(gfx::Canvas* canvas) override {
-    View::OnPaint(canvas);
-    render_text_->Draw(canvas);
-  }
-
-  gfx::Size GetPreferredSize() const override {
-    // Turn off multiline mode to get the single-line text size, which is the
-    // preferred size for this view.
-    render_text_->SetMultiline(false);
-    gfx::Size size(render_text_->GetContentWidth(),
-                   render_text_->GetStringSize().height());
-    size.Enlarge(GetInsets().width(), GetInsets().height());
-    render_text_->SetMultiline(true);
-    return size;
-  }
-
-  int GetHeightForWidth(int w) const override {
-    // TODO(ckocagil): Why does this happen?
-    if (w == 0)
-      return View::GetHeightForWidth(w);
-    const gfx::Rect old_rect = render_text_->display_rect();
-    gfx::Rect rect = old_rect;
-    rect.set_width(w - GetInsets().width());
-    render_text_->SetDisplayRect(rect);
-    int height = render_text_->GetStringSize().height() + GetInsets().height();
-    render_text_->SetDisplayRect(old_rect);
-    return height;
-  }
-
-  void SetText(const base::string16& new_contents) {
-    // Color and style the text inside |test_range| to test colors and styles.
-    const size_t range_max = new_contents.length();
-    gfx::Range color_range = ClampRange(gfx::Range(1, 21), range_max);
-    gfx::Range bold_range = ClampRange(gfx::Range(4, 10), range_max);
-    gfx::Range italic_range = ClampRange(gfx::Range(7, 13), range_max);
-
-    render_text_->SetText(new_contents);
-    render_text_->SetColor(SK_ColorBLACK);
-    render_text_->ApplyColor(0xFFFF0000, color_range);
-    render_text_->SetStyle(gfx::DIAGONAL_STRIKE, false);
-    render_text_->ApplyStyle(gfx::DIAGONAL_STRIKE, true, color_range);
-    render_text_->SetStyle(gfx::UNDERLINE, false);
-    render_text_->ApplyStyle(gfx::UNDERLINE, true, color_range);
-    render_text_->ApplyStyle(gfx::BOLD, true, bold_range);
-    render_text_->ApplyStyle(gfx::ITALIC, true, italic_range);
-    InvalidateLayout();
-  }
-
- private:
-  void OnBoundsChanged(const gfx::Rect& previous_bounds) override {
-    gfx::Rect bounds = GetLocalBounds();
-    bounds.Inset(GetInsets());
-    render_text_->SetDisplayRect(bounds);
-  }
-
-  std::unique_ptr<gfx::RenderText> render_text_;
-
-  DISALLOW_COPY_AND_ASSIGN(RenderTextView);
-};
-
-MultilineExample::MultilineExample()
-    : ExampleBase("Multiline RenderText"),
-      render_text_view_(NULL),
-      label_(NULL),
-      textfield_(NULL),
-      label_checkbox_(NULL) {
+MultilineExample::RenderTextView::RenderTextView()
+    : render_text_(gfx::RenderText::CreateInstanceForEditing()) {
+  render_text_->SetHorizontalAlignment(gfx::ALIGN_TO_HEAD);
+  render_text_->SetColor(SK_ColorBLACK);
+  render_text_->SetMultiline(true);
+  SetBorder(Border::CreateSolidBorder(2, SK_ColorGRAY));
 }
 
-MultilineExample::~MultilineExample() {
+MultilineExample::RenderTextView::~RenderTextView() {}
+
+void MultilineExample::RenderTextView::SetText(
+    const base::string16& new_contents) {
+  // Color and style the text inside |test_range| to test colors and styles.
+  const size_t range_max = new_contents.length();
+  gfx::Range color_range = ClampRange(gfx::Range(1, 21), range_max);
+  gfx::Range bold_range = ClampRange(gfx::Range(4, 10), range_max);
+  gfx::Range italic_range = ClampRange(gfx::Range(7, 13), range_max);
+
+  render_text_->SetText(new_contents);
+  render_text_->SetColor(SK_ColorBLACK);
+  render_text_->ApplyColor(0xFFFF0000, color_range);
+  render_text_->SetStyle(gfx::DIAGONAL_STRIKE, false);
+  render_text_->ApplyStyle(gfx::DIAGONAL_STRIKE, true, color_range);

[tapted, 2016/05/10 08:45:53]

One big factor seems to be these 4 "ApplyStyle" calls. There's a TODO in
render_text.cc

  // TODO(oshima|msw): Not all style change requires layout changes.
  // Consider optimizing based on the type of change.
  OnLayoutTextAttributeChanged(false);

Each time, there's a call to RTHB::IsValidCursorIndex which triggers
GetDisplayText and a full layout. This accounts for 56% of the CPU time, but it
could be a quarter of that if the styles were all applied "at once".

UpdateDisplayText shows up with 7 calls to RenderText::Elide (under
render_text.cc:1086 in UpdateDisplayText) accounting for about ~2/3 the time.
The rest is in the EnsureLayout call in UpdateDisplayText (line 1078)

Each of these goes to EnsureLayout goes to ShapeRun[WithFont] which goes to
hb_shape(..) that eats up CPU.

+  render_text_->SetStyle(gfx::UNDERLINE, false);
+  render_text_->ApplyStyle(gfx::UNDERLINE, true, color_range);
+  render_text_->ApplyStyle(gfx::BOLD, true, bold_range);
+  render_text_->ApplyStyle(gfx::ITALIC, true, italic_range);
+  InvalidateLayout();
+}
+
+void MultilineExample::RenderTextView::OnPaint(gfx::Canvas* canvas) {
+  View::OnPaint(canvas);
+  render_text_->Draw(canvas);
+}
+
+gfx::Size MultilineExample::RenderTextView::GetPreferredSize() const {
+  // Turn off multiline mode to get the single-line text size, which is the
+  // preferred size for this view.
+  render_text_->SetMultiline(false);
+  gfx::Size size(render_text_->GetContentWidth(),
+                 render_text_->GetStringSize().height());
+  size.Enlarge(GetInsets().width(), GetInsets().height());
+  render_text_->SetMultiline(true);
+  return size;
+}
+
+int MultilineExample::RenderTextView::GetHeightForWidth(int w) const {
+  // TODO(ckocagil): Why does this happen?
+  if (w == 0)
+    return View::GetHeightForWidth(w);
+  const gfx::Rect old_rect = render_text_->display_rect();
+  gfx::Rect rect = old_rect;
+  rect.set_width(w - GetInsets().width());
+  render_text_->SetDisplayRect(rect);
+  int height = render_text_->GetStringSize().height() + GetInsets().height();
+  render_text_->SetDisplayRect(old_rect);
+  return height;
+}
+
+void MultilineExample::RenderTextView::OnBoundsChanged(
+    const gfx::Rect& previous_bounds) {
+  gfx::Rect bounds = GetLocalBounds();
+  bounds.Inset(GetInsets());
+  render_text_->SetDisplayRect(bounds);
+}
+
+MultilineExample::MultilineExample(const char* name)
+    : ExampleBase(name),
+      render_text_view_(nullptr),
+      label_(nullptr),
+      textfield_(nullptr),
+      label_checkbox_(nullptr) {}
+
+MultilineExample::~MultilineExample() {}
+
+MultilineExample::RenderTextView* MultilineExample::CreateTextView() {
+  return new RenderTextView();
 }
 
 void MultilineExample::CreateExampleView(View* container) {
   const base::string16 kTestString = base::WideToUTF16(L"qwerty"
       L"\x627\x644\x631\x626\x64A\x633\x64A\x629"
       L"asdfgh");
 
-  render_text_view_ = new RenderTextView();
+  render_text_view_ = CreateTextView();
   render_text_view_->SetText(kTestString);
 
   label_ = new PreferredSizeLabel();
   label_->SetText(kTestString);
   label_->SetMultiLine(true);
   label_->SetBorder(Border::CreateSolidBorder(2, SK_ColorCYAN));
 
   label_checkbox_ = new Checkbox(ASCIIToUTF16("views::Label:"));
   label_checkbox_->SetChecked(true);
   label_checkbox_->set_listener(this);
@@ skipping 23 matching lines @@
   layout->StartRow(0, 0);
   layout->AddView(new Label(ASCIIToUTF16("Sample Text:")));
   layout->AddView(textfield_);
 }
 
 void MultilineExample::ContentsChanged(Textfield* sender,
                                        const base::string16& new_contents) {
   render_text_view_->SetText(new_contents);
   if (label_checkbox_->checked())
     label_->SetText(new_contents);
   container()->Layout();

[tapted, 2016/05/10 08:45:53]

about 38% of the CPU time is under this call. This triggers
RTHB::EnsureLayoutRunList, which does UpdateDisplayText (twice? rthb.cc:1086 and
:1078) that accounts for ~60% of this 38%. The rest is under RTHB::EnsureLayout.

Only 29/886 of samples (3% of that 38%, or 1.26% total) is spent in the
Mac-specific gfx::GetFallbackFonts

The non-multiline views::Label::GetHeightForWidth call is 65/886 samples under
this. So over 10 times faster.

The repaint that occurs for the views::TextField (also not multi-line) is not
under this, but it's similar (88 samples, or about 4%.

So these two comments account for about 56+38+4=98% of the CPU time. The rest is
random smaller things, including painting

   container()->SchedulePaint();
 }
 
 void MultilineExample::ButtonPressed(Button* sender, const ui::Event& event) {
   DCHECK_EQ(sender, label_checkbox_);
   label_->SetText(label_checkbox_->checked() ? textfield_->text() :
                                                base::string16());
   container()->Layout();
   container()->SchedulePaint();
 }
 
 }  // namespace examples
 }  // namespace views