Add multi-step IME support to TextInputModel

shell/platform/common/cpp/text_input_model.cc

@@ -1,7 +1,6 @@
 // Copyright 2013 The Flutter Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
-// FLUTTER_NOLINT
 
 #include "flutter/shell/platform/common/cpp/text_input_model.h"
 
@@ -39,22 +38,75 @@ void TextInputModel::SetText(const std::string& text) {
       utf16_converter;
   text_ = utf16_converter.from_bytes(text);
   selection_ = TextRange(0);
+  composing_range_ = TextRange(0);
 }
 
 bool TextInputModel::SetSelection(const TextRange& range) {
-  if (!text_range().Contains(range)) {
+  if (composing_ && !range.collapsed()) {
+    return false;
+  }
+  if (!editable_range().Contains(range)) {
     return false;
   }
   selection_ = range;
   return true;
 }
 
+bool TextInputModel::SetComposingRange(const TextRange& range,
+                                       size_t cursor_offset) {
+  if (!composing_ || !text_range().Contains(range)) {
+    return false;
+  }
+  composing_range_ = range;
+  selection_ = TextRange(range.start() + cursor_offset);
+  return true;
+}
+
+void TextInputModel::BeginComposing() {
+  composing_ = true;
+  composing_range_ = TextRange(selection_.start());
+}
+
+void TextInputModel::UpdateComposingText(const std::string& composing_text) {
+  std::wstring_convert<std::codecvt_utf8_utf16<char16_t>, char16_t>
+      utf16_converter;
+  std::u16string text = utf16_converter.from_bytes(composing_text);
+
+  // Preserve selection if we get a no-op update to the composing region.
+  if (text.length() == 0 && composing_range_.collapsed()) {
+    return;
+  }
+  DeleteSelected();
+  text_.replace(composing_range_.start(), composing_range_.length(), text);
+  composing_range_.set_end(composing_range_.start() + text.length());
+  selection_ = TextRange(composing_range_.end());
+}
+
+void TextInputModel::CommitComposing() {
+  // Preserve selection if no composing text was entered.
+  if (composing_range_.collapsed()) {
+    return;
+  }
+  composing_range_ = TextRange(composing_range_.end());
+  selection_ = composing_range_;
+}
+
+void TextInputModel::EndComposing() {
+  composing_ = false;
+  composing_range_ = TextRange(0);
+}
+
 bool TextInputModel::DeleteSelected() {
   if (selection_.collapsed()) {
     return false;
   }
-  text_.erase(selection_.start(), selection_.length());
-  selection_ = TextRange(selection_.start());
+  size_t start = selection_.start();
+  text_.erase(start, selection_.length());
+  selection_ = TextRange(start);
+  if (composing_) {
+    // This occurs only immediately after composing has begun with a selection.
+    composing_range_ = selection_;
+  }
   return true;
 }
 
@@ -74,6 +126,12 @@ void TextInputModel::AddCodePoint(char32_t c) {
 
 void TextInputModel::AddText(const std::u16string& text) {
   DeleteSelected();
+  if (composing_) {
+    // Delete the current composing text, set the cursor to composing start.
+    text_.erase(composing_range_.start(), composing_range_.length());
+    selection_ = TextRange(composing_range_.start());
+    composing_range_.set_end(composing_range_.start() + text.length());
+  }
   size_t position = selection_.position();
   text_.insert(position, text);
   selection_ = TextRange(position + text.length());
@@ -89,12 +147,15 @@ bool TextInputModel::Backspace() {
   if (DeleteSelected()) {
     return true;
   }
-  // If there's no selection, delete the preceding codepoint.
+  // There is no selection. Delete the preceding codepoint.
   size_t position = selection_.position();
-  if (position != 0) {
+  if (position != editable_range().start()) {
     int count = IsTrailingSurrogate(text_.at(position - 1)) ? 2 : 1;
     text_.erase(position - count, count);
     selection_ = TextRange(position - count);
+    if (composing_) {
+      composing_range_.set_end(composing_range_.end() - count);
+    }
     return true;
   }
   return false;
@@ -104,62 +165,74 @@ bool TextInputModel::Delete() {
   if (DeleteSelected()) {
     return true;
   }
-  // If there's no selection, delete the preceding codepoint.
+  // There is no selection. Delete the preceding codepoint.
   size_t position = selection_.position();
-  if (position != text_.length()) {
+  if (position < editable_range().end()) {
     int count = IsLeadingSurrogate(text_.at(position)) ? 2 : 1;
     text_.erase(position, count);
+    if (composing_) {
+      composing_range_.set_end(composing_range_.end() - count);
+    }
     return true;
   }
   return false;
 }
 
 bool TextInputModel::DeleteSurrounding(int offset_from_cursor, int count) {
+  size_t max_pos = editable_range().end();
   size_t start = selection_.extent();
   if (offset_from_cursor < 0) {
     for (int i = 0; i < -offset_from_cursor; i++) {
       // If requested start is before the available text then reduce the
       // number of characters to delete.
-      if (start == 0) {
+      if (start == editable_range().start()) {
         count = i;
         break;
       }
       start -= IsTrailingSurrogate(text_.at(start - 1)) ? 2 : 1;
     }
   } else {
-    for (int i = 0; i < offset_from_cursor && start != text_.length(); i++) {
+    for (int i = 0; i < offset_from_cursor && start != max_pos; i++) {
       start += IsLeadingSurrogate(text_.at(start)) ? 2 : 1;
     }
   }
 
   auto end = start;
-  for (int i = 0; i < count && end != text_.length(); i++) {
+  for (int i = 0; i < count && end != max_pos; i++) {
     end += IsLeadingSurrogate(text_.at(start)) ? 2 : 1;
   }
 
   if (start == end) {
     return false;
   }
 
-  text_.erase(start, end - start);
+  auto deleted_length = end - start;
+  text_.erase(start, deleted_length);
 
   // Cursor moves only if deleted area is before it.
   selection_ = TextRange(offset_from_cursor <= 0 ? start : selection_.start());
 
+  // Adjust composing range.
+  if (composing_) {
+    composing_range_.set_end(composing_range_.end() - deleted_length);
+  }
   return true;
 }
 
 bool TextInputModel::MoveCursorToBeginning() {
-  if (selection_.collapsed() && selection_.position() == 0)
+  size_t min_pos = editable_range().start();
+  if (selection_.collapsed() && selection_.position() == min_pos) {
     return false;
-  selection_ = TextRange(0);
+  }
+  selection_ = TextRange(min_pos);
   return true;
 }
 
 bool TextInputModel::MoveCursorToEnd() {
-  size_t max_pos = text_.length();
-  if (selection_.collapsed() && selection_.position() == max_pos)
+  size_t max_pos = editable_range().end();
+  if (selection_.collapsed() && selection_.position() == max_pos) {
     return false;
+  }
   selection_ = TextRange(max_pos);
   return true;
 }
@@ -172,7 +245,7 @@ bool TextInputModel::MoveCursorForward() {
   }
   // Otherwise, move the cursor forward.
   size_t position = selection_.position();
-  if (position != text_.length()) {
+  if (position != editable_range().end()) {
     int count = IsLeadingSurrogate(text_.at(position)) ? 2 : 1;
     selection_ = TextRange(position + count);
     return true;
@@ -188,7 +261,7 @@ bool TextInputModel::MoveCursorBack() {
   }
   // Otherwise, move the cursor backward.
   size_t position = selection_.position();
-  if (position != 0) {
+  if (position != editable_range().start()) {
     int count = IsTrailingSurrogate(text_.at(position - 1)) ? 2 : 1;
     selection_ = TextRange(position - count);
     return true;

shell/platform/common/cpp/text_input_model.h

@@ -28,8 +28,43 @@ class TextInputModel {
   // Attempts to set the text selection.
   //
   // Returns false if the selection is not within the bounds of the text.
+  // While in composing mode, the selection is restricted to the composing
+  // range; otherwise, it is restricted to the length of the text.
   bool SetSelection(const TextRange& range);
 
+  // Attempts to set the composing range.
+  //
+  // Returns false if the range or offset are out of range for the text, or if
+  // the offset is outside the composing range.
+  bool SetComposingRange(const TextRange& range, size_t cursor_offset);
+
+  // Begins IME composing mode.
+  //
+  // Resets the composing base and extent to the selection start. The existing
+  // selection is preserved in case composing is aborted with no changes. Until
+  // |EndComposing| is called, any further changes to selection base and extent
+  // are restricted to the composing range.
+  void BeginComposing();
+
+  // Replaces the composing range with new text.
+  //
+  // If a selection of non-zero length exists, it is deleted if the composing
+  // text is non-empty. The composing range is adjusted to the length of
+  // |composing_text| and the selection base and offset are set to the end of
+  // the composing range.
+  void UpdateComposingText(const std::string& composing_text);
+
+  // Commits composing range to the string.
+  //
+  // Causes the composing base and extent to be collapsed to the end of the
+  // range.
+  void CommitComposing();
+
+  // Ends IME composing mode.
+  //
+  // Collapses the composing base and offset to 0.
+  void EndComposing();
+
   // Adds a Unicode code point.
   //
   // Either appends after the cursor (when selection base and extent are the
@@ -52,48 +87,62 @@ class TextInputModel {
   // Deletes either the selection, or one character ahead of the cursor.
   //
   // Deleting one character ahead of the cursor occurs when the selection base
-  // and extent are the same.
+  // and extent are the same. When composing is active, deletions are
+  // restricted to text between the composing base and extent.
   //
   // Returns true if any deletion actually occurred.
   bool Delete();
 
   // Deletes text near the cursor.
   //
-  // A section is made starting at @offset code points past the cursor (negative
-  // values go before the cursor). @count code points are removed. The selection
-  // may go outside the bounds of the text and will result in only the part
-  // selection that covers the available text being deleted. The existing
-  // selection is ignored and removed after this operation.
+  // A section is made starting at |offset_from_cursor| code points past the
+  // cursor (negative values go before the cursor). |count| code points are
+  // removed. The selection may go outside the bounds of the available text and
+  // will result in only the part selection that covers the available text
+  // being deleted. The existing selection is ignored and removed after this
+  // operation. When composing is active, deletions are restricted to the
+  // composing range.
   //
   // Returns true if any deletion actually occurred.
   bool DeleteSurrounding(int offset_from_cursor, int count);
 
   // Deletes either the selection, or one character behind the cursor.
   //
   // Deleting one character behind the cursor occurs when the selection base
-  // and extent are the same.
+  // and extent are the same. When composing is active, deletions are
+  // restricted to the text between the composing base and extent.
   //
   // Returns true if any deletion actually occurred.
   bool Backspace();
 
   // Attempts to move the cursor backward.
   //
   // Returns true if the cursor could be moved. If a selection is active, moves
-  // to the start of the selection.
+  // to the start of the selection. If composing is active, motion is
+  // restricted to the composing range.
   bool MoveCursorBack();
 
   // Attempts to move the cursor forward.
   //
   // Returns true if the cursor could be moved. If a selection is active, moves
-  // to the end of the selection.
+  // to the end of the selection. If composing is active, motion is restricted
+  // to the composing range.
   bool MoveCursorForward();
 
   // Attempts to move the cursor to the beginning.
   //
+  // If composing is active, the cursor is moved to the beginning of the
+  // composing range; otherwise, it is moved to the beginning of the text. If
+  // composing is active, motion is restricted to the composing range.
+  //
   // Returns true if the cursor could be moved.
   bool MoveCursorToBeginning();
 
-  // Attempts to move the cursor to the back.
+  // Attempts to move the cursor to the end.
+  //
+  // If composing is active, the cursor is moved to the end of the composing
+  // range; otherwise, it is moved to the end of the text. If composing is
+  // active, motion is restricted to the composing range.
   //
   // Returns true if the cursor could be moved.
   bool MoveCursorToEnd();
@@ -108,18 +157,36 @@ class TextInputModel {
   // The current selection.
   TextRange selection() const { return selection_; }
 
+  // The composing range.
+  //
+  // If not in composing mode, returns a collapsed range at position 0.
+  TextRange composing_range() const { return composing_range_; }
+
+  // Whether multi-step input composing mode is active.
+  bool composing() const { return composing_; }
+
  private:
   // Deletes the current selection, if any.
   //
   // Returns true if any text is deleted. The selection base and extent are
   // reset to the start of the selected range.
   bool DeleteSelected();
 
+  // Returns the currently editable text range.
+  //
+  // In composing mode, returns the composing range; otherwise, returns a range
+  // covering the entire text.
+  TextRange editable_range() const {
+    return composing_ ? composing_range_ : text_range();
+  }
+
   // Returns a range covering the entire text.
   TextRange text_range() const { return TextRange(0, text_.length()); }
 
   std::u16string text_;
   TextRange selection_ = TextRange(0);
+  TextRange composing_range_ = TextRange(0);
+  bool composing_ = false;
 };
 
 }  // namespace flutter