public final class LineBreakMeasurer extends Object
LineBreakMeasurer class allows styled text to be
broken into lines (or segments) that fit within a particular visual
advance. This is useful for clients who wish to display a paragraph of
text that fits within a specific width, called the wrapping
width.
LineBreakMeasurer is constructed with an iterator over
styled text. The iterator's range should be a single paragraph in the
text.
LineBreakMeasurer maintains a position in the text for the
start of the next text segment. Initially, this position is the
start of text. Paragraphs are assigned an overall direction (either
left-to-right or right-to-left) according to the bidirectional
formatting rules. All segments obtained from a paragraph have the
same direction as the paragraph.
Segments of text are obtained by calling the method
nextLayout, which returns a TextLayout
representing the text that fits within the wrapping width.
The nextLayout method moves the current position
to the end of the layout returned from nextLayout.
LineBreakMeasurer implements the most commonly used
line-breaking policy: Every word that fits within the wrapping
width is placed on the line. If the first word does not fit, then all
of the characters that fit within the wrapping width are placed on the
line. At least one character is placed on each line.
The TextLayout instances returned by
LineBreakMeasurer treat tabs like 0-width spaces. Clients
who wish to obtain tab-delimited segments for positioning should use
the overload of nextLayout which takes a limiting offset
in the text.
The limiting offset should be the first character after the tab.
The TextLayout objects returned from this method end
at the limit provided (or before, if the text between the current
position and the limit won't fit entirely within the wrapping
width).
Clients who are laying out tab-delimited text need a slightly
different line-breaking policy after the first segment has been
placed on a line. Instead of fitting partial words in the
remaining space, they should place words which don't fit in the
remaining space entirely on the next line. This change of policy
can be requested in the overload of nextLayout which
takes a boolean parameter. If this parameter is
true, nextLayout returns
null if the first word won't fit in
the given space. See the tab sample below.
In general, if the text used to construct the
LineBreakMeasurer changes, a new
LineBreakMeasurer must be constructed to reflect
the change. (The old LineBreakMeasurer continues to
function properly, but it won't be aware of the text change.)
Nevertheless, if the text change is the insertion or deletion of a
single character, an existing LineBreakMeasurer can be
'updated' by calling insertChar or
deleteChar. Updating an existing
LineBreakMeasurer is much faster than creating a new one.
Clients who modify text based on user typing should take advantage
of these methods.
Examples:
Rendering a paragraph in a component
public void paint(Graphics graphics) {
Point2D pen = new Point2D(10, 20);
Graphics2D g2d = (Graphics2D)graphics;
FontRenderContext frc = g2d.getFontRenderContext();
// let styledText be an AttributedCharacterIterator containing at least
// one character
LineBreakMeasurer measurer = new LineBreakMeasurer(styledText, frc);
float wrappingWidth = getSize().width - 15;
while (measurer.getPosition() < fStyledText.length()) {
TextLayout layout = measurer.nextLayout(wrappingWidth);
pen.y += (layout.getAscent());
float dx = layout.isLeftToRight() ?
0 : (wrappingWidth - layout.getAdvance());
layout.draw(graphics, pen.x + dx, pen.y);
pen.y += layout.getDescent() + layout.getLeading();
}
}
Rendering text with tabs. For simplicity, the overall text direction is assumed to be left-to-right
public void paint(Graphics graphics) {
float leftMargin = 10, rightMargin = 310;
float[] tabStops = { 100, 250 };
// assume styledText is an AttributedCharacterIterator, and the number
// of tabs in styledText is tabCount
int[] tabLocations = new int[tabCount+1];
int i = 0;
for (char c = styledText.first(); c != styledText.DONE; c = styledText.next()) {
if (c == '\t') {
tabLocations[i++] = styledText.getIndex();
}
}
tabLocations[tabCount] = styledText.getEndIndex() - 1;
// Now tabLocations has an entry for every tab's offset in
// the text. For convenience, the last entry is tabLocations
// is the offset of the last character in the text.
LineBreakMeasurer measurer = new LineBreakMeasurer(styledText);
int currentTab = 0;
float verticalPos = 20;
while (measurer.getPosition() < styledText.getEndIndex()) {
// Lay out and draw each line. All segments on a line
// must be computed before any drawing can occur, since
// we must know the largest ascent on the line.
// TextLayouts are computed and stored in a Vector;
// their horizontal positions are stored in a parallel
// Vector.
// lineContainsText is true after first segment is drawn
boolean lineContainsText = false;
boolean lineComplete = false;
float maxAscent = 0, maxDescent = 0;
float horizontalPos = leftMargin;
Vector layouts = new Vector(1);
Vector penPositions = new Vector(1);
while (!lineComplete) {
float wrappingWidth = rightMargin - horizontalPos;
TextLayout layout =
measurer.nextLayout(wrappingWidth,
tabLocations[currentTab]+1,
lineContainsText);
// layout can be null if lineContainsText is true
if (layout != null) {
layouts.addElement(layout);
penPositions.addElement(new Float(horizontalPos));
horizontalPos += layout.getAdvance();
maxAscent = Math.max(maxAscent, layout.getAscent());
maxDescent = Math.max(maxDescent,
layout.getDescent() + layout.getLeading());
} else {
lineComplete = true;
}
lineContainsText = true;
if (measurer.getPosition() == tabLocations[currentTab]+1) {
currentTab++;
}
if (measurer.getPosition() == styledText.getEndIndex())
lineComplete = true;
else if (horizontalPos >= tabStops[tabStops.length-1])
lineComplete = true;
if (!lineComplete) {
// move to next tab stop
int j;
for (j=0; horizontalPos >= tabStops[j]; j++) {}
horizontalPos = tabStops[j];
}
}
verticalPos += maxAscent;
Enumeration layoutEnum = layouts.elements();
Enumeration positionEnum = penPositions.elements();
// now iterate through layouts and draw them
while (layoutEnum.hasMoreElements()) {
TextLayout nextLayout = (TextLayout) layoutEnum.nextElement();
Float nextPosition = (Float) positionEnum.nextElement();
nextLayout.draw(graphics, nextPosition.floatValue(), verticalPos);
}
verticalPos += maxDescent;
}
}
TextLayout| Constructor and Description |
|---|
LineBreakMeasurer(AttributedCharacterIterator text,
BreakIterator breakIter,
FontRenderContext frc)
Constructs a
LineBreakMeasurer for the specified text. |
LineBreakMeasurer(AttributedCharacterIterator text,
FontRenderContext frc)
Constructs a
LineBreakMeasurer for the specified text. |
| Modifier and Type | Method and Description |
|---|---|
void |
deleteChar(AttributedCharacterIterator newParagraph,
int deletePos)
Updates this
LineBreakMeasurer after a single
character is deleted from the text, and sets the current
position to the beginning of the paragraph. |
int |
getPosition()
Returns the current position of this
LineBreakMeasurer. |
void |
insertChar(AttributedCharacterIterator newParagraph,
int insertPos)
Updates this
LineBreakMeasurer after a single
character is inserted into the text, and sets the current
position to the beginning of the paragraph. |
TextLayout |
nextLayout(float wrappingWidth)
Returns the next layout, and updates the current position.
|
TextLayout |
nextLayout(float wrappingWidth,
int offsetLimit,
boolean requireNextWord)
Returns the next layout, and updates the current position.
|
int |
nextOffset(float wrappingWidth)
Returns the position at the end of the next layout.
|
int |
nextOffset(float wrappingWidth,
int offsetLimit,
boolean requireNextWord)
Returns the position at the end of the next layout.
|
void |
setPosition(int newPosition)
Sets the current position of this
LineBreakMeasurer. |
public LineBreakMeasurer(AttributedCharacterIterator text, FontRenderContext frc)
LineBreakMeasurer for the specified text.text - the text for which this LineBreakMeasurer
produces TextLayout objects; the text must contain
at least one character; if the text available through
iter changes, further calls to this
LineBreakMeasurer instance are undefined (except,
in some cases, when insertChar or
deleteChar are invoked afterward - see below)frc - contains information about a graphics device which is
needed to measure the text correctly;
text measurements can vary slightly depending on the
device resolution, and attributes such as antialiasing; this
parameter does not specify a translation between the
LineBreakMeasurer and user spaceinsertChar(java.text.AttributedCharacterIterator, int),
deleteChar(java.text.AttributedCharacterIterator, int)public LineBreakMeasurer(AttributedCharacterIterator text, BreakIterator breakIter, FontRenderContext frc)
LineBreakMeasurer for the specified text.text - the text for which this LineBreakMeasurer
produces TextLayout objects; the text must contain
at least one character; if the text available through
iter changes, further calls to this
LineBreakMeasurer instance are undefined (except,
in some cases, when insertChar or
deleteChar are invoked afterward - see below)breakIter - the BreakIterator which defines line
breaksfrc - contains information about a graphics device which is
needed to measure the text correctly;
text measurements can vary slightly depending on the
device resolution, and attributes such as antialiasing; this
parameter does not specify a translation between the
LineBreakMeasurer and user spaceIllegalArgumentException - if the text has less than one characterinsertChar(java.text.AttributedCharacterIterator, int),
deleteChar(java.text.AttributedCharacterIterator, int)public int nextOffset(float wrappingWidth)
LineBreakMeasurer.wrappingWidth - the maximum visible advance permitted for
the text in the next layoutTextLayout.public int nextOffset(float wrappingWidth,
int offsetLimit,
boolean requireNextWord)
LineBreakMeasurer.wrappingWidth - the maximum visible advance permitted for
the text in the next layoutoffsetLimit - the first character that can not be included
in the next layout, even if the text after the limit would fit
within the wrapping width; offsetLimit must be
greater than the current positionrequireNextWord - if true, the current position
that is returned if the entire next word does not fit within
wrappingWidth; if false, the offset
returned is at least one greater than the current positionTextLayoutpublic TextLayout nextLayout(float wrappingWidth)
wrappingWidth - the maximum visible advance permitted for
the text in the next layoutTextLayout, beginning at the current
position, which represents the next line fitting within
wrappingWidthpublic TextLayout nextLayout(float wrappingWidth, int offsetLimit, boolean requireNextWord)
wrappingWidth - the maximum visible advance permitted
for the text in the next layoutoffsetLimit - the first character that can not be
included in the next layout, even if the text after the limit
would fit within the wrapping width; offsetLimit
must be greater than the current positionrequireNextWord - if true, and if the entire word
at the current position does not fit within the wrapping width,
null is returned. If false, a valid
layout is returned that includes at least the character at the
current positionTextLayout, beginning at the current
position, that represents the next line fitting within
wrappingWidth. If the current position is at the end
of the text used by this LineBreakMeasurer,
null is returnedpublic int getPosition()
LineBreakMeasurer.LineBreakMeasurersetPosition(int)public void setPosition(int newPosition)
LineBreakMeasurer.newPosition - the current position of this
LineBreakMeasurer; the position should be within the
text used to construct this LineBreakMeasurer (or in
the text most recently passed to insertChar
or deleteChargetPosition()public void insertChar(AttributedCharacterIterator newParagraph, int insertPos)
LineBreakMeasurer after a single
character is inserted into the text, and sets the current
position to the beginning of the paragraph.newParagraph - the text after the insertioninsertPos - the position in the text at which the character
is insertedIndexOutOfBoundsException - if insertPos is less
than the start of newParagraph or greater than
or equal to the end of newParagraphNullPointerException - if newParagraph is
nulldeleteChar(java.text.AttributedCharacterIterator, int)public void deleteChar(AttributedCharacterIterator newParagraph, int deletePos)
LineBreakMeasurer after a single
character is deleted from the text, and sets the current
position to the beginning of the paragraph.newParagraph - the text after the deletiondeletePos - the position in the text at which the character
is deletedIndexOutOfBoundsException - if deletePos is
less than the start of newParagraph or greater
than the end of newParagraphNullPointerException - if newParagraph is
nullinsertChar(java.text.AttributedCharacterIterator, int)