QTextLayout Class▲
-
Header: QTextLayout
-
CMake:
find_package(Qt6 REQUIRED COMPONENTS Gui)
target_link_libraries(mytarget PRIVATE Qt6::Gui)
-
qmake: QT += gui
-
Group: QTextLayout is part of Rich Text Processing APIs
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 (1) {
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));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▲
See also QStaticText
Member Type Documentation▲
Member Function Documentation▲
QTextLayout::QTextLayout()▲
QTextLayout::QTextLayout(const QString &text)▲
Constructs a text layout to lay out the given text.
[since 5.13] 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.
This function was introduced in Qt 5.13.
QTextLayout::~QTextLayout()▲
Destructs the layout.
void QTextLayout::beginLayout()▲
Begins the layout process.
This will invalidate the layout, so all existing QTextLine objects that refer to the previous contents should now be discarded.
See Also▲
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▲
See also setCacheEnabled()
[since 5.6] void QTextLayout::clearFormats()▲
Clears the list of additional formats supported by the text layout.
This function was introduced in Qt 5.6.
See Also▲
See also formats(), setFormats()
void QTextLayout::clearLayout()▲
Clears the line information in the layout. After having called this function, lineCount() returns 0.
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▲
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()▲
QFont QTextLayout::font() const▲
Returns the current font that is used for the layout, or a default font if none is set.
See Also▲
See also setFont()
[since 5.6] QList<QTextLayout::FormatRange> QTextLayout::formats() const▲
Returns the list of additional formats supported by the text layout.
This function was introduced in Qt 5.6.
See Also▲
See also setFormats(), clearFormats()
QList<QGlyphRun> QTextLayout::glyphRuns(int from = -1, int length = -1) const▲
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.
See Also▲
See also draw(), 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▲
See also rightCursorPosition(), previousCursorPosition()
QTextLine QTextLayout::lineAt(int i) const▲
Returns the i-th line of text in this text layout.
See Also▲
See also lineCount(), lineForTextPosition()
int QTextLayout::lineCount() const▲
QTextLine QTextLayout::lineForTextPosition(int pos) const▲
Returns the line that contains the cursor position specified by pos.
See Also▲
See also isValidCursorPosition(), lineAt()
qreal QTextLayout::maximumWidth() const▲
The maximum width the layout could expand to; this is essentially the width of the entire text.
This function only returns a valid value after the layout has been done.
See Also▲
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.
This function only returns a valid value after the layout has been done.
See Also▲
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▲
See also isValidCursorPosition(), 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▲
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▲
See also preeditAreaText()
QString QTextLayout::preeditAreaText() const▲
Returns the text that is inserted in the layout before editing occurs.
See Also▲
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▲
See also isValidCursorPosition(), 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▲
See also leftCursorPosition(), 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▲
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▲
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▲
See also font()
[since 5.6] 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.
This function was introduced in Qt 5.6.
See Also▲
See also formats(), clearFormats()
void QTextLayout::setPosition(const QPointF &p)▲
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▲
See also preeditAreaPosition(), 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▲
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▲
See also textOption()
QString QTextLayout::text() const▲
const QTextOption &QTextLayout::textOption() const▲
Returns the current text option used to control the layout process.
See Also▲
See also setTextOption()