PySide6.QtCanvasPainter.QCanvasGradient¶

class QCanvasGradient¶

QCanvasGradient is the base class for all QCanvasPainter gradient brushes.

Details

QCanvasGradient is the base class for all QCanvasPainter gradient brushes. Currently there are four type of gradients: QCanvasLinearGradient , QCanvasRadialGradient , QCanvasConicalGradient and QCanvasBoxGradient .

If no stops are provided with setStartColor() , setEndColor() , setColorAt() or setStops() , the gradient is rendered as transparent black (0,0,0,0). If only a single stop is provided, the gradient is filled with this color.

QCanvasPainter uses two different approaches for painting gradients.

With maximum of 2 stops, the colors are passed into shader as 2 vec4 uniforms. This makes animating 2 stop gradients very performant, with no extra steps in between.

With more than 2 stops, the colors are passed into shader as a one dimensional texture. By default the texture size is 1x256 pixels, optimized for quality and performance. The textures are cached, so when gradient stops or colors don’t change, previous texture can be reused even when other gradient properties (like position, angle etc.) change. Although animating multi-stop gradients is fast, it will cause texture uploads, so consider if it is worth it.

There are few environment variables to control the gradients texture usage:

QCPAINTER_DISABLE_TEXTURE_USAGE_TRACKING - By default, gradient texture usage is tracked and kept under the max amount. Set this environment variable to disable the tracking and keep all gradient textures in memory.

QCPAINTER_MAX_TEXTURES - By default, the maximum amount of textures is 1024. Set this environt variable to contain number of desired maximum texture amount. The currently unused temporary gradient textures are automatically removed when the maximum amount is reached.

Note

This does not have an effect when the texture usage tracking has been disabled.

Inherited by: QCanvasRadialGradient, QCanvasLinearGradient, QCanvasConicalGradient, QCanvasBoxGradient

Synopsis¶

Methods¶

def __init__()
def addColorStop()
def endColor()
def __ne__()
def __eq__()
def setColorAt()
def setEndColor()
def setImage()
def setStartColor()
def setStops()
def startColor()
def stops()
def swap()
def type()

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__(type)¶

Parameters:: type – BrushType

__init__(brush)

Parameters:: brush – QCanvasBrush

__init__(arg__1)

Parameters:: arg__1 – QCanvasGradient

Copy-constructs an instance of QCanvasGradient.

addColorStop(position, color)¶

Parameters:

position – float
color – QColor

Creates a stop point at the given position with the given color. The given position must be in the range 0 to 1.

This method is provided for HTML CanvasGradient compatibility. It is equivalent to setColorAt() .

See also

setStops() stops()

endColor()¶

Return type:: QColor

Returns the gradient end color or the color at the largest position. If any stops have not been set, returns transparent black (0, 0, 0, 0).

See also

setEndColor()

__ne__(rhs)¶

Parameters:: rhs – QCanvasGradient
Return type:: bool

__eq__(rhs)¶

Parameters:: rhs – QCanvasGradient
Return type:: bool

setColorAt(position, color)¶

Parameters:

position – float
color – QColor

Creates a stop point at the given position with the given color. The given position must be in the range 0 to 1.

See also

setStops() stops()

setEndColor(color)¶

Parameters:: color – QColor

Sets the end color of gradient to color. This is equal to calling setColorAt() with position 1.

See also

endColor()

setImage(image[, index=0])¶

Parameters:

image – QCanvasImage
index – int

Uses the image as the gradient source at the y-coordinate index. This is an alternative for setting the gradient stops using e.g. setStops() or setColorAt() . The expected default width of the image is 256 pixels, but it can be adjusted by defining the QCPAINTER_GRADIENT_SIZE. Index parameter is optional and not needed when the height of the image is 1 pixel. The maximum value of index should be image height - 1.

Possible reasons to use this method instead of setting stops:

Slightly faster to create as stops don’t need to be parsed. Also, multiple gradients can be included in a single image using index.

The ability to use gradient from design / image directly, instead of converting it to set of stops.

The ability to have non-linear gradients, like e.g. Gaussian curve.

Note

If both the stops and the image have been set, stops will be used.

Here is a simple example of how to use a 256x1 gradient image:

gradient11

qcgradient-image2

static QImage image(":/gradient1.png");
QCanvasImage gradImage = p->addImage(image);
QRectF rect(0, 0, 200, 200);
QCanvasRadialGradient rg(rect.center(), 20, 150);
rg.setImage(gradImage);
p->setFillStyle(rg);
p->fillRect(rect);