- Qt 6.8
- Qt GUI
- C++ Classes
- QTextLayout
- Qt 6.8.2 Reference Documentation

# QTextLayout Class

The QTextLayout class is used to lay out and render text. More...

Header: | `#include <QTextLayout>`
CMake: | `find_package(Qt6 REQUIRED COMPONENTS Gui)` `target_link_libraries(mytarget PRIVATE Qt6::Gui)`
qmake: | `QT += gui`

- List of all members, including inherited members
- QTextLayout is part of Rich Text Processing APIs.

Note: All functions in this class are reentrant.

## Public Types

struct | FormatRange
enum | CursorMode { SkipCharacters, SkipWords }
`(since 6.5)` enum | GlyphRunRetrievalFlag { RetrieveGlyphIndexes, RetrieveGlyphPositions, RetrieveStringIndexes, RetrieveString, RetrieveAll }
flags | GlyphRunRetrievalFlags

## Public Functions

| QTextLayout()
| QTextLayout(const QString &text)
| QTextLayout(const QString &text, const QFont &font, const QPaintDevice *paintdevice = nullptr)
| ~QTextLayout()
void | beginLayout()
QRectF | boundingRect() const
bool | cacheEnabled() const
void | clearFormats()
void | clearLayout()
QTextLine | createLine()
Qt::CursorMoveStyle | cursorMoveStyle() const
void | draw(QPainter *p, const QPointF &pos, const QList<QTextLayout::FormatRange> &selections = QList<FormatRange>(), const QRectF &clip = QRectF()) const
void | drawCursor(QPainter *painter, const QPointF &position, int cursorPosition, int width) const
void | drawCursor(QPainter *painter, const QPointF &position, int cursorPosition) const
void | endLayout()
QFont | font() const
QList<QTextLayout::FormatRange> | formats() const
QList<QGlyphRun> | glyphRuns(int from = -1, int length = -1) const
`(since 6.5)` QList<QGlyphRun> | glyphRuns(int from, int length, QTextLayout::GlyphRunRetrievalFlags retrievalFlags) const
bool | isValidCursorPosition(int pos) const
int | leftCursorPosition(int oldPos) const
QTextLine | lineAt(int i) const
int | lineCount() const
QTextLine | lineForTextPosition(int pos) const
qreal | maximumWidth() const
qreal | minimumWidth() const
int | nextCursorPosition(int oldPos, QTextLayout::CursorMode mode = SkipCharacters) const
QPointF | position() const
int | preeditAreaPosition() const
QString | preeditAreaText() const
int | previousCursorPosition(int oldPos, QTextLayout::CursorMode mode = SkipCharacters) const
int | rightCursorPosition(int oldPos) const
void | setCacheEnabled(bool enable)
void | setCursorMoveStyle(Qt::CursorMoveStyle style)
void | setFont(const QFont &font)
void | setFormats(const QList<QTextLayout::FormatRange> &formats)
void | setPosition(const QPointF &p)
void | setPreeditArea(int position, const QString &text)
void | setText(const QString &string)
void | setTextOption(const QTextOption &option)
QString | text() const
const QTextOption & | textOption() const

## Detailed Description

It offers many features expected from a modern text layout engine, including Unicode compliant rendering, line breaking and handling of cursor positioning. It can also produce and render device independent layout, something that is important for WYSIWYG applications.

The class has a rather low level API and unless you intend to implement your own text rendering for some specialized widget, you probably won't need to use it directly.

QTextLayout can be used with both plain and rich text.

QTextLayout can be used to create a sequence of QTextLine instances with given widths and can position them independently on the screen. Once the layout is done, these lines can be drawn on a paint device.

The text to be laid out can be provided in the constructor or set with setText().

The layout can be seen as a sequence of QTextLine objects; use createLine() to create a QTextLine instance, and lineAt() or lineForTextPosition() to retrieve created lines.

Here is a code snippet that demonstrates the layout phase:

     int leading = fontMetrics.leading();
     qreal height = 0;
     textLayout.setCacheEnabled(true);
     textLayout.beginLayout();
     while (true) {
         QTextLine line = textLayout.createLine();
         if (!line.isValid())
             break;

         line.setLineWidth(lineWidth);
         height += leading;
         line.setPosition(QPointF(0, height));
         height += line.height();
     }
     textLayout.endLayout();

The text can then be rendered by calling the layout's draw() function:

     QPainter painter(this);
     textLayout.draw(&painter, QPoint(0, 0));

It is also possible to draw each line individually, for instance to draw the last line that fits into a widget elided:

     QPainter painter(this);
     QFontMetrics fontMetrics = painter.fontMetrics();

     int lineSpacing = fontMetrics.lineSpacing();
     int y = 0;

     QTextLayout textLayout(content, painter.font());
     textLayout.beginLayout();
     while (true) {
         QTextLine line = textLayout.createLine();

         if (!line.isValid())
             break;

         line.setLineWidth(width());
         const int nextLineY = y + lineSpacing;

         if (height() >= nextLineY + lineSpacing) {
             line.draw(&painter, QPoint(0, y));
             y = nextLineY;
         } else {
             const QString lastLine = content.mid(line.textStart());
             const QString elidedLastLine = fontMetrics.elidedText(lastLine, Qt::ElideRight, width());
             painter.drawText(QPoint(0, y + fontMetrics.ascent()), elidedLastLine);
             line = textLayout.createLine();
             break;
         }
     }
     textLayout.endLayout();

For a given position in the text you can find a valid cursor position with isValidCursorPosition(), nextCursorPosition(), and previousCursorPosition().

The QTextLayout itself can be positioned with setPosition(); it has a boundingRect(), and a minimumWidth() and a maximumWidth().

See also QStaticText.

## Member Type Documentation

### enum QTextLayout::CursorMode

Constant | Value
--- | ---
`QTextLayout::SkipCharacters` | `0`
`QTextLayout::SkipWords` | `1`

### `[since 6.5]` enum QTextLayout::GlyphRunRetrievalFlag
flags QTextLayout::GlyphRunRetrievalFlags

GlyphRunRetrievalFlag specifies flags passed to the glyphRuns() functions to determine which properties of the layout are returned in the QGlyphRun objects. Since each property will consume memory and may require additional allocations, it is a good practice to only request the properties you will need to access later.

Constant | Value | Description
--- | --- | ---
`QTextLayout::RetrieveGlyphIndexes` | `0x1` | Retrieves the indexes in the font which correspond to the glyphs.
`QTextLayout::RetrieveGlyphPositions` | `0x2` | Retrieves the relative positions of the glyphs in the layout.
`QTextLayout::RetrieveStringIndexes` | `0x4` | Retrieves the indexes in the original string that correspond to each of the glyphs.
`QTextLayout::RetrieveString` | `0x8` | Retrieves the original source string from the layout.
`QTextLayout::RetrieveAll` | `0xffff` | Retrieves all available properties of the layout.

This enum was introduced in Qt 6.5.

The GlyphRunRetrievalFlags type is a typedef for QFlags<GlyphRunRetrievalFlag>. It stores an OR combination of GlyphRunRetrievalFlag values.

See also glyphRuns() and QTextLine::glyphRuns().

## Member Function Documentation

### QTextLayout::QTextLayout()

Constructs an empty text layout.

See also setText().

### QTextLayout::QTextLayout(const QString &text)

Constructs a text layout to lay out the given text.

### QTextLayout::QTextLayout(const QString &text, const QFont &font, const QPaintDevice *paintdevice = nullptr)

Constructs a text layout to lay out the given text with the specified font.

All the metric and layout calculations will be done in terms of the paint device, paintdevice. If paintdevice is `nullptr` the calculations will be done in screen metrics.

### `[noexcept]` QTextLayout::~QTextLayout()

Destructs the layout.

### void QTextLayout::beginLayout()

Begins the layout process.

Warning: This will invalidate the layout, so all existing QTextLine objects that refer to the previous contents should now be discarded.

See also endLayout().

### QRectF QTextLayout::boundingRect() const

The smallest rectangle that contains all the lines in the layout.

### bool QTextLayout::cacheEnabled() const

Returns `true` if the complete layout information is cached; otherwise returns `false`.

See also setCacheEnabled().

### void QTextLayout::clearFormats()

Clears the list of additional formats supported by the text layout.

See also formats() and setFormats().

### void QTextLayout::clearLayout()

Clears the line information in the layout. After having called this function, lineCount() returns 0.

Warning: This will invalidate the layout, so all existing QTextLine objects that refer to the previous contents should now be discarded.

### QTextLine QTextLayout::createLine()

Returns a new text line to be laid out if there is text to be inserted into the layout; otherwise returns an invalid text line.

The text layout creates a new line object that starts after the last line in the layout, or at the beginning if the layout is empty. The layout maintains an internal cursor, and each line is filled with text from the cursor position onwards when the QTextLine::setLineWidth() function is called.

Once QTextLine::setLineWidth() is called, a new line can be created and filled with text. Repeating this process will lay out the whole block of text contained in the QTextLayout. If there is no text left to be inserted into the layout, the QTextLine returned will not be valid (isValid() will return false).

### Qt::CursorMoveStyle QTextLayout::cursorMoveStyle() const

The cursor movement style of this QTextLayout. The default is Qt::LogicalMoveStyle.

See also setCursorMoveStyle().

### void QTextLayout::draw(QPainter *p, const QPointF &pos, const QList<QTextLayout::FormatRange> &selections = QList<FormatRange>(), const QRectF &clip = QRectF()) const

Draws the whole layout on the painter p at the position specified by pos. The rendered layout includes the given selections and is clipped within the rectangle specified by clip.

### void QTextLayout::drawCursor(QPainter *painter, const QPointF &position, int cursorPosition, int width) const

Draws a text cursor with the current pen and the specified width at the given position using the painter specified. The corresponding position within the text is specified by cursorPosition.

### void QTextLayout::drawCursor(QPainter *painter, const QPointF &position, int cursorPosition) const

This is an overloaded function.

Draws a text cursor with the current pen at the given position using the painter specified. The corresponding position within the text is specified by cursorPosition.

### void QTextLayout::endLayout()

Ends the layout process.

See also beginLayout().

### QFont QTextLayout::font() const

Returns the current font that is used for the layout, or a default font if none is set.

See also setFont().

### QList<QTextLayout::FormatRange> QTextLayout::formats() const

Returns the list of additional formats supported by the text layout.

See also setFormats() and clearFormats().

### QList<QGlyphRun> QTextLayout::glyphRuns(int from = -1, int length = -1) const

This is an overloaded function.

Returns the glyph indexes and positions for all glyphs corresponding to the length characters starting at the position from in this QTextLayout. This is an expensive function, and should not be called in a time sensitive context.

If from is less than zero, then the glyph run will begin at the first character in the layout. If length is less than zero, it will span the entire string from the start position.

Note: This is equivalent to calling glyphRuns(from, length, QTextLayout::GlyphRunRetrievalFlag::GlyphIndexes | QTextLayout::GlyphRunRetrievalFlag::GlyphPositions).

See also draw() and QPainter::drawGlyphRun().

### `[since 6.5]` QList<QGlyphRun> QTextLayout::glyphRuns(int from, int length, QTextLayout::GlyphRunRetrievalFlags retrievalFlags) const

This is an overloaded function.

Returns the glyph indexes and positions for all glyphs corresponding to the length characters starting at the position from in this QTextLayout. This is an expensive function, and should not be called in a time sensitive context.

If from is less than zero, then the glyph run will begin at the first character in the layout. If length is less than zero, it will span the entire string from the start position.

The retrievalFlags specifies which properties of the QGlyphRun will be retrieved from the layout. To minimize allocations and memory consumption, this should be set to include only the properties that you need to access later.

This function was introduced in Qt 6.5.

See also draw() and QPainter::drawGlyphRun().

### bool QTextLayout::isValidCursorPosition(int pos) const

Returns `true` if position pos is a valid cursor position.

In a Unicode context some positions in the text are not valid cursor positions, because the position is inside a Unicode surrogate or a grapheme cluster.

A grapheme cluster is a sequence of two or more Unicode characters that form one indivisible entity on the screen. For example the latin character `Ä' can be represented in Unicode by two characters, `A' (0x41), and the combining diaeresis (0x308). A text cursor can only validly be positioned before or after these two characters, never between them since that wouldn't make sense. In indic languages every syllable forms a grapheme cluster.

### int QTextLayout::leftCursorPosition(int oldPos) const

Returns the cursor position to the left of oldPos, next to it. It's dependent on the visual position of characters, after bi-directional reordering.

See also rightCursorPosition() and previousCursorPosition().

### QTextLine QTextLayout::lineAt(int i) const

Returns the i-th line of text in this text layout.

See also lineCount() and lineForTextPosition().

### int QTextLayout::lineCount() const

Returns the number of lines in this text layout.

See also lineAt().

### QTextLine QTextLayout::lineForTextPosition(int pos) const

Returns the line that contains the cursor position specified by pos.

See also isValidCursorPosition() and lineAt().

### qreal QTextLayout::maximumWidth() const

The maximum width the layout could expand to; this is essentially the width of the entire text.

Warning: This function only returns a valid value after the layout has been done.

See also minimumWidth().

### qreal QTextLayout::minimumWidth() const

The minimum width the layout needs. This is the width of the layout's smallest non-breakable substring.

Warning: This function only returns a valid value after the layout has been done.

See also maximumWidth().

### int QTextLayout::nextCursorPosition(int oldPos, QTextLayout::CursorMode mode = SkipCharacters) const

Returns the next valid cursor position after oldPos that respects the given cursor mode. Returns value of oldPos, if oldPos is not a valid cursor position.

See also isValidCursorPosition() and previousCursorPosition().

### QPointF QTextLayout::position() const

The global position of the layout. This is independent of the bounding rectangle and of the layout process.

See also setPosition().

### int QTextLayout::preeditAreaPosition() const

Returns the position of the area in the text layout that will be processed before editing occurs.

See also preeditAreaText().

### QString QTextLayout::preeditAreaText() const

Returns the text that is inserted in the layout before editing occurs.

See also preeditAreaPosition().

### int QTextLayout::previousCursorPosition(int oldPos, QTextLayout::CursorMode mode = SkipCharacters) const

Returns the first valid cursor position before oldPos that respects the given cursor mode. Returns value of oldPos, if oldPos is not a valid cursor position.

See also isValidCursorPosition() and nextCursorPosition().

### int QTextLayout::rightCursorPosition(int oldPos) const

Returns the cursor position to the right of oldPos, next to it. It's dependent on the visual position of characters, after bi-directional reordering.

See also leftCursorPosition() and nextCursorPosition().

### void QTextLayout::setCacheEnabled(bool enable)

Enables caching of the complete layout information if enable is true; otherwise disables layout caching. Usually QTextLayout throws most of the layouting information away after a call to endLayout() to reduce memory consumption. If you however want to draw the laid out text directly afterwards enabling caching might speed up drawing significantly.

See also cacheEnabled().

### void QTextLayout::setCursorMoveStyle(Qt::CursorMoveStyle style)

Sets the visual cursor movement style to the given style. If the QTextLayout is backed by a document, you can ignore this and use the option in QTextDocument, this option is for widgets like QLineEdit or custom widgets without a QTextDocument. Default value is Qt::LogicalMoveStyle.

See also cursorMoveStyle().

### void QTextLayout::setFont(const QFont &font)

Sets the layout's font to the given font. The layout is invalidated and must be laid out again.

See also font().

### void QTextLayout::setFormats(const QList<QTextLayout::FormatRange> &formats)

Sets the additional formats supported by the text layout to formats. The formats are applied with preedit area text in place.

See also formats() and clearFormats().

### void QTextLayout::setPosition(const QPointF &p)

Moves the text layout to point p.

See also position().

### void QTextLayout::setPreeditArea(int position, const QString &text)

Sets the position and text of the area in the layout that is processed before editing occurs. The layout is invalidated and must be laid out again.

See also preeditAreaPosition() and preeditAreaText().

### void QTextLayout::setText(const QString &string)

Sets the layout's text to the given string. The layout is invalidated and must be laid out again.

Notice that when using this QTextLayout as part of a QTextDocument this method will have no effect.

See also text().

### void QTextLayout::setTextOption(const QTextOption &option)

Sets the text option structure that controls the layout process to the given option.

See also textOption().

### QString QTextLayout::text() const

Returns the layout's text.

See also setText().

### const QTextOption &QTextLayout::textOption() const

Returns the current text option used to control the layout process.

See also setTextOption().