gcc/libjava/classpath/javax/swing/text/Utilities.java

/* Utilities.java --
   Copyright (C) 2004, 2005, 2006  Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
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02110-1301 USA.

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permission to link this library with independent modules to produce an
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package javax.swing.text;

import java.awt.FontMetrics;
import java.awt.Graphics;
import java.awt.Point;
import java.text.BreakIterator;

import javax.swing.SwingConstants;
import javax.swing.text.Position.Bias;

/**
 * A set of utilities to deal with text. This is used by several other classes
 * inside this package.
 *
 * @author Roman Kennke (roman@ontographics.com)
 * @author Robert Schuster (robertschuster@fsfe.org)
 */
public class Utilities
{
  /**
   * The length of the char buffer that holds the characters to be drawn.
   */
  private static final int BUF_LENGTH = 64;

  /**
   * Creates a new <code>Utilities</code> object.
   */
  public Utilities()
  {
    // Nothing to be done here.
  }

  /**
   * Draws the given text segment. Contained tabs and newline characters
   * are taken into account. Tabs are expanded using the
   * specified {@link TabExpander}.
   *
   *
   * The X and Y coordinates denote the start of the <em>baseline</em> where
   * the text should be drawn.
   *
   * @param s the text fragment to be drawn.
   * @param x the x position for drawing.
   * @param y the y position for drawing.
   * @param g the {@link Graphics} context for drawing.
   * @param e the {@link TabExpander} which specifies the Tab-expanding
   *     technique.
   * @param startOffset starting offset in the text.
   * @return the x coordinate at the end of the drawn text.
   */
  public static final int drawTabbedText(Segment s, int x, int y, Graphics g,
                                         TabExpander e, int startOffset)
  {
    // This buffers the chars to be drawn.
    char[] buffer = s.array;

    // The font metrics of the current selected font.
    FontMetrics metrics = g.getFontMetrics();
    int ascent = metrics.getAscent();

    // The current x and y pixel coordinates.
    int pixelX = x;
    int pixelY = y - ascent;

    int pixelWidth = 0;
    int pos = s.offset;
    int len = 0;
    
    int end = s.offset + s.count;

    for (int offset = s.offset; offset < end; ++offset)
      {
        char c = buffer[offset];
        if (c == '\t' || c == '\n')
          {
            if (len > 0) {
              g.drawChars(buffer, pos, len, pixelX, pixelY + ascent);            
              pixelX += pixelWidth;
              pixelWidth = 0;
            }
            pos = offset+1;
            len = 0;
          }
        
	switch (c)
	  {
	  case '\t':
	    // In case we have a tab, we just 'jump' over the tab.
	    // When we have no tab expander we just use the width of ' '.
	    if (e != null)
	      pixelX = (int) e.nextTabStop((float) pixelX,
					   startOffset + offset - s.offset);
	    else
	      pixelX += metrics.charWidth(' ');
	    break;
	  case '\n':
	    // In case we have a newline, we must jump to the next line.
	    pixelY += metrics.getHeight();
	    pixelX = x;
	    break;
	  default:
            ++len;
	    pixelWidth += metrics.charWidth(buffer[offset]);
	    break;
	  }
      }

    if (len > 0)
      g.drawChars(buffer, pos, len, pixelX, pixelY + ascent);            
    
    return pixelX + pixelWidth;
  }

  /**
   * Determines the width, that the given text <code>s</code> would take
   * if it was printed with the given {@link java.awt.FontMetrics} on the
   * specified screen position.
   * @param s the text fragment
   * @param metrics the font metrics of the font to be used
   * @param x the x coordinate of the point at which drawing should be done
   * @param e the {@link TabExpander} to be used
   * @param startOffset the index in <code>s</code> where to start
   * @returns the width of the given text s. This takes tabs and newlines
   * into account.
   */
  public static final int getTabbedTextWidth(Segment s, FontMetrics metrics,
                                             int x, TabExpander e,
                                             int startOffset)
  {
    // This buffers the chars to be drawn.
    char[] buffer = s.array;

    // The current x coordinate.
    int pixelX = x;

    // The current maximum width.
    int maxWidth = 0;

    for (int offset = s.offset; offset < (s.offset + s.count); ++offset)
      {
	switch (buffer[offset])
	  {
	  case '\t':
	    // In case we have a tab, we just 'jump' over the tab.
	    // When we have no tab expander we just use the width of 'm'.
	    if (e != null)
	      pixelX = (int) e.nextTabStop((float) pixelX,
					   startOffset + offset - s.offset);
	    else
	      pixelX += metrics.charWidth(' ');
	    break;
	  case '\n':
	    // In case we have a newline, we must 'draw'
	    // the buffer and jump on the next line.
	    pixelX += metrics.charWidth(buffer[offset]);
	    maxWidth = Math.max(maxWidth, pixelX - x);
	    pixelX = x;
	    break;
	  default:
	    // Here we draw the char.
	    pixelX += metrics.charWidth(buffer[offset]);
	    break;
	  }
      }

    // Take the last line into account.
    maxWidth = Math.max(maxWidth, pixelX - x);

    return maxWidth;
  }

  /**
   * Provides a facility to map screen coordinates into a model location. For a
   * given text fragment and start location within this fragment, this method
   * determines the model location so that the resulting fragment fits best
   * into the span <code>[x0, x]</code>.
   *
   * The parameter <code>round</code> controls which model location is returned
   * if the view coordinates are on a character: If <code>round</code> is
   * <code>true</code>, then the result is rounded up to the next character, so
   * that the resulting fragment is the smallest fragment that is larger than
   * the specified span. If <code>round</code> is <code>false</code>, then the
   * resulting fragment is the largest fragment that is smaller than the
   * specified span.
   *
   * @param s the text segment
   * @param fm the font metrics to use
   * @param x0 the starting screen location
   * @param x the target screen location at which the requested fragment should
   *        end
   * @param te the tab expander to use; if this is <code>null</code>, TABs are
   *        expanded to one space character
   * @param p0 the starting model location
   * @param round if <code>true</code> round up to the next location, otherwise
   *        round down to the current location
   *
   * @return the model location, so that the resulting fragment fits within the
   *         specified span
   */
  public static final int getTabbedTextOffset(Segment s, FontMetrics fm, int x0,
                                              int x, TabExpander te, int p0,
                                              boolean round)
  {
    // At the end of the for loop, this holds the requested model location
    int pos;
    int currentX = x0;
    int width = 0;
    
    for (pos = 0; pos < s.count; pos++)
      {
        char nextChar = s.array[s.offset+pos];
        
        if (nextChar == 0)
            break;
        
        if (nextChar != '\t')
          width = fm.charWidth(nextChar);
        else
          {
            if (te == null)
              width = fm.charWidth(' ');
            else
              width = ((int) te.nextTabStop(currentX, pos)) - currentX;
          }
        
        if (round)
          {
            if (currentX + (width>>1) > x)
              break;
          }
        else
          {
            if (currentX + width > x)
              break;
          }
        
        currentX += width;
      }

    return pos + p0;
  }

  /**
   * Provides a facility to map screen coordinates into a model location. For a
   * given text fragment and start location within this fragment, this method
   * determines the model location so that the resulting fragment fits best
   * into the span <code>[x0, x]</code>.
   *
   * This method rounds up to the next location, so that the resulting fragment
   * will be the smallest fragment of the text, that is greater than the
   * specified span.
   *
   * @param s the text segment
   * @param fm the font metrics to use
   * @param x0 the starting screen location
   * @param x the target screen location at which the requested fragment should
   *        end
   * @param te the tab expander to use; if this is <code>null</code>, TABs are
   *        expanded to one space character
   * @param p0 the starting model location
   *
   * @return the model location, so that the resulting fragment fits within the
   *         specified span
   */
  public static final int getTabbedTextOffset(Segment s, FontMetrics fm, int x0,
                                              int x, TabExpander te, int p0)
  {
    return getTabbedTextOffset(s, fm, x0, x, te, p0, true);
  }
  
  /**
   * Finds the start of the next word for the given offset.
   * 
   * @param c
   *          the text component
   * @param offs
   *          the offset in the document
   * @return the location in the model of the start of the next word.
   * @throws BadLocationException
   *           if the offset is invalid.
   */
  public static final int getNextWord(JTextComponent c, int offs)
      throws BadLocationException
  {
    if (offs < 0 || offs > (c.getText().length() - 1))
      throw new BadLocationException("invalid offset specified", offs);
    String text = c.getText();
    BreakIterator wb = BreakIterator.getWordInstance();
    wb.setText(text);
        
    int last = wb.following(offs);
    int current = wb.next();
    int cp;

    while (current != BreakIterator.DONE)
      {
        for (int i = last; i < current; i++)
          {
            cp = text.codePointAt(i);
            
            // Return the last found bound if there is a letter at the current
            // location or is not whitespace (meaning it is a number or
            // punctuation). The first case means that 'last' denotes the
            // beginning of a word while the second case means it is the start
            // of something else.
            if (Character.isLetter(cp)
                || !Character.isWhitespace(cp))
              return last;
          }
        last = current;
        current = wb.next();
      }
    
    throw new BadLocationException("no more words", offs);
  }

  /**
   * Finds the start of the previous word for the given offset.
   * 
   * @param c
   *          the text component
   * @param offs
   *          the offset in the document
   * @return the location in the model of the start of the previous word.
   * @throws BadLocationException
   *           if the offset is invalid.
   */
  public static final int getPreviousWord(JTextComponent c, int offs)
      throws BadLocationException
  {
    String text = c.getText();
    
    if (offs <= 0 || offs > text.length())
      throw new BadLocationException("invalid offset specified", offs);
    
    BreakIterator wb = BreakIterator.getWordInstance();
    wb.setText(text);
    int last = wb.preceding(offs);
    int current = wb.previous();
    int cp;

    while (current != BreakIterator.DONE)
      {
        for (int i = last; i < offs; i++)
          {
            cp = text.codePointAt(i);
            
            // Return the last found bound if there is a letter at the current
            // location or is not whitespace (meaning it is a number or
            // punctuation). The first case means that 'last' denotes the
            // beginning of a word while the second case means it is the start
            // of some else.
            if (Character.isLetter(cp)
                || !Character.isWhitespace(cp))
              return last;
          }
        last = current;
        current = wb.previous();
      }
    
    return 0;
  }
  
  /**
   * Finds the start of a word for the given location.
   * @param c the text component
   * @param offs the offset location
   * @return the location of the word beginning
   * @throws BadLocationException if the offset location is invalid
   */
  public static final int getWordStart(JTextComponent c, int offs)
      throws BadLocationException
  {
    String text = c.getText();
    
    if (offs < 0 || offs > text.length())
      throw new BadLocationException("invalid offset specified", offs);
    
    BreakIterator wb = BreakIterator.getWordInstance();
    wb.setText(text);

    if (wb.isBoundary(offs))
      return offs;

    return wb.preceding(offs);
  }
  
  /**
   * Finds the end of a word for the given location.
   * @param c the text component
   * @param offs the offset location
   * @return the location of the word end
   * @throws BadLocationException if the offset location is invalid
   */
  public static final int getWordEnd(JTextComponent c, int offs)
      throws BadLocationException
  {
    if (offs < 0 || offs >= c.getText().length())
      throw new BadLocationException("invalid offset specified", offs);
    
    String text = c.getText();
    BreakIterator wb = BreakIterator.getWordInstance();
    wb.setText(text);
    return wb.following(offs);
  }
  
  /**
   * Get the model position of the end of the row that contains the 
   * specified model position.  Return null if the given JTextComponent
   * does not have a size.
   * @param c the JTextComponent
   * @param offs the model position
   * @return the model position of the end of the row containing the given 
   * offset
   * @throws BadLocationException if the offset is invalid
   */
  public static final int getRowEnd(JTextComponent c, int offs)
      throws BadLocationException
  {
    String text = c.getText();
    if (text == null)
      return -1;

    // Do a binary search for the smallest position X > offs
    // such that that character at positino X is not on the same
    // line as the character at position offs
    int high = offs + ((text.length() - 1 - offs) / 2);
    int low = offs;
    int oldHigh = text.length() + 1;
    while (true)
      {
        if (c.modelToView(high).y != c.modelToView(offs).y)
          {
            oldHigh = high;
            high = low + ((high + 1 - low) / 2);
            if (oldHigh == high)
              return high - 1;
          }
        else
          {
            low = high;
            high += ((oldHigh - high) / 2);
            if (low == high)
              return low;
          }
      }
  }
      
  /**
   * Get the model position of the start of the row that contains the specified
   * model position. Return null if the given JTextComponent does not have a
   * size.
   * 
   * @param c the JTextComponent
   * @param offs the model position
   * @return the model position of the start of the row containing the given
   *         offset
   * @throws BadLocationException if the offset is invalid
   */
  public static final int getRowStart(JTextComponent c, int offs)
      throws BadLocationException
  {
    String text = c.getText();
    if (text == null)
      return -1;

    // Do a binary search for the greatest position X < offs
    // such that the character at position X is not on the same
    // row as the character at position offs
    int high = offs;
    int low = 0;
    int oldLow = 0;
    while (true)
      {
        if (c.modelToView(low).y != c.modelToView(offs).y)
          {
            oldLow = low;
            low = high - ((high + 1 - low) / 2);
            if (oldLow == low)
              return low + 1;
          }
        else
          {
            high = low;
            low -= ((low - oldLow) / 2);
            if (low == high)
              return low;
          }
      }
  }
  
  /**
   * Determine where to break the text in the given Segment, attempting to find
   * a word boundary.
   * @param s the Segment that holds the text
   * @param metrics the font metrics used for calculating the break point
   * @param x0 starting view location representing the start of the text
   * @param x the target view location
   * @param e the TabExpander used for expanding tabs (if this is null tabs
   * are expanded to 1 space)
   * @param startOffset the offset in the Document of the start of the text
   * @return the offset at which we should break the text
   */
  public static final int getBreakLocation(Segment s, FontMetrics metrics,
                                           int x0, int x, TabExpander e,
                                           int startOffset)
  {
    int mark = Utilities.getTabbedTextOffset(s, metrics, x0, x, e, startOffset, false);
    BreakIterator breaker = BreakIterator.getWordInstance();
    breaker.setText(s);

    // If startOffset and s.offset differ then we need to use
    // that difference two convert the offset between the two metrics. 
    int shift = startOffset - s.offset;
    
    // If mark is equal to the end of the string, just use that position.
    if (mark >= shift + s.count)
      return mark;
    
    // Try to find a word boundary previous to the mark at which we 
    // can break the text.
    int preceding = breaker.preceding(mark + 1 - shift);
    
    if (preceding != 0)
      return preceding + shift;
    
    // If preceding is 0 we couldn't find a suitable word-boundary so
    // just break it on the character boundary
    return mark;
  }

  /**
   * Returns the paragraph element in the text component <code>c</code> at
   * the specified location <code>offset</code>.
   *
   * @param c the text component
   * @param offset the offset of the paragraph element to return
   *
   * @return the paragraph element at <code>offset</code>
   */
  public static final Element getParagraphElement(JTextComponent c, int offset)
  {
    Document doc = c.getDocument();
    Element par = null;
    if (doc instanceof StyledDocument)
      {
        StyledDocument styledDoc = (StyledDocument) doc;
        par = styledDoc.getParagraphElement(offset);
      }
    else
      {
        Element root = c.getDocument().getDefaultRootElement();
        int parIndex = root.getElementIndex(offset);
        par = root.getElement(parIndex);
      }
    return par;
  }

  /**
   * Returns the document position that is closest above to the specified x
   * coordinate in the row containing <code>offset</code>.
   *
   * @param c the text component
   * @param offset the offset
   * @param x the x coordinate
   *
   * @return  the document position that is closest above to the specified x
   *          coordinate in the row containing <code>offset</code>
   *
   * @throws BadLocationException if <code>offset</code> is not a valid offset
   */
  public static final int getPositionAbove(JTextComponent c, int offset, int x)
    throws BadLocationException
  {
    int offs = getRowStart(c, offset);
    
    if(offs == -1)
      return -1;

    // Effectively calculates the y value of the previous line.
    Point pt = c.modelToView(offs-1).getLocation();
    
    pt.x = x;
    
    // Calculate a simple fitting offset.
    offs = c.viewToModel(pt);
    
    // Find out the real x positions of the calculated character and its
    // neighbour.
    int offsX = c.modelToView(offs).getLocation().x;
    int offsXNext = c.modelToView(offs+1).getLocation().x;
    
    // Chose the one which is nearer to us and return its offset.
    if (Math.abs(offsX-x) <= Math.abs(offsXNext-x))
      return offs;
    else
      return offs+1;
  }

  /**
   * Returns the document position that is closest below to the specified x
   * coordinate in the row containing <code>offset</code>.
   *
   * @param c the text component
   * @param offset the offset
   * @param x the x coordinate
   *
   * @return  the document position that is closest above to the specified x
   *          coordinate in the row containing <code>offset</code>
   *
   * @throws BadLocationException if <code>offset</code> is not a valid offset
   */
  public static final int getPositionBelow(JTextComponent c, int offset, int x)
    throws BadLocationException
  {
    int offs = getRowEnd(c, offset);
    
    if(offs == -1)
      return -1;

    Point pt = null;
    
    // Note: Some views represent the position after the last
    // typed character others do not. Converting offset 3 in "a\nb"
    // in a PlainView will return a valid rectangle while in a
    // WrappedPlainView this will throw a BadLocationException.
    // This behavior has been observed in the RI.
    try
      {
        // Effectively calculates the y value of the next line.
        pt = c.modelToView(offs+1).getLocation();
      }
    catch(BadLocationException ble)
      {
        return offset;
      }
    
    pt.x = x;
    
    // Calculate a simple fitting offset.
    offs = c.viewToModel(pt);
    
    if (offs == c.getDocument().getLength())
      return offs;

    // Find out the real x positions of the calculated character and its
    // neighbour.
    int offsX = c.modelToView(offs).getLocation().x;
    int offsXNext = c.modelToView(offs+1).getLocation().x;
    
    // Chose the one which is nearer to us and return its offset.
    if (Math.abs(offsX-x) <= Math.abs(offsXNext-x))
      return offs;
    else
      return offs+1;
    }
  
  /** This is an internal helper method which is used by the
   * <code>javax.swing.text</code> package. It simply delegates the
   * call to a method with the same name on the <code>NavigationFilter</code>
   * of the provided <code>JTextComponent</code> (if it has one) or its UI.
   * 
   * If the underlying method throws a <code>BadLocationException</code> it
   * will be swallowed and the initial offset is returned.
   */
  static int getNextVisualPositionFrom(JTextComponent t, int offset, int direction)
  {
    NavigationFilter nf = t.getNavigationFilter();
    
    try
      {
        return (nf != null) 
          ? nf.getNextVisualPositionFrom(t,
                                         offset,
                                         Bias.Forward,
                                         direction,
                                         null)
          : t.getUI().getNextVisualPositionFrom(t,
                                                offset,
                                                Bias.Forward,
                                                direction,
                                                null);
      }
    catch (BadLocationException ble)
    {
      return offset;
    }
    
  }
  
}