Bug 5901: Marker Label does not display unless a Line Style is selected
Bug Number: 5901
Release notes (y/n): Yes
For Release Nums: 7.0.7

Marker text labels were not showing up when Marker Lines were hidden by 
setting the Line Style (line pattern) to "None" (in the Marker Configuration 
dialog).

This bug was fixed by overriding the QwtPlotMarker::drawLabel() virtual 
method and temporarily setting the QPainter's pen's Qt::PenStyle to 
something other than Qt::NoPen.

At the Qwt level, there are TWO WAYS of configuring a marker to not show 
lines (i.e. to instead show ONLY the text label and/or a point symbol).
We are sort of using the "wrong" way -- by  setting the marker's line pen 
(QPen) to Qt::NoPen (line pattern choice, e.g. solid, dashed, dotted).
The "right" way of doing that (which we don't currently support) is by 
setting the marker's QwtPlotMarker:: LineStyle to NoLine (instead of to 
HLine, VLine or Cross -- i.e. what we call "Marker Type" in the 
configuration dialog).

Note that a marker's Text Color is the color configured for its Line Color.

See the new method: PlotMarker::drawLabel (QPainter* ...) 
in Q3GUI/PlotMarker.cpp.

NOTES:

(1) Line-less text marker positioning works best with the 
'Cross' Marker Type selected (rather than 'Horizontal' or 
'Vertical').

(2) The marker's Text Color is the color configured for its 
Line Color.

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