Speed up rendering of the input method candidate window.

chrome/browser/chromeos/input_method/candidate_window.cc

 // Copyright (c) 2010 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 "chrome/browser/chromeos/input_method/candidate_window.h"
 
 #include <algorithm>
 #include <string>
 #include <vector>
 
@@ skipping 218 matching lines @@
     shortcut_label->SetText(
         CreateShortcutText(i, lookup_table.orientation));
     shortcut_column_width =
         std::max(shortcut_column_width,
                  wrapped_shortcut_label->GetPreferredSize().width());
   }
 
   return shortcut_column_width;
 }
 
+// Computes the page index. For instance, if the page size is 9, and the
+// cursor is pointing to 13th candidate, the page index will be 1 (2nd
+// page, as the index is zero-origin). Returns -1 on error.
+int ComputePageIndex(const chromeos::InputMethodLookupTable& lookup_table) {
+  if (lookup_table.page_size > 0)
+    return lookup_table.cursor_absolute_index / lookup_table.page_size;
+  return -1;
+}
+
 // Computes candidate column width.
 int ComputeCandidateColumnWidth(
     const chromeos::InputMethodLookupTable& lookup_table) {
   int candidate_column_width = 0;
   scoped_ptr<views::Label> candidate_label(
       CreateCandidateLabel(lookup_table.orientation));
 
   // Compute the start index of |lookup_table_|.
-  const int current_page_index =
-      lookup_table.cursor_absolute_index / lookup_table.page_size;
+  const int current_page_index = ComputePageIndex(lookup_table);
+  if (current_page_index < 0)
+    return 0;
   const size_t start_from = current_page_index * lookup_table.page_size;
 
   // Compute the max width in candidate labels.
   // We'll create temporary candidate labels, and choose the largest width.
   for (size_t i = 0; i < lookup_table.candidates.size(); ++i) {
     const size_t index = start_from + i;
 
     candidate_label->SetText(
         UTF8ToWide(lookup_table.candidates[index]));
     candidate_column_width =
         std::max(candidate_column_width,
                  candidate_label->GetPreferredSize().width());
   }
 
   return candidate_column_width;
 }
 
 // Computes annotation column width.
 int ComputeAnnotationColumnWidth(
     const chromeos::InputMethodLookupTable& lookup_table) {
   int annotation_column_width = 0;
   scoped_ptr<views::Label> annotation_label(
       CreateAnnotationLabel(lookup_table.orientation));
 
   // Compute the start index of |lookup_table_|.
-  const int current_page_index =
-      lookup_table.cursor_absolute_index / lookup_table.page_size;
+  const int current_page_index = ComputePageIndex(lookup_table);
+  if (current_page_index < 0)
+    return 0;
   const size_t start_from = current_page_index * lookup_table.page_size;
 
   // Compute max width in annotation labels.
   // We'll create temporary annotation labels, and choose the largest width.
   for (size_t i = 0; i < lookup_table.annotations.size(); ++i) {
     const size_t index = start_from + i;
 
     annotation_label->SetText(
         UTF8ToWide(lookup_table.annotations[index]));
     annotation_column_width =
@@ skipping 52 matching lines @@
 
   // Hides the auxiliary text.
   void HideAuxiliaryText();
 
   // Shows the auxiliary text.
   void ShowAuxiliaryText();
 
   // Updates the auxiliary text.
   void UpdateAuxiliaryText(const std::string& utf8_text);
 
+  // Returns true if we should update candidate views in the window.  For
+  // instance, if we are going to show the same candidates as before, we
+  // don't have to update candidate views. This happens when the user just
+  // moves the cursor in the same page in the candidate window.
+  bool ShouldUpdateCandidateViews(
+      const InputMethodLookupTable& previous_table,
+      const InputMethodLookupTable& current_table);
+
   // Updates candidates of the candidate window from |lookup_table|.
   // Candidates are arranged per |orientation|.
   void UpdateCandidates(const InputMethodLookupTable& lookup_table);
 
   // Resizes the parent frame and schedules painting. This needs to be
   // called when the visible contents of the candidate window are
   // modified.
   void ResizeAndSchedulePaint();
 
   // Returns the horizontal offset used for placing the vertical candidate
@@ skipping 412 matching lines @@
   ResizeAndSchedulePaint();
 }
 
 void CandidateWindowView::UpdateAuxiliaryText(const std::string& utf8_text) {
   views::Label* target_label = (
       lookup_table_.orientation == InputMethodLookupTable::kHorizontal ?
       header_label_ : footer_label_);
   target_label->SetText(UTF8ToWide(utf8_text));
 }
 
+bool CandidateWindowView::ShouldUpdateCandidateViews(
+    const InputMethodLookupTable& previous_table,
+    const InputMethodLookupTable& current_table) {
+  // Check if most table contents are identical.
+  if (previous_table.page_size == current_table.page_size &&
+      previous_table.orientation == current_table.orientation &&
+      previous_table.candidates == current_table.candidates &&
+      previous_table.labels == current_table.labels &&
+      previous_table.annotations == current_table.annotations &&
+      // Check if the page indexes are identical.
+      ComputePageIndex(previous_table) == ComputePageIndex(current_table)) {
+    // If all of the conditions are met, we don't have to update candidate
+    // views.
+    return false;
+  }
+  return true;
+}
+
 void CandidateWindowView::UpdateCandidates(
     const InputMethodLookupTable& lookup_table) {
-  // Initialize candidate views if necessary.
-  MaybeInitializeCandidateViews(lookup_table);
+  const bool should_update = ShouldUpdateCandidateViews(lookup_table_,
+                                                        lookup_table);
+  // Updating the candidate views is expensive. We'll skip this if possible.
+  if (should_update) {
+    // Initialize candidate views if necessary.
+    MaybeInitializeCandidateViews(lookup_table);
 
-  // In MaybeInitializeCandidateViews(),
-  // |lookup_table| values and |lookup_table_| values are compared,
-  // so this substitution is needed after the function.
+    // Compute the index of the current page.
+    if (lookup_table.page_size <= 0) {
+      LOG(ERROR) << "Invalid page size: " << lookup_table.page_size;
+      return;
+    }
+    current_page_index_ =
+        lookup_table.cursor_absolute_index / lookup_table.page_size;
+
+    // Update the candidates in the current page.
+    const size_t start_from = current_page_index_ * lookup_table.page_size;
+
+    // In some cases, engines send empty shortcut labels. For instance,
+    // ibus-mozc sends empty labels when they show suggestions. In this
+    // case, we should not show shortcut labels.
+    const bool no_shortcut_mode = (start_from < lookup_table.labels.size() &&
+                                   lookup_table.labels[start_from] == "");
+    for (size_t i = 0; i < candidate_views_.size(); ++i) {
+      const size_t index_in_page = i;
+      const size_t candidate_index = start_from + index_in_page;
+      CandidateView* candidate_view = candidate_views_[index_in_page];
+      // Set the shortcut text.
+      if (no_shortcut_mode) {
+        candidate_view->SetShortcutText(L"");
+      } else {
+        // At this moment, we don't use labels sent from engines for UX
+        // reasons. First, we want to show shortcut labels in empty rows
+        // (ex. show 6, 7, 8, ... in empty rows when the number of
+        // candidates is 5). Second, we want to add a period after each
+        // shortcut label when the candidate window is horizontal.
+        candidate_view->SetShortcutText(
+            CreateShortcutText(i, lookup_table.orientation));
+      }
+      // Set the candidate text.
+      if (candidate_index < lookup_table.candidates.size() &&
+          candidate_index < lookup_table.annotations.size()) {
+        candidate_view->SetCandidateText(
+            UTF8ToWide(lookup_table.candidates[candidate_index]));
+        candidate_view->SetAnnotationText(
+            UTF8ToWide(lookup_table.annotations[candidate_index]));
+        candidate_view->SetRowEnabled(true);
+      } else {
+        // Disable the empty row.
+        candidate_view->SetCandidateText(L"");
+        candidate_view->SetAnnotationText(L"");
+        candidate_view->SetRowEnabled(false);
+      }
+    }
+  }

[satorux1, 2010/12/01 09:25:32]

Hmm, rietveld didn't do a good job for showing diffs here. The contents in "if
(should_update)" block is almost identical to the original code.

   lookup_table_ = lookup_table;
 
-  // Compute the index of the current page.
-  current_page_index_ =
-      lookup_table.cursor_absolute_index / lookup_table.page_size;
-
-  // Update the candidates in the current page.
-  const size_t start_from = current_page_index_ * lookup_table.page_size;
-
-  // In some cases, engines send empty shortcut labels. For instance,
-  // ibus-mozc sends empty labels when they show suggestions. In this
-  // case, we should not show shortcut labels.
-  const bool no_shortcut_mode = (start_from < lookup_table_.labels.size() &&
-                                 lookup_table_.labels[start_from] == "");
-  for (size_t i = 0; i < candidate_views_.size(); ++i) {
-    const size_t index_in_page = i;
-    const size_t candidate_index = start_from + index_in_page;
-    CandidateView* candidate_view = candidate_views_[index_in_page];
-    // Set the shortcut text.
-    if (no_shortcut_mode) {
-      candidate_view->SetShortcutText(L"");
-    } else {
-      // At this moment, we don't use labels sent from engines for UX
-      // reasons. First, we want to show shortcut labels in empty rows
-      // (ex. show 6, 7, 8, ... in empty rows when the number of
-      // candidates is 5). Second, we want to add a period after each
-      // shortcut label when the candidate window is horizontal.
-      candidate_view->SetShortcutText(
-          CreateShortcutText(i, lookup_table_.orientation));
-    }
-    // Set the candidate text.
-    if (candidate_index < lookup_table_.candidates.size() &&
-        candidate_index < lookup_table_.annotations.size()) {
-      candidate_view->SetCandidateText(
-          UTF8ToWide(lookup_table_.candidates[candidate_index]));
-      candidate_view->SetAnnotationText(
-          UTF8ToWide(lookup_table_.annotations[candidate_index]));
-      candidate_view->SetRowEnabled(true);
-    } else {
-      // Disable the empty row.
-      candidate_view->SetCandidateText(L"");
-      candidate_view->SetAnnotationText(L"");
-      candidate_view->SetRowEnabled(false);
-    }
-  }
-
-  // Select the first candidate candidate in the page.
-  const int first_candidate_in_page =
+  // Select the current candidate in the page.
+  const int current_candidate_in_page =
       lookup_table.cursor_absolute_index % lookup_table.page_size;
-  SelectCandidateAt(first_candidate_in_page);
+  SelectCandidateAt(current_candidate_in_page);
 }
 
 void CandidateWindowView::MaybeInitializeCandidateViews(
     const InputMethodLookupTable& lookup_table) {
   const InputMethodLookupTable::Orientation orientation =
       lookup_table.orientation;
   const int page_size = lookup_table.page_size;
 
   // Current column width.
   int shortcut_column_width = 0;
   int candidate_column_width = 0;
   int annotation_column_width = 0;
 
   // If orientation is horizontal, don't need to compute width,
   // because each label is left aligned.
   if (orientation == InputMethodLookupTable::kVertical) {
     shortcut_column_width = ComputeShortcutColumnWidth(lookup_table);
     candidate_column_width = ComputeCandidateColumnWidth(lookup_table);
     annotation_column_width = ComputeAnnotationColumnWidth(lookup_table);
   }
 
   // If the requested number of views matches the number of current views, and
   // previous and current column width are same, just reuse these.
+  //
+  // Note that the early exit logic is not only useful for improving
+  // performance, but also necessary for the horizontal candidate window
+  // to be redrawn properly. If we get rid of the logic, the horizontal
+  // candidate window won't get redrawn properly for some reason when
+  // there is no size change. You can test this by removing "return" here
+  // and type "ni" with Pinyin input method.
   if (static_cast<int>(candidate_views_.size()) == page_size &&
       lookup_table_.orientation == orientation &&
       previous_shortcut_column_width_ == shortcut_column_width &&
       previous_candidate_column_width_ == candidate_column_width &&
       previous_annotation_column_width_ == annotation_column_width) {
     return;
   }
 
   // Update the previous column widths.
   previous_shortcut_column_width_ = shortcut_column_width;
@@ skipping 333 matching lines @@
     DLOG(INFO) << "Ignored set_cursor_location signal to prevent window shake";
     return;
   }
 
   // Remember the cursor location.
   controller->set_cursor_location(gfx::Rect(x, y, width, height));
   // Move the window per the cursor location.
   controller->MoveCandidateWindow(
       controller->cursor_location(),
       controller->candidate_window_->GetHorizontalOffset());
-  // The call is needed to ensure that the candidate window is redrawed
+  // The call is needed to ensure that the candidate window is redrawn
   // properly after the cursor location is changed.
   controller->candidate_window_->ResizeAndSchedulePaint();
 }
 
 void CandidateWindowController::Impl::OnUpdateAuxiliaryText(
     void* input_method_library,
     const std::string& utf8_text,
     bool visible) {
   CandidateWindowController::Impl* controller =
       static_cast<CandidateWindowController::Impl*>(input_method_library);
@@ skipping 56 matching lines @@
 
 CandidateWindowController::~CandidateWindowController() {
   delete impl_;
 }
 
 bool CandidateWindowController::Init() {
   return impl_->Init();
 }
 
 }  // namespace chromeos