Re: Issue with QwtPlotRescaler

[Sébastien P. <per...@ge...>]

Hi Uwe,

Thanks for the answer!

In playground/rescaler, the ellipses are supposed to be circles due to
   const QRectF area( x - r, y - r , 2 * r, 2 * r );
but this is not the case on display, of course if the rescaler mode is
None, but also for the other mode.

I add some code in RectItem::draw() to illustrate this (see code below).
It displays the ratio between the y scale and the x scale and then we can
see that the ratio is exactly 1 only if the canvas is a square.
We can also see that the line const QRectF rect =
QwtScaleMap::transform( xMap, yMap, d_rect ); does not return a square even
if d_rect is a square.

Unlike I wrote in my previous message, it seems to have nothing to do with
the flag alignCanvasToScale ...

The problem for me is that in my PlotItem::draw() implementation I rely on
a ratio equal to 1 to correctly display a not distorted rotated rectangle.

Sebastien.

    virtual void draw( QPainter *painter,

        const QwtScaleMap &xMap, const QwtScaleMap &yMap,

        const QRectF & ) const

    {

        if ( d_rect.isValid() )

        {

*          const double x_scale = qAbs((xMap.p2()-xMap.p1()) /
(xMap.s2()-xMap.s1()));*

*          const double y_scale = qAbs((yMap.p2()-yMap.p1()) /
(yMap.s2()-yMap.s1()));*


          const QRectF rect = QwtScaleMap::transform(

                xMap, yMap, d_rect );


*          const QString text = QString("%1 %2\n%3\n%4 %5")*

*
.arg(d_rect.width()).arg(d_rect.height()).arg(y_scale / x_scale)*

*                               .arg(rect.width()).arg(rect.height());*


            painter->setPen( d_pen );

            painter->setBrush( d_brush );


            if ( d_type == Ellipse )

                QwtPainter::drawEllipse( painter, rect );

            else

                QwtPainter::drawRect( painter, rect );


*            QwtPainter::drawText(painter, rect, Qt::AlignCenter, text);*

        }

    }






Le mar. 10 sept. 2019 à 08:34, Uwe Rathmann <Uwe...@ti...> a
écrit :

> On 9/9/19 11:20 AM, Sébastien Perseval wrote:
>
> > I think the problem is that the method QwtPlotRescaler::rescale(const
> > QSize &oldSize, const QSize &newSize) uses the size of the canvas to
> > update the axes according to the reference axis, ignoring the actual
> > size of the axes.
>
> playground/rescaler shows the different modes of QwtPlotRescaler and how
> they are supposed to work.
>
> Could you please explain what exactly is missing or going wrong by
> modifying this example ?
>
> Uwe
>
>
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