QwtPlotIntervalCurve's constant width.

[Uwe]

Well then the size of the square depends on some QFontMetrics and is of course in widget coordinates.

This is something you can do with symbols - in you case ( as you need to draw a value inside ) it would be a symbol made of a QPixmap or QwtGraphic ( what would give nicer results in a PDF document ). All geometries of a symbol are in widget coordinates, what means, that a square remains a square ( but don't you have this already using QwtPlotMarker ? ).

Another option would be to derive from QwtPlotItem and do the squares for each vector in YourItem::draw(). Implementing such an item wouldn't be hard - simply translating the center into widget coordinates, then doing a QPainter::fillRect() followed by a QPainter::drawText().

Uwe

[Toniy]

Thanks! I almost get it. One more question: are coordinates on canvas widget and coordinates that shown at QwtScaleDraw not the same (coordinates that shown at QwtScaleDraw are converted coordinates of canvas widget)? I mean if, for example, our Y axis has 100 as min value and 200 for max value and X axis has the same limits, then is point [0;0] of canvas widget (top-left corner) the same as point [200, 100] of our graph (or it is more complicated)?

[Uwe]

The widget coordinates are usually bounded by plot->canvas()->contentsRect() ( = QWidget::rect() without margins ). Then it depends on your configuration how the scales are aligned to the canvas - f.e. there might be extra margins to have some space for the tick labels ( see QwtPlotLayout ). The necessary space depends on some factors f.e if a horizontal scale can be extended below a vertical scale etc.

So the answer is yes - usually it is more complicated. Better use QwtPlot::canvasMap() to translate between plot ( = what is spanned by the scales ) and paint device coordinates ( = widget ).

Uwe