PySide6.QtCanvasPainter.QCanvasPainterItemRenderer

class QCanvasPainterItemRenderer

The QCanvasPainterItemRenderer handles all painting for a QCanvasPainterItem .

Details

Warning

This section contains snippets that were automatically translated from C++ to Python and may contain errors.

Implement the paint() method to perform the rendering.

To expose data from the item to the renderer in a thread-safe manner, implement synchronize() .

The renderer object lives and operates on the Qt Quick scene graph render thread, if there is one, since that is the thread on which createItemRenderer() and all the functions in this class are invoked.

If the QCanvasPainterItem is moved to a different window, it will get associated with a new QRhi. Therefore, the renderer object is automatically destroyed, and a new one is created by invoking createItemRenderer() again. This allows simple management of QCanvasImage and QCanvasOffscreenCanvas objects, because they can be member variables in renderer, set up either in initializeResources() or in paint() , without having to reset them when the graphics resources are lost due to the window and QRhi change, since it all happens implicitly by the destruction of the whole renderer object.

The below code snippet shows the typical structure of a QCanvasPainterItemRenderer subclass. See QCanvasPainterItem for an example of the MyItem class.

class MyRenderer(QCanvasPainterItemRenderer):

# public
    def synchronize(item):

        # copy a custom property value from item in a thread-safe manner
        m_value = MyItem(item).value()

    def initializeResources(p):

        # load assets
        if m_image.isNull():
            m_image = p.addImage(QImage("image.png"), QCanvasPainter.ImageFlag.Repeat)

    def prePaint(p):

        # this is where offscreen canvases are drawn into
        if m_canvas.isNull():
            m_canvas = p.createCanvas(QSize(640, 480))
            beginCanvasPainting(m_canvas)
            # ... draw into the offscreen canvas
            endCanvasPainting(m_canvas)
            m_canvasImage = p.addImage(m_canvas)


    def paint(p):

        center = QPointF(width() / 2, height() / 2)
        # ... draw using m_value, m_image, and m_canvasImage

    m_image = QCanvasImage()
    m_canvas = QCanvasOffscreenCanvas()
    m_canvasImage = QCanvasImage()
    m_value = float()

See also

QCanvasPainterItem

Synopsis

Methods

• def __init__()

• def beginCanvasPainting()

• def endCanvasPainting()

• def fillColor()

• def hasSharedPainter()

• def height()

• def painter()

• def setSharedPainter()

• def width()

Virtual methods

• def initializeResources()

• def paint()

• def prePaint()

• def synchronize()

Note

This documentation may contain snippets that were automatically translated from C++ to Python. We always welcome contributions to the snippet translation. If you see an issue with the translation, you can also let us know by creating a ticket on https:/bugreports.qt.io/projects/PYSIDE

__init__()

Constructs a QCanvasPainterItemRenderer .

beginCanvasPainting(canvas)

Parameters:

canvas – QCanvasOffscreenCanvas

Starts recording QCanvasPainter draw commands targeting canvas.

Note

This function should only be called from prePaint() .

beginCanvasPainting() must always be followed by corresponding endCanvasPainting() before returning from prePaint() .

endCanvasPainting()

Indicates the end of the drawing targeting the canvas specified in beginCanvasPainting() .

Note

This function should only be called from prePaint() .

beginCanvasPainting() must always be followed by corresponding endCanvasPainting() before returning from prePaint() .

fillColor()

Return type:

QColor

Return the current fill color of the item. This can be set by the parent QCanvasPainterItem .

hasSharedPainter()

Return type:

bool

Returns true if this item renderer uses a shared painter.

See also

setSharedPainter

height()

Return type:

float

Returns the height of the painted area, in logical units, without the scale factor (device pixel ratio). This is usually the same as the painter item’s height, unless QQuickRhiItem::fixedColorBufferHeight has been set.

initializeResources(painter)

Parameters:

painter – QCanvasPainter

Reimplement this method to initialize resources using painter. This will be called once before the first synchronize() .

Note

This function is not called when the size of the QCanvasPainterItem changes.

See also

addImage createCanvas

paint(painter)

Parameters:

painter – QCanvasPainter

Reimplement this method to paint using painter.

This will get called after the item has been filled with fillColor() .

paint() is called from renderer thread. To access item data safely, copy it in synchronize() .

See also

synchronize()

painter()

Return type:

QCanvasPainter

Returns the painter attached to this painter item.

prePaint(painter)

Parameters:

painter – QCanvasPainter

This function is called at the start of rendering using painter, before paint() .

There is no render target active when this function is invoked. Call beginCanvasPainting() to initialize drawing into an offscreen canvas.

See also

beginCanvasPainting() endCanvasPainting()

setSharedPainter(enable)

Parameters:

enable – bool

Disable painter sharing if enable is false.

Painter sharing is enabled by default.

When painter sharing is enabled, all painter items inside the same QQuickWindow will use the same QCanvasPainter .

If disabling painter sharing is desired, this function must be called early enough, for example from the derived class’ constructor. Changing it afterwards, when the item has already initialized for painting, will have no effect.

If two items use dedicated, non-shared painters, each other’s graphics resources, such as the ones backing QCanvasImage or QOffscreenCanvas, will not be visible to them. Whereas if the items are in the same window, and sharing is enabled, they can use images or canvases created by the other item, because they both use the same QCanvasPainter .

Note

Even when enable is true, painters are not shared between items belonging to different QQuickWindow instances, and by extension, to different scene graphs.

See also

hasSharedPainter

synchronize(item)

Parameters:

item – QCanvasPainterItem

Reimplement this method to synchronize data between item and item painter instances. This will be called before paint() each time item needs to be repainted.

This method is the only place where it is safe for the painter and the item to read and write each others variables.

Usually you should static_cast item to your real item type, and then exchange the data.

Note

Make sure to reimplement this overload, taking a QCanvasPainterItem , instead of the base class’ version that takes a QQuickRhiItem.

width()

Return type:

float

Returns the width of the painted area, in logical units, without the scale factor (device pixel ratio). This is usually the same as the painter item’s width, unless QQuickRhiItem::fixedColorBufferWidth has been set.