QwtPlotShapeItem critical paint error (filling differ from contour pen)

[vnuss]

Hello @all.

I have used the QwtPlotShapeItem with the following program code:

QColor color(225,46,28,58);

QPainterPath Path;
this->PaintCircle(&Path,5, QPointF(0,0));

QwtPlotShapeItem *Item = new QwtPlotShapeItem( "Shape Name" );
Item->setItemAttribute( QwtPlotItem::Legend, true );
Item->setRenderHint( QwtPlotItem::RenderAntialiased, true );
Item->setShape( Path );
Item->setPen( color );

Item->setBrush( color );
Item->attach( Plot );

QwtShapteItem.jpg


With this code i get a shape like in the attached picture.
--> The shape filling differ from contour pen.

Can anybody help me to solve this problem?

[Uwe]

All I can see is that your code is calling some PaintCircle method to create the QPainterPath.

Uwe

[vnuss]

The PaintCircle method creates a circle with QPainterPath.

Code:

path.addEllipse ( QPointF(0,0), 5, 5 )

This painterpath i am setting as shape in an object of the class QwtPlotShapeItem.

Item->setShape( Path );

This shape item i am attaching to the plot.

Item->attach( Plot );

The problem i have is, that the contour of the path don't fit to the filling of the shape.
This problem can be observed in the attached picture.

Thanks for help.

[Uwe]

The PaintCircle method creates a circle with QPainterPath.

Your screenshot shows something at coordinates, where a circle with a radius of 5.0 and a center at 0.0 will never be !

But ignoring this: QwtPlotShapeItem does nothing beside translating the coordinates of the painter path from plot into widget coordinates forwarding it to QPainter::drawPath. With which type of paint engine does this problem happen ?

Uwe

PS: an easy workaround might be draw with a brush, but without pen ( item->setPen( Qt::NoPen ) ).

[vnuss]

Screenshot:
I have zoomed into the plot, till i see the contour / pen difference.

Radius of 5 was a value for an example.


I am working with qt verson 4.8.5 and qwt version 6.1.



Thanks for the workaround, but in my case i couldn't use that, because i need both, contour and filling.

Can you reproduce this problem?


Zoom is realised with:

QwtPlotMagnifier *magnifier = new QwtPlotMagnifier( Plot->canvas() );
magnifier->setMouseButton( Qt::NoButton );

[Uwe]

I am working with qt verson 4.8.5 and qwt version 6.1.:

The paint engine depends on the operating system, f.e raster on Windows. On X11 you have the option between native ( = X11 ) and raster ( default since Qt 4.8 ).
What is your environment ?

Can you reproduce this problem?

Upload a minimal compilable demo showing the issue. Please use axis ranges, where it happens without having to zoom in/out.

Uwe

[Uwe]

O.k I have checked the issue with the itemeditor example and I can confirm the bug for a pen width <= 1 with Qt 4.8/raster and Qt5.1/raster. Qt 4.7/raster or Qt4.8/X11 are o.k.
Seems to be one more of those bugs that have been introduced recently to the raster paint engine ( see Qt bug tracker ). Add a bug report if you can't find one already.

If a pen width > 1 is acceptable for your application you can try this as a workaround., another option might be to downgrade Qt to the version before the bug has been introduced.

Uwe

[vnuss]

Ok. Thank you for help.