Class: QgsPaintEffect¶

Base class for visual effects which can be applied to QPicture drawings.

QgsPaintEffect objects can be used to modify QPicture drawings prior to rendering them with a QPainter operation. There are two methods for drawing using an effect, either drawing a picture directly, or by intercepting drawing operations to a render context.

To directly draw a picture, use the render() method with a source QPicture and destination render context.

Intercepting drawing operations to a render context is achieved by first calling the begin() method, passing a render context. Any drawing operations performed on the render context will not directly affect the context’s paint device. When the drawing operations have been completed, call the end() method. This will perform the paint effect on the intercepted drawing operations and render the result to the render context’s paint device.

See also

QgsPaintEffectRegistry

Note

This is an abstract class, with methods which must be implemented by a subclass.

The following methods must be implemented: clone(), draw(), properties(), readProperties(), type()

Class Hierarchy¶

Subclasses¶

`QgsBlurEffect`	A paint effect which blurs a source picture, using a number of different blur methods.
`QgsColorEffect`	A paint effect which alters the colors (e.g., brightness, contrast) in a source picture.
`QgsDrawSourceEffect`	A paint effect which draws the source picture with minor or no alterations.
`QgsShadowEffect`	Base class for paint effects which render offset, blurred shadows.
`QgsEffectStack`	A paint effect which consists of a stack of other chained paint effects.
`QgsGlowEffect`	Base class for paint effects which draw a glow inside or outside a picture.
`QgsTransformEffect`	A paint effect which applies transformations (such as move, scale and rotate) to a picture.

Abstract Methods

`clone`	Duplicates an effect by creating a deep copy of the effect
`draw`	Handles drawing of the effect's result on to the specified render context.
`properties`	Returns the properties describing the paint effect encoded in a string format.
`readProperties`	Reads a string map of an effect's properties and restores the effect to the state described by the properties map.
`type`	Returns the effect type.

Methods

`drawMode`	Returns the draw mode for the effect.
`drawSource`	Draws the source QPicture onto the specified painter.
`enabled`	Returns whether the effect is enabled
`fixQPictureDpi`	Applies a workaround to a QPainter to avoid an issue with incorrect scaling when drawing QPictures.
`imageOffset`	Returns the offset which should be used when drawing the source image on to a destination render context.
`setDrawMode`	Sets the draw mode for the effect.
`setEnabled`	Sets whether the effect is enabled
`source`	Returns the source QPicture.
`sourceAsImage`	Returns the source QPicture rendered to a new QImage.

Virtual Methods

In PyQGIS, only methods marked as virtual can be safely overridden in a Python subclass of QgsPaintEffect. See the FAQ for more details.

`begin`	Begins intercepting paint operations to a render context.
`boundingRect`	Returns the bounding rect required for drawing the effect.
`end`	Ends interception of paint operations to a render context, and draws the result to the render context after being modified by the effect.
`flags`	Returns flags which specify how the paint effect behaves.
`render`	Renders a picture using the effect.
`saveProperties`	Saves the current state of the effect to a DOM element.

Attributes

`Modifier`
`ModifyAndRender`
`Render`

class qgis.core.QgsPaintEffect[source]¶

Bases: object

class DrawMode¶: Bases: int

Modifier = 0¶

ModifyAndRender = 2¶

Render = 1¶

virtual begin(self, context: QgsRenderContext)[source]¶

Begins intercepting paint operations to a render context. When the corresponding end() member is called all intercepted paint operations will be drawn to the render context after being modified by the effect.

Parameters:: context (QgsRenderContext) – destination render context

See also

end()

See also

render()

virtual boundingRect(self, rect: QRectF, context: QgsRenderContext) → QRectF[source]¶

Returns the bounding rect required for drawing the effect. This method can be used to expand the bounding rect of a source picture to account for offset or blurring effects.

Parameters:

rect (QRectF) – original source bounding rect
context (QgsRenderContext) – destination render context

Return type:

QRectF

Returns:

modified bounding rect

See also

sourceAsImage()

abstract clone(self) → QgsPaintEffect | None[source]¶

Duplicates an effect by creating a deep copy of the effect

Return type:: Optional[QgsPaintEffect]
Returns:: clone of paint effect

abstract draw(self, context: QgsRenderContext)[source]¶

Handles drawing of the effect’s result on to the specified render context. Derived classes must reimplement this method to apply any transformations to the source QPicture and draw the result using the context’s painter.

Parameters:: context (QgsRenderContext) – destination render context

See also

drawSource()

drawMode(self) → QgsPaintEffect.DrawMode[source]¶

Returns the draw mode for the effect. This property only has an effect if the paint effect is used in a QgsEffectStack.

Return type:: QgsPaintEffect.DrawMode
Returns:: draw mode for effect

See also

setDrawMode()

drawSource(self, painter: QPainter)[source]¶

Draws the source QPicture onto the specified painter. Handles scaling of the picture to account for the destination painter’s DPI.

Parameters:: painter (QPainter) – destination painter

See also

source()

See also

sourceAsImage()

enabled(self) → bool[source]¶

Returns whether the effect is enabled

Return type:: bool
Returns:: True if effect is enabled

See also

setEnabled()

virtual end(self, context: QgsRenderContext)[source]¶

Ends interception of paint operations to a render context, and draws the result to the render context after being modified by the effect.

Parameters:: context (QgsRenderContext) – destination render context

See also

begin()

fixQPictureDpi(self, painter: QPainter | None)[source]¶

Applies a workaround to a QPainter to avoid an issue with incorrect scaling when drawing QPictures. This may need to be called by derived classes prior to rendering results onto a painter.

Parameters:: painter (Optional[QPainter]) – destination painter

Deprecated since version 3.40: Use QgsPainting.drawPicture() or QgsPainting.applyScaleFixForQPictureDpi() instead.

virtual flags(self) → Qgis.PaintEffectFlags[source]¶

Returns flags which specify how the paint effect behaves.

Added in version 3.44.

Return type:: Qgis.PaintEffectFlags

imageOffset(self, context: QgsRenderContext) → QPointF[source]¶

Returns the offset which should be used when drawing the source image on to a destination render context.

Parameters:: context (QgsRenderContext) – destination render context
Return type:: QPointF
Returns:: point offset for image top left corner

See also

sourceAsImage()

abstract properties(self) → Dict[str, Any][source]¶

Returns the properties describing the paint effect encoded in a string format.

Return type:: Dict[str, Any]
Returns:: string map of properties, in the form property key, value

See also

readProperties()

See also

saveProperties()

abstract readProperties(self, props: Dict[str, Any])[source]¶

Reads a string map of an effect’s properties and restores the effect to the state described by the properties map.

Parameters:: props (Dict[str, Any]) – effect properties encoded in a string map

See also

properties()

abstract readProperties(self, element: QDomElement) → bool[source]

Restores the effect to the state described by a DOM element.

Parameters:: element (QDomElement) – DOM element describing an effect’s state
Return type:: bool
Returns:: True if read was successful

See also

saveProperties()

virtual render(self, picture: QPicture, context: QgsRenderContext)[source]¶

Renders a picture using the effect.

Parameters:

picture (QPicture) – source QPicture to render
context (QgsRenderContext) – destination render context

See also

begin()

virtual saveProperties(self, doc: QDomDocument, element: QDomElement) → bool[source]¶

Saves the current state of the effect to a DOM element. The default behavior is to save the properties string map returned by properties().

Parameters:

doc (QDomDocument) – destination DOM document
element (QDomElement) – destination DOM element

Return type:

bool

Returns:

True if save was successful

See also

readProperties()

setDrawMode(self, drawMode: QgsPaintEffect.DrawMode)[source]¶

Sets the draw mode for the effect. This property only has an effect if the paint effect is used in a QgsEffectStack.

Parameters:: drawMode (QgsPaintEffect.DrawMode) – draw mode for effect

See also

drawMode()

setEnabled(self, enabled: bool)[source]¶

Sets whether the effect is enabled

Parameters:: enabled (bool) – set to False to disable the effect

See also

enabled()

source(self) → QPicture¶

Returns the source QPicture. The draw() member can utilize this when drawing the effect.

Return type:: QPicture
Returns:: source QPicture

See also

drawSource()

See also

sourceAsImage()

sourceAsImage(self, context: QgsRenderContext) → QImage[source]¶

Returns the source QPicture rendered to a new QImage. The draw() member can utilize this when drawing the effect. The image will be padded or cropped from the original source QPicture by the results of the boundingRect() method. The result is cached to speed up subsequent calls to sourceAsImage.