QwtGraphic¶
- class qwt.graphic.QwtGraphic(*args)[source]¶
A paint device for scalable graphics
QwtGraphic is the representation of a graphic that is tailored for scalability. Like QPicture it will be initialized by QPainter operations and can be replayed later to any target paint device.
While the usual image representations QImage and QPixmap are not scalable Qt offers two paint devices, that might be candidates for representing a vector graphic:
QPicture:
Unfortunately QPicture had been forgotten, when Qt4 introduced floating point based render engines. Its API is still on integers, what make it unusable for proper scaling.
QSvgRenderer, QSvgGenerator:
Unfortunately QSvgRenderer hides to much information about its nodes in internal APIs, that are necessary for proper layout calculations. Also it is derived from QObject and can’t be copied like QImage/QPixmap.
QwtGraphic maps all scalable drawing primitives to a QPainterPath and stores them together with the painter state changes ( pen, brush, transformation … ) in a list of QwtPaintCommands. For being a complete QPaintDevice it also stores pixmaps or images, what is somehow against the idea of the class, because these objects can’t be scaled without a loss in quality.
The main issue about scaling a QwtGraphic object are the pens used for drawing the outlines of the painter paths. While non cosmetic pens ( QPen.isCosmetic() ) are scaled with the same ratio as the path, cosmetic pens have a fixed width. A graphic might have paths with different pens - cosmetic and non-cosmetic.
QwtGraphic caches 2 different rectangles:
control point rectangle:
The control point rectangle is the bounding rectangle of all control point rectangles of the painter paths, or the target rectangle of the pixmaps/images.
bounding rectangle:
The bounding rectangle extends the control point rectangle by what is needed for rendering the outline with an unscaled pen.
Because the offset for drawing the outline depends on the shape of the painter path ( the peak of a triangle is different than the flat side ) scaling with a fixed aspect ratio always needs to be calculated from the control point rectangle.
- class QwtGraphic¶
Initializes a null graphic
- class QwtGraphic(other)
Copy constructor
- Parameters
other (qwt.graphic.QwtGraphic) – Source
- boundingRect()[source]¶
The bounding rectangle is the
controlPointRect()
extended by the areas needed for rendering the outlines with unscaled pens.- Returns
Bounding rectangle of the graphic
See also
- controlPointRect()[source]¶
The control point rectangle is the bounding rectangle of all control points of the paths and the target rectangles of the images/pixmaps.
- Returns
Control point rectangle
See also
- scaledBoundingRect(sx, sy)[source]¶
Calculate the target rectangle for scaling the graphic
- Parameters
sx (float) – Horizontal scaling factor
sy (float) – Vertical scaling factor
- Returns
Scaled bounding rectangle
Note
In case of paths that are painted with a cosmetic pen (see
QPen.isCosmetic()
) the target rectangle is different to multiplying the bounding rectangle.See also
- sizeMetrics()[source]¶
Return Ceiled
defaultSize()
- setDefaultSize(size)[source]¶
The default size is used in all methods rendering the graphic, where no size is explicitly specified. Assigning an empty size means, that the default size will be calculated from the bounding rectangle.
- Parameters
size (QSizeF) – Default size
See also
- defaultSize()[source]¶
When a non empty size has been assigned by setDefaultSize() this size will be returned. Otherwise the default size is the size of the bounding rectangle.
The default size is used in all methods rendering the graphic, where no size is explicitly specified.
- Returns
Default size
See also
- render(*args)[source]¶
- render(painter)[source]
Replay all recorded painter commands
- Parameters
painter (QPainter) – Qt painter
- render(painter, size, aspectRatioMode)[source]
Replay all recorded painter commands
The graphic is scaled to fit into the rectangle of the given size starting at ( 0, 0 ).
- Parameters
painter (QPainter) – Qt painter
size (QSizeF) – Size for the scaled graphic
aspectRatioMode (Qt.AspectRatioMode) – Mode how to scale
- render(painter, rect, aspectRatioMode)[source]
Replay all recorded painter commands
The graphic is scaled to fit into the given rectangle
- Parameters
painter (QPainter) – Qt painter
rect (QRectF) – Rectangle for the scaled graphic
aspectRatioMode (Qt.AspectRatioMode) – Mode how to scale
- render(painter, pos, aspectRatioMode)[source]
Replay all recorded painter commands
The graphic is scaled to the
defaultSize()
and aligned to a position.- Parameters
painter (QPainter) – Qt painter
pos (QPointF) – Reference point, where to render
aspectRatioMode (Qt.AspectRatioMode) – Mode how to scale
- toPixmap(*args)[source]¶
Convert the graphic to a QPixmap
All pixels of the pixmap get initialized by Qt.transparent before the graphic is scaled and rendered on it.
The size of the pixmap is the default size ( ceiled to integers ) of the graphic.
- Returns
The graphic as pixmap in default size
See also
- toImage(*args)[source]¶
- toImage()[source]
Convert the graphic to a QImage
All pixels of the image get initialized by 0 ( transparent ) before the graphic is scaled and rendered on it.
The format of the image is QImage.Format_ARGB32_Premultiplied.
The size of the image is the default size ( ceiled to integers ) of the graphic.
- Returns
The graphic as image in default size
- toImage(size[, aspectRatioMode=Qt.IgnoreAspectRatio])[source]
Convert the graphic to a QImage
All pixels of the image get initialized by 0 ( transparent ) before the graphic is scaled and rendered on it.
The format of the image is QImage.Format_ARGB32_Premultiplied.
- Parameters
size (QSize) – Size of the image
aspectRatioMode (Qt.AspectRatioMode) – Aspect ratio how to scale the graphic
- Returns
The graphic as image
See also
- drawPath(path)[source]¶
Store a path command in the command list
- Parameters
path (QPainterPath) – Painter path
See also
QPaintEngine.drawPath()
- drawPixmap(rect, pixmap, subRect)[source]¶
Store a pixmap command in the command list
- Parameters
rect (QRectF) – target rectangle
pixmap (QPixmap) – Pixmap to be painted
subRect (QRectF) – Reactangle of the pixmap to be painted
See also
QPaintEngine.drawPixmap()
- drawImage(rect, image, subRect, flags)[source]¶
Store a image command in the command list
- Parameters
rect (QRectF) – target rectangle
image (QImage) – Pixmap to be painted
subRect (QRectF) – Reactangle of the pixmap to be painted
flags (Qt.ImageConversionFlags) – Pixmap to be painted
See also
QPaintEngine.drawImage()