Class LineBreakMeasurer
- java.lang.Object
-
- java.awt.font.LineBreakMeasurer
public final class LineBreakMeasurer extends Object
The 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) { float dx = 0f, dy = 5f; Graphics2D g2d = (Graphics2D)graphics; FontRenderContext frc = g2d.getFontRenderContext(); AttributedString text = new AttributedString("....."); AttributedCharacterIterator paragraph = text.getIterator(); LineBreakMeasurer measurer = new LineBreakMeasurer(paragraph, frc); measurer.setPosition(paragraph.getBeginIndex()); float wrappingWidth = (float)getSize().width; while (measurer.getPosition() < paragraph.getEndIndex()) { TextLayout layout = measurer.nextLayout(wrappingWidth); dy += (layout.getAscent()); float dx = layout.isLeftToRight() ? 0 : (wrappingWidth - layout.getAdvance()); layout.draw(graphics, dx, dy); dy += 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; } }
- See Also:
TextLayout
Constructor Summary
Constructor | Description |
---|---|
LineBreakMeasurer(AttributedCharacterIterator text,
FontRenderContext frc) | Constructs a |
LineBreakMeasurer(AttributedCharacterIterator text,
BreakIterator breakIter,
FontRenderContext frc) | Constructs a |
Method Summary
Modifier and Type | Method | Description |
---|---|---|
void | deleteChar(AttributedCharacterIterator newParagraph,
int deletePos) | Updates this |
int | getPosition() | Returns the current position of this |
void | insertChar(AttributedCharacterIterator newParagraph,
int insertPos) | Updates this |
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 |
Methods declared in class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
Constructor Detail
LineBreakMeasurer
public LineBreakMeasurer(AttributedCharacterIterator text, FontRenderContext frc)
Constructs a LineBreakMeasurer
for the specified text.
- Parameters:
-
text
- the text for which thisLineBreakMeasurer
producesTextLayout
objects; the text must contain at least one character; if the text available throughiter
changes, further calls to thisLineBreakMeasurer
instance are undefined (except, in some cases, wheninsertChar
ordeleteChar
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 theLineBreakMeasurer
and user space - See Also:
-
insertChar(java.text.AttributedCharacterIterator, int)
,deleteChar(java.text.AttributedCharacterIterator, int)
LineBreakMeasurer
public LineBreakMeasurer(AttributedCharacterIterator text, BreakIterator breakIter, FontRenderContext frc)
Constructs a LineBreakMeasurer
for the specified text.
- Parameters:
-
text
- the text for which thisLineBreakMeasurer
producesTextLayout
objects; the text must contain at least one character; if the text available throughiter
changes, further calls to thisLineBreakMeasurer
instance are undefined (except, in some cases, wheninsertChar
ordeleteChar
are invoked afterward - see below) -
breakIter
- theBreakIterator
which defines line breaks -
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 theLineBreakMeasurer
and user space - Throws:
-
IllegalArgumentException
- if the text has less than one character - See Also:
-
insertChar(java.text.AttributedCharacterIterator, int)
,deleteChar(java.text.AttributedCharacterIterator, int)
Method Detail
nextOffset
public int nextOffset(float wrappingWidth)
Returns the position at the end of the next layout. Does NOT update the current position of this LineBreakMeasurer
.
- Parameters:
-
wrappingWidth
- the maximum visible advance permitted for the text in the next layout - Returns:
- an offset in the text representing the limit of the next
TextLayout
.
nextOffset
public int nextOffset(float wrappingWidth, int offsetLimit, boolean requireNextWord)
Returns the position at the end of the next layout. Does NOT update the current position of this LineBreakMeasurer
.
- Parameters:
-
wrappingWidth
- the maximum visible advance permitted for the text in the next layout -
offsetLimit
- 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 position -
requireNextWord
- iftrue
, the current position that is returned if the entire next word does not fit withinwrappingWidth
; iffalse
, the offset returned is at least one greater than the current position - Returns:
- an offset in the text representing the limit of the next
TextLayout
nextLayout
public TextLayout nextLayout(float wrappingWidth)
Returns the next layout, and updates the current position.
- Parameters:
-
wrappingWidth
- the maximum visible advance permitted for the text in the next layout - Returns:
- a
TextLayout
, beginning at the current position, which represents the next line fitting withinwrappingWidth
nextLayout
public TextLayout nextLayout(float wrappingWidth, int offsetLimit, boolean requireNextWord)
Returns the next layout, and updates the current position.
- Parameters:
-
wrappingWidth
- the maximum visible advance permitted for the text in the next layout -
offsetLimit
- 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 position -
requireNextWord
- iftrue
, and if the entire word at the current position does not fit within the wrapping width,null
is returned. Iffalse
, a valid layout is returned that includes at least the character at the current position - Returns:
- a
TextLayout
, beginning at the current position, that represents the next line fitting withinwrappingWidth
. If the current position is at the end of the text used by thisLineBreakMeasurer
,null
is returned
getPosition
public int getPosition()
Returns the current position of this LineBreakMeasurer
.
- Returns:
- the current position of this
LineBreakMeasurer
- See Also:
setPosition(int)
setPosition
public void setPosition(int newPosition)
Sets the current position of this LineBreakMeasurer
.
- Parameters:
-
newPosition
- the current position of thisLineBreakMeasurer
; the position should be within the text used to construct thisLineBreakMeasurer
(or in the text most recently passed toinsertChar
ordeleteChar
- See Also:
getPosition()
insertChar
public 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.
- Parameters:
-
newParagraph
- the text after the insertion -
insertPos
- the position in the text at which the character is inserted - Throws:
-
IndexOutOfBoundsException
- ifinsertPos
is less than the start ofnewParagraph
or greater than or equal to the end ofnewParagraph
-
NullPointerException
- ifnewParagraph
isnull
- See Also:
deleteChar(java.text.AttributedCharacterIterator, int)
deleteChar
public 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.
- Parameters:
-
newParagraph
- the text after the deletion -
deletePos
- the position in the text at which the character is deleted - Throws:
-
IndexOutOfBoundsException
- ifdeletePos
is less than the start ofnewParagraph
or greater than the end ofnewParagraph
-
NullPointerException
- ifnewParagraph
isnull
- See Also:
insertChar(java.text.AttributedCharacterIterator, int)