QgsMapCanvasItem class

An abstract class for items that can be placed on the map canvas.

Reference

Derived classes

class QgsAdvancedDigitizingCanvasItem: The QgsAdvancedDigitizingCanvasItem class draws the graphical elements of the CAD tools (.
class QgsGeometryRubberBand: A rubberband class for QgsAbstractGeometry (considering curved geometries)
class QgsHighlight: A class for highlight features on the map.
class QgsMapCanvasAnnotationItem: An interactive map canvas item which displays a QgsAnnotation.
class QgsRubberBand: A class for drawing transient features (e.g.
class QgsSnapToGridCanvasItem: Shows a grid on the map canvas given a spatial resolution.
class QgsVertexMarker: A class for marking vertices of features using e.g.

Constructors, destructors, conversion operators

QgsMapCanvasItem(QgsMapCanvas* mapCanvas) protected: protected constructor: cannot be constructed directly

Public functions

auto rect() const -> QgsRectangle: returns canvas item rectangle in map units
void setRect(const QgsRectangle& r, bool resetRotation = true): sets canvas item rectangle in map units
auto toCanvasCoordinates(const QgsPointXY& point) const -> QPointF: transformation from map coordinates to screen coordinates
auto toMapCoordinates(QPoint point) const -> QgsPointXY: transformation from screen coordinates to map coordinates
void updatePosition() virtual: called on changed extent or resize event to update position of the item

Protected functions

void paint(QPainter* painter) pure virtual: function to be implemented by derived classes
auto setRenderContextVariables(QPainter* p, QgsRenderContext& context) const -> bool: Sets render context parameters.
void updateCanvas(): schedules map canvas for repaint

Protected variables

QSizeF mItemSize: cached size of the item (to return in boundingRect())
QgsMapCanvas* mMapCanvas: pointer to map canvas
QgsRectangle mRect: cached canvas item rectangle in map coordinates encodes position (xmin,ymax) and size (width/height) used to re-position and re-size the item on zoom/pan while waiting for the renderer to complete.

Function documentation

bool QgsMapCanvasItem::setRenderContextVariables(QPainter* p, QgsRenderContext& context) const protected

Sets render context parameters.

Parameters
p	painter for rendering
context	out: configured context
Returns	true in case of success

Variable documentation

QgsRectangle QgsMapCanvasItem::mRect protected

cached canvas item rectangle in map coordinates encodes position (xmin,ymax) and size (width/height) used to re-position and re-size the item on zoom/pan while waiting for the renderer to complete.

NOTE: does not include rotation information, so cannot be used to correctly present pre-rendered map on rotation change