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Processing is a programming language, development environment, and online community. This PDE package contains the Processing IDE.
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package processing.app.syntax.im;

import java.awt.Font;
import java.awt.FontMetrics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.Rectangle;
import java.awt.RenderingHints;
import java.awt.font.FontRenderContext;
import java.awt.font.TextAttribute;
import java.awt.font.TextLayout;
import java.text.AttributedCharacterIterator;
import java.text.AttributedString;
import java.text.CharacterIterator;

import javax.swing.text.BadLocationException;

import processing.app.Base;
import processing.app.Messages;
import processing.app.Preferences;
import processing.app.syntax.JEditTextArea;
import processing.app.syntax.TextAreaPainter;

/**
 * This class Manage texts from input method
 * by begin-process-end steps.
 *
 * First, if a user start inputing via input method,
 * beginCompositionText is called from InputMethodSupport.
 * Second, the user continues from input method, processCompositionText is called
 * and reflect user inputs to text area.
 * Finally the user try to commit text, endCompositionText is called.
 *
 * @author Takashi Maekawa ([email protected])
 */

public class CompositionTextManager {
  private JEditTextArea textArea;
  private String prevComposeString;
  private int prevCommittedCount;
  private boolean isInputProcess;
  private int initialCaretPosition;
  public static final int COMPOSING_UNDERBAR_HEIGHT = 5;

  /**
   * Create text manager class with a textarea.
   * @param textArea texarea component for PDE.
   */
  public CompositionTextManager(JEditTextArea textArea) {
    this.textArea = textArea;
    prevComposeString = "";
    isInputProcess = false;
    prevCommittedCount = 0;
  }

  /**
   * Get this text manager is whether in input process or not.
   */
  public boolean getIsInputProcess() {
    return isInputProcess;
  }
  /**
   * Insert full width space
   */
  public void insertFullWidthSpace() {
    initialCaretPosition = textArea.getCaretPosition();
    int layoutCaretPosition = initialCaretPosition;
    try {
      textArea.getDocument().insertString(layoutCaretPosition, "\u3000", null);
    } catch (BadLocationException e) {
      e.printStackTrace();
    }
  }

  /**
   * Called when a user begins input from input method.
   * This method initializes text manager.
   *
   * @param text Text from InputMethodEvent.
   * @param commited_count Numbers of committed characters in text.
   */
  public void beginCompositionText(AttributedCharacterIterator text, int committed_count) {
    isInputProcess = true;
    prevComposeString = "";
    initialCaretPosition = textArea.getCaretPosition();
    processCompositionText(text, committed_count);
  }

  /**
   * Called when a user processing input characters and
   * select candidates from input method.
   *
   * @param text Text from InputMethodEvent.
   * @param commited_count Numbers of committed characters in text.
   */
  public void processCompositionText(AttributedCharacterIterator text, int committed_count) {
    int layoutCaretPosition = initialCaretPosition + committed_count;
    CompositionTextPainter compositionPainter = textArea.getPainter().getCompositionTextpainter();
    compositionPainter.setComposedTextLayout(getTextLayout(text, committed_count), layoutCaretPosition);
    int textLength = text.getEndIndex() - text.getBeginIndex() - committed_count;
    StringBuilder unCommitedStringBuf = new StringBuilder(textLength);
    char c;
    for (c = text.setIndex(committed_count); c != CharacterIterator.DONE
        && textLength > 0; c = text.next(), --textLength) {
      unCommitedStringBuf.append(c);
    }
    String unCommittedString = unCommitedStringBuf.toString();
    try {
      if(canRemovePreviousInput(committed_count)){
        textArea.getDocument().remove(layoutCaretPosition, prevComposeString.length());
      }
      textArea.getDocument().insertString(layoutCaretPosition, unCommittedString, null);
      if(committed_count > 0){
        initialCaretPosition = initialCaretPosition + committed_count;
      }
      prevComposeString = unCommittedString;
      prevCommittedCount = committed_count;
    } catch (BadLocationException e) {
      e.printStackTrace();
    }
  }

  private boolean canRemovePreviousInput(int committed_count){
    return (prevCommittedCount == committed_count || prevCommittedCount > committed_count);
  }

  /**
   * Called when a user fixed text from input method or delete all
   * composition text. This method resets CompositionTextPainter.
   *
   * @param text Text from InputMethodEvent.
   * @param commited_count Numbers of committed characters in text.
   */
  public void endCompositionText(AttributedCharacterIterator text, int committed_count) {
    /*
     * If there are no committed characters, remove it all from textarea.
     * This case will happen if a user delete all composing characters by backspace or delete key.
     * If it does, these previous characters are needed to be deleted.
     */
    if(committed_count == 0){
      removeNotCommittedText(text);
    }
    CompositionTextPainter compositionPainter = textArea.getPainter().getCompositionTextpainter();
    compositionPainter.invalidateComposedTextLayout(initialCaretPosition + committed_count);
    prevComposeString = "";
    isInputProcess = false;
  }

  private void removeNotCommittedText(AttributedCharacterIterator text){
    if (prevComposeString.length() == 0) {
      return;
    }
    try {
        textArea.getDocument().remove(initialCaretPosition, prevComposeString.length());
    } catch (BadLocationException e) {
      e.printStackTrace();
    }
  }
  
  private TextLayout getTextLayout(AttributedCharacterIterator text, int committedCount) {
    boolean antialias = Preferences.getBoolean("editor.smooth");
    TextAreaPainter painter = textArea.getPainter();
    
    // create attributed string with font info.
    AttributedString composed = new AttributedString(text, committedCount, text.getEndIndex());
    Font font = painter.getFontMetrics().getFont();
    composed.addAttribute(TextAttribute.FONT, font);
    
    // set hint of antialiasing to render target.
    Graphics2D g2d = (Graphics2D)painter.getGraphics();
    g2d.setRenderingHint(RenderingHints.KEY_TEXT_ANTIALIASING,
                        antialias ?
                        RenderingHints.VALUE_TEXT_ANTIALIAS_ON :
                        RenderingHints.VALUE_TEXT_ANTIALIAS_OFF);
    FontRenderContext frc = g2d.getFontRenderContext();
    if (Base.DEBUG) {
      Messages.log("debug: FontRenderContext is Antialiased = " + frc.getAntiAliasingHint());
    }

    return new TextLayout(composed.getIterator(), frc);
  }

  private Point getCaretLocation() {
    Point loc = new Point();
    TextAreaPainter painter = textArea.getPainter();
    FontMetrics fm = painter.getFontMetrics();
    int offsetY = fm.getHeight() - COMPOSING_UNDERBAR_HEIGHT;
    int lineIndex = textArea.getCaretLine();
    loc.y = lineIndex * fm.getHeight() + offsetY;
    int offsetX = textArea.getCaretPosition()
        - textArea.getLineStartOffset(lineIndex);
    loc.x = textArea.offsetToX(lineIndex, offsetX);
    return loc;
  }

  public Rectangle getTextLocation() {
    Point caret = getCaretLocation();
    return getCaretRectangle(caret.x, caret.y);
  }

  private Rectangle getCaretRectangle(int x, int y) {
    TextAreaPainter painter = textArea.getPainter();
    Point origin = painter.getLocationOnScreen();
    int height = painter.getFontMetrics().getHeight();
    return new Rectangle(origin.x + x, origin.y + y, 0, height);
  }

  public AttributedCharacterIterator getCommittedText(int beginIndex, int endIndex) {
    int length = endIndex - beginIndex;
    String textAreaString = textArea.getText(beginIndex, length);
    return new AttributedString(textAreaString).getIterator();
  }

  public int getInsertPositionOffset() {
    return textArea.getCaretPosition() * -1;
  }
}