Keep the suggestion window on one side and draw it upside down above

The suggestion window grows and shrinks while typing, and it was flipped
above the preedit only when the current size did not fit below. Near the
bottom of the screen it jumped up and down on every key stroke.

Decide the side with the size of a full suggestion window (3 rows) and,
when it is above the preedit, draw it upside down: the best candidate is
next to the preedit and the footer is at the top. Conversion windows are
unchanged.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: nameless911

src/renderer/win32/candidate_window.cc

@@ -329,7 +329,7 @@ void CandidateWindow::HandleMouseEvent(UINT nFlags, const CPoint& point,
     const commands::CandidateWindow::Candidate& candidate =
         candidate_window_->candidate(i);
 
-    const CRect rect = ToCRect(table_layout_->GetRowRect(i));
+    const CRect rect = ToCRect(FlipIfUpsideDown(table_layout_->GetRowRect(i)));
     if (rect.PtInRect(point)) {
       commands::SessionCommand command;
       if (close_candidatewindow) {
@@ -636,7 +636,8 @@ Rect CandidateWindow::GetSelectionRectInScreenCord() const {
       focused_array_index < candidate_window_->candidate_size()) {
     (void)candidate_window_->candidate(focused_array_index);
 
-    CRect rect = ToCRect(table_layout_->GetRowRect(focused_array_index));
+    CRect rect = ToCRect(
+        FlipIfUpsideDown(table_layout_->GetRowRect(focused_array_index)));
     ClientToScreen(&rect);
     return Rect(rect.left, rect.top, rect.Width(), rect.Height());
   }
@@ -654,7 +655,27 @@ Rect CandidateWindow::GetFirstRowInClientCord() const {
   DCHECK(table_layout_->IsLayoutFrozen()) << "Table layout is not frozen.";
   DCHECK_GT(table_layout_->number_of_rows(), 0)
       << "number of rows should be positive";
-  return table_layout_->GetRowRect(0);
+  return FlipIfUpsideDown(table_layout_->GetRowRect(0));
+}
+
+void CandidateWindow::SetUpsideDown(bool upside_down) {
+  if (upside_down_ == upside_down) {
+    return;
+  }
+  upside_down_ = upside_down;
+  if (m_hWnd != nullptr) {
+    Invalidate();
+  }
+}
+
+Rect CandidateWindow::FlipIfUpsideDown(Rect rect) const {
+  if (!upside_down_) {
+    return rect;
+  }
+  // Mirror vertically within the window so that the first row comes to the
+  // bottom and the footer comes to the top.
+  rect.origin.y = table_layout_->GetTotalSize().height - rect.Bottom();
+  return rect;
 }
 
 void CandidateWindow::DrawCells(HDC dc) {
@@ -676,15 +697,17 @@ void CandidateWindow::DrawCells(HDC dc) {
           candidate_window_->candidate(i);
       const std::wstring display_string =
           GetDisplayStringByColumn(candidate, column_type);
-      const Rect text_rect = table_layout_->GetCellRect(i, column_type);
+      const Rect text_rect =
+          FlipIfUpsideDown(table_layout_->GetCellRect(i, column_type));
       display_list.push_back(TextRenderingInfo(display_string, text_rect));
     }
     text_renderer_->RenderTextList(dc, display_list, font_type);
   }
 }
 
 void CandidateWindow::DrawVScrollBar(HDC dc) {
-  const Rect& vscroll_rect = table_layout_->GetVScrollBarRect();
+  const Rect vscroll_rect =
+      FlipIfUpsideDown(table_layout_->GetVScrollBarRect());
 
   if (!vscroll_rect.IsRectEmpty() && candidate_window_->candidate_size() > 0) {
     const int begin_index = candidate_window_->candidate(0).index();
@@ -697,8 +720,9 @@ void CandidateWindow::DrawVScrollBar(HDC dc) {
     FillSolidRect(dc, &background_crect,
                   ToColorRef(style_.scrollbar_background_color()));
 
-    const mozc::Rect& indicator_rect = table_layout_->GetVScrollIndicatorRect(
-        begin_index, end_index, candidates_total);
+    const mozc::Rect indicator_rect =
+        FlipIfUpsideDown(table_layout_->GetVScrollIndicatorRect(
+            begin_index, end_index, candidates_total));
 
     const CRect indicator_crect = ToCRect(indicator_rect);
     FillSolidRect(dc, &indicator_crect,
@@ -708,7 +732,8 @@ void CandidateWindow::DrawVScrollBar(HDC dc) {
 
 void CandidateWindow::DrawShortcutBackground(HDC dc) {
   if (table_layout_->number_of_columns() > 0) {
-    Rect shortcut_colmun_rect = table_layout_->GetColumnRect(0);
+    Rect shortcut_colmun_rect =
+        FlipIfUpsideDown(table_layout_->GetColumnRect(0));
     if (!shortcut_colmun_rect.IsRectEmpty()) {
       // Due to the mismatch of the implementation of the TableLayout class
       // and the design requiement, we have to *fix* the width and origin
@@ -727,27 +752,32 @@ void CandidateWindow::DrawShortcutBackground(HDC dc) {
 }
 
 void CandidateWindow::DrawFooter(HDC dc) {
-  const Rect& footer_rect = table_layout_->GetFooterRect();
+  const Rect footer_rect = FlipIfUpsideDown(table_layout_->GetFooterRect());
   if (!candidate_window_->has_footer() || footer_rect.IsRectEmpty()) {
     return;
   }
 
   const int footer_separator_height = style_.footer_border_colors_size();
 
   // DC pen is available in Windows 2000 and later.
+  // The separator faces the rows: at the top of the footer normally, and at
+  // the bottom of the footer when the window is upside down.
   {
     wil::unique_select_object prev_pen =
         wil::SelectObject(dc, static_cast<HPEN>(::GetStockObject(DC_PEN)));
-    for (size_t i = 0, y = footer_rect.Top(); i < footer_separator_height;
-         y++, i++) {
+    for (int i = 0; i < footer_separator_height; ++i) {
+      const int y =
+          upside_down_ ? footer_rect.Bottom() - 1 - i : footer_rect.Top() + i;
       ::SetDCPenColor(dc, ToColorRef(style_.footer_border_colors(i)));
       ::MoveToEx(dc, footer_rect.Left(), y, nullptr);
       ::LineTo(dc, footer_rect.Right(), y);
     }
   }
 
   const Rect footer_content_rect(
-      footer_rect.Left(), footer_rect.Top() + footer_separator_height,
+      footer_rect.Left(),
+      upside_down_ ? footer_rect.Top()
+                   : footer_rect.Top() + footer_separator_height,
       footer_rect.Width(), footer_rect.Height() - footer_separator_height);
 
   // Draw gradient rect in the footer area
@@ -843,8 +873,8 @@ void CandidateWindow::DrawSelectedRect(HDC dc) {
       focused_array_index < candidate_window_->candidate_size()) {
     (void)candidate_window_->candidate(focused_array_index);
 
-    const CRect selected_rect =
-        ToCRect(table_layout_->GetRowRect(focused_array_index));
+    const CRect selected_rect = ToCRect(
+        FlipIfUpsideDown(table_layout_->GetRowRect(focused_array_index)));
     FillSolidRect(dc, &selected_rect,
                   ToColorRef(style_.focused_background_color()));
 
@@ -859,7 +889,7 @@ void CandidateWindow::DrawInformationIcon(HDC dc) {
   const double scale_factor = GetDPIScalingFactor(dpi_);
   for (size_t i = 0; i < candidate_window_->candidate_size(); ++i) {
     if (candidate_window_->candidate(i).has_information_id()) {
-      CRect rect = ToCRect(table_layout_->GetRowRect(i));
+      CRect rect = ToCRect(FlipIfUpsideDown(table_layout_->GetRowRect(i)));
       rect.left = rect.right - (6.0 * scale_factor);
       rect.right = rect.right - (2.0 * scale_factor);
       rect.top += (2.0 * scale_factor);

src/renderer/win32/candidate_window.h

@@ -117,9 +117,17 @@ class CandidateWindow : public ATL::CWindowImpl<CandidateWindow, ATL::CWindow,
   Rect GetCandidateColumnInClientCord() const;
   Rect GetFirstRowInClientCord() const;
 
+  // When |upside_down| is true, the rows are drawn from the bottom (the first
+  // candidate at the bottom) and the footer is drawn at the top. This is used
+  // when the window is placed above the preedit.
+  void SetUpsideDown(bool upside_down);
+
  private:
   void DoPaint(HDC dc);
 
+  // Converts a rect from |table_layout_| according to |upside_down_|.
+  Rect FlipIfUpsideDown(Rect rect) const;
+
   void DrawCells(HDC dc);
   void DrawVScrollBar(HDC dc);
   void DrawShortcutBackground(HDC dc);
@@ -206,6 +214,7 @@ class CandidateWindow : public ATL::CWindowImpl<CandidateWindow, ATL::CWindow,
   int indicator_width_;
   bool metrics_changed_;
   bool mouse_moving_;
+  bool upside_down_ = false;
   RendererStyle style_;
 };
 

src/renderer/win32/window_manager.cc

@@ -281,10 +281,39 @@ void WindowManager::UpdateLayout(const commands::RendererCommand& command) {
     if (!vertical) {
       new_target_point.y = preedit_rect.Bottom();
     }
+    // The suggestion window grows and shrinks while typing, and WindowUtil
+    // flips it above the preedit only when it does not fit below. To keep it
+    // from jumping up and down, decide the side with the size of a full
+    // suggestion window instead of the current one.
+    const bool is_suggestion =
+        !vertical && candidate_window.category() == commands::SUGGESTION;
+    Size placement_size = main_window_size;
+    if (is_suggestion) {
+      constexpr int kMaxSuggestionRows = 3;
+      const int rows = candidate_window.candidate_size();
+      if (rows < kMaxSuggestionRows) {
+        placement_size.height += (kMaxSuggestionRows - rows) *
+                                 main_window_->GetFirstRowInClientCord().Height();
+      }
+    }
     main_window_rect =
         WindowUtil::GetWindowRectForMainWindowFromTargetPointAndPreedit(
-            new_target_point, preedit_rect, main_window_size,
+            new_target_point, preedit_rect, placement_size,
             main_window_zero_point, working_area, vertical);
+
+    // When the suggestion window is above the preedit, anchor its bottom to
+    // the preedit and draw it upside down so that the best candidate is the
+    // closest to the preedit.
+    bool upside_down = false;
+    if (is_suggestion) {
+      upside_down = main_window_rect.Top() < preedit_rect.Top();
+      if (upside_down) {
+        main_window_rect.origin.y =
+            main_window_rect.Bottom() - main_window_size.height;
+      }
+      main_window_rect.size.height = main_window_size.height;
+    }
+    main_window_->SetUpsideDown(upside_down);
   }
 
   const DWORD set_windows_pos_flags = SWP_NOACTIVATE | SWP_SHOWWINDOW;