- Qt 6.11
- Qt Canvas Painter
- C++ Classes
- QtCanvasPainter (Technical Preview)
- QCanvasPath
- Qt Canvas Painter | Commercial or GPLv3

# QCanvasPath Class

QCanvasPath is the native path format of QCanvasPainter. More...

Header: | `#include <QCanvasPath>`
CMake: | `find_package(Qt6 REQUIRED COMPONENTS CanvasPainter)` `target_link_libraries(mytarget PRIVATE Qt6::CanvasPainter)`
Since: | Qt 6.11
Status: | Technical Preview

- List of all members, including inherited members

## Public Functions

| QCanvasPath()
| QCanvasPath(qsizetype commandsSize, qsizetype commandsDataSize = -1)
| QCanvasPath(const QCanvasPath &path)
| QCanvasPath(QCanvasPath &&other)
| ~QCanvasPath()
void | addPath(const QCanvasPath &path, const QTransform &transform = QTransform())
void | addPath(const QCanvasPath &path, qsizetype start, qsizetype count, const QTransform &transform = QTransform())
void | arc(float centerX, float centerY, float radius, float a0, float a1, QCanvasPainter::PathWinding direction = QCanvasPainter::PathWinding::ClockWise, QCanvasPainter::PathConnection connection = QCanvasPainter::PathConnection::Connected)
void | arc(QPointF centerPoint, float radius, float a0, float a1, QCanvasPainter::PathWinding direction = QCanvasPainter::PathWinding::ClockWise, QCanvasPainter::PathConnection connection = QCanvasPainter::PathConnection::Connected)
void | arcTo(float x1, float y1, float x2, float y2, float radius)
void | arcTo(QPointF point1, QPointF point2, float radius)
void | beginHoleSubPath()
void | beginSolidSubPath()
void | bezierCurveTo(float cp1X, float cp1Y, float cp2X, float cp2Y, float x, float y)
void | bezierCurveTo(QPointF controlPoint1, QPointF controlPoint2, QPointF endPoint)
void | circle(float x, float y, float radius)
void | circle(QPointF centerPoint, float radius)
void | clear()
void | closePath()
qsizetype | commandsCapacity() const
qsizetype | commandsDataCapacity() const
qsizetype | commandsDataSize() const
qsizetype | commandsSize() const
QPointF | currentPosition() const
void | ellipse(float x, float y, float radiusX, float radiusY)
void | ellipse(const QRectF &rect)
bool | isEmpty() const
void | lineTo(QPointF point)
void | lineTo(float x, float y)
void | moveTo(QPointF point)
void | moveTo(float x, float y)
QPointF | positionAt(qsizetype index) const
void | quadraticCurveTo(float cpX, float cpY, float x, float y)
void | quadraticCurveTo(QPointF controlPoint, QPointF endPoint)
void | rect(float x, float y, float width, float height)
void | rect(const QRectF &rect)
void | reserve(qsizetype commandsSize, qsizetype commandsDataSize)
void | reserve(qsizetype commandsSize)
void | roundRect(float x, float y, float width, float height, float radius)
void | roundRect(float x, float y, float width, float height, float radiusTopLeft, float radiusTopRight, float radiusBottomRight, float radiusBottomLeft)
void | roundRect(const QRectF &rect, float radius)
void | roundRect(const QRectF &rect, float radiusTopLeft, float radiusTopRight, float radiusBottomRight, float radiusBottomLeft)
void | setPathWinding(QCanvasPainter::PathWinding winding)
QCanvasPath | sliced(qsizetype start, qsizetype count, const QTransform &transform = QTransform()) const
void | squeeze()
void | swap(QCanvasPath &other)
| operator QVariant() const
QCanvasPath & | operator=(QCanvasPath &&other)
QCanvasPath & | operator=(const QCanvasPath &path)

## Related Non-Members

bool | operator!=(const QCanvasPath &lhs, const QCanvasPath &rhs)
bool | operator==(const QCanvasPath &lhs, const QCanvasPath &rhs)

## Detailed Description

A painter path is an object composed of a number of graphical building blocks, such as rectangles, ellipses, lines, and curves. QCanvasPath API matches to QCanvasPainter path painting, making it easy to adjust code between paintind directly or painting into a path. The main reason use QCanvasPath is to avoid recreating the (static) paths and be able to cache the paths GPU buffers.

Compared to QPainterPath, QCanvasPath is more optimized for rendering with fewer features for comparing or adjusting the paths. In particular:

- There are no methods for intersection or subtraction between two paths.
- There is no method for translating the path.
- There is no method for adding text.
- The fill rule is always `WindingFill` (nonzero), `OddEvenFill` is not supported.

From a functionality point of view, QCanvasPath is more similar to HTML Canvas Path2D, with some additions and the API matching to QCanvasPainter.

### PathGroups and caching

Painting paths through QCanvasPath allows the engine to cache the path geometry (vertices). This improves the performance of static paths, while potentially increasing GPU memory consumption.

When painting paths using fill() or stroke() that take QCanvasPath as a parameter, it is possible to set a `pathGroup` as a second parameter. This defines the GPU buffer where the path is cached. By default, `pathGroup` is `0`, meaning that the first buffer is used. Setting the `pathGroup` to `-1` means that the path does not allocate its own buffer, and the same dynamic buffer is used as with direct painting using beginPath() followed by commands and fill/stroke.

Arranging paths into path groups allows efficient optimization of the rendering performance and the GPU memory usage. Paths that belong together and often change at the same time should be in the same group for optimal buffer usage.

When the path changes, its geometry (vertex buffer) is automatically updated. Things that cause a geometry update of the path group are:

- Clearing the path elements or adding new elements.
- Changing the stroke line width (QCanvasPainter::setLineWidth()).
- Adjusting antialiasing amount (QCanvasPainter::setAntialias()).
- Changing line cap or line join type (QCanvasPainter::setLineCap(), QCanvasPainter::setLineJoin()).

Note that changing the state transform (QCanvasPainter::transform(), QCanvasPainter::rotate() etc.) does not invalidate the path, so moving/scaling/rotating a cached path is very efficient.

In cases where the path does not need to be painted anymore, or the application should release GPU memory, the cache can be released by calling QCanvasPainter::removePathGroup(). This isn't usually needed, as the cached paths are automatically released during the painter destructor.

See also QCanvasPainter::addPath() and QCanvasPainter::removePathGroup().

## Member Function Documentation

### QCanvasPath::QCanvasPath()

Constructs an empty path.

### `[explicit]` QCanvasPath::QCanvasPath(qsizetype commandsSize, qsizetype commandsDataSize = -1)

Constructs an empty path, allocating space for commandsSize amount of commands and optionally commandsDataSize amount of data. If commandsDataSize parameter is not given, space is automatically reserved for `2 * commandsSize` amount of data, which is optimal amount when the path commands are straight lines (moveTo(), lineTo(), rect()).

Reserving correct space is an optimization for path creation and memory usage. It isn't mandatory as sufficient space will automatically be ensured while adding commands to the path.

See also reserve().

### QCanvasPath::QCanvasPath(const QCanvasPath &path)

Constructs a path that is a copy of the given path.

### QCanvasPath::QCanvasPath(QCanvasPath &&other)

Move-constructs a new QCanvasPath from other.

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

Destroys the path.

### void QCanvasPath::addPath(const QCanvasPath &path, const QTransform &transform = QTransform())

Adds path into this path, optionally using transform to alter the path points. When transform is not provided (or it is identity matrix), this operation is very fast as it reuses the path data.

### void QCanvasPath::addPath(const QCanvasPath &path, qsizetype start, qsizetype count, const QTransform &transform = QTransform())

Adds path into the current path, starting from the command at start and including count amount of commands. Optionally using transform to alter the path points. The range of start and count is checked, so that commands are not accessed more than QCanvasPath::commandsSize(). In case the path shouldn't continue from the current path position, call first moveTo() with `path.positionAt(start - 1)`.

### void QCanvasPath::arc(float centerX, float centerY, float radius, float a0, float a1, QCanvasPainter::PathWinding direction = QCanvasPainter::PathWinding::ClockWise, QCanvasPainter::PathConnection connection = QCanvasPainter::PathConnection::Connected)

Creates an arc centered on QPointF(centerX, centerY) with the given radius, starting at an angle of a0 radians and ending at a1 radians. The arc spans the given direction. When connection is NotConnected, the previous path is closed and a new sub-path is started.

### void QCanvasPath::arc(QPointF centerPoint, float radius, float a0, float a1, QCanvasPainter::PathWinding direction = QCanvasPainter::PathWinding::ClockWise, QCanvasPainter::PathConnection connection = QCanvasPainter::PathConnection::Connected)

Creates an arc centered on centerPoint with the given radius, starting at an angle of a0 radians and ending at a1 radians. The arc spans the given direction. When connection is NotConnected, the previous path is closed and a new sub-path is started.

This is an overloaded function.

### void QCanvasPath::arcTo(float x1, float y1, float x2, float y2, float radius)

Creates an arc using the points QPointF(x1, y1) and QPointF(x2, y2) with the given radius.

### void QCanvasPath::arcTo(QPointF point1, QPointF point2, float radius)

Creates an arc using the points point1 and point2 with the given radius.

This is an overloaded function.

### void QCanvasPath::beginHoleSubPath()

Start a hole subpath. This is equivalent to `setPathWinding(QCanvasPainter::PathWinding::ClockWise)`)

See also beginSolidSubPath().

### void QCanvasPath::beginSolidSubPath()

Start a solid subpath. This is equivalent to `setPathWinding(QCanvasPainter::PathWinding::CounterClockWise)`)

See also beginHoleSubPath().

### void QCanvasPath::bezierCurveTo(float cp1X, float cp1Y, float cp2X, float cp2Y, float x, float y)

Adds a cubic Bezier curve between the current position and the end point specified by x and y, using the control points specified by cp1X, cp1Y, cp2X, and cp2Y.

After the curve is added, the current position is updated to be at the end point of the curve.

### void QCanvasPath::bezierCurveTo(QPointF controlPoint1, QPointF controlPoint2, QPointF endPoint)

Adds a cubic Bezier curve between the current position and the given endPoint using the control points specified by controlPoint1, and controlPoint2.

After the curve is added, the current position is updated to be at the end point of the curve.

This is an overloaded function.

### void QCanvasPath::circle(float x, float y, float radius)

Adds a circle with center at QPointF(x, y) and the given radius to the path.

### void QCanvasPath::circle(QPointF centerPoint, float radius)

Adds a circle with center at centerPoint and the given radius to the path.

This is an overloaded function.

### void QCanvasPath::clear()

Clears the path commands and data.

Call this when the path commands change to recreate the path. This does not affect the memory usage, use reserve() and squeeze() for that.

See also reserve() and squeeze().

### void QCanvasPath::closePath()

Closes the current subpath by drawing a line to the beginning of the subpath, automatically starting a new path.

### qsizetype QCanvasPath::commandsCapacity() const

Returns the capacity of commands in the path.

See also commandsDataCapacity() and reserve().

### qsizetype QCanvasPath::commandsDataCapacity() const

Returns the capacity of commands data in the path.

See also commandsCapacity() and reserve().

### qsizetype QCanvasPath::commandsDataSize() const

Returns the amount of commands data in the path.

Commands data basically means the points required by the commands.

Note: Some path elements require several data points. For example closePath requires `0`, moveTo and lineTo require `2`, bezierCurveTo requires 6 and roundRect requires `34` data points.

### qsizetype QCanvasPath::commandsSize() const

Returns the amount of commands in the path.

Note: Some path elements require several commands. For example moveTo and lineTo require `1` command, bezierCurveTo requires `6` commands and roundRect `10` commands.

### QPointF QCanvasPath::currentPosition() const

Returns the current position of the path. This means position where previous path command (moveTo, lineTo, bezierCurveTo etc.) has ended. When the path is empty, returns (0.0, 0.0).

### void QCanvasPath::ellipse(float x, float y, float radiusX, float radiusY)

Creates an ellipse centered at (x, y), with radii defined by radiusX, radiusY and adds it to the path as a closed subpath.

### void QCanvasPath::ellipse(const QRectF &rect)

Creates an ellipse within the rectangle rect and adds it to the path as a closed subpath.

This is an overloaded function.

### bool QCanvasPath::isEmpty() const

Returns true when the path is empty.

See also clear.

### void QCanvasPath::lineTo(QPointF point)

Adds a straight line from the current position to the given point. After the line is drawn, the current position is updated to be at the end point of the line.

This is an overloaded function.

### void QCanvasPath::lineTo(float x, float y)

Draws a line from the current position to the point (x, y).

This is an overloaded function.

### void QCanvasPath::moveTo(QPointF point)

Moves the current point to the given point, implicitly starting a new subpath and closing the previous one.

This is an overloaded function.

### void QCanvasPath::moveTo(float x, float y)

Moves the current position to (x, y) and starts a new subpath, implicitly closing the previous path.

This is an overloaded function.

### QPointF QCanvasPath::positionAt(qsizetype index) const

Returns the position of the path at index. This means position where path command (moveTo, lineTo, bezierCurveTo etc.) is at index. The index need to be between `0` and commandsSize() - 1. When the path is empty, returns (0.0, 0.0).

### void QCanvasPath::quadraticCurveTo(float cpX, float cpY, float x, float y)

Adds a quadratic Bezier curve between the current point and the endpoint (x, y) with the control point specified by (cpX, cpY).

### void QCanvasPath::quadraticCurveTo(QPointF controlPoint, QPointF endPoint)

Adds a quadratic Bezier curve between the current position and the given endPoint with the control point specified by controlPoint.

This is an overloaded function.

### void QCanvasPath::rect(float x, float y, float width, float height)

Creates a rectangle positioned at QPointF(x, y) with the given width and height.

### void QCanvasPath::rect(const QRectF &rect)

Creates a rectangle specified by rect

This is an overloaded function.

### void QCanvasPath::reserve(qsizetype commandsSize, qsizetype commandsDataSize)

Reserves a given amounts of space in QCanvasPath's internal memory.

Attempts to allocate memory for at least commandsSize commands and commandsDataSize data points. Some path elements require multiple commands, see commandsSize() and commandsDataSize().

Reserving correct space is an optimization for path creation and memory usage. It isn't mandatory as sufficient space will automatically be ensured while adding commands into the path.

See also squeeze(), commandsCapacity(), and commandsDataCapacity().

### void QCanvasPath::reserve(qsizetype commandsSize)

Reserves a given amounts of space in QCanvasPath's internal memory.

Attempts to allocate memory for at least commandsSize commands. Some path elements require multiple commands, see commandsSize() and commandsDataSize().

Space is automatically reserved for `2 * commandsSize` amount of data, which is optimal amount when the path commands are straight lines (moveTo(), lineTo(), rect()).

Reserving correct space is an optimization for path creation and memory usage. It isn't mandatory as sufficient space will automatically be ensured while adding commands into the path.

This is an overloaded function.

See also squeeze(), commandsCapacity(), and commandsDataCapacity().

### void QCanvasPath::roundRect(float x, float y, float width, float height, float radius)

Adds the given rectangle x, y, width, height with rounded corners to the path. The corners are quarter circles with the given radius.

### void QCanvasPath::roundRect(float x, float y, float width, float height, float radiusTopLeft, float radiusTopRight, float radiusBottomRight, float radiusBottomLeft)

Adds the rectangle x, y, width, height with rounded corners to the path. The corners are quarter circles with radius radiusTopLeft, radiusTopRight radiusBottomRight and radiusBottomLeft, respectively.

### void QCanvasPath::roundRect(const QRectF &rect, float radius)

Adds the given rectangle rect with rounded corners to the path. The corners are quarter circles with the given radius.

This is an overloaded function.

### void QCanvasPath::roundRect(const QRectF &rect, float radiusTopLeft, float radiusTopRight, float radiusBottomRight, float radiusBottomLeft)

Adds the rectangle rect with rounded corners to the path. The corners are quarter circles with radius radiusTopLeft, radiusTopRight radiusBottomRight and radiusBottomLeft, respectively.

This is an overloaded function.

### void QCanvasPath::setPathWinding(QCanvasPainter::PathWinding winding)

Sets the current sub-path winding to either `QCanvasPainter::CounterClockWise` (default) or `QCanvasPainter::ClockWise`. CounterClockWise draws solid subpaths while ClockWise draws holes.

### QCanvasPath QCanvasPath::sliced(qsizetype start, qsizetype count, const QTransform &transform = QTransform()) const

Returns a new path containing the commands from this path, starting from the command at start and including count amount of commands, optionally using transform to alter the path points.

The range of start and count is checked, so that commands are not accessed more than commandsSize(). In case the command at start is not `MoveTo`, the first command will be replaced with `MoveTo` so that this slice is an individual path.

### void QCanvasPath::squeeze()

Releases any memory not required to store the path commands and data. This can be used to reduce the memory usage after calling the reserve().

Normally this is not needed to be used, but it can be useful when the path size has been big due to reserving or adding many elements (lineTo, bezierCurveTo etc.) and then size is expected to be much smaller in future so calling first `reserve()` and then `squeeze()`, will release some memory.

See also reserve().

### `[noexcept]` void QCanvasPath::swap(QCanvasPath &other)

Swaps this path with other. This operation is very fast and never fails.

### QCanvasPath::operator QVariant() const

Returns the path as a QVariant.

### `[noexcept]` QCanvasPath &QCanvasPath::operator=(QCanvasPath &&other)

Move-assigns other to this QCanvasPath instance.

### QCanvasPath &QCanvasPath::operator=(const QCanvasPath &path)

Assigns the given path to this path and returns a reference to this path.

## Related Non-Members

### `[noexcept]` bool operator!=(const QCanvasPath &lhs, const QCanvasPath &rhs)

Returns `true` if the path lhs is different from rhs; `false` otherwise.

See also operator==().

### `[noexcept]` bool operator==(const QCanvasPath &lhs, const QCanvasPath &rhs)

Returns `true` if the path lhs is equal to rhs; `false` otherwise.

See also operator!=().