- java.lang.Object
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- java.awt.font.LineBreakMeasurer
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public final class LineBreakMeasurer extends Object
TheLineBreakMeasurerclass 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.LineBreakMeasureris constructed with an iterator over styled text. The iterator's range should be a single paragraph in the text.LineBreakMeasurermaintains 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 aTextLayoutrepresenting the text that fits within the wrapping width. ThenextLayoutmethod moves the current position to the end of the layout returned fromnextLayout.LineBreakMeasurerimplements 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
TextLayoutinstances returned byLineBreakMeasurertreat tabs like 0-width spaces. Clients who wish to obtain tab-delimited segments for positioning should use the overload ofnextLayoutwhich takes a limiting offset in the text. The limiting offset should be the first character after the tab. TheTextLayoutobjects 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
nextLayoutwhich takes abooleanparameter. If this parameter istrue,nextLayoutreturnsnullif the first word won't fit in the given space. See the tab sample below.In general, if the text used to construct the
LineBreakMeasurerchanges, a newLineBreakMeasurermust be constructed to reflect the change. (The oldLineBreakMeasurercontinues 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 existingLineBreakMeasurercan be 'updated' by callinginsertCharordeleteChar. Updating an existingLineBreakMeasureris 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
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Constructor Summary
Constructors Constructor Description LineBreakMeasurer(AttributedCharacterIterator text, FontRenderContext frc)Constructs aLineBreakMeasurerfor the specified text.LineBreakMeasurer(AttributedCharacterIterator text, BreakIterator breakIter, FontRenderContext frc)Constructs aLineBreakMeasurerfor the specified text.
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description voiddeleteChar(AttributedCharacterIterator newParagraph, int deletePos)Updates thisLineBreakMeasurerafter a single character is deleted from the text, and sets the current position to the beginning of the paragraph.intgetPosition()Returns the current position of thisLineBreakMeasurer.voidinsertChar(AttributedCharacterIterator newParagraph, int insertPos)Updates thisLineBreakMeasurerafter a single character is inserted into the text, and sets the current position to the beginning of the paragraph.TextLayoutnextLayout(float wrappingWidth)Returns the next layout, and updates the current position.TextLayoutnextLayout(float wrappingWidth, int offsetLimit, boolean requireNextWord)Returns the next layout, and updates the current position.intnextOffset(float wrappingWidth)Returns the position at the end of the next layout.intnextOffset(float wrappingWidth, int offsetLimit, boolean requireNextWord)Returns the position at the end of the next layout.voidsetPosition(int newPosition)Sets the current position of thisLineBreakMeasurer.
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Constructor Detail
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LineBreakMeasurer
public LineBreakMeasurer(AttributedCharacterIterator text, FontRenderContext frc)
Constructs aLineBreakMeasurerfor the specified text.- Parameters:
text- the text for which thisLineBreakMeasurerproducesTextLayoutobjects; the text must contain at least one character; if the text available throughiterchanges, further calls to thisLineBreakMeasurerinstance are undefined (except, in some cases, wheninsertCharordeleteCharare 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 theLineBreakMeasurerand user space- See Also:
insertChar(java.text.AttributedCharacterIterator, int),deleteChar(java.text.AttributedCharacterIterator, int)
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LineBreakMeasurer
public LineBreakMeasurer(AttributedCharacterIterator text, BreakIterator breakIter, FontRenderContext frc)
Constructs aLineBreakMeasurerfor the specified text.- Parameters:
text- the text for which thisLineBreakMeasurerproducesTextLayoutobjects; the text must contain at least one character; if the text available throughiterchanges, further calls to thisLineBreakMeasurerinstance are undefined (except, in some cases, wheninsertCharordeleteCharare invoked afterward - see below)breakIter- theBreakIteratorwhich 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 theLineBreakMeasurerand user space- Throws:
IllegalArgumentException- if the text has less than one character- See Also:
insertChar(java.text.AttributedCharacterIterator, int),deleteChar(java.text.AttributedCharacterIterator, int)
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Method Detail
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nextOffset
public int nextOffset(float wrappingWidth)
Returns the position at the end of the next layout. Does NOT update the current position of thisLineBreakMeasurer.- 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.
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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 thisLineBreakMeasurer.- Parameters:
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;offsetLimitmust be greater than the current positionrequireNextWord- 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
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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
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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 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;offsetLimitmust be greater than the current positionrequireNextWord- iftrue, and if the entire word at the current position does not fit within the wrapping width,nullis 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,nullis returned
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getPosition
public int getPosition()
Returns the current position of thisLineBreakMeasurer.- Returns:
- the current position of this
LineBreakMeasurer - See Also:
setPosition(int)
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setPosition
public void setPosition(int newPosition)
Sets the current position of thisLineBreakMeasurer.- 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 toinsertCharordeleteChar- See Also:
getPosition()
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insertChar
public void insertChar(AttributedCharacterIterator newParagraph, int insertPos)
Updates thisLineBreakMeasurerafter 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 insertioninsertPos- the position in the text at which the character is inserted- Throws:
IndexOutOfBoundsException- ifinsertPosis less than the start ofnewParagraphor greater than or equal to the end ofnewParagraphNullPointerException- ifnewParagraphisnull- See Also:
deleteChar(java.text.AttributedCharacterIterator, int)
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deleteChar
public void deleteChar(AttributedCharacterIterator newParagraph, int deletePos)
Updates thisLineBreakMeasurerafter 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 deletiondeletePos- the position in the text at which the character is deleted- Throws:
IndexOutOfBoundsException- ifdeletePosis less than the start ofnewParagraphor greater than the end ofnewParagraphNullPointerException- ifnewParagraphisnull- See Also:
insertChar(java.text.AttributedCharacterIterator, int)
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