QgsEffectStack class

A paint effect which consists of a stack of other chained paint effects.

Reference

Effect stacks can be used to apply multiple paint effects to a QPicture. For instance, an effect stack may blur then apply a drop shadow.

The way in which effects apply to a stack is controlled by the effect's drawMode. Effects can either render their results onto the destination paint device, or just modify the source picture which is drawn by subsequent effects in the stack. For instance, a blur effect with a Modifier drawMode will blur the source picture for the following drop shadow effect without actually drawing the blurred picture to the paint device. If the blur effect had a Render drawMode then the blurred picture will be drawn on the paint device, but the following drop shadow effect will be drawn using the original picture, not the blurred version.

Base classes

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

Public static functions

static auto create(const QgsStringMap& map) -> QgsPaintEffect*: Creates a new QgsEffectStack effect.

Constructors, destructors, conversion operators

QgsEffectStack() defaulted: Constructor for empty QgsEffectStack.
QgsEffectStack(const QgsPaintEffect& effect) explicit: Creates a new QgsEffectStack effect from a single initial effect.

Public functions

void appendEffect(QgsPaintEffect* effect): Appends an effect to the end of the stack.
auto changeEffect(int index, QgsPaintEffect* effect) -> bool: Replaces the effect at a specified position within the stack.
auto clone() const -> QgsEffectStack* override: Duplicates an effect by creating a deep copy of the effect.
auto count() const -> int: Returns count of effects contained by the stack.
auto effect(int index) const -> QgsPaintEffect*: Returns a pointer to the effect at a specified index within the stack.
auto effectList() -> QList<QgsPaintEffect*>*: Returns a pointer to the list of effects currently contained by the stack.
auto insertEffect(int index, QgsPaintEffect* effect) -> bool: Inserts an effect at a specified index within the stack.
auto properties() const -> QgsStringMap override: Unused for QgsEffectStack, will always return an empty string map.
auto readProperties(const QDomElement& element) -> bool override: Restores the effect to the state described by a DOM element.
void readProperties(const QgsStringMap& props) override: Unused for QgsEffectStack, props parameter will be ignored.
auto saveProperties(QDomDocument& doc, QDomElement& element) const -> bool override: Saves the current state of the effect to a DOM element.
auto takeEffect(int index) -> QgsPaintEffect*: Removes an effect from the stack and returns a pointer to it.
auto type() const -> QString override: Returns the effect type.

Protected functions

void draw(QgsRenderContext& context) override: Handles drawing of the effect's result on to the specified render context.

Function documentation

static QgsPaintEffect* QgsEffectStack::create(const QgsStringMap& map)

Creates a new QgsEffectStack effect.

Parameters
map	unused encoded properties string map
Returns	new QgsEffectStack

This method ignores the map parameter, and always returns an empty effect stack.

QgsEffectStack::QgsEffectStack(const QgsPaintEffect& effect) explicit

Creates a new QgsEffectStack effect from a single initial effect.

Parameters
effect	initial effect to add to the stack. The effect will be cloned, so ownership is not transferred to the stack.
Returns	new QgsEffectStack containing initial effect

void QgsEffectStack::appendEffect(QgsPaintEffect* effect)

Appends an effect to the end of the stack.

Parameters
effect	QgsPaintEffect to append. Ownership of the effect will be transferred to the stack object.

bool QgsEffectStack::changeEffect(int index, QgsPaintEffect* effect)

Replaces the effect at a specified position within the stack.

Parameters
index	position of effect to replace
effect	QgsPaintEffect to replace with. Ownership of the effect will be transferred to the stack object.

QgsEffectStack* QgsEffectStack::clone() const override

Duplicates an effect by creating a deep copy of the effect.

Returns	clone of paint effect

int QgsEffectStack::count() const

Returns count of effects contained by the stack.

Returns	count of effects

QgsPaintEffect* QgsEffectStack::effect(int index) const

Returns a pointer to the effect at a specified index within the stack.

Parameters
index	position of effect to return
Returns	QgsPaintEffect at specified position

QList<QgsPaintEffect> QgsEffectStack::effectList()

Returns a pointer to the list of effects currently contained by the stack.

Returns	list of QgsPaintEffects within the stack

bool QgsEffectStack::insertEffect(int index, QgsPaintEffect* effect)

Inserts an effect at a specified index within the stack.

Parameters
index	position to insert the effect
effect	QgsPaintEffect to insert. Ownership of the effect will be transferred to the stack object.

bool QgsEffectStack::readProperties(const QDomElement& element) override

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

Parameters
element	DOM element describing an effect's state
Returns	true if read was successful

bool QgsEffectStack::saveProperties(QDomDocument& doc, QDomElement& element) const override

Saves the current state of the effect to a DOM element.

Parameters
doc	destination DOM document
element	destination DOM element
Returns	true if save was successful

The default behavior is to save the properties string map returned by properties().

QgsPaintEffect* QgsEffectStack::takeEffect(int index)

Removes an effect from the stack and returns a pointer to it.

Parameters
index	position of effect to take

QString QgsEffectStack::type() const override

Returns the effect type.

Returns	unique string representation of the effect type

void QgsEffectStack::draw(QgsRenderContext& context) override protected

Handles drawing of the effect's result on to the specified render context.

Parameters
context	destination 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.