How to redraw everything while panning the canvas?

[Stig]

Hi there. I'm evaluating the Qwt library, and so far it has impressed me in several aspects.

But I've encountered two important issues regarding panning. I've added a QwtPlotPanner to the canvas, and the grid moves while I pan. There are however some additional items I want to have redrawn for each move event. for to make a nice and smooth plot.

Issue 1: The axes are only redrawn when I release the mouse button. I want the axes/ruler to be drawn while moving (with the grid) to make it a smooth experience for the user.
Issue 2: The grid is moved, but this is only the pixmap created before the move started. Hence new lines in the grid is not created outside of the initial area.


I did partly solve issue 1 by replacing

emit moved(d_data->pos.x() - d_data->initialPos.x(), 
            d_data->pos.y() - d_data->initialPos.y());

emit moved(d_data->pos.x() - d_data->initialPos.x(), 
            d_data->pos.y() - d_data->initialPos.y());

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in the widgetMouseMoveEvent in qwt.panner.cpp to

emit panned(d_data->pos.x() - d_data->initialPos.x(),
            d_data->pos.y() - d_data->initialPos.y());
        d_data->initialPos = d_data->pos;

emit panned(d_data->pos.x() - d_data->initialPos.x(),
            d_data->pos.y() - d_data->initialPos.y());
        d_data->initialPos = d_data->pos;

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The moved signal doesn't seem to be connected to anything anyway. This fix will introduce a bug with the grid moving; the grid flickers because of the setting of the initialPos in the middle of move events.

How can these two issues be solved?

Thanks in advance,
Stig

[Uwe]

QwtPanner grabs the content of the canvas into a pixmap and moves the pixmap only. This is done for performance reasons, because rendering the plot items might be too slow for mouse movements. If you don't want this - don't use the panner.

Instead catch all mouse events of the plot canvas using an event filter. Translate the mouse movements into coordinates of the plot using the canvas maps ( QwtPlot::canvasMap ) and adjust the scales.