QgsHeatmapRenderer class

A renderer which draws points as a live heatmap.

Reference

Public static functions

static auto create(QDomElement& element, const QgsReadWriteContext& context) -> QgsFeatureRenderer*: Creates a new heatmap renderer instance from XML.

Constructors, destructors, conversion operators

QgsHeatmapRenderer(const QgsHeatmapRenderer&) deleted: Direct copies are forbidden. Use clone() instead.

Public functions

auto clone() const -> QgsHeatmapRenderer* override: Create a deep copy of this renderer.
auto colorRamp() const -> QgsColorRamp*: Returns the color ramp used for shading the heatmap.
auto dump() const -> QString override: Returns debug information about this renderer.
auto maximumValue() const -> double: Returns the maximum value used for shading the heatmap.
void modifyRequestExtent(QgsRectangle& extent, QgsRenderContext& context) override: Allows for a renderer to modify the extent of a feature request prior to rendering.
auto operator=(const QgsHeatmapRenderer&) -> QgsHeatmapRenderer& deleted: Direct copies are forbidden. Use clone() instead.
auto radius() const -> double: Returns the radius for the heatmap.
auto radiusMapUnitScale() const -> const QgsMapUnitScale&: Returns the map unit scale used for the heatmap's radius.
auto radiusUnit() const -> QgsUnitTypes::RenderUnit: Returns the units used for the heatmap's radius.
auto renderFeature(const QgsFeature& feature, QgsRenderContext& context, int layer = -1, bool selected = false, bool drawVertexMarker = false) -> bool override: Render a feature using this renderer in the given context.
auto renderQuality() const -> double: Returns the render quality used for drawing the heatmap.
auto save(QDomDocument& doc, const QgsReadWriteContext& context) -> QDomElement override: store renderer info to XML element
void setColorRamp(QgsColorRamp* ramp): Sets the color ramp to use for shading the heatmap.
void setMaximumValue(const double value): Sets the maximum value used for shading the heatmap.
void setRadius(const double radius): Sets the radius for the heatmap.
void setRadiusMapUnitScale(const QgsMapUnitScale& scale): Sets the map unit scale used for the heatmap's radius.
void setRadiusUnit(const QgsUnitTypes::RenderUnit unit): Sets the units used for the heatmap's radius.
void setRenderQuality(const int quality): Sets the render quality used for drawing the heatmap.
void setWeightExpression(const QString& expression): Sets the expression used for weighting points when generating the heatmap.
void startRender(QgsRenderContext& context, const QgsFields& fields) override: Must be called when a new render cycle is started.
void stopRender(QgsRenderContext& context) override: Must be called when a render cycle has finished, to allow the renderer to clean up.
auto symbolForFeature(const QgsFeature& feature, QgsRenderContext& context) const -> QgsSymbol* override
auto symbols(QgsRenderContext& context) const -> QgsSymbolList override
auto usedAttributes(const QgsRenderContext& context) const -> QSet<QString> override: Returns a list of attributes required by this renderer.
auto weightExpression() const -> QString: Returns the expression used for weighting points when generating the heatmap.

Function documentation

QgsHeatmapRenderer* QgsHeatmapRenderer::clone() const override

Create a deep copy of this renderer.

Returns	A copy of this renderer

Should be implemented by all subclasses and generate a proper subclass.

QgsColorRamp* QgsHeatmapRenderer::colorRamp() const

Returns the color ramp used for shading the heatmap.

Returns	color ramp for heatmap

double QgsHeatmapRenderer::maximumValue() const

Returns the maximum value used for shading the heatmap.

Returns	maximum value for heatmap shading. If 0, then maximum value will be automatically calculated.

void QgsHeatmapRenderer::modifyRequestExtent(QgsRectangle& extent, QgsRenderContext& context) override

Allows for a renderer to modify the extent of a feature request prior to rendering.

Parameters
extent	reference to request's filter extent. Modify extent to change the extent of feature request
context	render context

double QgsHeatmapRenderer::radius() const

Returns the radius for the heatmap.

Returns	heatmap radius

const QgsMapUnitScale& QgsHeatmapRenderer::radiusMapUnitScale() const

Returns the map unit scale used for the heatmap's radius.

Returns	map unit scale for heatmap's radius

QgsUnitTypes::RenderUnit QgsHeatmapRenderer::radiusUnit() const

Returns the units used for the heatmap's radius.

Returns	units for heatmap radius

bool QgsHeatmapRenderer::renderFeature(const QgsFeature& feature, QgsRenderContext& context, int layer = -1, bool selected = false, bool drawVertexMarker = false) override

Render a feature using this renderer in the given context.

Must be called between startRender() and stopRender() calls. Default implementation renders a symbol as determined by symbolForFeature() call. Returns true if the feature has been returned (this is used for example to determine whether the feature may be labelled).

If layer is not -1, the renderer should draw only a particula layer from symbols (in order to support symbol level rendering).

double QgsHeatmapRenderer::renderQuality() const

Returns the render quality used for drawing the heatmap.

Returns	render quality. A value of 1 indicates maximum quality, and increasing the value will result in faster drawing but lower quality rendering.

void QgsHeatmapRenderer::setColorRamp(QgsColorRamp* ramp)

Sets the color ramp to use for shading the heatmap.

Parameters
ramp	color ramp for heatmap. Ownership of ramp is transferred to the renderer.

void QgsHeatmapRenderer::setMaximumValue(const double value)

Sets the maximum value used for shading the heatmap.

Parameters
value	maximum value for heatmap shading. Set to 0 for automatic calculation of maximum value.

void QgsHeatmapRenderer::setRadius(const double radius)

Sets the radius for the heatmap.

Parameters
radius	heatmap radius

void QgsHeatmapRenderer::setRadiusMapUnitScale(const QgsMapUnitScale& scale)

Sets the map unit scale used for the heatmap's radius.

Parameters
scale	map unit scale for heatmap's radius

void QgsHeatmapRenderer::setRadiusUnit(const QgsUnitTypes::RenderUnit unit)

Sets the units used for the heatmap's radius.

Parameters
unit	units for heatmap radius

void QgsHeatmapRenderer::setRenderQuality(const int quality)

Sets the render quality used for drawing the heatmap.

Parameters
quality	render quality. A value of 1 indicates maximum quality, and increasing the value will result in faster drawing but lower quality rendering.

void QgsHeatmapRenderer::setWeightExpression(const QString& expression)

Sets the expression used for weighting points when generating the heatmap.

Parameters
expression	point weight expression. If set to empty, all points are equally weighted.

void QgsHeatmapRenderer::startRender(QgsRenderContext& context, const QgsFields& fields) override

Must be called when a new render cycle is started.

Parameters
context	Additional information passed to the renderer about the job which will be rendered
fields	The fields available for rendering

A call to startRender() must always be followed by a corresponding call to stopRender() after all features have been rendered.

void QgsHeatmapRenderer::stopRender(QgsRenderContext& context) override

Must be called when a render cycle has finished, to allow the renderer to clean up.

Calls to stopRender() must always be preceded by a call to startRender().

QgsSymbol* QgsHeatmapRenderer::symbolForFeature(const QgsFeature& feature, QgsRenderContext& context) const override

QgsSymbolList QgsHeatmapRenderer::symbols(QgsRenderContext& context) const override

QSet<QString> QgsHeatmapRenderer::usedAttributes(const QgsRenderContext& context) const override

Returns a list of attributes required by this renderer.

Returns	A set of attributes

Attributes not listed in here may not have been requested from the provider at rendering time.

QString QgsHeatmapRenderer::weightExpression() const

Returns the expression used for weighting points when generating the heatmap.

Returns	point weight expression. If empty, all points are equally weighted.