int.html

JSP中文介绍,对于菜鸟有用

on either side.
Spaces are either left-to-right or right-to-left characters depending on what 
is next to them. If the characters on both sides of a space are the same 
kind of character, the space is that kind of character too. Spaces between 
Arabic words are treated like Arabic characters, and spaces between English 
words are treated like English characters. When the characters on both sides 
are different, spaces are treated like the overall direction of the paragraph:
If the paragraph as a whole is left-to-right, the space is left-to-right, and 
if the paragraph as a whole is right-to-left, the space is right-to-left.
<P>
In the Hit Test sample, the overall text is right-to-left. The spaces on each 
side of <I>Hello</I> each have one neighbor that is left-to-right (the English) 
and one that is right-to-left (the Hebrew). Because the text is right-to-left,
the spaces are right-to-left too, and the split carets appear next to the <I>o</I> 
and <I>H</I> because the spaces being right-to-left belong to the right-to-left 
text on either side.  
<P>
<A NAME="testing"></A>
<H3>Hit Testing</H3>

In code, a point returned by a mouse click is passed to the 
<CODE>TextLayout.hitTestChar</CODE> method, which returns a 
<CODE>TextHitInfo</CODE> object that represents the character and side of the 
character where the end user clicked. If the end user clicks on the <I>o</I>, 
the hit is to position 5.
<P>
<IMG SRC="./Art/RightCO.gif">
<P>
However, in the source text, position 5 is before the <I>H</I>, so
the <CODE>TextLayout</CODE> object checks the <CODE>TextHitInfo</CODE>
object to find out what side of the character the hit is on and  displays 
the dual carets if the hit is on the side of the <I>o</I> towards
the Hebrew. If the hit is on the side of the <I>o</I> towards the
<I>l</I>, a single caret is drawn between the <I>l</I> and the
<I>o</I> to indicate that the end user will insert English text
at that location.
<P>
The source text is initialized the way the words are spoken, and
not the way they are printed. The source text looks like this:

<PRE>
&quot;\u05D0\u05E0\u05D9 Hello 
   \u05DC\u05D0 \u05DE\u05D1\u05D9\ u05DF &quot; +
&quot;\u05E2\u05D1\u05E8\u05D9\u05EA Arabic 
   \u0644\u0645\u062C\ u0645\u0648\u0639\u0629&quot;, map);
</PRE>

<P>
The first three unicode characters and the space <CODE>\u05D0\u05E0\u05D9 </CODE>
define what you see on the display starting on the right side up to the <I>o</I>.
You can see that the <I>H</I> is next in the source code, but the <I>o</I> is
next on the display. This is because in the right-to-left run, the English
word <I>Hello</I> is turned around to display correctly in an embedded
left-to-right run.  
<P>
Determining the location of the insertion point is taken care of
by the <CODE>TextLayout</CODE> object.  All you need to do in your 
code is specify the caret colors, get the mouse click location, return 
a <CODE>TextHitInfo</CODE> object, and draw the layout and carets. 
<P>
Here is the code to initialize the colors for the strong
and weak carets:

<BLOCKQUOTE>

<PRE>
private static final Color 
  STRONG_CARET_COLOR = Color.red;
private static final Color 
  WEAK_CARET_COLOR = Color.black;
</PRE>
</BLOCKQUOTE>

Here is the code that draws the <CODE>TextLayout</CODE> and
the carets. The <CODE>insertionPoint</CODE> variable is
retrieved from a <CODE>TextHitInfo</CODE> object in the
<CODE>HitTestMouseListener</CODE> method.
If the insertion point is not between text running in different
directions, only the strong caret draws.

<PRE>
// Draw textLayout.
textLayout.draw(graphics2D, 0, 0);

// Retrieve caret Shapes for insertionIndex.
Shape[] carets = 
  textLayout.getCaretShapes(insertionIndex);

// Draw the carets.  carets[0] is the strong caret, and
// is never null.  carets[1], if it is not null, is the
// weak caret.
graphics2D.setColor(STRONG_CARET_COLOR);
graphics2D.draw(carets[0]);

if (carets[1] != null) {
  graphics2D.setColor(WEAK_CARET_COLOR);
  graphics2D.draw(carets[1]);
}
</PRE>

Here is the <CODE>HitTestMouseListener</CODE> method: 

<PRE>
private class HitTestMouseListener 
    extends MouseAdapter {

  /**
   * Compute the character position of the mouse click.
  */
  public void mouseClicked(MouseEvent e) {

    Point2D origin = computeLayoutOrigin();

    // Compute the mouse click location relative to
    // textLayout's origin.
    float clickX = (float) (e.getX() - origin.getX());
    float clickY = (float) (e.getY() - origin.getY());

    // Get the character position of the mouse click.
    TextHitInfo currentHit = 
      textLayout.hitTestChar(clickX,  clickY);
    insertionIndex = currentHit.getInsertionIndex();

    // Repaint the Component so the new caret(s) 
    // will be displayed.
    repaint();
  }
}
</PRE>

And here is the complete <A HREF="./Code/HitTestSample.java">HitTestSample.java</A>
source code.


<A NAME="highlighting"></A>
<H3>Selection Highlighting</H3>

The next figure shows how a
contiguous range of characters in the source text (on the top)
might not map to a contiguous highlight region (on the bottom)
on screen if the selection range includes left-to-right and right-to-left
characters. When the Arabic text is turned around to run right-to-left on
the display, the selected portion of the Arabic text is not contiguous 
with the <I>is</I> and space before it, althout these characters
are contiguous in the source text.
<P>
<IMG SRC="./Art/lhigh.gif">
<P>
The next figure shows how a contiguous highlight region on the 
display (on the bottom) might not map to a single contiguous range
of characters in the source text (on the top).
This point is illustrated in the next figure.
<P>
<IMG SRC="./Art/vhigh.gif">
<P>
A <CODE>TextLayout</CODE> object provides two strategies for selection 
highlighting to handle these two situations: logical highlighting and visual
highlighting.
<P>
With logical highlighting, the selected characters are always contiguous
in the source text, and the highlight region is allowed to be discontiguous
on the display.  With visual highlighting, there might be more than one
range of selected characters, but the highlight region is always contiguous. 
<P>
Logical highlighting is simpler for programmers to use because the selected
characters are always contiguous in the source. The
<CODE>TextLayout.getLogicalHighlightShape</CODE> method takes two insertion
offsets and returns a <CODE>Shape</CODE> that represents the highlight
region marked by the two offsets. A recommended way to show highlighting
is to fill the <CODE>Shape</CODE> with the highlight color, and then draw
the <CODE>TextLayout</CODE> over the <CODE>Shape</CODE>.
<P>
Here is the code to get and draw the selection range:

<PRE>
// Retrieve highlight region for selection range.
Shape highlight = 
  textLayout.getLogicalHighlightShape(
  anchorEnd, activeEnd);
// Fill the highlight region with the highlight color.
graphics2D.setColor(HIGHLIGHT_COLOR);
graphics2D.fill(highlight);
</PRE>

Here is the complete <A HREF="./Code/SelectionSample.java">SelectionSample.java</A>
source code.

<A NAME="moving"></A>
<H3>Moving the Caret</H3>

In bidirectional text, the cursor should move smoothly through
the text on the display in the direction that corresponds to 
the direction of the Arrow key being pressed. The problem, is 
that right-to-left text
is positioned in the source text in the direction it is spoken
and not in the direction it is displayed. For a caret to
have a smooth journey across the display, the character offset
does not move smoothly through the source text. This point is
illustrated by the figure.  
<P>
<IMG SRC="./Art/image33.gif">
<P>
Progressing through the three screen positions shown on the bottom
of the figure from left-to-right corresponds to progressing through
the character offsets in the source text in the order of 7, 19, and 18.
<P>
The <CODE>TextLayout</CODE> object handles the details for you. All 
your code needs to do is update the insertion index in response to
an arrow key press:

<PRE>
private class ArrowKeyListener extends KeyAdapter {
  /**
* Update the insertion index in response to an arrow key.
  */        
  private void handleArrowKey(boolean rightArrow) {
    TextHitInfo newPosition;
    if (rightArrow) {
      newPosition = 
        textLayout.getNextRightHit(insertionIndex);
    }
    else {
      newPosition = 
        textLayout.getNextLeftHit(insertionIndex);
    }

    // getNextRightHit() / getNextLeftHit() will 
    // return null if there is not a caret position 
    // to the right (left) of the current position.
    if (newPosition != null) {
      // Update insertionIndex.
      insertionIndex = newPosition.getInsertionIndex();
      // Repaint the Component so the new caret(s) 
      // will be displayed.
      repaint();
    }
  }
  public void keyPressed(KeyEvent e) {
    int keyCode = e.getKeyCode();
    if (keyCode == KeyEvent.VK_LEFT || 
      keyCode == KeyEvent.VK_RIGHT) {
        handleArrowKey(keyCode == KeyEvent.VK_RIGHT);
     }
  }
}
</PRE>

Here is the complete 
<A HREF="./Code/ArrowKeySample.java">ArrowKeySample.java</A>
source code.

<A NAME="multi"></A>
<H3>Multiline Text</H3>

As you learned in the <A HREF="style.html#multiple">Draw Multiple
Lines of Text</A> section of Lesson 2,
a <CODE>LineBreakMeasurer</CODE> breaks a paragraph
of styled text into lines to fit into the display area. 
The <CODE>LineBreakMeasurer</CODE>
object encapsulates enough information about bidirectional
text to produce a correct <CODE>TextLayout</CODE> without any additional
code on your part.
<P>
Here is the complete 
<A HREF="./Code/LineBreakSample.java">LineBreakSample.java</A> source code. 

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